Where to look for life on Titan

Saturn’s largest moon Titan as seen by the Cassini spacecraft. This world’s liquid methane and ethane rivers, lakes and seas might support some kind of life, and scientists now think they know the best places to look. Image via NASA/JPL-Caltech.

NASA’s Cassini spacecraft and ESA’s Huygens lander showed that Saturn’s large moon Titan mimics Earth in many ways. But Titan displays different kinds of chemistry in a far colder environment. Given the similarities, the question of life inevitably arises: could Titan support some kind of simple life? Given the differences, scientists ponder the best places to look for Titan life. In late July, 2018, a new study published in the journal Astrobiology and reported on in Astrobiology Magazine suggests the best places on Titan to look for evidence of life.

Titan is a geological wonderland for planetary scientists. It has rivers, lakes and seas of actual liquid – not water, but the hydrocarbons methane and ethane – and it has mountain ranges, possible ice volcanoes (aka cryovolcanoes) and vast hydrocarbon dunes. There is also evidence for a subsurface ocean of water, similar to those believed to lie beneath the surface of Jupiter’s moon Europa and Saturn’s moon Enceladus.

Perhaps surprisingly, the research team, led by Catherine Neish, a planetary scientist specializing in impact cratering at the University of Western Ontario, suggested that the best locations to look for life on Titan would not be the lakes or seas. Instead, the new work shows a better place to look would be within impact craters and cryovolcanoes on Titan.

The scientists reason that these areas are where water ice in Titan’s crust could temporarily melt into a liquid. Water is still the only solvent known to be able to support life as we know it.

A large, fairly young crater on Titan, about 25 miles (40 km) in diameter. Such craters could temporarily melt frozen water in the crust, providing an environment for pre-biotic or biotic molecules to form. Image via NASA/JPL-Caltech.

Various studies have suggested that liquid methane and ethane could support life. But Saturn’s moon Titan – some nine farther from the sun than Earth – is very cold, with surface temperatures hovering around -300 degrees Fahrenheit (–179 degrees Celsius). Methane and ethane do remain liquid at Titan’s surface temperature, but it’s too cold there for biochemical processes, at least as far as we know (although that, too, is a matter of debate).

Titan’s surface is also covered with tholins, which are large, complex organic molecules produced when gases are subjected to cosmic radiation. When mixed with liquid water, tholins can produce amino acids, which are, essentially, life’s building blocks. According to researcher Morgan Cable at NASA’s Jet Propulsion Laboratory in Pasadena, California:

When we mix tholins with liquid water, we make amino acids really fast. So any place where there is liquid water on Titan’s surface or near its surface could be generating the precursors to life – biomolecules – that would be important for life as we know it, and that’s really exciting.

The temperatures on Titan’s surface are too cold for liquid water, so where could it be found? The answer is Titan’s craters and cryovolcanoes. The processes involved with both of these geologic features can melt water ice into liquid, even if only temporarily.

But that might be enough for more complex organic molecules like amino acids to form.

Sotra Facula is a possible cryovolcano on Titan, one of the few candidates known. Image via NASA/JPL–Caltech/USGS/University of Arizona.

Another view of Sotra Facula. This image was built from radar topography with infrared colors overlaid on top. Image via NASA/JPL–Caltech/USGS/University of Arizona.

Between craters and cryovolcanoes, it would seem that craters would be the most ideal location for pre-biotic or biotic chemistry to occur. As Neish explained:

Craters really emerged as the clear winner for three main reasons. One, is that we’re pretty sure there are craters on Titan. Cratering is a very common geologic process and we see circular features that are almost certainly craters on the surface.

Neish also noted that craters would produce more liquid water melt than a cryovolcano, so any water would remain liquid for a longer period of time. She also added:

The last point is that impact craters should produce water that’s at a higher temperature than a cryovolcano.

Warmer water would allow for faster chemical reaction rates, which would help in the creation of per-biotic or even biotic molecules. The largest known craters on Titan are Sinlap (70 miles/112 kms in diameter), Selk (56 miles/90 kms) and Menrva (244 miles/392 kms). These would be the primary locations to look for biomolecules. 

David Grinspoon at the Planetary Science Institute isn’t convinced yet, however. He commented:

We don’t know where to search even with results like this. I wouldn’t use it to guide our next mission to Titan. It’s premature.

Titan is well-known for its lakes and seas of liquid methane/ethane, such as Ligiea Mare, shown here. Image via NASA/JPL-Caltech/ASI/Cornell.

So what about cryovolcanoes? They haven’t actually been confirmed yet to exist on Titan, and if they do, they are more rare than craters (even though craters are also relatively rare on Titan). The most likely feature to be a cryovolcano is a mountain with a caldera on top called Sotra Facula. Other than that, they seem to be few and far between. As Neish said:

Cryovolcanism is the harder thing to do and there is very little evidence of it on Titan.

Diagram illustrating how biosignatures could also be transported from the subsurface ocean to the surface of Titan. Image via Athanasios Karagiotas/Theoni Shalamberidze.

There is also, of course, a possible subsurface ocean of water on Titan, but, if it exists, it is deep below the moon’s surface and inaccessible to any robotic probes in the near future. For now, we can only imagine what might be in that alien abyss.

The methane/ethane lakes and seas should still be explored too; they are the only other known bodies of liquid on the surface of another moon or planet in the solar system. Methane-based life could theoretically exist in such environments, so it would obviously be a good idea to look, at least.

Bottom line: Titan is a world that is eerily similar to Earth in some ways, yet still uniquely alien. Whether it supports any kind of life is still a big question, but researchers now think they know the best places to search for it.

Source: Strategies for Detecting Biological Molecules on Titan

Via Astrobiology Magazine

from EarthSky https://ift.tt/2LVhVIh

Saturn’s largest moon Titan as seen by the Cassini spacecraft. This world’s liquid methane and ethane rivers, lakes and seas might support some kind of life, and scientists now think they know the best places to look. Image via NASA/JPL-Caltech.

NASA’s Cassini spacecraft and ESA’s Huygens lander showed that Saturn’s large moon Titan mimics Earth in many ways. But Titan displays different kinds of chemistry in a far colder environment. Given the similarities, the question of life inevitably arises: could Titan support some kind of simple life? Given the differences, scientists ponder the best places to look for Titan life. In late July, 2018, a new study published in the journal Astrobiology and reported on in Astrobiology Magazine suggests the best places on Titan to look for evidence of life.

Titan is a geological wonderland for planetary scientists. It has rivers, lakes and seas of actual liquid – not water, but the hydrocarbons methane and ethane – and it has mountain ranges, possible ice volcanoes (aka cryovolcanoes) and vast hydrocarbon dunes. There is also evidence for a subsurface ocean of water, similar to those believed to lie beneath the surface of Jupiter’s moon Europa and Saturn’s moon Enceladus.

Perhaps surprisingly, the research team, led by Catherine Neish, a planetary scientist specializing in impact cratering at the University of Western Ontario, suggested that the best locations to look for life on Titan would not be the lakes or seas. Instead, the new work shows a better place to look would be within impact craters and cryovolcanoes on Titan.

The scientists reason that these areas are where water ice in Titan’s crust could temporarily melt into a liquid. Water is still the only solvent known to be able to support life as we know it.

A large, fairly young crater on Titan, about 25 miles (40 km) in diameter. Such craters could temporarily melt frozen water in the crust, providing an environment for pre-biotic or biotic molecules to form. Image via NASA/JPL-Caltech.

Various studies have suggested that liquid methane and ethane could support life. But Saturn’s moon Titan – some nine farther from the sun than Earth – is very cold, with surface temperatures hovering around -300 degrees Fahrenheit (–179 degrees Celsius). Methane and ethane do remain liquid at Titan’s surface temperature, but it’s too cold there for biochemical processes, at least as far as we know (although that, too, is a matter of debate).

Titan’s surface is also covered with tholins, which are large, complex organic molecules produced when gases are subjected to cosmic radiation. When mixed with liquid water, tholins can produce amino acids, which are, essentially, life’s building blocks. According to researcher Morgan Cable at NASA’s Jet Propulsion Laboratory in Pasadena, California:

When we mix tholins with liquid water, we make amino acids really fast. So any place where there is liquid water on Titan’s surface or near its surface could be generating the precursors to life – biomolecules – that would be important for life as we know it, and that’s really exciting.

The temperatures on Titan’s surface are too cold for liquid water, so where could it be found? The answer is Titan’s craters and cryovolcanoes. The processes involved with both of these geologic features can melt water ice into liquid, even if only temporarily.

