Mercury farthest from sun in sky on November 28

Mercury, the innermost planet, reaches its greatest elongation from the sun on November 28, 2019. In other words, that date marks Mercury’s farthest point from the sunrise on the sky’s dome for this morning apparition. Mercury will be 20 degrees west of the sun. You’ll find it at dawn, more or less on line with the red planet Mars and the bright blue-white star Spica in the constellation Virgo.

Mercury is easier to see from the Northern Hemisphere at this morning apparition than in the Southern Hemisphere. In short, the farther north you live, the more time that Mercury spends above the horizon before sunrise; and the farther south you live, the closer that Mercury rises to sunrise. At mid-northern latitudes, Mercury rises about 1 3/4 hours before the sun.

As seen from temperate latitudes in the Southern Hemisphere, Mercury comes up less than an hour before sunrise. Chances are that both Spica and Mars will fade from view by the time that Mercury rises. From temperate latitudes in the Southern Hemisphere, you may need binoculars to spot Mercury before sunrise.

At present, Mercury shines about three times more brilliantly than a 1st-magnitude star. By late November, it’ll be shining some four times brighter. Don’t know how bright a 1st-magnitude star is? No problem. Blue-white Spica, which lights up the predawn darkness, provides a prime example of a 1st-magnitude star in the early morning sky right now.

The red planet Mars, which is also up before dawn’s first light, is found below Spica and above Mercury. However, Mars is about half as bright as Spica, and may fade from view by the time that Mercury rises. If you’re up before dawn, Mercury may have yet to rise. Keep in mind, though, that an imaginary line drawn from Spica through Mars pretty much points to Mercury’s rising point on the horizon.

For your specific view of Mercury, Mars and Spica on various dates, try Stellarium online

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

View at EarthSky Community Photos. | Karl Diefenderfer was in Doylestown, Pennsylvania on Monday morning, November 25, 2019 when he caught the very old moon and Mercury. Thanks, Karl!

From northerly latitudes, Mercury will remain in fine view into the first week or two of December. Watch for this world near the sunrise point on the horizon as the predawn darkness begins to give way to dawn. We give the approximate rising time for Mercury – for around late November/early December – at various latitudes (given a level horizon):

60 degrees north latitude
Mercury rises more than 2 hours before the sun

40 degrees north latitude
Mercury rises 1 2/3 hours before the sun

Equator (0 degrees latitude)
Mercury rises 1 1/3 hours before the sun

35 degrees south latitude
Mercury rises less than 1 hour before the sun

Want more specific information? Click here for a recommended almanac

The planet Mars and Zubenelgenubi – the alpha star of Libra the Scales – shine near each other in the predawn sky by early December, but may fade from view by the time that Mercury rises. Look for Mars very close to Zubenelgenubi on December 12, 2019.

How should you look for Mercury? After all, it’s often called the most elusive planet – not because it’s faint – but because it’s always near the sun in the sky, generally only visible in twilight. First and foremost, find an unobstructed horizon in the direction of sunrise. At mid-northern and far-northern latitudes, you may well see the celestial line-up – Spica, Mars and Mercury – in the darkness before daybreak.

Your best bet for spotting Mercury, the innermost planet, is to get up before dawn’s first light, or the beginning of astronomical twilight. Extending the Spica-Mars line to the horizon shows you (more or less) where Mercury will rise into your sky, as the predawn darkness gives way to morning twilight.

Visit Sunrise Sunset Calendars to find out when astronomical twilight comes to your sky, remembering to check the astronomical twilight box.

Bottom line: Mercury’s greatest elongation is November 28, 2019, but don’t let that stop you from looking for the planet for some mornings to come. Look east before sunup. Mercury will be on a line with the bright star Spica and red planet Mars. If you’re in the Southern Hemisphere, the view is tougher to catch; bring along binoculars. Catch Mercury now because – for all of us – this world will become lost in the glare of sunrise before 2019 ends.

from EarthSky https://ift.tt/2scRV2G

Mercury, the innermost planet, reaches its greatest elongation from the sun on November 28, 2019. In other words, that date marks Mercury’s farthest point from the sunrise on the sky’s dome for this morning apparition. Mercury will be 20 degrees west of the sun. You’ll find it at dawn, more or less on line with the red planet Mars and the bright blue-white star Spica in the constellation Virgo.

Mercury is easier to see from the Northern Hemisphere at this morning apparition than in the Southern Hemisphere. In short, the farther north you live, the more time that Mercury spends above the horizon before sunrise; and the farther south you live, the closer that Mercury rises to sunrise. At mid-northern latitudes, Mercury rises about 1 3/4 hours before the sun.

As seen from temperate latitudes in the Southern Hemisphere, Mercury comes up less than an hour before sunrise. Chances are that both Spica and Mars will fade from view by the time that Mercury rises. From temperate latitudes in the Southern Hemisphere, you may need binoculars to spot Mercury before sunrise.

At present, Mercury shines about three times more brilliantly than a 1st-magnitude star. By late November, it’ll be shining some four times brighter. Don’t know how bright a 1st-magnitude star is? No problem. Blue-white Spica, which lights up the predawn darkness, provides a prime example of a 1st-magnitude star in the early morning sky right now.

The red planet Mars, which is also up before dawn’s first light, is found below Spica and above Mercury. However, Mars is about half as bright as Spica, and may fade from view by the time that Mercury rises. If you’re up before dawn, Mercury may have yet to rise. Keep in mind, though, that an imaginary line drawn from Spica through Mars pretty much points to Mercury’s rising point on the horizon.

For your specific view of Mercury, Mars and Spica on various dates, try Stellarium online

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

View at EarthSky Community Photos. | Karl Diefenderfer was in Doylestown, Pennsylvania on Monday morning, November 25, 2019 when he caught the very old moon and Mercury. Thanks, Karl!

From northerly latitudes, Mercury will remain in fine view into the first week or two of December. Watch for this world near the sunrise point on the horizon as the predawn darkness begins to give way to dawn. We give the approximate rising time for Mercury – for around late November/early December – at various latitudes (given a level horizon):

60 degrees north latitude
Mercury rises more than 2 hours before the sun

40 degrees north latitude
Mercury rises 1 2/3 hours before the sun

Equator (0 degrees latitude)
Mercury rises 1 1/3 hours before the sun

35 degrees south latitude
Mercury rises less than 1 hour before the sun

Want more specific information? Click here for a recommended almanac

The planet Mars and Zubenelgenubi – the alpha star of Libra the Scales – shine near each other in the predawn sky by early December, but may fade from view by the time that Mercury rises. Look for Mars very close to Zubenelgenubi on December 12, 2019.

How should you look for Mercury? After all, it’s often called the most elusive planet – not because it’s faint – but because it’s always near the sun in the sky, generally only visible in twilight. First and foremost, find an unobstructed horizon in the direction of sunrise. At mid-northern and far-northern latitudes, you may well see the celestial line-up – Spica, Mars and Mercury – in the darkness before daybreak.

Your best bet for spotting Mercury, the innermost planet, is to get up before dawn’s first light, or the beginning of astronomical twilight. Extending the Spica-Mars line to the horizon shows you (more or less) where Mercury will rise into your sky, as the predawn darkness gives way to morning twilight.

Visit Sunrise Sunset Calendars to find out when astronomical twilight comes to your sky, remembering to check the astronomical twilight box.

Bottom line: Mercury’s greatest elongation is November 28, 2019, but don’t let that stop you from looking for the planet for some mornings to come. Look east before sunup. Mercury will be on a line with the bright star Spica and red planet Mars. If you’re in the Southern Hemisphere, the view is tougher to catch; bring along binoculars. Catch Mercury now because – for all of us – this world will become lost in the glare of sunrise before 2019 ends.

from EarthSky https://ift.tt/2scRV2G

Science Surgery: ‘Why do some cancers metastasise, but others don’t?’

