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A closer look at Io’s weird volcanoes

Large crescent banded planet with small varicolored moon in front of it.

A montage of Jupiter and its volcanic moon Io, taken during by the New Horizons spacecraft – en route to Pluto – in early 2007. Notice the volcanic plume above Io’s darkened surface. Image via NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Goddard Space Flight Center/Cosmos.

When we hear about volcanoes, we naturally tend to think of some of Earth’s most famous ones, including the Hawaiian volcanoes, Krakatoa or Mount St. Helens. Earth is a very volcanically active place; however, it is not the most active in the solar system. That would be Jupiter’s moon Io.

We on Earth first learned about Io’s volcanoes nearly 40 years ago, when NASA’s Voyager 1 spacecraft flew past this Jovian moon. Now, scientists have completed a comprehensive new peer-reviewed report on Io’s volcanoes, first published in The Astrophysical Journal on June 21, 2019, based on ground-based observations. The report covers five years of observations from 2013-2018, using advanced instrumentation on the Keck and Gemini telescopes.

Scientists had already known how volcanically active Io is. Its surface is dotted with hundreds of active volcanoes, despite this moon’s small size and its location at Jupiter’s orbit, much farther from the sun than Earth, in a much-colder part of the solar system. The new study shows, again, that Io is essentially continuously erupting, and it also reveals some new mysteries. In other words, nearly 40 years after Voyager 1’s momentous discovery, Io’s volcanoes aren’t behaving exactly as scientists expected.

For example, there are volcanoes in the “wrong” places, with the biggest eruptions mostly limited to a single hemisphere on Io. And Loki Patera – an 8,100-square-mile caldera filled with lava and Io’s most active volcano – is an enigma in itself.

Jupiter's moon Io, close up, with Loki Patera indicated, many large and small bright-colored splotches.

NASA’s Galileo spacecraft obtained this view of Io on September 19, 1997, at a range of more than 310,000 miles (500,000 km). In this image, deposits of sulfur dioxide frost appear in white and gray hues while yellowish and brownish hues are probably due to other sulfurous materials. Bright red materials and dark spots with low brightness mark areas of recent volcanic activity and are usually associated with high temperatures and surface changes. Image via NASA/JPL/University of Arizona/Sci-News.com.

Small blue eruption on a the horizon of a colorful moon.

An erupting volcano on Io, as seen by NASA’s Galileo spacecraft in November 1997. Image via NASA/JPL/University of Arizona/NASA Science|Solar System Exploration.

The kinds of eruptions occurring now on Io are also thought to be similar to ones on Earth when it was much younger. As Ashley Davies, a volcanologist at NASA’s Jet Propulsion Laboratory said simply:

It’s a window into Earth’s past.

Loki Patera, the source of 10 percent of Io’s heat output, shows an odd pattern of brightening and dimming. The pattern was found by combining old and new data, and repeats about every 460-480 days, which is consistent with repeated variations in Io’s elliptical orbit. But the pattern isn’t always consistent. An eruption was predicted for May 2018, and it happened, but then the scientists predicted another big eruption September of this year, and it came early, in early July, ending just a few days later. As noted by Julie Rathbun, a scientist at the Planetary Science Institute:

We need to stop naming features after trickster gods!

Scientists aren’t sure yet why Loki Patera brightens and dims the way it does, but it may have something to do with a nearby lava lake that regenerates. When parts of the lava lake cool, they sink beneath the surface, possibly triggering a progressive, sweeping wave pattern seen at the surface. Wow … yes?

Another mystery is why the biggest eruptions tend to occur on the trailing hemisphere of Io, as it orbits Jupiter. Why this disparity?

Earth, moon, Io and Europa.

Io is just slightly larger than our moon and Europa. Image via Galileo’s Pendulum.

Also, computer models predicted that Io’s volcanoes should be concentrated either near the poles or near the equator. But that’s not what is seen, and so there is an unexplained mismatch.

Scientists also still don’t know what the subsurface of Io is really like. It’s been theorized that there is an underground ocean of magma but there may actually just be pockets of magma instead, or even a fluid-filled sponge layer.

Io’s volcanic eruptions can also be very powerful, with one blast sometimes causing the moon’s brightness to double. But that itself is another mystery. Katherine de Kleer, a scientist at the California Institute of Technology, saw three of them in just two weeks in 2013, but then nothing for the next five years:

That’s weird. Where are they?

The weirdness of Io’s volcanoes is an opportunity to not only understand the Jovian moon itself better, but also volcanism on other solar system bodies, including Earth. As Alfred McEwen, a planetary geologist at the University of Arizona, noted:

The history of volcanology is that you look at ancient deposits and you’re puzzled. Then you see it erupt, and then you go, Ah-ha, now I understand.

Io's mottled terrain. Gray background with large irregular black and blue spots.

A mosaic of images of Io’s south polar region, from Voyager 1. Image via NASA/JPL/USGS/Universe Today.

Since Io is continuously erupting, its surface is covered by sulfur lava flows new and old, giving it a very colorful and mottled appearance. That surface is no more than a couple million years old at the most at any given time, even though Io itself is about 4.5 billion years old. The moon has been described as basically turning itself inside out on an ongoing basis, thanks to Jupiter’s powerful gravity tugging at its insides. The lava flows can reach 3,000 degrees Fahrenheit (1650 Celsius) in temperature, although the surface temperature on average is -202 degrees F (-130 C). This is because Io has virtually no atmosphere to trap heat, much like our own moon.

Io’s volcanoes may be reminiscent of Earth’s, but they seem to “dance to their own tune” as it were, behaving in unexpected and puzzling ways. Io is a very strange and alien place.