But that might be enough for more complex organic molecules like amino acids to form.

Sotra Facula is a possible cryovolcano on Titan, one of the few candidates known. Image via NASA/JPL–Caltech/USGS/University of Arizona.

Another view of Sotra Facula. This image was built from radar topography with infrared colors overlaid on top. Image via NASA/JPL–Caltech/USGS/University of Arizona.

Between craters and cryovolcanoes, it would seem that craters would be the most ideal location for pre-biotic or biotic chemistry to occur. As Neish explained:

Craters really emerged as the clear winner for three main reasons. One, is that we’re pretty sure there are craters on Titan. Cratering is a very common geologic process and we see circular features that are almost certainly craters on the surface.

Neish also noted that craters would produce more liquid water melt than a cryovolcano, so any water would remain liquid for a longer period of time. She also added:

The last point is that impact craters should produce water that’s at a higher temperature than a cryovolcano.

Warmer water would allow for faster chemical reaction rates, which would help in the creation of per-biotic or even biotic molecules. The largest known craters on Titan are Sinlap (70 miles/112 kms in diameter), Selk (56 miles/90 kms) and Menrva (244 miles/392 kms). These would be the primary locations to look for biomolecules. 

David Grinspoon at the Planetary Science Institute isn’t convinced yet, however. He commented:

We don’t know where to search even with results like this. I wouldn’t use it to guide our next mission to Titan. It’s premature.

Titan is well-known for its lakes and seas of liquid methane/ethane, such as Ligiea Mare, shown here. Image via NASA/JPL-Caltech/ASI/Cornell.

So what about cryovolcanoes? They haven’t actually been confirmed yet to exist on Titan, and if they do, they are more rare than craters (even though craters are also relatively rare on Titan). The most likely feature to be a cryovolcano is a mountain with a caldera on top called Sotra Facula. Other than that, they seem to be few and far between. As Neish said:

Cryovolcanism is the harder thing to do and there is very little evidence of it on Titan.

Diagram illustrating how biosignatures could also be transported from the subsurface ocean to the surface of Titan. Image via Athanasios Karagiotas/Theoni Shalamberidze.

There is also, of course, a possible subsurface ocean of water on Titan, but, if it exists, it is deep below the moon’s surface and inaccessible to any robotic probes in the near future. For now, we can only imagine what might be in that alien abyss.

The methane/ethane lakes and seas should still be explored too; they are the only other known bodies of liquid on the surface of another moon or planet in the solar system. Methane-based life could theoretically exist in such environments, so it would obviously be a good idea to look, at least.

Bottom line: Titan is a world that is eerily similar to Earth in some ways, yet still uniquely alien. Whether it supports any kind of life is still a big question, but researchers now think they know the best places to search for it.

Source: Strategies for Detecting Biological Molecules on Titan

Via Astrobiology Magazine

from EarthSky https://ift.tt/2LVhVIh

How to see a full circle rainbow

Full circle rainbow was captured over Cottesloe Beach near Perth, Australia in 2013 by Colin Leonhardt of Birdseye View Photography. He was in a helicopter flying between a setting sun and a downpour. Used with permission. Order prints of this photo.

When sunlight and raindrops combine to make a rainbow, they can make a whole circle of light in the sky. But it’s a very rare sight. Sky conditions have to be just right for this, and even if they are, the bottom part of a full-circle rainbow is usually blocked by your horizon. That’s why we see rainbows not as circles, but as arcs across our sky.

When you see a rainbow, notice the height of the sun. It helps determine how much of an arc you’ll see. The lower the sun, the higher the top of the rainbow. If you could get up high enough, you’d see that some rainbows continue below the horizon seen from closer to sea-level. Mountain climbers sometimes see more of a full-circle rainbow, though even a high mountain isn’t high enough to show you the whole circle.

Pilots do sometimes report seeing genuine full-circle rainbows. They’d be tough to see out the small windows we passengers look through, but pilots have a much better view from up front.

By the way, we searched for images of full-circle rainbows. But most of the ones we found weren’t really rainbows. They were either halos around the sun – or airplane glories.

What’s NOT a rainbow? Hear from a master of sky optics

In this photo, the shadow of the photographer’s head – bottom, center – marks the center of the rainbow circle. This double rainbow was captured in Wrangell-St. Elias National Park, Alaska. Photo via Eric Rolph at Wikimedia Commons

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Bottom line: Can you ever see a full-circle rainbow in the sky? Yes, but they’re most often seen by pilots, who have a good view of the sky from the wide front windows of a plane.

from EarthSky https://ift.tt/17ANoUk

Full circle rainbow was captured over Cottesloe Beach near Perth, Australia in 2013 by Colin Leonhardt of Birdseye View Photography. He was in a helicopter flying between a setting sun and a downpour. Used with permission. Order prints of this photo.

When sunlight and raindrops combine to make a rainbow, they can make a whole circle of light in the sky. But it’s a very rare sight. Sky conditions have to be just right for this, and even if they are, the bottom part of a full-circle rainbow is usually blocked by your horizon. That’s why we see rainbows not as circles, but as arcs across our sky.

When you see a rainbow, notice the height of the sun. It helps determine how much of an arc you’ll see. The lower the sun, the higher the top of the rainbow. If you could get up high enough, you’d see that some rainbows continue below the horizon seen from closer to sea-level. Mountain climbers sometimes see more of a full-circle rainbow, though even a high mountain isn’t high enough to show you the whole circle.

Pilots do sometimes report seeing genuine full-circle rainbows. They’d be tough to see out the small windows we passengers look through, but pilots have a much better view from up front.

By the way, we searched for images of full-circle rainbows. But most of the ones we found weren’t really rainbows. They were either halos around the sun – or airplane glories.

What’s NOT a rainbow? Hear from a master of sky optics

In this photo, the shadow of the photographer’s head – bottom, center – marks the center of the rainbow circle. This double rainbow was captured in Wrangell-St. Elias National Park, Alaska. Photo via Eric Rolph at Wikimedia Commons

Enjoying EarthSky? Sign up for our free daily newsletter today!

Bottom line: Can you ever see a full-circle rainbow in the sky? Yes, but they’re most often seen by pilots, who have a good view of the sky from the wide front windows of a plane.

from EarthSky https://ift.tt/17ANoUk

Climate change made 2018 European heatwave up to ‘five times’ more likely

This is a re-post from Carbon Brief

A rapid assessment by scientists of the ongoing heatwave across northern Europe this summer has found that human-caused climate change made it as much as five times more likely to have occurred.

The preliminary analysis, by a team of scientists at the World Weather Attribution network, uses data from seven weather stations in Ireland, the Netherlands, Denmark, Sweden, Norway and Finland. The team were not able to get sufficient data at short notice to include a UK station.

The findings suggest that rising global temperatures have increased the likelihood of such hot temperatures by five times in Denmark, three times in the Netherlands and two times in Ireland.

The sizeable year-to-year fluctuations in summer weather in Scandinavia makes it harder to pin down a specific change in likelihood for the heatwaves in Norway, Sweden and Finland, the researchers say. However, “we can state that, yes, heatwaves have increased – and are increasing – in Scandinavia as in the rest of Europe”, says one of the scientists involved.

Climate change link

From the UK to Canada through to Oman and Japan, the northern hemisphere has seen a pattern of prolonged heatwaves in recent weeks. The record-breaking temperatures have been linked to wildfires in Sweden, Greece and California and heatwave deaths in several countries.

Many news reports have speculated on the potential role that rising global temperatures could be having on the spate of extremes this summer. Carbon Brief has published a summary of all the media coverage from recent weeks.

Now, in a rapid analysis over the past few days, scientists have been able to quantify the impact that climate change is having.

The study uses data from individual weather stations, explained Dr Friederike Otto, the deputy director of the Environmental Change Institute at the University of Oxford, in a press conference this morning:

“What we have done in this study is look at locations – individual weather stations, so at the place where people live – to represent the heatwave that people are actually experiencing.”

These stations were selected because they had “data immediately available to us”, added Otto, and also because they had long records that could be analysed. Because the team needed data as close to real-time as possible – while they were carrying out their analysis – they used forecasts of temperature for the most recent few days.

The locations of each station were: Dublin, Ireland; De Bilt, Netherlands; Copenhagen, Denmark; Oslo, Norway; Linköping, Sweden; Sodankyla, northern Finland; and Jokioinen, southern Finland.

The researchers defined the heatwave at each location by taking the hottest three-day period in the year so far. Although this is a short period compared to the extended heatwave for much of Europe this summer, using longer period would have left fewer hot events to analyse, the researchers say.