Our Science Surgery series answers your cancer science questions.

Sara asked: ‘Why do some cancers metastasise but others don’t, even if they’re present in the body for many years?’

“We have so many unanswered questions about how and why cancer spreads around the body,” says Dr Seth Coffelt, an expert in the immune system and cancer spread (metastasis) at the Cancer Research UK Beatson Institute in Glasgow. “But one thing we do know is that not all cancers seem to metastasise, and some do it faster than others.”

These differences are especially apparent in skin cancer. On the one hand you have a type of non-melanoma skin cancer called basal cell skin cancer. This is the most common form of skin cancer, but it hardly ever spreads. On the other hand, a rarer form of skin cancer called melanoma often spreads, unless it can be treated in time.

“When we say cancer has metastasised, what we mean is that cells from a tumour in one part of the body, such as the breast, lung or bowel, have escaped into the bloodstream and travelled to a different part of the body and started to grow into a new secondary tumour there.”

Coffelt says these secondary cancers often grow in predictable sites, such as the brain, bones or liver, depending on the type of cancer in question.

And where cancer settles isn’t the only thing that differs between cancer types. “Something we’re learning, for example in breast cancer, is that metastasis happens at different rates. In one type of breast cancer, recurrence is most likely in the first 5 years. But in another type, the risk persists 20 years after patients were diagnosed and treated.”

Read more: the scientists working to predict how and when breast cancer returns to help personalise treatment plans.

The problem with metastasis

Although the speed of this process differs from one cancer to another, in general the later the cancer is diagnosed, the more time it has had to spread.

“This is bad news for the body,” says Coffelt. “Cancer cells that have escaped from the first tumour can be more resistant to cancer drugs and there can be more than one, or even several secondary tumours. So metastatic cancer is harder to treat.”

For patients with bowel cancer that’s spread, also referred to by doctors as stage 4 cancer, the likelihood of someone surviving their cancer for at least 5 years is less than 1 in 5, compared with more than 9 in 10 if diagnosed at the earliest stage. This is a key reason why we’re investing in research to detect cancer early, as well working with government to get more cancers diagnosed at an early stage.

But scientists are also interested in understanding how cancer spreads. Coffelt says there are several steps that have to happen to allow cancer to move around the body and establish a new tumour.

“The cancer cells need to leave the primary tumour, they have to survive the journey without being spotted by the immune system and then they have to be able to grow in a different environment,” says Coffelt.

“My research looks at one important step in this process: how the immune system gets switched off, specifically at the sites of metastasis.”

Tricked into helping

Coffelt is investigating how one type of immune cell in particular can either help or hinder cancer’s spread.

“Cancer couldn’t spread around the body without help. Looking at breast cancer cells, we’ve discovered that they can get some help by manipulating a particular type of immune cell, called gamma delta T cells.”

Gamma delta T cells are just one of several different types of immune cells know as T cells, which circulate in our bodies and protect us from disease. What makes gamma delta T cells unique is their ability to tell other T cells what to do. Under their instructions, other T cells in the bloodstream can either attack cancer cells or let them go free.

“Gamma delta T cells orchestrate this key process,” says Coffelt. Even when these immune cells are sitting in other parts of the body, they’re still able to pick up signals being produced by cancer cells. They take these signals and release their own messages that in turn switch off killer immune cells in the blood.

“It’s like a long-distance insidious communication system.” And this series of signals helps to give cancer cells protection as they move around the body.

“Cancer cells are heading out into the body and this signalling means they don’t have to worry about coming under attack, they can avoid being killed and land wherever they want to land.”

Taking on a new challenge

Coffelt and his team are now investigating if this communication system exists in other types of cancer too, in particular pancreatic cancer.

The odds of surviving pancreatic cancer are low compared to other types of the disease and a key reason for this is that more than half of patients are diagnosed when the cancer has already spread to other parts of the body.

“If we’re trying to understand why some cancers metastasise but others don’t, pancreatic cancer is an important but challenging area to work on. Fortunately here at the Beatson, we already have a team of researchers with expertise in how pancreatic cancer grows and develops.”

Getting the immune system back on side

Figuring out why some cancers spread is vital, but it’s not the ultimate goal.

As Coffelt’s research suggests, our body’s immune cells have the potential both to protect us from disease, but also to be tricked into helping cancer grow and spread. Boosting the positive traits of these cells or halting their negative influence to fight cancer is a job for treatments known as immunotherapies.

This is not only an exciting area of research for many of our scientists, it’s also starting to make its way into the clinic for treating some types of cancer. And Coffelt thinks immunotherapy might be a useful strategy to help stop cancer spread.

“We are trying to understand this T cell signalling process better and how to reverse it, because that could ultimately form the basis for a new type of cancer treatment.”

Coffelt believes that tackling metastasis in this way could have wide-ranging benefits. He says that once a cancer starts to spread, it can move to lots of different sites around the body. “Once this happens, we don’t have many treatment options to stop the cancer moving around.” Something that Coffelt is working to change.

“Our research might stop cancer from metastasising in patients with early stage disease, but it might also help us find a way to treat patients whose cancer has already spread.”

Kerry Noble is a freelance science writer

from Cancer Research UK – Science blog https://ift.tt/2pTO3D9

Our Science Surgery series answers your cancer science questions.

Sara asked: ‘Why do some cancers metastasise but others don’t, even if they’re present in the body for many years?’

“We have so many unanswered questions about how and why cancer spreads around the body,” says Dr Seth Coffelt, an expert in the immune system and cancer spread (metastasis) at the Cancer Research UK Beatson Institute in Glasgow. “But one thing we do know is that not all cancers seem to metastasise, and some do it faster than others.”

These differences are especially apparent in skin cancer. On the one hand you have a type of non-melanoma skin cancer called basal cell skin cancer. This is the most common form of skin cancer, but it hardly ever spreads. On the other hand, a rarer form of skin cancer called melanoma often spreads, unless it can be treated in time.

“When we say cancer has metastasised, what we mean is that cells from a tumour in one part of the body, such as the breast, lung or bowel, have escaped into the bloodstream and travelled to a different part of the body and started to grow into a new secondary tumour there.”

Coffelt says these secondary cancers often grow in predictable sites, such as the brain, bones or liver, depending on the type of cancer in question.

And where cancer settles isn’t the only thing that differs between cancer types. “Something we’re learning, for example in breast cancer, is that metastasis happens at different rates. In one type of breast cancer, recurrence is most likely in the first 5 years. But in another type, the risk persists 20 years after patients were diagnosed and treated.”

Read more: the scientists working to predict how and when breast cancer returns to help personalise treatment plans.

The problem with metastasis

Although the speed of this process differs from one cancer to another, in general the later the cancer is diagnosed, the more time it has had to spread.

“This is bad news for the body,” says Coffelt. “Cancer cells that have escaped from the first tumour can be more resistant to cancer drugs and there can be more than one, or even several secondary tumours. So metastatic cancer is harder to treat.”

For patients with bowel cancer that’s spread, also referred to by doctors as stage 4 cancer, the likelihood of someone surviving their cancer for at least 5 years is less than 1 in 5, compared with more than 9 in 10 if diagnosed at the earliest stage. This is a key reason why we’re investing in research to detect cancer early, as well working with government to get more cancers diagnosed at an early stage.

But scientists are also interested in understanding how cancer spreads. Coffelt says there are several steps that have to happen to allow cancer to move around the body and establish a new tumour.

“The cancer cells need to leave the primary tumour, they have to survive the journey without being spotted by the immune system and then they have to be able to grow in a different environment,” says Coffelt.

“My research looks at one important step in this process: how the immune system gets switched off, specifically at the sites of metastasis.”