Bottom line: Not only is Io the most volcanically active body in the solar system, its volcanoes are also some of the most unusual. This new report highlights Io’s most puzzling mysteries.

Source: Io’s Volcanic Activity from Time Domain Adaptive Optics Observations: 2013–2018

Via National Geographic



from EarthSky https://ift.tt/2Ku5akW
Large crescent banded planet with small varicolored moon in front of it.

A montage of Jupiter and its volcanic moon Io, taken during by the New Horizons spacecraft – en route to Pluto – in early 2007. Notice the volcanic plume above Io’s darkened surface. Image via NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Goddard Space Flight Center/Cosmos.

When we hear about volcanoes, we naturally tend to think of some of Earth’s most famous ones, including the Hawaiian volcanoes, Krakatoa or Mount St. Helens. Earth is a very volcanically active place; however, it is not the most active in the solar system. That would be Jupiter’s moon Io.

We on Earth first learned about Io’s volcanoes nearly 40 years ago, when NASA’s Voyager 1 spacecraft flew past this Jovian moon. Now, scientists have completed a comprehensive new peer-reviewed report on Io’s volcanoes, first published in The Astrophysical Journal on June 21, 2019, based on ground-based observations. The report covers five years of observations from 2013-2018, using advanced instrumentation on the Keck and Gemini telescopes.

Scientists had already known how volcanically active Io is. Its surface is dotted with hundreds of active volcanoes, despite this moon’s small size and its location at Jupiter’s orbit, much farther from the sun than Earth, in a much-colder part of the solar system. The new study shows, again, that Io is essentially continuously erupting, and it also reveals some new mysteries. In other words, nearly 40 years after Voyager 1’s momentous discovery, Io’s volcanoes aren’t behaving exactly as scientists expected.

For example, there are volcanoes in the “wrong” places, with the biggest eruptions mostly limited to a single hemisphere on Io. And Loki Patera – an 8,100-square-mile caldera filled with lava and Io’s most active volcano – is an enigma in itself.

Jupiter's moon Io, close up, with Loki Patera indicated, many large and small bright-colored splotches.

NASA’s Galileo spacecraft obtained this view of Io on September 19, 1997, at a range of more than 310,000 miles (500,000 km). In this image, deposits of sulfur dioxide frost appear in white and gray hues while yellowish and brownish hues are probably due to other sulfurous materials. Bright red materials and dark spots with low brightness mark areas of recent volcanic activity and are usually associated with high temperatures and surface changes. Image via NASA/JPL/University of Arizona/Sci-News.com.

Small blue eruption on a the horizon of a colorful moon.

An erupting volcano on Io, as seen by NASA’s Galileo spacecraft in November 1997. Image via NASA/JPL/University of Arizona/NASA Science|Solar System Exploration.

The kinds of eruptions occurring now on Io are also thought to be similar to ones on Earth when it was much younger. As Ashley Davies, a volcanologist at NASA’s Jet Propulsion Laboratory said simply:

It’s a window into Earth’s past.

Loki Patera, the source of 10 percent of Io’s heat output, shows an odd pattern of brightening and dimming. The pattern was found by combining old and new data, and repeats about every 460-480 days, which is consistent with repeated variations in Io’s elliptical orbit. But the pattern isn’t always consistent. An eruption was predicted for May 2018, and it happened, but then the scientists predicted another big eruption September of this year, and it came early, in early July, ending just a few days later. As noted by Julie Rathbun, a scientist at the Planetary Science Institute:

We need to stop naming features after trickster gods!

Scientists aren’t sure yet why Loki Patera brightens and dims the way it does, but it may have something to do with a nearby lava lake that regenerates. When parts of the lava lake cool, they sink beneath the surface, possibly triggering a progressive, sweeping wave pattern seen at the surface. Wow … yes?

Another mystery is why the biggest eruptions tend to occur on the trailing hemisphere of Io, as it orbits Jupiter. Why this disparity?

Earth, moon, Io and Europa.

Io is just slightly larger than our moon and Europa. Image via Galileo’s Pendulum.

Also, computer models predicted that Io’s volcanoes should be concentrated either near the poles or near the equator. But that’s not what is seen, and so there is an unexplained mismatch.

Scientists also still don’t know what the subsurface of Io is really like. It’s been theorized that there is an underground ocean of magma but there may actually just be pockets of magma instead, or even a fluid-filled sponge layer.

Io’s volcanic eruptions can also be very powerful, with one blast sometimes causing the moon’s brightness to double. But that itself is another mystery. Katherine de Kleer, a scientist at the California Institute of Technology, saw three of them in just two weeks in 2013, but then nothing for the next five years:

That’s weird. Where are they?

The weirdness of Io’s volcanoes is an opportunity to not only understand the Jovian moon itself better, but also volcanism on other solar system bodies, including Earth. As Alfred McEwen, a planetary geologist at the University of Arizona, noted:

The history of volcanology is that you look at ancient deposits and you’re puzzled. Then you see it erupt, and then you go, Ah-ha, now I understand.

Io's mottled terrain. Gray background with large irregular black and blue spots.

A mosaic of images of Io’s south polar region, from Voyager 1. Image via NASA/JPL/USGS/Universe Today.

Since Io is continuously erupting, its surface is covered by sulfur lava flows new and old, giving it a very colorful and mottled appearance. That surface is no more than a couple million years old at the most at any given time, even though Io itself is about 4.5 billion years old. The moon has been described as basically turning itself inside out on an ongoing basis, thanks to Jupiter’s powerful gravity tugging at its insides. The lava flows can reach 3,000 degrees Fahrenheit (1650 Celsius) in temperature, although the surface temperature on average is -202 degrees F (-130 C). This is because Io has virtually no atmosphere to trap heat, much like our own moon.