The map below shows how the hottest three-day period across Europe this summer so far compares to the hottest three-days in an average summer. The orange and red shading show higher-than-average temperatures, while the blues show lower. It illustrates how unusually warm Northern Europe, in particular, has been.

The hottest 3-day consecutive period in 2018 (up to the end of July) compared to the average for the 1981-2010. Based on observed data up to 24 July, forecasts up to 31 July. Source: World Weather Attribution

The researchers used the long-term observed records of temperature to work out how rare this year’s heatwaves have been. They found that such warm three-day periods would occur once every five-to-eight years in Ireland, Denmark, Norway and the Netherlands, but just once every 30 years in Sweden and less than once every 90 years in Finland.

For the weather station in northern Finland, the recent heat is unlike anything on record, said Dr Geert Jan van Oldenborgh, from the Royal Netherlands Meteorological Institute:

“We found that for the weather station in the far north, in the Arctic Circle, the current heat wave is just extraordinary – unprecedented in the historical record.”

Using a collection of climate models, they then assessed the probability of such an event occurring in the current climate – which includes the influence of human-caused climate change – and in the past before the human impact on climate was detectable. Before using each model, they checked it could simulate heatwaves in each location accurately.

The findings suggest that climate change made the heatwave around twice as likely in Dublin (between a range of 1.2 and 3.3 times), five times as likely in Copenhagen (with a range of 2.4-12) and more than three times as likely in De Bild (with a range of 1.6-16).

The change in likelihood was “much harder to quantify” for the more northerly stations, the researchers say.

‘Heatwaves have increased’

The team also looked into how the frequency of heatwaves has changed over the long records of each station, explained van Oldenborgh in the press conference:

“For Ireland, Netherlands and Denmark, there is a clear trend in the observations towards more heatwaves. In the Netherlands, that trend is really large.”

For Norway, Sweden and Finland, there is not yet a statistically significant trend in heatwave changes in the observed data, noted van Oldenborgh:

“The reason for that is the variability of the weather from year to year is very large in this region and so it hides any trend.”

As a result, the team were “hesitant to put an actual number on the increase” in the region, said van Oldenborgh. Despite this, “we can state that, yes, heatwaves have increased – and are increasing – in Scandinavia as in the rest of Europe”, he added.

Single-event attribution

The new research is the latest in what are known as “single-event attribution” studies. The fast-moving area of research aims to identify the influence that human-caused climate change does – or does not – have on extreme weather events around the world. Carbon Brief has previously mapped all the peer-reviewed attribution studies in the scientific literature.

The research was conducted by World Weather Attribution – a network of scientists in six institutions established to provide near-real time analysis of possible links between climate change and extreme weather events.

It should be noted that the findings are still only preliminary, the researchers say:

“It is important to note that, compared to other attribution analyses of European summers, attributing a heatwave early in the season with the whole of August still to come will only give a preliminary result of the 2018 northern hemisphere heatwave season.”

The findings also have not yet been peer-reviewed. The researchers will be submitting the results to a journal once the summer is over. However, the methods underlying the findings are well established and have been published in previous attribution studies.

from Skeptical Science https://ift.tt/2M9CflZ

This is a re-post from Carbon Brief

A rapid assessment by scientists of the ongoing heatwave across northern Europe this summer has found that human-caused climate change made it as much as five times more likely to have occurred.

The preliminary analysis, by a team of scientists at the World Weather Attribution network, uses data from seven weather stations in Ireland, the Netherlands, Denmark, Sweden, Norway and Finland. The team were not able to get sufficient data at short notice to include a UK station.

The findings suggest that rising global temperatures have increased the likelihood of such hot temperatures by five times in Denmark, three times in the Netherlands and two times in Ireland.

The sizeable year-to-year fluctuations in summer weather in Scandinavia makes it harder to pin down a specific change in likelihood for the heatwaves in Norway, Sweden and Finland, the researchers say. However, “we can state that, yes, heatwaves have increased – and are increasing – in Scandinavia as in the rest of Europe”, says one of the scientists involved.

Climate change link

From the UK to Canada through to Oman and Japan, the northern hemisphere has seen a pattern of prolonged heatwaves in recent weeks. The record-breaking temperatures have been linked to wildfires in Sweden, Greece and California and heatwave deaths in several countries.

Many news reports have speculated on the potential role that rising global temperatures could be having on the spate of extremes this summer. Carbon Brief has published a summary of all the media coverage from recent weeks.

Now, in a rapid analysis over the past few days, scientists have been able to quantify the impact that climate change is having.

The study uses data from individual weather stations, explained Dr Friederike Otto, the deputy director of the Environmental Change Institute at the University of Oxford, in a press conference this morning:

“What we have done in this study is look at locations – individual weather stations, so at the place where people live – to represent the heatwave that people are actually experiencing.”

These stations were selected because they had “data immediately available to us”, added Otto, and also because they had long records that could be analysed. Because the team needed data as close to real-time as possible – while they were carrying out their analysis – they used forecasts of temperature for the most recent few days.

The locations of each station were: Dublin, Ireland; De Bilt, Netherlands; Copenhagen, Denmark; Oslo, Norway; Linköping, Sweden; Sodankyla, northern Finland; and Jokioinen, southern Finland.

The researchers defined the heatwave at each location by taking the hottest three-day period in the year so far. Although this is a short period compared to the extended heatwave for much of Europe this summer, using longer period would have left fewer hot events to analyse, the researchers say.

The map below shows how the hottest three-day period across Europe this summer so far compares to the hottest three-days in an average summer. The orange and red shading show higher-than-average temperatures, while the blues show lower. It illustrates how unusually warm Northern Europe, in particular, has been.

The hottest 3-day consecutive period in 2018 (up to the end of July) compared to the average for the 1981-2010. Based on observed data up to 24 July, forecasts up to 31 July. Source: World Weather Attribution

The researchers used the long-term observed records of temperature to work out how rare this year’s heatwaves have been. They found that such warm three-day periods would occur once every five-to-eight years in Ireland, Denmark, Norway and the Netherlands, but just once every 30 years in Sweden and less than once every 90 years in Finland.

For the weather station in northern Finland, the recent heat is unlike anything on record, said Dr Geert Jan van Oldenborgh, from the Royal Netherlands Meteorological Institute:

“We found that for the weather station in the far north, in the Arctic Circle, the current heat wave is just extraordinary – unprecedented in the historical record.”

Using a collection of climate models, they then assessed the probability of such an event occurring in the current climate – which includes the influence of human-caused climate change – and in the past before the human impact on climate was detectable. Before using each model, they checked it could simulate heatwaves in each location accurately.

The findings suggest that climate change made the heatwave around twice as likely in Dublin (between a range of 1.2 and 3.3 times), five times as likely in Copenhagen (with a range of 2.4-12) and more than three times as likely in De Bild (with a range of 1.6-16).

The change in likelihood was “much harder to quantify” for the more northerly stations, the researchers say.

‘Heatwaves have increased’

The team also looked into how the frequency of heatwaves has changed over the long records of each station, explained van Oldenborgh in the press conference:

“For Ireland, Netherlands and Denmark, there is a clear trend in the observations towards more heatwaves. In the Netherlands, that trend is really large.”

For Norway, Sweden and Finland, there is not yet a statistically significant trend in heatwave changes in the observed data, noted van Oldenborgh:

“The reason for that is the variability of the weather from year to year is very large in this region and so it hides any trend.”

As a result, the team were “hesitant to put an actual number on the increase” in the region, said van Oldenborgh. Despite this, “we can state that, yes, heatwaves have increased – and are increasing – in Scandinavia as in the rest of Europe”, he added.

Single-event attribution

The new research is the latest in what are known as “single-event attribution” studies. The fast-moving area of research aims to identify the influence that human-caused climate change does – or does not – have on extreme weather events around the world. Carbon Brief has previously mapped all the peer-reviewed attribution studies in the scientific literature.

The research was conducted by World Weather Attribution – a network of scientists in six institutions established to provide near-real time analysis of possible links between climate change and extreme weather events.

It should be noted that the findings are still only preliminary, the researchers say:

“It is important to note that, compared to other attribution analyses of European summers, attributing a heatwave early in the season with the whole of August still to come will only give a preliminary result of the 2018 northern hemisphere heatwave season.”