Tricked into helping

Coffelt is investigating how one type of immune cell in particular can either help or hinder cancer’s spread.

“Cancer couldn’t spread around the body without help. Looking at breast cancer cells, we’ve discovered that they can get some help by manipulating a particular type of immune cell, called gamma delta T cells.”

Gamma delta T cells are just one of several different types of immune cells know as T cells, which circulate in our bodies and protect us from disease. What makes gamma delta T cells unique is their ability to tell other T cells what to do. Under their instructions, other T cells in the bloodstream can either attack cancer cells or let them go free.

“Gamma delta T cells orchestrate this key process,” says Coffelt. Even when these immune cells are sitting in other parts of the body, they’re still able to pick up signals being produced by cancer cells. They take these signals and release their own messages that in turn switch off killer immune cells in the blood.

“It’s like a long-distance insidious communication system.” And this series of signals helps to give cancer cells protection as they move around the body.

“Cancer cells are heading out into the body and this signalling means they don’t have to worry about coming under attack, they can avoid being killed and land wherever they want to land.”

Taking on a new challenge

Coffelt and his team are now investigating if this communication system exists in other types of cancer too, in particular pancreatic cancer.

The odds of surviving pancreatic cancer are low compared to other types of the disease and a key reason for this is that more than half of patients are diagnosed when the cancer has already spread to other parts of the body.

“If we’re trying to understand why some cancers metastasise but others don’t, pancreatic cancer is an important but challenging area to work on. Fortunately here at the Beatson, we already have a team of researchers with expertise in how pancreatic cancer grows and develops.”

Getting the immune system back on side

Figuring out why some cancers spread is vital, but it’s not the ultimate goal.

As Coffelt’s research suggests, our body’s immune cells have the potential both to protect us from disease, but also to be tricked into helping cancer grow and spread. Boosting the positive traits of these cells or halting their negative influence to fight cancer is a job for treatments known as immunotherapies.

This is not only an exciting area of research for many of our scientists, it’s also starting to make its way into the clinic for treating some types of cancer. And Coffelt thinks immunotherapy might be a useful strategy to help stop cancer spread.

“We are trying to understand this T cell signalling process better and how to reverse it, because that could ultimately form the basis for a new type of cancer treatment.”

Coffelt believes that tackling metastasis in this way could have wide-ranging benefits. He says that once a cancer starts to spread, it can move to lots of different sites around the body. “Once this happens, we don’t have many treatment options to stop the cancer moving around.” Something that Coffelt is working to change.

“Our research might stop cancer from metastasising in patients with early stage disease, but it might also help us find a way to treat patients whose cancer has already spread.”

Kerry Noble is a freelance science writer

from Cancer Research UK – Science blog https://ift.tt/2pTO3D9

Summer Triangle in northern autumn

In late November and early December, look west in the evening for the Summer Triangle. It’s the signature star formation of our Northern Hemisphere summer, but you can see it in northern autumn, too. The Summer Triangle showcases three brilliant stars – Vega, Deneb and Altair – in three separate constellations. The Summer Triangle still shines in the western evening sky (at mid-northern latitudes or farther north).

What’s more, the Summer Triangle will continue to shine after dark throughout December and January. Look for it tonight at early evening, high in your western sky.

In the month of June – around the June solstice – the Summer Triangle pops out in the east as darkness falls and shines all night long. But now – in late November – the Summer Triangle appears way high in the west at evening. As evening deepens, the Summer Triangle descends westward, with all three of its stars staying above the horizon until mid-to-late evening.

Altair – the Summer Triangle’s most southerly star – will set around 9:30 to 10:30 p.m. tonight at mid-northern latitudes. Notice where you see the Summer Triangle at a given time this evening. The Summer Triangle will return to this same place in the sky some four minutes earlier with each passing day, or two hours earlier with each passing month.

As the Summer Triangle sinks close the western horizon around mid-evening, turn around to see Orion – the signpost constellation of winter – rising in the east.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Nils Ribi caught this photo of the Summer Triangle in November 2014.

Bottom line: Look westward this evening for the three brilliant stars of the humongous Summer Triangle: Vega, Deneb and Altair.

EarthSky astronomy kits are perfect for beginners. Order yours from the EarthSky store.

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

In late November and early December, look west in the evening for the Summer Triangle. It’s the signature star formation of our Northern Hemisphere summer, but you can see it in northern autumn, too. The Summer Triangle showcases three brilliant stars – Vega, Deneb and Altair – in three separate constellations. The Summer Triangle still shines in the western evening sky (at mid-northern latitudes or farther north).

What’s more, the Summer Triangle will continue to shine after dark throughout December and January. Look for it tonight at early evening, high in your western sky.

In the month of June – around the June solstice – the Summer Triangle pops out in the east as darkness falls and shines all night long. But now – in late November – the Summer Triangle appears way high in the west at evening. As evening deepens, the Summer Triangle descends westward, with all three of its stars staying above the horizon until mid-to-late evening.

Altair – the Summer Triangle’s most southerly star – will set around 9:30 to 10:30 p.m. tonight at mid-northern latitudes. Notice where you see the Summer Triangle at a given time this evening. The Summer Triangle will return to this same place in the sky some four minutes earlier with each passing day, or two hours earlier with each passing month.

As the Summer Triangle sinks close the western horizon around mid-evening, turn around to see Orion – the signpost constellation of winter – rising in the east.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Nils Ribi caught this photo of the Summer Triangle in November 2014.

Bottom line: Look westward this evening for the three brilliant stars of the humongous Summer Triangle: Vega, Deneb and Altair.

EarthSky astronomy kits are perfect for beginners. Order yours from the EarthSky store.

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

Was ‘Oumuamua a cosmic dust bunny?

Artist’s concept of ‘Oumuamua, whose actual appearance is unknown. This illustration is based on the limited observations available. What was ‘Oumuamua? We know it entered our solar system – swept near our sun on September 9, 2017 – then headed back to interstellar space again. Astronomers are still trying to piece its story together. Image via ESO/ M. Kornmesser.

When astronomers first spied ‘Oumuamua – in the fall of 2017 – they weren’t sure if it was one of our solar system’s asteroids or comets, or something else. It turned out to be an interstellar interloper, the first-known interstellar object. The astronomers watched it speed through the solar system, disappearing from view of even the largest earthly telescopes around January 2018 … as theories about its odd shape and behavior raged. Some said it was an unusually long asteroid. Others even proposed an extraterrestrial spacecraft, reminiscent of the one in Arthur C. Clarke’s famous sci-fi novel “Rendezvous with Rama.” The astronomers eventually settled on its being either an asteroid or comet from another solar system, albeit a weird one.

Now there’s a new idea. ‘Oumuamua might not be an interstellar asteroid or comet, but instead something never seen before: neither ice nor rock, but rather a very lightweight and “fluffy” conglomerate of dust and ice grains, sort of like a “cosmic dust bunny.” The new peer-reviewed research was published in The Astrophysical Journal Letters on November 11, 2019.

The study suggests that ‘Oumuamua might be so porous that sunbeams could actually push it and give it its observed momentum.

When ‘Oumuamua was first found, it was already on its way out of the solar system, so there was limited time to observe it, and it was already far away in the outer solar system. But astronomers did notice something odd: it was increasing slightly in speed. Comets could do that, as they lost ice and dust particles behind them in their tails. But ‘Oumuamua didn’t have any tail at all.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Our best view of ‘Oumuamua – from the William Herschel Telescope on the island of La Palma in the Canary Islands, Spain – on October 29, 2017. Image via A. Fitzsimmons, QUB/Isaac Newton Group of Telescopes.