Io’s volcanoes may be reminiscent of Earth’s, but they seem to “dance to their own tune” as it were, behaving in unexpected and puzzling ways. Io is a very strange and alien place.

Bottom line: Not only is Io the most volcanically active body in the solar system, its volcanoes are also some of the most unusual. This new report highlights Io’s most puzzling mysteries.

Source: Io’s Volcanic Activity from Time Domain Adaptive Optics Observations: 2013–2018

Via National Geographic



from EarthSky https://ift.tt/2Ku5akW

A big earthquake in the US Pacific Northwest?

Field with yellow flowers, and in the distance, a conical snow-capped mountain.

What’s going on about 90 miles (150 km) below the Earth’s surface? Image via Good Free Photos.

By Miles Bodmer, University of Oregon and Doug Toomey, University of Oregon

The Pacific Northwest is known for many things – its beer, its music, its mythical large-footed creatures. Most people don’t associate it with earthquakes, but they should. It’s home to the Cascadia megathrust fault that runs 600 miles (966 km) from Northern California up to Vancouver Island in Canada, spanning several major metropolitan areas including Seattle and Portland, Oregon.

This geologic fault has been relatively quiet in recent memory. There haven’t been many widely felt quakes along the Cascadia megathrust, certainly nothing that would rival a catastrophic event like the 1989 Loma Prieta earthquake along the active San Andreas in California. That doesn’t mean it will stay quiet, though. Scientists know it has the potential for large earthquakes – as big as magnitude 9.

Geophysicists have known for over a decade that not all portions of the Cascadia megathrust fault behave the same. The northern and southern sections are much more seismically active than the central section – with frequent small earthquakes and ground deformations that residents don’t often notice. But why do these variations exist and what gives rise to them?

Our research tries to answer these questions by constructing images of what’s happening deep within the Earth, more than 90 miles (144 km) below the fault. We’ve identified regions that are rising up beneath these active sections which we think are leading to the observable differences along the Cascadia fault.

Cascadia and the ‘Really Big One’

The Cascadia subduction zone is a region where two tectonic plates are colliding. The Juan de Fuca, a small oceanic plate, is being driven under the North American plate, atop which the continental U.S. sits.

Diagram of US Pacific Northwest coast with tectonic plate features and earthquake locations.

The Juan de Fuca plate meets the North American plate beneath the Cascadia fault. Image via USGS.

Subduction systems – where one tectonic plate slides over another – are capable of producing the world’s largest known earthquakes. A prime example is the 2011 Tohoku earthquake that rocked Japan.

Cascadia is seismically very quiet compared to other subduction zones – but it’s not completely inactive. Research indicates the fault ruptured in a magnitude 9.0 event in 1700. That’s roughly 30 times more powerful than the largest predicted San Andreas earthquake. Researchers suggest that we are within the roughly 300- to 500-year window during which another large Cascadia event may occur.

Many smaller undamaging and unfelt events take place in northern and southern Cascadia every year. However, in central Cascadia, underlying most of Oregon, there is very little seismicity. Why would the same fault behave differently in different regions?

Over the last decade, scientists have made several additional observations that highlight variations along the fault.

One has to do with plate locking, which tells us where stress is accumulating along the fault. If the tectonic plates are locked – that is, really stuck together and unable to move past each other – stress builds. Eventually that stress can be released rapidly as an earthquake, with the magnitude depending on how large the patch of fault that ruptures is.

Metal dome on tripod of three short poles next to a metal box on a pole, in a field.

A GPS geosensor in Washington. Image via Bdelisle.

Geologists have recently been able to deploy hundreds of GPS monitors across Cascadia to record the subtle ground deformations that result from the plates’ inability to slide past each other. Just like historic seismicity, plate locking is more common in the northern and southern parts of Cascadia.

Geologists are also now able to observe difficult-to-detect seismic rumblings known as tremor. These events occur over the time span of several minutes up to weeks, taking much longer than a typical earthquake. They don’t cause large ground motions even though they can release significant amounts of energy. Researchers have only discovered these signals in the last 15 years, but permanent seismic stations have helped build a robust catalog of events. Tremor, too, seems to be more concentrated along the northern and southern parts of the fault.

What would cause this situation, with the area beneath Oregon relatively less active by all these measures? To explain we had to look deep, over 100 kilometers (60 miles) below the surface, into the Earth’s mantle.

Map of US Pacific Northwest covered with little green triangles and blue circles.

Green dots and blue triangles show locations of seismic monitoring stations. Image via Bodmer et al., 2018, Geophysical Research Letters.

Imaging the Earth using distant quakes

Physicians use electromagnetic waves to “see” internal structures like bones without needing to open up a human patient to view them directly. Geologists image the Earth in much the same way. Instead of X-rays, we use seismic energy radiating out from distant magnitude 6.0-plus earthquakes to help us “see” features we physically just can’t get to. This energy travels like sound waves through the structures of the Earth. When rock is hotter or partially molten by even a tiny amount, seismic waves slow down. By measuring the arrival times of seismic waves, we create 3-D images showing how fast or slow the seismic waves travel through specific parts of the Earth.

Deck of ship with orange boxes and spheres lined up, and waves crashing over the stern.

Ocean bottom seismometers waiting to be deployed during the Cascadia Initiative. Image via Emilie Hooft.