The findings also have not yet been peer-reviewed. The researchers will be submitting the results to a journal once the summer is over. However, the methods underlying the findings are well established and have been published in previous attribution studies.

from Skeptical Science https://ift.tt/2M9CflZ

Exploring the Watershed

 by Tom Damm

To fully appreciate why two EPA regions are working to improve the Delaware River Watershed, it helps to experience the area’s natural wonders.

I had the opportunity to do so recently on two kayaking day trips.

The first was an intimate tour of a county lake that connects with Assunpink Creek and eventually the Delaware River near Trenton, New Jersey.

The next day, I joined paddlers on the final day of the 2018 Delaware River Sojourn as we explored the Abbott Marshlands via two winding creeks.

At Mercer Lake, Mercer County Park Naturalist Christy Athmejvar led a group of us on a tour of the lake’s nooks and crannies, wisely advising us to keep our binoculars handy as she spied cool critters and plant life.

In one hidden cove, as we passed a beaver dam, we saw 14 painted turtles basking on a log and three bullfrogs staring ahead with their bulbous eyes and wide mouths just above the water.

Paddling near the shoreline, Christy would quickly interrupt herself to point out a red-winged blackbird or an American goldfinch soaring above or, to her delight, a double-crested cormorant tucked in the water with only its head and long, curved neck visible.

Toward the end of the tour, her visual sweeps of the treetops scored the highlights of the day – two bald eagles.  We kept our binoculars trained on the majestic birds as we bobbed in the kayaks, savoring our lucky finds.

A day later, it was time to join the sojourn that was completing its 24^th annual, eight-day trip down sections of the Delaware River.

Fortunate that a thunderstorm threat never materialized, our sojourners, ranging from youth groups to seasoned veterans of the journey, paddled the warm, gentle waters of Crosswicks and Watson creeks on an eight-mile round-trip to the Tulpehacking Nature Center in Hamilton, New Jersey.

We started and finished at Bordentown Beach at the confluence of the Delaware River and Crosswicks Creek.  Along the way, we struck up conversations and at times joined our kayaks and canoes, drifting with the tide as we heard presentations about the Abbott Marshlands.

The talks focused on successful efforts to preserve and expand the marshlands, their rich cultural and historic legacy, and the support they provide for more than 1,200 species of plants and wildlife.

Whether on water or land, head out to some of the natural attractions of the Delaware River Watershed to get a better sense for why its restoration is so important to EPA and its partners.

And for what you can do to help, check out this site.

 

About the Author: Tom Damm has been with EPA since 2002 and now serves as communications coordinator for the region’s Water Protection Division.

 

from The EPA Blog https://ift.tt/2n4DTu5

 by Tom Damm

To fully appreciate why two EPA regions are working to improve the Delaware River Watershed, it helps to experience the area’s natural wonders.

I had the opportunity to do so recently on two kayaking day trips.

The first was an intimate tour of a county lake that connects with Assunpink Creek and eventually the Delaware River near Trenton, New Jersey.

The next day, I joined paddlers on the final day of the 2018 Delaware River Sojourn as we explored the Abbott Marshlands via two winding creeks.

At Mercer Lake, Mercer County Park Naturalist Christy Athmejvar led a group of us on a tour of the lake’s nooks and crannies, wisely advising us to keep our binoculars handy as she spied cool critters and plant life.

In one hidden cove, as we passed a beaver dam, we saw 14 painted turtles basking on a log and three bullfrogs staring ahead with their bulbous eyes and wide mouths just above the water.

Paddling near the shoreline, Christy would quickly interrupt herself to point out a red-winged blackbird or an American goldfinch soaring above or, to her delight, a double-crested cormorant tucked in the water with only its head and long, curved neck visible.

Toward the end of the tour, her visual sweeps of the treetops scored the highlights of the day – two bald eagles.  We kept our binoculars trained on the majestic birds as we bobbed in the kayaks, savoring our lucky finds.

A day later, it was time to join the sojourn that was completing its 24^th annual, eight-day trip down sections of the Delaware River.

Fortunate that a thunderstorm threat never materialized, our sojourners, ranging from youth groups to seasoned veterans of the journey, paddled the warm, gentle waters of Crosswicks and Watson creeks on an eight-mile round-trip to the Tulpehacking Nature Center in Hamilton, New Jersey.

We started and finished at Bordentown Beach at the confluence of the Delaware River and Crosswicks Creek.  Along the way, we struck up conversations and at times joined our kayaks and canoes, drifting with the tide as we heard presentations about the Abbott Marshlands.

The talks focused on successful efforts to preserve and expand the marshlands, their rich cultural and historic legacy, and the support they provide for more than 1,200 species of plants and wildlife.

Whether on water or land, head out to some of the natural attractions of the Delaware River Watershed to get a better sense for why its restoration is so important to EPA and its partners.

And for what you can do to help, check out this site.

 

About the Author: Tom Damm has been with EPA since 2002 and now serves as communications coordinator for the region’s Water Protection Division.

 

from The EPA Blog https://ift.tt/2n4DTu5

Expect moonless nights for 2018’s Perseid meteors

Perseid meteor on the morning of August 12, 2017, from Hrvoje Crnjak in Šibenik, Croatia. Notice the variations in brightness and color throughout, and the little “pop” of brightness toward the bottom. A brightness “pop” like that comes from a clump of vaporizing debris. Thank you, Hrvoje! Click for more 2017 Perseids.

No matter where you live worldwide, the 2018 Perseid meteor shower will probably produce the greatest number of meteors on the mornings of August 11, 12 and 13. In a dark, moonless sky, this annual shower often produces 50 or more meteors per hour. And this year, in 2018, there will be no moonlight to ruin the show.

It should be an awesome year to watch the Perseids!

In the Northern Hemisphere, we rank the August Perseids as an all-time favorite meteor shower of every year. For us, this major shower takes place during the lazy, hazy days of summer, when many families are on vacation. And what could be more luxurious than taking a siesta in the heat of the day and watching this summertime classic in the relative coolness of night?

People tend to focus on the peak mornings of the shower and that’s entirely appropriate. But meteors in annual showers – which come from streams of debris left behind in space by comets – typically last weeks, not days. Perseid meteors have been streaking across our skies since around July 17. We’ll see Perseids for 10 days or so after the peak mornings on August 11, 12 and 13. What’s more, the Perseids tend to build up gradually, yet fall off rapidly. So it’s often wise to watch in the couple of weeks prior to the peak … but not this year.

We can’t start watching for Perseids in early August in 2018, because the moon is in the way.

This is about the moon phase you’ll see on August 1, 2018. It’s a waning gibbous moon, rising in late evening, casting its light around in the peak hours for watching meteors between midnight and dawn. Wait until about mid-week next week – say, around August 7 or 8, 2018 – to start any serious meteor watching. Between now and then, look for the brightest Perseids in moonlight! Photo by Lunar101-MoonBook.

When and how should I watch the Perseid meteor shower in 2018? The best time to watch most meteor showers is between midnight and dawn, and the Perseids are no exception. The best mornings are probably August 11, 12 and 13. The best skies are those far from city lights.

Between early August and the peak mornings, you might catch a Perseid meteor in moonlight. New moon will be August 11, but don’t think you have to wait until then to see any meteors. The moon will be a slim crescent in the days prior to August 11, and a crescent moon is easy to blot out by sitting in the shadow of a tree or building. Plus, as the days leading up to new moon pass, the moon will be rising closer and closer to the time of sunrise.

Also remember, the the Delta Aquarid meteor shower is still rambling along steadily. You’ll see mostly Perseids but also a few Delta Aquarids in the mix.

No matter how many meteors you see, you might see something, and it might be a lot of fun.

Composite of 12 images acquired on August 13 by Felix Zai in Toronto. He wrote: “Perseid meteor shower gave a good show even though the moon light drown out most of the fainter ones. A huge fireball was captured in this photo.” Thanks, Felix! By the way, it’s only in a meteor “storm” that you’d see this many meteors at once. Even in a rich shower, you typically see only 1 or 2 meteors at a time. Click for more 2017 Perseids.

Don’t rule out early evenings, either. In a typical year, although the meteor numbers increase after midnight, the Perseid meteors still start to fly at mid-to-late evening from northerly latitudes. South of the equator, the Perseids start to streak the sky around midnight. If fortune smiles upon you, the evening hours might offer you an earthgrazer – a looooong, slow, colorful meteor traveling horizontally across the evening sky. Earthgrazer meteors are rare but memorable. Perseid earthgrazers appear before midnight, when the radiant point of the shower is close to the horizon.

From mid-northern latitudes, the constellation Perseus, the stars Capella and Aldebaran, and the Pleiades cluster light up the northeast sky in the wee hours after midnight on August nights. The meteors radiate from Perseus.