So what else could cause the object to increase in speed? One idea was that sunlight itself was responsible. But that wouldn’t work if it was an asteroid, as it would require a very large flat surface to catch enough of the light particles from the sun. This led to the even wilder possibility that ‘Oumuamua was artificial, something like a large flat light sail.

But then another possibility was posited by Amaya Moro-Martín, an astronomer at the Space Telescope Science Institute. ‘Oumuamua might be “fluffy,” a lightweight conglomerate of dust and ice grains, known as a fractal aggregate. In essence, a dust fractal or “cosmic dust bunny.” The porous patterns in it would be repeated across different size scales, like a fractal. As co-author Eirik Flekkøy, a physicist at the University of Oslo, stated:

It’s a completely new thing. I think if you hit this thing it would be a little bit like hitting a spider web.

Could such a delicate structure actually travel through space – between stars – and survive? Flekkøy and his colleagues decided to test that idea. Something else that had been observed, a slowing in the object’s rotation, would fit the theory since the speed of the slowing was observed to fit with a phenomenon where light can push harder on some parts of a surface – such as shinier parts – than it pushes on others. If ‘Oumuamua could be turned by sunbeams alone, then it could be sped up, as well. The theory is that when the object cools after being heated up by the sun, the departure of heat also exerts gentle pushes. The uneven nudges could add up to make a lumpy object spin faster or slower over time.

Artist’s illustration of a light sail. Some people have speculated that ‘Oumuamua could be an alien version of something similar, but larger. Image via Josh Spradling/The Planetary Society.

This could explain the object’s slowing rotation and increase in speed, but would such a lightweight structure hold together? According to Flekkøy:

If this is such a filamentary, porous, fractal structure, would it survive. And the answer is fairly safely, yes.

Other researchers are doubtful about this explanation, however. They point out that the way ‘Oumuamua responded to sunlight would require it to be 100 times less dense than air at sea level. Scientists can now create similar lightweight materials – called aerogels – but the material ‘Oumuamua would be composed of would need to be even lighter than that. As Roman Rafikov, an astrophysicist at the University of Cambridge, pointed out:

How do you reconstruct this in interstellar space?

The idea that ‘Oumuamua could be a cosmic dust bunny of sorts is a strange one, although it might have some basis in reality. Smaller versions of this are thought to have been possible in the early solar system, forming from small particles bumping into each other. But to survive, and be able to cross interstellar space, such a dust bunny would need to grow larger. At the moment though, Rafikov doesn’t have any better suggestions:

If I had an alternative, I would have published it long ago.

The trajectory of ‘Oumuamua through the solar system. Image via Universal Workshop.

Of course, this also brings up the speculative possibility of such an object being made artificially by some advanced civilization, much like our own aerogels, but an obvious question would be “why?” Unfortunately, ‘Oumuamua is now too far away to do any further studies, so its actual nature will probably always remain a mystery.

On August 30 of this year, the second-known interstellar object was discovered – called C/2019 Q4 (Borisov) – but this one appears to have the characteristics of a normal comet. So why was ‘Oumuamua so weird? We’ll probably never know. But if anything like it shows up again, we may be better prepared to study it, according to Rafikov:

In my career so far, ‘Oumuamua was the most puzzling object. If [similar objects] actually keep coming into our solar system, we might be better prepared for this kind of analysis.

Bottom line: ‘Oumuamua – the weird object that entered our solar system a few years ago – may not be an asteroid or comet at all, but rather a “cosmic dust bunny.”

Source: The Interstellar Object ‘Oumuamua as a Fractal Dust Aggregate

Via Popular Science

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

Artist’s concept of ‘Oumuamua, whose actual appearance is unknown. This illustration is based on the limited observations available. What was ‘Oumuamua? We know it entered our solar system – swept near our sun on September 9, 2017 – then headed back to interstellar space again. Astronomers are still trying to piece its story together. Image via ESO/ M. Kornmesser.

When astronomers first spied ‘Oumuamua – in the fall of 2017 – they weren’t sure if it was one of our solar system’s asteroids or comets, or something else. It turned out to be an interstellar interloper, the first-known interstellar object. The astronomers watched it speed through the solar system, disappearing from view of even the largest earthly telescopes around January 2018 … as theories about its odd shape and behavior raged. Some said it was an unusually long asteroid. Others even proposed an extraterrestrial spacecraft, reminiscent of the one in Arthur C. Clarke’s famous sci-fi novel “Rendezvous with Rama.” The astronomers eventually settled on its being either an asteroid or comet from another solar system, albeit a weird one.

Now there’s a new idea. ‘Oumuamua might not be an interstellar asteroid or comet, but instead something never seen before: neither ice nor rock, but rather a very lightweight and “fluffy” conglomerate of dust and ice grains, sort of like a “cosmic dust bunny.” The new peer-reviewed research was published in The Astrophysical Journal Letters on November 11, 2019.

The study suggests that ‘Oumuamua might be so porous that sunbeams could actually push it and give it its observed momentum.

When ‘Oumuamua was first found, it was already on its way out of the solar system, so there was limited time to observe it, and it was already far away in the outer solar system. But astronomers did notice something odd: it was increasing slightly in speed. Comets could do that, as they lost ice and dust particles behind them in their tails. But ‘Oumuamua didn’t have any tail at all.

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Our best view of ‘Oumuamua – from the William Herschel Telescope on the island of La Palma in the Canary Islands, Spain – on October 29, 2017. Image via A. Fitzsimmons, QUB/Isaac Newton Group of Telescopes.

So what else could cause the object to increase in speed? One idea was that sunlight itself was responsible. But that wouldn’t work if it was an asteroid, as it would require a very large flat surface to catch enough of the light particles from the sun. This led to the even wilder possibility that ‘Oumuamua was artificial, something like a large flat light sail.

But then another possibility was posited by Amaya Moro-Martín, an astronomer at the Space Telescope Science Institute. ‘Oumuamua might be “fluffy,” a lightweight conglomerate of dust and ice grains, known as a fractal aggregate. In essence, a dust fractal or “cosmic dust bunny.” The porous patterns in it would be repeated across different size scales, like a fractal. As co-author Eirik Flekkøy, a physicist at the University of Oslo, stated:

It’s a completely new thing. I think if you hit this thing it would be a little bit like hitting a spider web.

Could such a delicate structure actually travel through space – between stars – and survive? Flekkøy and his colleagues decided to test that idea. Something else that had been observed, a slowing in the object’s rotation, would fit the theory since the speed of the slowing was observed to fit with a phenomenon where light can push harder on some parts of a surface – such as shinier parts – than it pushes on others. If ‘Oumuamua could be turned by sunbeams alone, then it could be sped up, as well. The theory is that when the object cools after being heated up by the sun, the departure of heat also exerts gentle pushes. The uneven nudges could add up to make a lumpy object spin faster or slower over time.

Artist’s illustration of a light sail. Some people have speculated that ‘Oumuamua could be an alien version of something similar, but larger. Image via Josh Spradling/The Planetary Society.

This could explain the object’s slowing rotation and increase in speed, but would such a lightweight structure hold together? According to Flekkøy:

If this is such a filamentary, porous, fractal structure, would it survive. And the answer is fairly safely, yes.

Other researchers are doubtful about this explanation, however. They point out that the way ‘Oumuamua responded to sunlight would require it to be 100 times less dense than air at sea level. Scientists can now create similar lightweight materials – called aerogels – but the material ‘Oumuamua would be composed of would need to be even lighter than that. As Roman Rafikov, an astrophysicist at the University of Cambridge, pointed out:

How do you reconstruct this in interstellar space?

The idea that ‘Oumuamua could be a cosmic dust bunny of sorts is a strange one, although it might have some basis in reality. Smaller versions of this are thought to have been possible in the early solar system, forming from small particles bumping into each other. But to survive, and be able to cross interstellar space, such a dust bunny would need to grow larger. At the moment though, Rafikov doesn’t have any better suggestions:

If I had an alternative, I would have published it long ago.