To see these signals, we need records from seismic monitoring stations. More sensors provide better resolution and a clearer image – but gathering more data can be problematic when half the area you’re interested in is underwater. To address this challenge, we were part of a team of scientists that deployed hundreds of seismometers on the ocean floor off the western U.S. over the span of four years, starting in 2011. This experiment, the Cascadia Initiative, was the first ever to cover an entire tectonic plate with instruments at a spacing of roughly 30 miles (50 km).

What we found are two anomalous regions beneath the fault where seismic waves travel slower than expected. These anomalies are large, about 90 miles (150 km) in diameter, and show up beneath the northern and southern sections of the fault. Remember, that’s where researchers have already observed increased activity: the seismicity. Interestingly, the anomalies are not present beneath the central part of the fault, under Oregon, where we see a decrease in activity.

Three maps of coast with long colored areas.

Regions where seismic waves moved more slowly, on average, are redder, while the areas where they moved more quickly are bluer. The slower anomalous areas 90 miles (150 km) beneath the Earth’s surface corresponded to where the colliding plates are more locked and where tremor is more common. Image via Bodmer et al., 2018, Geophysical Research Letters.

So what exactly are these anomalies?

The tectonic plates float on the Earth’s rocky mantle layer. Where the mantle is slowly rising over millions of years, the rock decompresses. Since it’s at such high temperatures, nearly 1500 degrees Celsius (2700 F) at 100 km (60 mi) depth, it can melt ever so slightly.

These physical changes cause the anomalous regions to be more buoyant – melted hot rock is less dense than solid cooler rock. It’s this buoyancy that we believe is affecting how the fault above behaves. The hot, partially molten region pushes upwards on what’s above, similar to how a helium balloon might rise up against a sheet draped over it. We believe this increases the forces between the two plates, causing them to be more strongly coupled and thus more fully locked.

A general prediction for where, but not when

Our results provide new insights into how this subduction zone, and possibly others, behaves over geologic timeframes of millions of years. Unfortunately our results can’t predict when the next large Cascadia megathrust earthquake will occur. This will require more research and dense active monitoring of the subduction zone, both onshore and offshore, using seismic and GPS-like stations to capture short-term phenomena.

Our work does suggest that a large event is more likely to start in either the northern or southern sections of the fault, where the plates are more fully locked, and gives a possible reason for why that may be the case.

It remains important for the public and policymakers to stay informed about the potential risk involved in cohabiting with a subduction zone fault and to support programs such as Earthquake Early Warning that seek to expand our monitoring capabilities and mitigate loss in the event of a large rupture.

Miles Bodmer, Ph.D. Student in Earth Sciences, University of Oregon and Doug Toomey, Professor of Earth Sciences, University of Oregon

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Parts of the Pacific Northwest’s Cascadia fault are more seismically active than others. Imaging data suggests why.

The Conversation



from EarthSky https://ift.tt/2ZDRZ7K
Field with yellow flowers, and in the distance, a conical snow-capped mountain.

What’s going on about 90 miles (150 km) below the Earth’s surface? Image via Good Free Photos.

By Miles Bodmer, University of Oregon and Doug Toomey, University of Oregon

The Pacific Northwest is known for many things – its beer, its music, its mythical large-footed creatures. Most people don’t associate it with earthquakes, but they should. It’s home to the Cascadia megathrust fault that runs 600 miles (966 km) from Northern California up to Vancouver Island in Canada, spanning several major metropolitan areas including Seattle and Portland, Oregon.

This geologic fault has been relatively quiet in recent memory. There haven’t been many widely felt quakes along the Cascadia megathrust, certainly nothing that would rival a catastrophic event like the 1989 Loma Prieta earthquake along the active San Andreas in California. That doesn’t mean it will stay quiet, though. Scientists know it has the potential for large earthquakes – as big as magnitude 9.

Geophysicists have known for over a decade that not all portions of the Cascadia megathrust fault behave the same. The northern and southern sections are much more seismically active than the central section – with frequent small earthquakes and ground deformations that residents don’t often notice. But why do these variations exist and what gives rise to them?

Our research tries to answer these questions by constructing images of what’s happening deep within the Earth, more than 90 miles (144 km) below the fault. We’ve identified regions that are rising up beneath these active sections which we think are leading to the observable differences along the Cascadia fault.

Cascadia and the ‘Really Big One’

The Cascadia subduction zone is a region where two tectonic plates are colliding. The Juan de Fuca, a small oceanic plate, is being driven under the North American plate, atop which the continental U.S. sits.

Diagram of US Pacific Northwest coast with tectonic plate features and earthquake locations.

The Juan de Fuca plate meets the North American plate beneath the Cascadia fault. Image via USGS.

Subduction systems – where one tectonic plate slides over another – are capable of producing the world’s largest known earthquakes. A prime example is the 2011 Tohoku earthquake that rocked Japan.

Cascadia is seismically very quiet compared to other subduction zones – but it’s not completely inactive. Research indicates the fault ruptured in a magnitude 9.0 event in 1700. That’s roughly 30 times more powerful than the largest predicted San Andreas earthquake. Researchers suggest that we are within the roughly 300- to 500-year window during which another large Cascadia event may occur.

Many smaller undamaging and unfelt events take place in northern and southern Cascadia every year. However, in central Cascadia, underlying most of Oregon, there is very little seismicity. Why would the same fault behave differently in different regions?

Over the last decade, scientists have made several additional observations that highlight variations along the fault.