Here’s a cool binocular object to look for while you’re watching the meteors. The constellation Cassiopeia points out the famous Double Cluster in northern tip of the constellation Perseus. Plus, the Double Cluster nearly marks the radiant of the Perseid meteor shower. Photo by Flickr user madmiked

General rules for Perseid-watching. No special equipment, or knowledge of the constellations, needed.

Find a dark, open sky to enjoy the show. An open sky is essential because these meteors fly across the sky in many different directions and in front of numerous constellations.

Give yourself at least an hour of observing time, for these meteors in meteor showers come in spurts and are interspersed with lulls. Remember, your eyes can take as long as 20 minutes to adapt to the darkness of night. So don’t rush the process.

Know that the meteors all come from a single point in the sky. If you trace the paths of the Perseid meteors backwards, you’d find they all come from a point in front of the constellation Perseus. Don’t worry about which stars are Perseus. Just enjoying knowing and observing that they all come from one place on the sky’s dome.

Enjoy the comfort of a reclining lawn chair. Bring along some other things you might enjoy also, like a thermos filled with a hot drink.

Remember … all good things come to those who wait. Meteors are part of nature. There’s no way to predict exactly how many you’ll see on any given night. Find a good spot, watch, wait.

You’ll see some.

Earth encounters debris from comet, via AstroBob

What’s the source of the Perseid meteor shower? Every year, from around July 17 to August 24, our planet Earth crosses the orbital path of Comet Swift-Tuttle, the parent of the Perseid meteor shower. Debris from this comet litters the comet’s orbit, but we don’t really get into the thick of the comet rubble until after the first week of August. The bits and pieces from Comet Swift-Tuttle slam into the Earth’s upper atmosphere at some 130,000 miles (210,000 km) per hour, lighting up the nighttime with fast-moving Perseid meteors.

If our planet happens to pass through an unusually dense clump of meteoroids – comet rubble – we’ll see an elevated number of meteors. We can always hope!

Comet Swift-Tuttle has a very eccentric – oblong – orbit that takes this comet outside the orbit of Pluto when farthest from the sun, and inside the Earth’s orbit when closest to the sun. It orbits the sun in a period of about 133 years. Every time this comet passes through the inner solar system, the sun warms and softens up the ices in the comet, causing it to release fresh comet material into its orbital stream.

Comet Swift-Tuttle last reached perihelion – closest point to the sun – in December 1992 and will do so next in July 2126.

The radiant point for the Perseid meteor shower is in the constellation Perseus. But you don’t have to find a shower’s radiant point to see meteors. Instead, the meteors will be flying in all parts of the sky.

What is the radiant point for the Perseid meteor shower? If you trace all the Perseid meteors backward, they all seem to come from the constellation Perseus, near the famous Double Cluster. Hence, the meteor shower is named in the honor of the constellation Perseus the Hero.

However, this is a chance alignment of the meteor shower radiant with the constellation Perseus. The stars in Perseus are light-years distant while these meteors burn up about 100 kilometers (60 miles) above the Earth’s surface. If any meteor survives its fiery plunge to hit the ground intact, the remaining portion is called a meteorite. Few – if any – meteors in meteor showers become meteorites, however, because of the flimsy nature of comet debris. Most meteorites are the remains of asteroids.

In ancient Greek star lore, Perseus is the son of the god Zeus and the mortal Danae. It is said that the Perseid shower commemorates the time when Zeus visited Danae, the mother of Perseus, in a shower of gold.

Russ Adams caught these 2 meteors, traveling on parallel paths, on the morning of August 11, 2017. Click for more 2017 Perseids.

Bottom line: The 2018 Perseid meteor shower is expected to produce the most meteors in the predawn hours this weekend – on August 11, 12, and 13.

Everything you need to know: Delta Aquarid meteor shower

from EarthSky https://ift.tt/15Sj88b

Perseid meteor on the morning of August 12, 2017, from Hrvoje Crnjak in Šibenik, Croatia. Notice the variations in brightness and color throughout, and the little “pop” of brightness toward the bottom. A brightness “pop” like that comes from a clump of vaporizing debris. Thank you, Hrvoje! Click for more 2017 Perseids.

No matter where you live worldwide, the 2018 Perseid meteor shower will probably produce the greatest number of meteors on the mornings of August 11, 12 and 13. In a dark, moonless sky, this annual shower often produces 50 or more meteors per hour. And this year, in 2018, there will be no moonlight to ruin the show.

It should be an awesome year to watch the Perseids!

In the Northern Hemisphere, we rank the August Perseids as an all-time favorite meteor shower of every year. For us, this major shower takes place during the lazy, hazy days of summer, when many families are on vacation. And what could be more luxurious than taking a siesta in the heat of the day and watching this summertime classic in the relative coolness of night?

People tend to focus on the peak mornings of the shower and that’s entirely appropriate. But meteors in annual showers – which come from streams of debris left behind in space by comets – typically last weeks, not days. Perseid meteors have been streaking across our skies since around July 17. We’ll see Perseids for 10 days or so after the peak mornings on August 11, 12 and 13. What’s more, the Perseids tend to build up gradually, yet fall off rapidly. So it’s often wise to watch in the couple of weeks prior to the peak … but not this year.

We can’t start watching for Perseids in early August in 2018, because the moon is in the way.

This is about the moon phase you’ll see on August 1, 2018. It’s a waning gibbous moon, rising in late evening, casting its light around in the peak hours for watching meteors between midnight and dawn. Wait until about mid-week next week – say, around August 7 or 8, 2018 – to start any serious meteor watching. Between now and then, look for the brightest Perseids in moonlight! Photo by Lunar101-MoonBook.

When and how should I watch the Perseid meteor shower in 2018? The best time to watch most meteor showers is between midnight and dawn, and the Perseids are no exception. The best mornings are probably August 11, 12 and 13. The best skies are those far from city lights.

Between early August and the peak mornings, you might catch a Perseid meteor in moonlight. New moon will be August 11, but don’t think you have to wait until then to see any meteors. The moon will be a slim crescent in the days prior to August 11, and a crescent moon is easy to blot out by sitting in the shadow of a tree or building. Plus, as the days leading up to new moon pass, the moon will be rising closer and closer to the time of sunrise.

Also remember, the the Delta Aquarid meteor shower is still rambling along steadily. You’ll see mostly Perseids but also a few Delta Aquarids in the mix.

No matter how many meteors you see, you might see something, and it might be a lot of fun.

Composite of 12 images acquired on August 13 by Felix Zai in Toronto. He wrote: “Perseid meteor shower gave a good show even though the moon light drown out most of the fainter ones. A huge fireball was captured in this photo.” Thanks, Felix! By the way, it’s only in a meteor “storm” that you’d see this many meteors at once. Even in a rich shower, you typically see only 1 or 2 meteors at a time. Click for more 2017 Perseids.

Don’t rule out early evenings, either. In a typical year, although the meteor numbers increase after midnight, the Perseid meteors still start to fly at mid-to-late evening from northerly latitudes. South of the equator, the Perseids start to streak the sky around midnight. If fortune smiles upon you, the evening hours might offer you an earthgrazer – a looooong, slow, colorful meteor traveling horizontally across the evening sky. Earthgrazer meteors are rare but memorable. Perseid earthgrazers appear before midnight, when the radiant point of the shower is close to the horizon.

From mid-northern latitudes, the constellation Perseus, the stars Capella and Aldebaran, and the Pleiades cluster light up the northeast sky in the wee hours after midnight on August nights. The meteors radiate from Perseus.

Here’s a cool binocular object to look for while you’re watching the meteors. The constellation Cassiopeia points out the famous Double Cluster in northern tip of the constellation Perseus. Plus, the Double Cluster nearly marks the radiant of the Perseid meteor shower. Photo by Flickr user madmiked

General rules for Perseid-watching. No special equipment, or knowledge of the constellations, needed.

Find a dark, open sky to enjoy the show. An open sky is essential because these meteors fly across the sky in many different directions and in front of numerous constellations.

Give yourself at least an hour of observing time, for these meteors in meteor showers come in spurts and are interspersed with lulls. Remember, your eyes can take as long as 20 minutes to adapt to the darkness of night. So don’t rush the process.

Know that the meteors all come from a single point in the sky. If you trace the paths of the Perseid meteors backwards, you’d find they all come from a point in front of the constellation Perseus. Don’t worry about which stars are Perseus. Just enjoying knowing and observing that they all come from one place on the sky’s dome.