The trajectory of ‘Oumuamua through the solar system. Image via Universal Workshop.

Of course, this also brings up the speculative possibility of such an object being made artificially by some advanced civilization, much like our own aerogels, but an obvious question would be “why?” Unfortunately, ‘Oumuamua is now too far away to do any further studies, so its actual nature will probably always remain a mystery.

On August 30 of this year, the second-known interstellar object was discovered – called C/2019 Q4 (Borisov) – but this one appears to have the characteristics of a normal comet. So why was ‘Oumuamua so weird? We’ll probably never know. But if anything like it shows up again, we may be better prepared to study it, according to Rafikov:

In my career so far, ‘Oumuamua was the most puzzling object. If [similar objects] actually keep coming into our solar system, we might be better prepared for this kind of analysis.

Bottom line: ‘Oumuamua – the weird object that entered our solar system a few years ago – may not be an asteroid or comet at all, but rather a “cosmic dust bunny.”

Source: The Interstellar Object ‘Oumuamua as a Fractal Dust Aggregate

Via Popular Science

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Algal blooms are getting worse in lakes worldwide

Water laden with algae on the shores of Pelee Island, Lake Erie, in 2009. Image via Tom Archer.

The intensity of harmful algal blooms in many lakes around the world has increased according to satellite imagery collected over nearly three decades. The new research was published in the peer-reviewed journal Nature on October 14, 2019.

Harmful algal blooms (overgrowth of algae in water) tend to peak in summertime in response to three key environmental conditions – nutrients, sunlight, and warm water – which are conducive to explosive algal growth. These blooms often appear as thick, green goop on or near the surface of a waterbody, and the color changes in the water can be detected by satellites. When the abundant algae die off and decompose, oxygen levels drop to levels that can be deadly to aquatic life. Some blooms even produce toxins that can contaminate drinking water supplies and make it dangerous for people and their pets to go swimming.

Jeff Ho, a scientist affiliated with the Carnegie Institution for Science in California and lead author of the new study, discussed the impacts of these types of algal blooms in a statement. He said:

Toxic algal blooms affect drinking water supplies, agriculture, fishing, recreation, and tourism. Studies indicate that just in the United States, freshwater blooms result in the loss of $4 billion each year.

Several scientific studies have noted an uptick in freshwater algal blooms in certain regions, but the new research represents the first long-term, global study of large lakes using advanced imagery from the U.S. Geological Survey’s Landsat 5 satellite. Data from 71 large lakes located in 33 countries on six continents showed that the intensity of summertime algal blooms has increased in the majority (68 percent) of the areas studied.

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Landsat 8 satellite image of an algal bloom in the western part of Lake Erie collected on July 28, 2015. Image via NASA Earth Observatory/Carnegie Science.

The increasing intensity of freshwater algal blooms in summer is likely being driven by a combination of factors. While previous research on individual lakes has definitively linked changes in algal blooms to increased nutrient loading caused by human activities (think fertilizers and sewage), and it is known that warming water temperatures can exacerbate blooms (see Blooms Like it Hot), the drivers of the trends in the new study were not as clear cut. Interestingly, the few lakes that showed a decrease in bloom intensity were the ones that had warmed less than the other lakes. Thus, the findings suggest that warming waters may have played an important role in the observed trends.

Anna Michalak, a co-author of the new study, is a senior scientist at the Carnegie Institution of Science. She said:

This finding illustrates how important it is to identify the factors that make some lakes more susceptible to climate change. We need to develop water management strategies that better reflect the ways that local hydrological conditions are affected by a changing climate.

Nima Pahlevan of NASA’s Goddard Space Flight Center also contributed to the new research published in Nature.

Florida’s Lake Okeechobee. Toxic algal blooms resulted in states of emergency being declared in Florida in 2016 and 2018. Image via NASA Earth Observatory/Carnegie Science.

Bottom line: The intensity of harmful algal blooms in many freshwater lakes around the world is increasing, according to new satellite data collected over nearly three decades.

Source: Widespread global increase in intense lake phytoplankton blooms since the 1980s

Via Carnegie Institution of Science

from EarthSky https://ift.tt/2XP5fpQ

Water laden with algae on the shores of Pelee Island, Lake Erie, in 2009. Image via Tom Archer.

The intensity of harmful algal blooms in many lakes around the world has increased according to satellite imagery collected over nearly three decades. The new research was published in the peer-reviewed journal Nature on October 14, 2019.

Harmful algal blooms (overgrowth of algae in water) tend to peak in summertime in response to three key environmental conditions – nutrients, sunlight, and warm water – which are conducive to explosive algal growth. These blooms often appear as thick, green goop on or near the surface of a waterbody, and the color changes in the water can be detected by satellites. When the abundant algae die off and decompose, oxygen levels drop to levels that can be deadly to aquatic life. Some blooms even produce toxins that can contaminate drinking water supplies and make it dangerous for people and their pets to go swimming.

Jeff Ho, a scientist affiliated with the Carnegie Institution for Science in California and lead author of the new study, discussed the impacts of these types of algal blooms in a statement. He said:

Toxic algal blooms affect drinking water supplies, agriculture, fishing, recreation, and tourism. Studies indicate that just in the United States, freshwater blooms result in the loss of $4 billion each year.

Several scientific studies have noted an uptick in freshwater algal blooms in certain regions, but the new research represents the first long-term, global study of large lakes using advanced imagery from the U.S. Geological Survey’s Landsat 5 satellite. Data from 71 large lakes located in 33 countries on six continents showed that the intensity of summertime algal blooms has increased in the majority (68 percent) of the areas studied.

EarthSky 2020 lunar calendars are available! They make great gifts. Order now. Going fast!

Landsat 8 satellite image of an algal bloom in the western part of Lake Erie collected on July 28, 2015. Image via NASA Earth Observatory/Carnegie Science.

The increasing intensity of freshwater algal blooms in summer is likely being driven by a combination of factors. While previous research on individual lakes has definitively linked changes in algal blooms to increased nutrient loading caused by human activities (think fertilizers and sewage), and it is known that warming water temperatures can exacerbate blooms (see Blooms Like it Hot), the drivers of the trends in the new study were not as clear cut. Interestingly, the few lakes that showed a decrease in bloom intensity were the ones that had warmed less than the other lakes. Thus, the findings suggest that warming waters may have played an important role in the observed trends.

Anna Michalak, a co-author of the new study, is a senior scientist at the Carnegie Institution of Science. She said:

This finding illustrates how important it is to identify the factors that make some lakes more susceptible to climate change. We need to develop water management strategies that better reflect the ways that local hydrological conditions are affected by a changing climate.

Nima Pahlevan of NASA’s Goddard Space Flight Center also contributed to the new research published in Nature.

Florida’s Lake Okeechobee. Toxic algal blooms resulted in states of emergency being declared in Florida in 2016 and 2018. Image via NASA Earth Observatory/Carnegie Science.

Bottom line: The intensity of harmful algal blooms in many freshwater lakes around the world is increasing, according to new satellite data collected over nearly three decades.

Source: Widespread global increase in intense lake phytoplankton blooms since the 1980s

Via Carnegie Institution of Science

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Scientists confirm Europa’s water vapor geysers … maybe

Artist’s concept of a water vapor plume on Jupiter’s large moon Europa. It’s thought that this moon has a liquid ocean of water beneath its icy crust. Image via NASA/ESA/K. Retherford/SwRI/SYFY.