One has to do with plate locking, which tells us where stress is accumulating along the fault. If the tectonic plates are locked – that is, really stuck together and unable to move past each other – stress builds. Eventually that stress can be released rapidly as an earthquake, with the magnitude depending on how large the patch of fault that ruptures is.

Metal dome on tripod of three short poles next to a metal box on a pole, in a field.

A GPS geosensor in Washington. Image via Bdelisle.

Geologists have recently been able to deploy hundreds of GPS monitors across Cascadia to record the subtle ground deformations that result from the plates’ inability to slide past each other. Just like historic seismicity, plate locking is more common in the northern and southern parts of Cascadia.

Geologists are also now able to observe difficult-to-detect seismic rumblings known as tremor. These events occur over the time span of several minutes up to weeks, taking much longer than a typical earthquake. They don’t cause large ground motions even though they can release significant amounts of energy. Researchers have only discovered these signals in the last 15 years, but permanent seismic stations have helped build a robust catalog of events. Tremor, too, seems to be more concentrated along the northern and southern parts of the fault.

What would cause this situation, with the area beneath Oregon relatively less active by all these measures? To explain we had to look deep, over 100 kilometers (60 miles) below the surface, into the Earth’s mantle.

Map of US Pacific Northwest covered with little green triangles and blue circles.

Green dots and blue triangles show locations of seismic monitoring stations. Image via Bodmer et al., 2018, Geophysical Research Letters.

Imaging the Earth using distant quakes

Physicians use electromagnetic waves to “see” internal structures like bones without needing to open up a human patient to view them directly. Geologists image the Earth in much the same way. Instead of X-rays, we use seismic energy radiating out from distant magnitude 6.0-plus earthquakes to help us “see” features we physically just can’t get to. This energy travels like sound waves through the structures of the Earth. When rock is hotter or partially molten by even a tiny amount, seismic waves slow down. By measuring the arrival times of seismic waves, we create 3-D images showing how fast or slow the seismic waves travel through specific parts of the Earth.

Deck of ship with orange boxes and spheres lined up, and waves crashing over the stern.

Ocean bottom seismometers waiting to be deployed during the Cascadia Initiative. Image via Emilie Hooft.

To see these signals, we need records from seismic monitoring stations. More sensors provide better resolution and a clearer image – but gathering more data can be problematic when half the area you’re interested in is underwater. To address this challenge, we were part of a team of scientists that deployed hundreds of seismometers on the ocean floor off the western U.S. over the span of four years, starting in 2011. This experiment, the Cascadia Initiative, was the first ever to cover an entire tectonic plate with instruments at a spacing of roughly 30 miles (50 km).

What we found are two anomalous regions beneath the fault where seismic waves travel slower than expected. These anomalies are large, about 90 miles (150 km) in diameter, and show up beneath the northern and southern sections of the fault. Remember, that’s where researchers have already observed increased activity: the seismicity. Interestingly, the anomalies are not present beneath the central part of the fault, under Oregon, where we see a decrease in activity.

Three maps of coast with long colored areas.

Regions where seismic waves moved more slowly, on average, are redder, while the areas where they moved more quickly are bluer. The slower anomalous areas 90 miles (150 km) beneath the Earth’s surface corresponded to where the colliding plates are more locked and where tremor is more common. Image via Bodmer et al., 2018, Geophysical Research Letters.

So what exactly are these anomalies?

The tectonic plates float on the Earth’s rocky mantle layer. Where the mantle is slowly rising over millions of years, the rock decompresses. Since it’s at such high temperatures, nearly 1500 degrees Celsius (2700 F) at 100 km (60 mi) depth, it can melt ever so slightly.

These physical changes cause the anomalous regions to be more buoyant – melted hot rock is less dense than solid cooler rock. It’s this buoyancy that we believe is affecting how the fault above behaves. The hot, partially molten region pushes upwards on what’s above, similar to how a helium balloon might rise up against a sheet draped over it. We believe this increases the forces between the two plates, causing them to be more strongly coupled and thus more fully locked.

A general prediction for where, but not when

Our results provide new insights into how this subduction zone, and possibly others, behaves over geologic timeframes of millions of years. Unfortunately our results can’t predict when the next large Cascadia megathrust earthquake will occur. This will require more research and dense active monitoring of the subduction zone, both onshore and offshore, using seismic and GPS-like stations to capture short-term phenomena.

Our work does suggest that a large event is more likely to start in either the northern or southern sections of the fault, where the plates are more fully locked, and gives a possible reason for why that may be the case.

It remains important for the public and policymakers to stay informed about the potential risk involved in cohabiting with a subduction zone fault and to support programs such as Earthquake Early Warning that seek to expand our monitoring capabilities and mitigate loss in the event of a large rupture.

Miles Bodmer, Ph.D. Student in Earth Sciences, University of Oregon and Doug Toomey, Professor of Earth Sciences, University of Oregon

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Bottom line: Parts of the Pacific Northwest’s Cascadia fault are more seismically active than others. Imaging data suggests why.

The Conversation



from EarthSky https://ift.tt/2ZDRZ7K

How mosquitoes find us

Close-up of long-legged winged insect against a black background.

A tethered mosquito. Image via Kiley Riffell.

First they smell our breath, then they coming looking for us.

A new study, using behavioral experiments and real-time recording of the female mosquito brain, looked at how mosquitoes integrates signals from two sensory systems — visual and olfactory — to identify, track and hone in on a potential host for her next blood meal.

Only female mosquitoes feed on blood. The new findings, published July 18, 2019 in the journal Current Biology, suggest that an olfactory cue – a smell – triggers the mosquito brain to start scanning her surroundings for specific types of shapes and fly towards them.