Enjoy the comfort of a reclining lawn chair. Bring along some other things you might enjoy also, like a thermos filled with a hot drink.

Remember … all good things come to those who wait. Meteors are part of nature. There’s no way to predict exactly how many you’ll see on any given night. Find a good spot, watch, wait.

You’ll see some.

Earth encounters debris from comet, via AstroBob

What’s the source of the Perseid meteor shower? Every year, from around July 17 to August 24, our planet Earth crosses the orbital path of Comet Swift-Tuttle, the parent of the Perseid meteor shower. Debris from this comet litters the comet’s orbit, but we don’t really get into the thick of the comet rubble until after the first week of August. The bits and pieces from Comet Swift-Tuttle slam into the Earth’s upper atmosphere at some 130,000 miles (210,000 km) per hour, lighting up the nighttime with fast-moving Perseid meteors.

If our planet happens to pass through an unusually dense clump of meteoroids – comet rubble – we’ll see an elevated number of meteors. We can always hope!

Comet Swift-Tuttle has a very eccentric – oblong – orbit that takes this comet outside the orbit of Pluto when farthest from the sun, and inside the Earth’s orbit when closest to the sun. It orbits the sun in a period of about 133 years. Every time this comet passes through the inner solar system, the sun warms and softens up the ices in the comet, causing it to release fresh comet material into its orbital stream.

Comet Swift-Tuttle last reached perihelion – closest point to the sun – in December 1992 and will do so next in July 2126.

The radiant point for the Perseid meteor shower is in the constellation Perseus. But you don’t have to find a shower’s radiant point to see meteors. Instead, the meteors will be flying in all parts of the sky.

What is the radiant point for the Perseid meteor shower? If you trace all the Perseid meteors backward, they all seem to come from the constellation Perseus, near the famous Double Cluster. Hence, the meteor shower is named in the honor of the constellation Perseus the Hero.

However, this is a chance alignment of the meteor shower radiant with the constellation Perseus. The stars in Perseus are light-years distant while these meteors burn up about 100 kilometers (60 miles) above the Earth’s surface. If any meteor survives its fiery plunge to hit the ground intact, the remaining portion is called a meteorite. Few – if any – meteors in meteor showers become meteorites, however, because of the flimsy nature of comet debris. Most meteorites are the remains of asteroids.

In ancient Greek star lore, Perseus is the son of the god Zeus and the mortal Danae. It is said that the Perseid shower commemorates the time when Zeus visited Danae, the mother of Perseus, in a shower of gold.

Russ Adams caught these 2 meteors, traveling on parallel paths, on the morning of August 11, 2017. Click for more 2017 Perseids.

Bottom line: The 2018 Perseid meteor shower is expected to produce the most meteors in the predawn hours this weekend – on August 11, 12, and 13.

Everything you need to know: Delta Aquarid meteor shower

from EarthSky https://ift.tt/15Sj88b

Dust in space: 10 cool things to know

Dark lanes of dust crisscross the giant elliptical galaxy Centaurus A in this image from NASA’s Hubble Space Telescope. Image via NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.

By Preston Dyches/NASA Science

To most of us, dust is something to be cleaned up, washed off or wiped away. But the tiny particles that float about and settle on surfaces play an important role in a variety of processes on Earth and across the solar system. So put away that feather duster for a few moments, as we share with you 10 things to know about dust.

1. Dust doesn’t mean dirty, it means tiny

Not all of what we call “dust” is made of the same stuff. Dust in your home generally consists of things like particles of sand and soil, pollen, dander (dead skin cells), pet hair, furniture fibers and cosmetics. But in space, dust can refer to any sort of fine particles smaller than a grain of sand. Dust is most commonly bits of rock or carbon-rich, soot-like grains, but in the outer solar system, far from the sun’s warmth, it’s also common to find tiny grains of ice as well. Galaxies, including our Milky Way, contain giant clouds of fine dust that are light years across – the ingredients for future generations of planetary systems like ours.

Dramatic plumes, both large and small, spray water ice particles and vapor along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus. Image via NASA/JPL/Space Science Institute.

2. Some are big, some are small (and big ones tend to fall)

Dust grains come in a range of sizes, which affects their properties. Particles can be extremely tiny, from only a few tens of nanometers (mere billionths of a meter) wide, to nearly a millimeter wide. As you might expect, smaller dust grains are more easily lifted and pushed around, be it by winds or magnetic, electrical and gravitational forces. Even the gentle pressure of sunlight is enough to move smaller dust particles in space. Bigger particles tend to be heavier, and they settle out more easily under the influence of gravity.

For example, on Earth, powerful winds can whip up large amounts of dust into the atmosphere. While the smaller grains can be transported over great distances, the heavier particles generally sink back to the ground near their source. On Saturn’s moon Enceladus, jets of icy dust particles spray hundreds of miles up from the surface; the bigger particles are lofted only a few tens of miles (or kilometers) and fall back to the ground, while the finest particles escape the moon’s gravity and go into orbit around Saturn to create the planet’s E ring.

Dust in the spiral galaxy M74 appears red in this image from NASA’s Spitzer Space Telescope. Data from Spitzer provided evidence that supernovae – the explosive deaths of massive stars – act as “dust factories,” seeding galaxies with cosmic dust particles. Image via NASA/JPL-Caltech/STScI.

3. It’s EVERYWHERE

Generally speaking, the space between the planets is pretty empty, but not completely so. Particles cast off by comets and ground up bits of asteroids are found throughout the solar system. Take any volume of space half a mile (1 kilometer) on a side, and you’d average a few micron-sized particles (grains the thickness of a red blood cell).

Dust in the solar system was a lot more abundant in the past. There was a huge amount of it present as the planets began to coalesce out of the disk of material that formed the sun. In fact, motes of dust gently sticking together were likely some of the earliest seeds of the planet-building process. But where did all that dust come from, originally? Some of it comes from stars like our sun, which blow off their outer layers in their later years. But lots of it also comes from exploding stars, which blast huge amounts of dust and gas into space when they go boom.

This mosaic of images from NASA’s Galileo spacecraft shows Jupiter’s ring system, which was only discovered after spacecraft had flown past the planet and could see the rings backlit by the sun. Image via NASA/JPL-Caltech/Cornell University.

4. From a certain point of view

Dust is easier to see from certain viewing angles. Tiny particles scatter light depending on how big their grains are. Larger particles tend to scatter light back in the direction from which it came, while very tiny particles tend to scatter light forward, more or less in the direction it was already going. Because of this property, structures like planetary rings made of the finest dusty particles are best viewed with the sun illuminating them from behind. For example, Jupiter’s rings were only discovered after the Voyager 1 spacecraft passed by the planet, where it could look back and see them backlit by the sun. You can see the same effect looking through a dusty windshield at sunset; when you face toward the sun, the dust becomes much more apparent.

Side-by-side movies show how dust enveloped the red planet in 2018, courtesy of NASA’s Mars Reconnaissance Orbiter. Image via NASA/JPL-Caltech/MSSS.

5. Dust storms are common on Mars

Local dust storms occur frequently on Mars, and occasionally grow or merge to form regional systems, particularly during the southern spring and summer, when Mars is closest to the Sun. On rare occasions, regional storms produce a dust haze that encircles the planet and obscures surface features beneath. A few of these events may become truly global storms, such as one in 1971 that greeted the first spacecraft to orbit Mars, NASA’s Mariner 9. In mid-2018, a global dust storm enshrouded Mars, hiding much of the Red Planet’s surface from view and threatening the continued operation of NASA’s uber long-lived Opportunity rover. We’ve also seen global dust storms in 1977, 1982, 1994, 2001 and 2007.

Dust storms will likely present challenges for future astronauts on the Red Planet. Although the force of the wind on Mars is not as strong as portrayed in an early scene in the movie The Martian, dust lofted during storms could affect electronics and health, as well as the availability of solar energy.

Sarharan dust is carried by winds to South America, where it helps fertilize the Amazon. Via NASA’s Goddard Space Flight Center.

6. Dust from the Sahara goes global

Earth’s largest, hottest desert is connected to its largest tropical rain forest by dust. The Sahara Desert is a near-uninterrupted brown band of sand and scrub across the northern third of Africa. The Amazon rain forest is a dense green mass of humid jungle that covers northeast South America. But after strong winds sweep across the Sahara, a dusty cloud rises in the air, stretches between the continents, and ties together the desert and the jungle.