Jupiter’s large moon Europa is one of the most intriguing places in the solar system, an ocean world that might support life of some kind. As well as a subsurface ocean, it might also share another characteristic of Saturn’s moon Enceladus: geyser-like water vapor plumes bursting through its icy surface. The evidence for geysers on Europa has been tentative up to now, but this month (November 18, 2019) scientists said they’ve found what might be new confirmation: they reported the direct detection of water vapor above the moon’s surface.

The peer-reviewed findings, from scientists at NASA’s Goddard Space Flight Center, were published in the journal Nature Astronomy on November 18, 2019.

Like Enceladus, Europa has a deep ocean below the outer ice crust. On Enceladus, water percolates up to the surface from the ocean below, erupting into space through cracks in the ice as water vapor. It has long been thought that the same thing could be happening on Europa, but the evidence hasn’t been as solid yet, with hints of activity seen by the Hubble Space Telescope (HST).

According to NASA scientist Lucas Paganini:

Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third — liquid water — is somewhat hard to find beyond Earth. While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapor form.

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Composite photos from the Hubble Space Telescope and the Galileo spacecraft, showing a suspected plume erupting on Europa in 2014 and 2016. Image via NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center/JPL.

Another composite image from the Hubble Space Telescope and the Galileo spacecraft, showing a “finger-like” plume in the lower left in 2016. Image via NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.

Europa’s cracked icy surface as seen by NASA’s Galileo spacecraft in the late 1990s. Yellowish regions on the moon’s surface have now been confirmed to be irradiated sodium chloride, aka table salt. Image via NASA/JPL-Caltech/SETI Institute.

So how much water vapor was detected?

According to Paganini, about 5,202 pounds (2,360 kilograms) per second, enough to fill an Olympic-size swimming pool within minutes.

But like earlier observations have suggested, the outbursts of water vapor appear to be infrequent, unlike those on Enceladus, which erupt on a regular basis. Paganini said:

For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method.

The signal of water vapor is distinct but faint, and was only seen once in 17 nights of observations in 2016 and 2017. That suggests that Europa’s plumes are much more sporadic than those on Enceladus. The science team detected the water molecules on Europa’s leading hemisphere, the side of the moon that’s always facing in the direction of the moon’s orbit around Jupiter. Like Earth’s moon, Europa is gravitationally locked to its planet, so the leading hemisphere always faces the direction of the orbit, while the trailing hemisphere always faces in the opposite direction. The detection was made using a spectrograph at the W. M. Keck Observatory on Mauna Kea in Hawaii. The spectrograph measures the chemical composition of planetary atmospheres through the infrared light they emit or absorb. From the paper:

Previous investigations proved the existence of local density enhancements in Europa’s atmosphere, advancing the idea of a possible origination from water plumes. These measurement strategies, however, were sensitive either to total absorption or atomic emissions, which limited the ability to assess the water content. Here we present direct searches for water vapor on Europa spanning dates from February 2016 to May 2017 with the Keck Observatory. Our global survey at infrared wavelengths resulted in non-detections on 16 out of 17 dates, with upper limits below the water abundances inferred from previous estimates. On one date (26 April 2016) we measured 2,095 ± 658 tonnes of water vapor at Europa’s leading hemisphere. We suggest that the outgassing of water vapor on Europa occurs at lower levels than previously estimated, with only rare localized events of stronger activity.

Some of the tentative evidence for Europa’s plumes came from studying data sent back by the Galileo spacecraft. The disturbances in Jupiter’s magnetic field that provided clues about the subsurface ocean also hinted at possible plumes, according to researchers in 2018. In 2013, the HST had detected the chemical elements hydrogen and oxygen in plume-like configurations in Europa’s extremely tenuous atmosphere. Then, in 2016, Hubble imaged “finger-like projections” in silhouette while Europa passed in front of Jupiter. All of these findings were tantalizing, but still tentative. But now the first detection of water vapor itself is additional evidence for the plumes. As Lorenz Roth, an astronomer and physicist at the KTH Royal Institute of Technology, said:

This first direct identification of water vapor on Europa is a critical confirmation of our original detections of atomic species, and it highlights the apparent sparsity of large plumes on this icy world.

One problem that Paganini and his team needed to address, however, was that water in Earth’s atmosphere can distort the readings of water vapor on distant worlds taken by ground-based telescopes like Keck. To compensate, complex mathematical and computer modeling was used to simulate the conditions of Earth’s atmosphere so they could differentiate Earth’s atmospheric water from Europa’s in the data. According to Avi Mandell, a Goddard planetary scientist:

We performed diligent safety checks to remove possible contaminants in ground-based observations. But, eventually, we’ll have to get closer to Europa to see what’s really going on.

Saturn’s moon Enceladus was confirmed to have water vapor plumes by the Cassini spacecraft. This stunning photo shows then erupting through cracks in the ice crust at the moon’s south pole. Image via NASA Science.

Not all researchers, however, are convinced that the new findings prove the existence of the plumes, and emphasize how they show that the geyser activity is probably lower than had been anticipated. Astronomer Phil Plait wrote about this in an addendum to his Nov. 19, 2019, article on SYFY about the news:

Correction, and it’s a big one: When I wrote this, I thought the conclusions based on the observations were much more solid than they were reported in a NASA press release. But after being alerted by a couple of astronomers, and looking things over again, I see that the idea that a plume of water from a geyser is not “confirmed” as I originally wrote, but more like “maybe.” The detection by itself was marginally statistically significant, but was part of 16 other observations that showed nothing. I was thinking about the single observation taken alone, but when placed in context of the other observations the statistical significance drops. That means the likelihood of this observation being real – that is, that the light from a plume of water was definitely seen – is lower than I originally stated.

So at this point, it may be safer to say that the new observations add to the evidence for water vapor geysers on Europa, but are still not 100% conclusive. This does not take away from the abundant evidence for the subsurface ocean, it only addresses how much of that water may actually make it to the surface and erupt as vapor into space. Hopefully NASA’s upcoming Europa Clipper mission – due to launch in the mid-2020s – will be able to finally settle the question of whether the geysers are real or not, and how frequent they are, if other observations don’t beforehand. It could even sample them directly, just like Cassini did at Enceladus.

Bottom line: Scientists have found new evidence for water vapor geysers on Europa, although whether they have actually been proven now is a matter of debate.

Source: A measurement of water vapour amid a largely quiescent environment on Europa

Via NASA

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

Artist’s concept of a water vapor plume on Jupiter’s large moon Europa. It’s thought that this moon has a liquid ocean of water beneath its icy crust. Image via NASA/ESA/K. Retherford/SwRI/SYFY.

Jupiter’s large moon Europa is one of the most intriguing places in the solar system, an ocean world that might support life of some kind. As well as a subsurface ocean, it might also share another characteristic of Saturn’s moon Enceladus: geyser-like water vapor plumes bursting through its icy surface. The evidence for geysers on Europa has been tentative up to now, but this month (November 18, 2019) scientists said they’ve found what might be new confirmation: they reported the direct detection of water vapor above the moon’s surface.

The peer-reviewed findings, from scientists at NASA’s Goddard Space Flight Center, were published in the journal Nature Astronomy on November 18, 2019.

Like Enceladus, Europa has a deep ocean below the outer ice crust. On Enceladus, water percolates up to the surface from the ocean below, erupting into space through cracks in the ice as water vapor. It has long been thought that the same thing could be happening on Europa, but the evidence hasn’t been as solid yet, with hints of activity seen by the Hubble Space Telescope (HST).

According to NASA scientist Lucas Paganini:

Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third — liquid water — is somewhat hard to find beyond Earth. While scientists have not yet detected liquid water directly, we’ve found the next best thing: water in vapor form.

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Composite photos from the Hubble Space Telescope and the Galileo spacecraft, showing a suspected plume erupting on Europa in 2014 and 2016. Image via NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center/JPL.