The smell cue that the study focused on was carbon dioxide, or CO2. For mosquitoes, smelling CO2 is a telltale sign that a potential meal is nearby. Jeffrey Riffell is a University of Washington professor of biology and a co-author of the study. He said in a statement:

Our breath is just loaded with CO2. It’s a long-range attractant, which mosquitoes use to locate a potential host that could be more than 100 feet (30 meters) away.

Cylinder lined with green LEDs with tweezers and test tubes.

The team collected data from approximately 250 individual mosquitoes during behavioral trials conducted in a small circular arena, about 7 inches in diameter. A 360-degree LED display framed the arena and a tungsten wire tether in the middle held each mosquito. This is a top-view image of the arena, or flight simulator, used to present different visual objects and olfactory cues to tethered mosquitoes. More about how the scientists conducted the study. Image via Kiley Riffell.

That potential host could be a person or another warm-blooded animal. Prior research suggested that smelling CO2 can “prime” the mosquito’s visual system to hunt for a host. In this new research, the researchers measured how CO2 triggers precise changes in mosquito flight behavior and visualized how the mosquito brain responds to combinations of olfactory and visual cues. Riffell said:

We found that CO2 influences the mosquito’s ability to turn toward an object that isn’t directly in their flight path. When they smell the CO2, they essentially turn toward the object in their visual field faster and more readily than they would without CO2.

Magnified image of mosquito attached to a wire against a green background.

A tethered Aedes aegypti mosquito flying in the arena. Image via Kiley Riffell.

According to the study results, the mosquito sense of smell operates at long distances, picking up scents more than 100 feet (30.5 meters) away. But their eyesight is most effective for objects 15-20 feet (4.5-6 meters) away, said Riffell.

Olfaction is a long-range sense for mosquitoes, while vision is for intermediate-range tracking. So, it makes sense that we see an odor — in this case CO2 — affecting parts of the mosquito brain that control vision, and not the reverse.

Bottom line: Female mosquitoes use smell and sight to find their next blood meal.

Source: Visual-Olfactory Integration in the Human Disease Vector Mosquito Aedes aegypti

Via University of Washington



from EarthSky https://ift.tt/2T6Ooww
Close-up of long-legged winged insect against a black background.

A tethered mosquito. Image via Kiley Riffell.

First they smell our breath, then they coming looking for us.

A new study, using behavioral experiments and real-time recording of the female mosquito brain, looked at how mosquitoes integrates signals from two sensory systems — visual and olfactory — to identify, track and hone in on a potential host for her next blood meal.

Only female mosquitoes feed on blood. The new findings, published July 18, 2019 in the journal Current Biology, suggest that an olfactory cue – a smell – triggers the mosquito brain to start scanning her surroundings for specific types of shapes and fly towards them.

The smell cue that the study focused on was carbon dioxide, or CO2. For mosquitoes, smelling CO2 is a telltale sign that a potential meal is nearby. Jeffrey Riffell is a University of Washington professor of biology and a co-author of the study. He said in a statement:

Our breath is just loaded with CO2. It’s a long-range attractant, which mosquitoes use to locate a potential host that could be more than 100 feet (30 meters) away.

Cylinder lined with green LEDs with tweezers and test tubes.

The team collected data from approximately 250 individual mosquitoes during behavioral trials conducted in a small circular arena, about 7 inches in diameter. A 360-degree LED display framed the arena and a tungsten wire tether in the middle held each mosquito. This is a top-view image of the arena, or flight simulator, used to present different visual objects and olfactory cues to tethered mosquitoes. More about how the scientists conducted the study. Image via Kiley Riffell.

That potential host could be a person or another warm-blooded animal. Prior research suggested that smelling CO2 can “prime” the mosquito’s visual system to hunt for a host. In this new research, the researchers measured how CO2 triggers precise changes in mosquito flight behavior and visualized how the mosquito brain responds to combinations of olfactory and visual cues. Riffell said:

We found that CO2 influences the mosquito’s ability to turn toward an object that isn’t directly in their flight path. When they smell the CO2, they essentially turn toward the object in their visual field faster and more readily than they would without CO2.

Magnified image of mosquito attached to a wire against a green background.

A tethered Aedes aegypti mosquito flying in the arena. Image via Kiley Riffell.

According to the study results, the mosquito sense of smell operates at long distances, picking up scents more than 100 feet (30.5 meters) away. But their eyesight is most effective for objects 15-20 feet (4.5-6 meters) away, said Riffell.

Olfaction is a long-range sense for mosquitoes, while vision is for intermediate-range tracking. So, it makes sense that we see an odor — in this case CO2 — affecting parts of the mosquito brain that control vision, and not the reverse.

Bottom line: Female mosquitoes use smell and sight to find their next blood meal.

Source: Visual-Olfactory Integration in the Human Disease Vector Mosquito Aedes aegypti

Via University of Washington



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2019 SkS Weekly Climate Change & Global Warming Digest #31

Story of the Week... Toon of the Week... Coming Soon on SkS... Poster of the Week... SkS Week in Review... 

Story of the Week...

China’s emissions ‘could peak 10 years earlier than Paris climate pledge’

Coal-fired Power Plant in China

Shutterstock

CO2 emissions in China may peak up to a decade earlier than the nation has pledged under the Paris Agreement, according to a new study.

With its enormous population and heavy reliance on coal, China is by far the world’s biggest polluter, responsible for more emissions than the US and EU combined.

One of the drivers behind Chinese emissions is the intense urbanisation that has taken place across the country in recent years, as millions of people flock from rural areas to rapidly expanding cities.