This trans-continental journey of dust is important because of what is in the dust. Specifically, the dust picked up from the Bodélé Depression in Chad – an ancient lake bed where minerals composed of dead microorganisms are loaded with phosphorus. Phosphorus is an essential nutrient for plant proteins and growth, which the nutrient-poor Amazon rain forest depends on in order to flourish.

Saturn’s icy rings, backlit by the sun. The outer, bluish looking ring is composed entirely of icy dust particles sprayed into space by the moon Enceladus. Image via NASA/JPL-Caltech/SSI.

7. Rings and things

The rings of the giant planets contain a variety of different dusty materials. Jupiter’s rings are made of fine rock dust. Saturn’s rings are mostly pure water ice, with a sprinkling of other materials. (Side note about Saturn’s rings: While most of the particles are boulder-sized, there’s also lots of fine dust, and some of the fainter rings are mostly dust with few or no large particles.) Dust in the rings of Uranus and Neptune is made of dark, sooty material, probably rich in carbon.

Over time, dust gets removed from ring systems due to a variety of processes. For example, some of the dust falls into the planet’s atmosphere, while some gets swept up by the planets’ magnetic fields, and other dust settles onto the surfaces of the moons and other ring particles. Larger particles eventually form new moons or get ground down and mixed with incoming material. This means rings can change a lot over time, so understanding how the tiniest ring particles are being moved about has bearing on the history, origins and future of the rings.

Dark moon dust clings to the spacesuit of Apollo 17 astronaut Gene Cernan following an excursion on the lunar surface. Image via NASA.

8. Moon dust is clingy and might make you sick

So, dust is kind of a thing on the moon. When the Apollo astronauts visited the Moon, they found that lunar dust quickly coated their spacesuits and was difficult to remove. It was quite abrasive, causing wear on their spacesuit fabrics, seals and faceplates. It also clogged mechanisms like the joints in spacesuit limbs, and interfered with fasteners like zippers and Velcro. The astronauts also noted that it had a distinctive, pungent odor, not unlike gunpowder, and it was an eye and lung irritant.

Many of these properties apparently can be explained by the fact that lunar dust particles are quite rough and jagged. While dust particles on Earth get tumbled and ground by the wind into smoother shapes, this sort of weathering doesn’t happen so much on the moon. The roughness of moon dust grains makes it very easy for them to cling to surfaces and scratch them up. It also means they’re not the sort of thing you would want to inhale, as their jagged edges could damage delicate tissues in the lung.

Hubble Space Telescope image of comet ISON, taken in 2013. Image via NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

9. Dust is what makes comets so pretty

Most comets are basically clods of dust, rock and ice. They spend most of their time far from the sun, out in the refrigerated depths of the outer solar system, where they’re peacefully dormant. But when their orbits carry them closer to the sun – that is, roughly inside the orbit of Jupiter – comets wake up. In response to warming temperatures, the ices on and near their surfaces begin to turn into gases, expanding outward and away from the comet, and creating focused jets of material in places. Dust gets carried away by this rapidly expanding gas, creating a fuzzy cloud around the comet’s nucleus called a coma. Some of the dust also is drawn out into a long trail – the comet’s tail.

The dark object at center is the dusty disk of a newborn planetary system, seen edge-on by the Hubble Space Telescope. Image via NASA/ESA/STScI/J. Bally (Univ. Colorado) and H. Throop (SWRI).

10. We’re not the only ones who’re so dusty

Dust in our solar system is continually replenished by comets whizzing past the sun and the occasional asteroid collision, and it’s always being moved about, thanks to a variety of factors like the gravity of the planets and even the pressure of sunlight. Some of it even gets ejected from our solar system altogether.

With telescopes, we also observe dusty debris disks around many other stars. As in our own system, the dust in such disks should evolve over time, settling on planetary surfaces or being ejected, and this means the dust must be replenished in those star systems as well. So studying the dust in our planetary environs can tell us about other systems, and vice versa. Grains of dust from other planetary systems also pass through our neighborhood – a few spacecraft have actually captured and analyzed some them – offering us a tangible way to study material from other stars.

Bottom line: Ten facts about dust in space and on Earth.

from EarthSky https://ift.tt/2M8kZ0k

Dark lanes of dust crisscross the giant elliptical galaxy Centaurus A in this image from NASA’s Hubble Space Telescope. Image via NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration.

By Preston Dyches/NASA Science

To most of us, dust is something to be cleaned up, washed off or wiped away. But the tiny particles that float about and settle on surfaces play an important role in a variety of processes on Earth and across the solar system. So put away that feather duster for a few moments, as we share with you 10 things to know about dust.

1. Dust doesn’t mean dirty, it means tiny

Not all of what we call “dust” is made of the same stuff. Dust in your home generally consists of things like particles of sand and soil, pollen, dander (dead skin cells), pet hair, furniture fibers and cosmetics. But in space, dust can refer to any sort of fine particles smaller than a grain of sand. Dust is most commonly bits of rock or carbon-rich, soot-like grains, but in the outer solar system, far from the sun’s warmth, it’s also common to find tiny grains of ice as well. Galaxies, including our Milky Way, contain giant clouds of fine dust that are light years across – the ingredients for future generations of planetary systems like ours.

Dramatic plumes, both large and small, spray water ice particles and vapor along the famed “tiger stripes” near the south pole of Saturn’s moon Enceladus. Image via NASA/JPL/Space Science Institute.

2. Some are big, some are small (and big ones tend to fall)

Dust grains come in a range of sizes, which affects their properties. Particles can be extremely tiny, from only a few tens of nanometers (mere billionths of a meter) wide, to nearly a millimeter wide. As you might expect, smaller dust grains are more easily lifted and pushed around, be it by winds or magnetic, electrical and gravitational forces. Even the gentle pressure of sunlight is enough to move smaller dust particles in space. Bigger particles tend to be heavier, and they settle out more easily under the influence of gravity.

For example, on Earth, powerful winds can whip up large amounts of dust into the atmosphere. While the smaller grains can be transported over great distances, the heavier particles generally sink back to the ground near their source. On Saturn’s moon Enceladus, jets of icy dust particles spray hundreds of miles up from the surface; the bigger particles are lofted only a few tens of miles (or kilometers) and fall back to the ground, while the finest particles escape the moon’s gravity and go into orbit around Saturn to create the planet’s E ring.

Dust in the spiral galaxy M74 appears red in this image from NASA’s Spitzer Space Telescope. Data from Spitzer provided evidence that supernovae – the explosive deaths of massive stars – act as “dust factories,” seeding galaxies with cosmic dust particles. Image via NASA/JPL-Caltech/STScI.

3. It’s EVERYWHERE

Generally speaking, the space between the planets is pretty empty, but not completely so. Particles cast off by comets and ground up bits of asteroids are found throughout the solar system. Take any volume of space half a mile (1 kilometer) on a side, and you’d average a few micron-sized particles (grains the thickness of a red blood cell).

Dust in the solar system was a lot more abundant in the past. There was a huge amount of it present as the planets began to coalesce out of the disk of material that formed the sun. In fact, motes of dust gently sticking together were likely some of the earliest seeds of the planet-building process. But where did all that dust come from, originally? Some of it comes from stars like our sun, which blow off their outer layers in their later years. But lots of it also comes from exploding stars, which blast huge amounts of dust and gas into space when they go boom.

This mosaic of images from NASA’s Galileo spacecraft shows Jupiter’s ring system, which was only discovered after spacecraft had flown past the planet and could see the rings backlit by the sun. Image via NASA/JPL-Caltech/Cornell University.

4. From a certain point of view

Dust is easier to see from certain viewing angles. Tiny particles scatter light depending on how big their grains are. Larger particles tend to scatter light back in the direction from which it came, while very tiny particles tend to scatter light forward, more or less in the direction it was already going. Because of this property, structures like planetary rings made of the finest dusty particles are best viewed with the sun illuminating them from behind. For example, Jupiter’s rings were only discovered after the Voyager 1 spacecraft passed by the planet, where it could look back and see them backlit by the sun. You can see the same effect looking through a dusty windshield at sunset; when you face toward the sun, the dust becomes much more apparent.

Side-by-side movies show how dust enveloped the red planet in 2018, courtesy of NASA’s Mars Reconnaissance Orbiter. Image via NASA/JPL-Caltech/MSSS.

5. Dust storms are common on Mars

Local dust storms occur frequently on Mars, and occasionally grow or merge to form regional systems, particularly during the southern spring and summer, when Mars is closest to the Sun. On rare occasions, regional storms produce a dust haze that encircles the planet and obscures surface features beneath. A few of these events may become truly global storms, such as one in 1971 that greeted the first spacecraft to orbit Mars, NASA’s Mariner 9. In mid-2018, a global dust storm enshrouded Mars, hiding much of the Red Planet’s surface from view and threatening the continued operation of NASA’s uber long-lived Opportunity rover. We’ve also seen global dust storms in 1977, 1982, 1994, 2001 and 2007.