Another composite image from the Hubble Space Telescope and the Galileo spacecraft, showing a “finger-like” plume in the lower left in 2016. Image via NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center.

Europa’s cracked icy surface as seen by NASA’s Galileo spacecraft in the late 1990s. Yellowish regions on the moon’s surface have now been confirmed to be irradiated sodium chloride, aka table salt. Image via NASA/JPL-Caltech/SETI Institute.

So how much water vapor was detected?

According to Paganini, about 5,202 pounds (2,360 kilograms) per second, enough to fill an Olympic-size swimming pool within minutes.

But like earlier observations have suggested, the outbursts of water vapor appear to be infrequent, unlike those on Enceladus, which erupt on a regular basis. Paganini said:

For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method.

The signal of water vapor is distinct but faint, and was only seen once in 17 nights of observations in 2016 and 2017. That suggests that Europa’s plumes are much more sporadic than those on Enceladus. The science team detected the water molecules on Europa’s leading hemisphere, the side of the moon that’s always facing in the direction of the moon’s orbit around Jupiter. Like Earth’s moon, Europa is gravitationally locked to its planet, so the leading hemisphere always faces the direction of the orbit, while the trailing hemisphere always faces in the opposite direction. The detection was made using a spectrograph at the W. M. Keck Observatory on Mauna Kea in Hawaii. The spectrograph measures the chemical composition of planetary atmospheres through the infrared light they emit or absorb. From the paper:

Previous investigations proved the existence of local density enhancements in Europa’s atmosphere, advancing the idea of a possible origination from water plumes. These measurement strategies, however, were sensitive either to total absorption or atomic emissions, which limited the ability to assess the water content. Here we present direct searches for water vapor on Europa spanning dates from February 2016 to May 2017 with the Keck Observatory. Our global survey at infrared wavelengths resulted in non-detections on 16 out of 17 dates, with upper limits below the water abundances inferred from previous estimates. On one date (26 April 2016) we measured 2,095 ± 658 tonnes of water vapor at Europa’s leading hemisphere. We suggest that the outgassing of water vapor on Europa occurs at lower levels than previously estimated, with only rare localized events of stronger activity.

Some of the tentative evidence for Europa’s plumes came from studying data sent back by the Galileo spacecraft. The disturbances in Jupiter’s magnetic field that provided clues about the subsurface ocean also hinted at possible plumes, according to researchers in 2018. In 2013, the HST had detected the chemical elements hydrogen and oxygen in plume-like configurations in Europa’s extremely tenuous atmosphere. Then, in 2016, Hubble imaged “finger-like projections” in silhouette while Europa passed in front of Jupiter. All of these findings were tantalizing, but still tentative. But now the first detection of water vapor itself is additional evidence for the plumes. As Lorenz Roth, an astronomer and physicist at the KTH Royal Institute of Technology, said:

This first direct identification of water vapor on Europa is a critical confirmation of our original detections of atomic species, and it highlights the apparent sparsity of large plumes on this icy world.

One problem that Paganini and his team needed to address, however, was that water in Earth’s atmosphere can distort the readings of water vapor on distant worlds taken by ground-based telescopes like Keck. To compensate, complex mathematical and computer modeling was used to simulate the conditions of Earth’s atmosphere so they could differentiate Earth’s atmospheric water from Europa’s in the data. According to Avi Mandell, a Goddard planetary scientist:

We performed diligent safety checks to remove possible contaminants in ground-based observations. But, eventually, we’ll have to get closer to Europa to see what’s really going on.

Saturn’s moon Enceladus was confirmed to have water vapor plumes by the Cassini spacecraft. This stunning photo shows then erupting through cracks in the ice crust at the moon’s south pole. Image via NASA Science.

Not all researchers, however, are convinced that the new findings prove the existence of the plumes, and emphasize how they show that the geyser activity is probably lower than had been anticipated. Astronomer Phil Plait wrote about this in an addendum to his Nov. 19, 2019, article on SYFY about the news:

Correction, and it’s a big one: When I wrote this, I thought the conclusions based on the observations were much more solid than they were reported in a NASA press release. But after being alerted by a couple of astronomers, and looking things over again, I see that the idea that a plume of water from a geyser is not “confirmed” as I originally wrote, but more like “maybe.” The detection by itself was marginally statistically significant, but was part of 16 other observations that showed nothing. I was thinking about the single observation taken alone, but when placed in context of the other observations the statistical significance drops. That means the likelihood of this observation being real – that is, that the light from a plume of water was definitely seen – is lower than I originally stated.

So at this point, it may be safer to say that the new observations add to the evidence for water vapor geysers on Europa, but are still not 100% conclusive. This does not take away from the abundant evidence for the subsurface ocean, it only addresses how much of that water may actually make it to the surface and erupt as vapor into space. Hopefully NASA’s upcoming Europa Clipper mission – due to launch in the mid-2020s – will be able to finally settle the question of whether the geysers are real or not, and how frequent they are, if other observations don’t beforehand. It could even sample them directly, just like Cassini did at Enceladus.

Bottom line: Scientists have found new evidence for water vapor geysers on Europa, although whether they have actually been proven now is a matter of debate.

Source: A measurement of water vapour amid a largely quiescent environment on Europa

Via NASA

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

Achernar is the End of the River

In a dark sky, you can see that Achernar marks the end of a great stream of stars known to the ancients as a celestial River. This is the constellation Eridanus the River, and Achernar is its brightest star.

The ninth brightest star in all the heavens, Achernar, is a well-known sight to observers in the Southern Hemisphere. But many northern stargazers know this star by name only. That’s because – despite its magnitude of 0.45, making it shine brightly as the brightest stars visible from Earth – it’s extremely far south on the dome of stars surrounding Earth. If you’re north of about 33 degrees north latitude, Achernar never rises above your horizon at all. And yet this star remains one of the sky’s most famous stars as the star at the end of the River.

The River is – of course – the constellation Eridanus, which is large and easy to see in a dark-enough sky, even if you’re fairly far north on Earth’s globe. That’s because the northern part of this constellation is located near the extremely prominent constellation Orion the Hunter. Eridanus appears to swell up in a great loop near Orion, then meander southward, finally – for most in the Northern Hemisphere – dropping out of sight below the southern horizon before it reaches its end.

But if you are far enough south – below 33 degrees north latitude – you’ll easily spot the River’s end as the bright star Achernar.

Come to know Eridanus, and someday – from some southerly latitude, maybe while on vacation – you’ll enjoy spotting Achernar!

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A more detailed chart showing Achernar’s location in southernmost Eridanus, via Wikimedia Commons.

How to see Achernar. For all practical purposes, you must be even further south – around 25 degrees north latitude – to see Achernar well. That is a line drawn around the entire globe passing through, say, Miami in the U.S. state of Florida and Taipei in China.

Nowhere in North America has it easy, seeing this star. For example, from Key West, Achernar rises only about 8 degrees above the southern horizon. Even farther south, from the southern tip of Hawaii’s Big Island, Achernar never quite makes it to 14 degrees.

And yet, if you are far-enough south, you can see Achernar easily. After all, this star is very bright!

Just as Eridanus marks the end of the River, so the River has a beginning, the star Beta Eridani or Cursa, which itself is easily visible from the northern hemisphere, very near Orion’s brightest star, Rigel.

On most nights of the year, Achernar cannot be seen from anywhere in North America, but around October 20 it skirts the southern horizon around midnight, never getting very high. Then as the months pass, it is seen earlier at night – around 10 p.m. in November, 8 p.m. in December and just after sunset in January. Being far to the south with no bright stars around it, Achernar stands out in its isolation. If you have a dark sky, and are far enough south, you’ll easily see Achernar’s constellation Eridanus making its loop under the constellation Orion.