However, in new analysis published in Nature Sustainability, a team of researchers has shown that as China’s burgeoning cities become wealthier, their per capita emissions begin to drop.

According to their analysis, this trend could in turn trigger an overall dip in CO2 levels across the nation, and mean that despite the current target for emissions peaking by 2030, they may in fact level out at some point between 2021 and 2025.

It is not the first time a study has suggested a premature dip in China’s emissions, but its timing is significant given an imminent UN summit where world leaders will under pressure to step up their Paris targets.

China’s emissions ‘could peak 10 years earlier than Paris climate pledge’ by Josh Gabbatiss, Rest of World Emissions, Carbon Brief, July 29, 2019 


Toon of the Week...

2019 Toon 31 

 


Coming Soon on SkS...

  • Climate change made Europe’s 2019 record heatwave up to ‘100 times more likely’ (Daisy Dunne)
  • Skeptical Science New Research for Week #31 (Doug Bostrom)
  • Why German coal power is falling fast in 2019 (Karsten Capion)
  • What psychotherapy can do for the climate and biodiversity crises (Caroline Hickman)
  • How climate change is making hurricanes more dangerous (Jeff Berardelli)
  • 2019 SkS Weekly Climate Change & Global Warming News Roundup #32 (John Hartz)
  • 2019 SkS Weekly Climate Change & Global Warming Digest #32 (John Hartz)

Poster of the Week...

2019 Poster 31 


SkS Week in Review...  



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

Story of the Week... Toon of the Week... Coming Soon on SkS... Poster of the Week... SkS Week in Review... 

Story of the Week...

China’s emissions ‘could peak 10 years earlier than Paris climate pledge’

Coal-fired Power Plant in China

Shutterstock

CO2 emissions in China may peak up to a decade earlier than the nation has pledged under the Paris Agreement, according to a new study.

With its enormous population and heavy reliance on coal, China is by far the world’s biggest polluter, responsible for more emissions than the US and EU combined.

One of the drivers behind Chinese emissions is the intense urbanisation that has taken place across the country in recent years, as millions of people flock from rural areas to rapidly expanding cities.

However, in new analysis published in Nature Sustainability, a team of researchers has shown that as China’s burgeoning cities become wealthier, their per capita emissions begin to drop.

According to their analysis, this trend could in turn trigger an overall dip in CO2 levels across the nation, and mean that despite the current target for emissions peaking by 2030, they may in fact level out at some point between 2021 and 2025.

It is not the first time a study has suggested a premature dip in China’s emissions, but its timing is significant given an imminent UN summit where world leaders will under pressure to step up their Paris targets.

China’s emissions ‘could peak 10 years earlier than Paris climate pledge’ by Josh Gabbatiss, Rest of World Emissions, Carbon Brief, July 29, 2019 


Toon of the Week...

2019 Toon 31 

 


Coming Soon on SkS...

  • Climate change made Europe’s 2019 record heatwave up to ‘100 times more likely’ (Daisy Dunne)
  • Skeptical Science New Research for Week #31 (Doug Bostrom)
  • Why German coal power is falling fast in 2019 (Karsten Capion)
  • What psychotherapy can do for the climate and biodiversity crises (Caroline Hickman)
  • How climate change is making hurricanes more dangerous (Jeff Berardelli)
  • 2019 SkS Weekly Climate Change & Global Warming News Roundup #32 (John Hartz)
  • 2019 SkS Weekly Climate Change & Global Warming Digest #32 (John Hartz)

Poster of the Week...

2019 Poster 31 


SkS Week in Review...  



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

Moon swings by star Spica August 4 to 6

On August 4, 5 and 6, 2019, watch for the waxing crescent moon to move past Spica, the brightest star in the constellation Virgo the Maiden. It’s best to catch the moon and Spica at relatively early evening, especially from northerly latitudes. The moon and Spica are fairly high up at nightfall, but then follow the sun beneath the horizon by around mid-evening.

Visit this U.S. Naval Observatory page to know the moon and Spica’s setting time in your sky.

On all of these evenings, the moon is a waxing crescent. Watch for it in the west, the sunset direction, beginning shortly after sunset as day fades to night. Look for the moon and Spica to be closest around August 5. On the following evening, August 6, the moon will be a larger crescent, still near Spica on our sky’s dome.

Chart of western sky showing Big Dipper and arrows pointing from it to Arcturus and Spica.

You don’t need the moon to find Spica. If you live in the Northern Hemisphere, and you’re familiar with the Big Dipper, you can let it guide you to Spica. Simply extend the Big Dipper handle to arc to the brilliant yellow-orange star Arcturus (“follow the arc to Arcturus”) and then extend that line to Spica (“speed on to Spica”), a blue-white gem of a star. If you have difficulty discerning stellar color with the eye alone, try your luck with binoculars.

Spica is one of four 1st-magnitude stars shining close to the ecliptic, which is the plane of Earth’s orbit around the sun, projected onto our sky. The green line on the chart at top represents the ecliptic. There are three other bright stars near the ecliptic. They are Antares of the constellation Scorpius, Aldebaran of the constellation Taurus, and Regulus of the constellation Leo.

The moon and planets always travel near the ecliptic in our sky. That’s because the moon orbits Earth, and the planets orbit the sun, on nearly the same plane that Earth orbits the sun. Hence, the moon in its monthly orbit around Earth always sweeps close to Spica every month; and all the solar system planets always pass near Spica at certain points in their orbits.