Dust storms will likely present challenges for future astronauts on the Red Planet. Although the force of the wind on Mars is not as strong as portrayed in an early scene in the movie The Martian, dust lofted during storms could affect electronics and health, as well as the availability of solar energy.

Sarharan dust is carried by winds to South America, where it helps fertilize the Amazon. Via NASA’s Goddard Space Flight Center.

6. Dust from the Sahara goes global

Earth’s largest, hottest desert is connected to its largest tropical rain forest by dust. The Sahara Desert is a near-uninterrupted brown band of sand and scrub across the northern third of Africa. The Amazon rain forest is a dense green mass of humid jungle that covers northeast South America. But after strong winds sweep across the Sahara, a dusty cloud rises in the air, stretches between the continents, and ties together the desert and the jungle.

This trans-continental journey of dust is important because of what is in the dust. Specifically, the dust picked up from the Bodélé Depression in Chad – an ancient lake bed where minerals composed of dead microorganisms are loaded with phosphorus. Phosphorus is an essential nutrient for plant proteins and growth, which the nutrient-poor Amazon rain forest depends on in order to flourish.

Saturn’s icy rings, backlit by the sun. The outer, bluish looking ring is composed entirely of icy dust particles sprayed into space by the moon Enceladus. Image via NASA/JPL-Caltech/SSI.

7. Rings and things

The rings of the giant planets contain a variety of different dusty materials. Jupiter’s rings are made of fine rock dust. Saturn’s rings are mostly pure water ice, with a sprinkling of other materials. (Side note about Saturn’s rings: While most of the particles are boulder-sized, there’s also lots of fine dust, and some of the fainter rings are mostly dust with few or no large particles.) Dust in the rings of Uranus and Neptune is made of dark, sooty material, probably rich in carbon.

Over time, dust gets removed from ring systems due to a variety of processes. For example, some of the dust falls into the planet’s atmosphere, while some gets swept up by the planets’ magnetic fields, and other dust settles onto the surfaces of the moons and other ring particles. Larger particles eventually form new moons or get ground down and mixed with incoming material. This means rings can change a lot over time, so understanding how the tiniest ring particles are being moved about has bearing on the history, origins and future of the rings.

Dark moon dust clings to the spacesuit of Apollo 17 astronaut Gene Cernan following an excursion on the lunar surface. Image via NASA.

8. Moon dust is clingy and might make you sick

So, dust is kind of a thing on the moon. When the Apollo astronauts visited the Moon, they found that lunar dust quickly coated their spacesuits and was difficult to remove. It was quite abrasive, causing wear on their spacesuit fabrics, seals and faceplates. It also clogged mechanisms like the joints in spacesuit limbs, and interfered with fasteners like zippers and Velcro. The astronauts also noted that it had a distinctive, pungent odor, not unlike gunpowder, and it was an eye and lung irritant.

Many of these properties apparently can be explained by the fact that lunar dust particles are quite rough and jagged. While dust particles on Earth get tumbled and ground by the wind into smoother shapes, this sort of weathering doesn’t happen so much on the moon. The roughness of moon dust grains makes it very easy for them to cling to surfaces and scratch them up. It also means they’re not the sort of thing you would want to inhale, as their jagged edges could damage delicate tissues in the lung.

Hubble Space Telescope image of comet ISON, taken in 2013. Image via NASA, ESA, and the Hubble Heritage Team (STScI/AURA).

9. Dust is what makes comets so pretty

Most comets are basically clods of dust, rock and ice. They spend most of their time far from the sun, out in the refrigerated depths of the outer solar system, where they’re peacefully dormant. But when their orbits carry them closer to the sun – that is, roughly inside the orbit of Jupiter – comets wake up. In response to warming temperatures, the ices on and near their surfaces begin to turn into gases, expanding outward and away from the comet, and creating focused jets of material in places. Dust gets carried away by this rapidly expanding gas, creating a fuzzy cloud around the comet’s nucleus called a coma. Some of the dust also is drawn out into a long trail – the comet’s tail.

The dark object at center is the dusty disk of a newborn planetary system, seen edge-on by the Hubble Space Telescope. Image via NASA/ESA/STScI/J. Bally (Univ. Colorado) and H. Throop (SWRI).

10. We’re not the only ones who’re so dusty

Dust in our solar system is continually replenished by comets whizzing past the sun and the occasional asteroid collision, and it’s always being moved about, thanks to a variety of factors like the gravity of the planets and even the pressure of sunlight. Some of it even gets ejected from our solar system altogether.

With telescopes, we also observe dusty debris disks around many other stars. As in our own system, the dust in such disks should evolve over time, settling on planetary surfaces or being ejected, and this means the dust must be replenished in those star systems as well. So studying the dust in our planetary environs can tell us about other systems, and vice versa. Grains of dust from other planetary systems also pass through our neighborhood – a few spacecraft have actually captured and analyzed some them – offering us a tangible way to study material from other stars.

Bottom line: Ten facts about dust in space and on Earth.

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Orion the Hunter returns before dawn

Meteors ahead! Everything you need to know: Perseid meteor shower

Around early August, if you’re up early and have an unobstructed view to the east, be sure to look in that direction in the hour before dawn. You might find a familiar figure – a constellation that always returns to the sky around this time of year. It’s the beautiful constellation Orion the Hunter – recently behind the sun as seen from our earthly vantage point – now ascending once more in the east before sunrise.

The Hunter appears each northern winter as a mighty constellation arcing across the south during the evening hours. Many people see it then, and notice it, because the pattern of Orion’s stars is so distinctive.

But, at the crack of dawn in late summer, you can spot Orion in the east. Thus Orion has been called the ghost of the shimmering summer dawn.

The Hunter rises on his side, with his three Belt stars – Mintaka, Alnitak and Alnilam – pointing straight up.

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The constellation Orion as viewed at morning dawn in early August. Image via Flickr user Micheal C. Rael

Also, notice the star Aldebaran in the constellation Taurus the Bull. Aldebaran is the brightest star in Taurus the Bull. It’s said to be the Bull’s fiery red eye. See the V-shaped pattern of stars around Aldebaran? This pattern represents the Bull’s face. In skylore, Orion is said to be holding up a great shield . . . fending off the charging Bull. Can you imagine this by looking at the chart at top? It’s easy to imagine when you look at the real sky before dawn at this time of year.

Bottom line: The return of Orion and Taurus to your predawn sky happens around late July or early August every year. In the Northern Hemisphere, Orion is sometimes called the ghost of the summer dawn.

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EarthSky’s meteor shower guide for 2018

from EarthSky https://ift.tt/11uxCb3

Meteors ahead! Everything you need to know: Perseid meteor shower

Around early August, if you’re up early and have an unobstructed view to the east, be sure to look in that direction in the hour before dawn. You might find a familiar figure – a constellation that always returns to the sky around this time of year. It’s the beautiful constellation Orion the Hunter – recently behind the sun as seen from our earthly vantage point – now ascending once more in the east before sunrise.

The Hunter appears each northern winter as a mighty constellation arcing across the south during the evening hours. Many people see it then, and notice it, because the pattern of Orion’s stars is so distinctive.

But, at the crack of dawn in late summer, you can spot Orion in the east. Thus Orion has been called the ghost of the shimmering summer dawn.

The Hunter rises on his side, with his three Belt stars – Mintaka, Alnitak and Alnilam – pointing straight up.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

The constellation Orion as viewed at morning dawn in early August. Image via Flickr user Micheal C. Rael

Also, notice the star Aldebaran in the constellation Taurus the Bull. Aldebaran is the brightest star in Taurus the Bull. It’s said to be the Bull’s fiery red eye. See the V-shaped pattern of stars around Aldebaran? This pattern represents the Bull’s face. In skylore, Orion is said to be holding up a great shield . . . fending off the charging Bull. Can you imagine this by looking at the chart at top? It’s easy to imagine when you look at the real sky before dawn at this time of year.

Bottom line: The return of Orion and Taurus to your predawn sky happens around late July or early August every year. In the Northern Hemisphere, Orion is sometimes called the ghost of the summer dawn.

Donate: Your support means the world to us

EarthSky’s meteor shower guide for 2018

from EarthSky https://ift.tt/11uxCb3