Earthly rivers are sometimes known for meandering. In the sky. the stars representing Eridanus the River – Achernar’s constellation – have a similar quality.

Achernar’s history and mythology. In fact, the name Achernar derives from an Arabic phrase meaning End of the River.

Interestingly, in early classical times the name Achernar was given to the star we now know as Theta Eridani, or Acamar. At that time Acamar was the brightest star of the constellation visible from Greece, and thus was considered the River’s end.

When voyagers discovered the brighter star farther to the south, it became Achernar, and the former Achernar became Acamar.

Apparently both names derive from the same phrase, “Al Ahir al Nahr” according to Richard Hinckley Allen, whose 1899 book on Star Names (Their Lore and Meaning) is still the best around.

Artist’s concept contrasting the size, shape and color of our sun with several flattened stars, including Achernar.

Science of Achernar. Data from the Hipparcos mission placed Achernar at about 144 light-years away. It is a B3V star, meaning that it belongs to the main sequence of stars.

Still, Achernar is much hotter and brighter than our sun.

In fact, it’s nearly 1,100 times as bright, visually, as our sun. Brighter, hotter (and bluer) than the sun, Achernar produces more energy in the non-visible ultraviolet (UV) wavelengths. When you take this into consideration, it pumps out some 3,000 to as much as 5,000 times the solar energy level. The discrepancy is due to an uncertainty in the amount of UV radiation it produces.

Achernar’s mass is 6-8 times that of our sun, and its average diameter is nearly 8-10 times that of the sun. But, while our sun spins on its axis once about every 25 days, Achernar completes one rotation in slightly more than two days, or nearly 15 times faster than our sun. This fast rotation produces an odd, flattened shape, first discovered by the European Southern Observatory’s Very Large Telescope (VLT) in 2003. Up close, Achernar would look more like a blue M&M, while our sun would look more like an orange. Read more about Achernar’s flattened shape from ESO.

This flattening of Achernar makes an exact surface temperature for this star hard to determine, because the flattening actually causes the star’s poles to be hotter than the equator. Estimates range from about 14,500 to 19,300 k (around 26,000 to about 32,000 F).

Achernar’s position is RA: 01h 37m 42.8s, dec: -57° 14′ 12″.

A simple artist’s concept of the star Achernar. It’s flattened because – despite being about 6 to 8 times more massive than our sun, it rotates or spins on its axis about 15 times more rapidly, completing one rotation in 2 Earth-days, in contrast to the sun’s 25-day rotation. Observations have suggested a disk of ionized gas at the star’s equator. Image via Wikimedia Commons.

Bottom line: Achernar – the ninth brightest star – is the southernmost bright star in the constellation Eridanus the River.

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In a dark sky, you can see that Achernar marks the end of a great stream of stars known to the ancients as a celestial River. This is the constellation Eridanus the River, and Achernar is its brightest star.

The ninth brightest star in all the heavens, Achernar, is a well-known sight to observers in the Southern Hemisphere. But many northern stargazers know this star by name only. That’s because – despite its magnitude of 0.45, making it shine brightly as the brightest stars visible from Earth – it’s extremely far south on the dome of stars surrounding Earth. If you’re north of about 33 degrees north latitude, Achernar never rises above your horizon at all. And yet this star remains one of the sky’s most famous stars as the star at the end of the River.

The River is – of course – the constellation Eridanus, which is large and easy to see in a dark-enough sky, even if you’re fairly far north on Earth’s globe. That’s because the northern part of this constellation is located near the extremely prominent constellation Orion the Hunter. Eridanus appears to swell up in a great loop near Orion, then meander southward, finally – for most in the Northern Hemisphere – dropping out of sight below the southern horizon before it reaches its end.

But if you are far enough south – below 33 degrees north latitude – you’ll easily spot the River’s end as the bright star Achernar.

Come to know Eridanus, and someday – from some southerly latitude, maybe while on vacation – you’ll enjoy spotting Achernar!

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A more detailed chart showing Achernar’s location in southernmost Eridanus, via Wikimedia Commons.

How to see Achernar. For all practical purposes, you must be even further south – around 25 degrees north latitude – to see Achernar well. That is a line drawn around the entire globe passing through, say, Miami in the U.S. state of Florida and Taipei in China.

Nowhere in North America has it easy, seeing this star. For example, from Key West, Achernar rises only about 8 degrees above the southern horizon. Even farther south, from the southern tip of Hawaii’s Big Island, Achernar never quite makes it to 14 degrees.

And yet, if you are far-enough south, you can see Achernar easily. After all, this star is very bright!

Just as Eridanus marks the end of the River, so the River has a beginning, the star Beta Eridani or Cursa, which itself is easily visible from the northern hemisphere, very near Orion’s brightest star, Rigel.

On most nights of the year, Achernar cannot be seen from anywhere in North America, but around October 20 it skirts the southern horizon around midnight, never getting very high. Then as the months pass, it is seen earlier at night – around 10 p.m. in November, 8 p.m. in December and just after sunset in January. Being far to the south with no bright stars around it, Achernar stands out in its isolation. If you have a dark sky, and are far enough south, you’ll easily see Achernar’s constellation Eridanus making its loop under the constellation Orion.

Earthly rivers are sometimes known for meandering. In the sky. the stars representing Eridanus the River – Achernar’s constellation – have a similar quality.

Achernar’s history and mythology. In fact, the name Achernar derives from an Arabic phrase meaning End of the River.

Interestingly, in early classical times the name Achernar was given to the star we now know as Theta Eridani, or Acamar. At that time Acamar was the brightest star of the constellation visible from Greece, and thus was considered the River’s end.

When voyagers discovered the brighter star farther to the south, it became Achernar, and the former Achernar became Acamar.

Apparently both names derive from the same phrase, “Al Ahir al Nahr” according to Richard Hinckley Allen, whose 1899 book on Star Names (Their Lore and Meaning) is still the best around.

Artist’s concept contrasting the size, shape and color of our sun with several flattened stars, including Achernar.

Science of Achernar. Data from the Hipparcos mission placed Achernar at about 144 light-years away. It is a B3V star, meaning that it belongs to the main sequence of stars.

Still, Achernar is much hotter and brighter than our sun.

In fact, it’s nearly 1,100 times as bright, visually, as our sun. Brighter, hotter (and bluer) than the sun, Achernar produces more energy in the non-visible ultraviolet (UV) wavelengths. When you take this into consideration, it pumps out some 3,000 to as much as 5,000 times the solar energy level. The discrepancy is due to an uncertainty in the amount of UV radiation it produces.

Achernar’s mass is 6-8 times that of our sun, and its average diameter is nearly 8-10 times that of the sun. But, while our sun spins on its axis once about every 25 days, Achernar completes one rotation in slightly more than two days, or nearly 15 times faster than our sun. This fast rotation produces an odd, flattened shape, first discovered by the European Southern Observatory’s Very Large Telescope (VLT) in 2003. Up close, Achernar would look more like a blue M&M, while our sun would look more like an orange. Read more about Achernar’s flattened shape from ESO.

This flattening of Achernar makes an exact surface temperature for this star hard to determine, because the flattening actually causes the star’s poles to be hotter than the equator. Estimates range from about 14,500 to 19,300 k (around 26,000 to about 32,000 F).

Achernar’s position is RA: 01h 37m 42.8s, dec: -57° 14′ 12″.

A simple artist’s concept of the star Achernar. It’s flattened because – despite being about 6 to 8 times more massive than our sun, it rotates or spins on its axis about 15 times more rapidly, completing one rotation in 2 Earth-days, in contrast to the sun’s 25-day rotation. Observations have suggested a disk of ionized gas at the star’s equator. Image via Wikimedia Commons.

Bottom line: Achernar – the ninth brightest star – is the southernmost bright star in the constellation Eridanus the River.

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