For instance, on this date two years ago – August 4, 2017 – the king planet Jupiter shone rather close to Spica on the sky’s dome. One year later – on August 4, 2018 – Jupiter paired up with the modestly-bright zodiacal star Zubenelgenubi. This year, in 2019, Jupiter is found in the vicinity of the star Antares.

The ecliptic also shows you the sun’s annual path in front of the constellations of the zodiac. If we could see the stars during the daytime, we’d see the sun crossing in front of the constellation Virgo from about September 17 to October 31.

The sun swings by the all the stars and planets of the zodiac every year, and the moon does likewise … but it does so every month. Watch for the moon to pair up with Spica on or near August 5, and then to couple up with Jupiter on or near August 9.

Chart, black stars on white background, of long constellation Virgo with Spica marked prominently.

The sun spends far more time in front of Virgo than any other constellation. This year, in 2019, the sun enters Virgo on September 17 and leaves Virgo on October 31. Sky chart of the constellation Virgo via the IAU (International Astronomical Union).

Bottom line: On August 4 to 6, 2019, the moon is a waxing crescent in the sunset direction. Look for it shortly after sunset, as day fades to night. The moon will be below Spica August 4, closest to it August 5 and above it August 6.



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

On August 4, 5 and 6, 2019, watch for the waxing crescent moon to move past Spica, the brightest star in the constellation Virgo the Maiden. It’s best to catch the moon and Spica at relatively early evening, especially from northerly latitudes. The moon and Spica are fairly high up at nightfall, but then follow the sun beneath the horizon by around mid-evening.

Visit this U.S. Naval Observatory page to know the moon and Spica’s setting time in your sky.

On all of these evenings, the moon is a waxing crescent. Watch for it in the west, the sunset direction, beginning shortly after sunset as day fades to night. Look for the moon and Spica to be closest around August 5. On the following evening, August 6, the moon will be a larger crescent, still near Spica on our sky’s dome.

Chart of western sky showing Big Dipper and arrows pointing from it to Arcturus and Spica.

You don’t need the moon to find Spica. If you live in the Northern Hemisphere, and you’re familiar with the Big Dipper, you can let it guide you to Spica. Simply extend the Big Dipper handle to arc to the brilliant yellow-orange star Arcturus (“follow the arc to Arcturus”) and then extend that line to Spica (“speed on to Spica”), a blue-white gem of a star. If you have difficulty discerning stellar color with the eye alone, try your luck with binoculars.

Spica is one of four 1st-magnitude stars shining close to the ecliptic, which is the plane of Earth’s orbit around the sun, projected onto our sky. The green line on the chart at top represents the ecliptic. There are three other bright stars near the ecliptic. They are Antares of the constellation Scorpius, Aldebaran of the constellation Taurus, and Regulus of the constellation Leo.

The moon and planets always travel near the ecliptic in our sky. That’s because the moon orbits Earth, and the planets orbit the sun, on nearly the same plane that Earth orbits the sun. Hence, the moon in its monthly orbit around Earth always sweeps close to Spica every month; and all the solar system planets always pass near Spica at certain points in their orbits.

For instance, on this date two years ago – August 4, 2017 – the king planet Jupiter shone rather close to Spica on the sky’s dome. One year later – on August 4, 2018 – Jupiter paired up with the modestly-bright zodiacal star Zubenelgenubi. This year, in 2019, Jupiter is found in the vicinity of the star Antares.

The ecliptic also shows you the sun’s annual path in front of the constellations of the zodiac. If we could see the stars during the daytime, we’d see the sun crossing in front of the constellation Virgo from about September 17 to October 31.

The sun swings by the all the stars and planets of the zodiac every year, and the moon does likewise … but it does so every month. Watch for the moon to pair up with Spica on or near August 5, and then to couple up with Jupiter on or near August 9.

Chart, black stars on white background, of long constellation Virgo with Spica marked prominently.

The sun spends far more time in front of Virgo than any other constellation. This year, in 2019, the sun enters Virgo on September 17 and leaves Virgo on October 31. Sky chart of the constellation Virgo via the IAU (International Astronomical Union).

Bottom line: On August 4 to 6, 2019, the moon is a waxing crescent in the sunset direction. Look for it shortly after sunset, as day fades to night. The moon will be below Spica August 4, closest to it August 5 and above it August 6.



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

Albireo, beloved double star

Image via Tom Wildoner

Albireo, one star blue and the other golden. Photo via Tom Wildoner.

Albireo – also called Beta Cygni – isn’t the brightest star in the sky. It looks like an ordinary single star to the eye. But peer at it through a telescope, you’ll learn why stargazers love Albireo. With a telescope, you’ll easily see Albireo as a beautiful double star, with the brighter star gold and the dimmer star blue.

How can you see Albireo as two stars? They are best viewed at 30X (“30 power” or a magnification of 30). Unless you have exceedingly powerful binoculars, mounted on a tripod, binoculars won’t show you Albireo as two stars, but any small telescope will. When you do see Albireo as two stars, notice the striking color contrast between the two.

How can you spot Albireo in the night sky? It’s easy to find, if you can located Cygnus the Swan. Cygnus has an easy-to-recognize shape, that of a cross, and the constellation is also known as the Northern Cross. The brightest star in Cygnus, called Deneb, marks the head of the Cross or the Tail of the Swan. Albireo marks the base of the Cross or the Head of Cygnus.

The constellation Cygnus the Swan. The bright star Deneb is in the Tail of Cygnus. Image via Constellation of Words

The constellation Cygnus the Swan. The bright star Deneb is in the Tail of Cygnus, while Albireo is at the Head of the Swan. Albireo represents the Swan’s Beak or Eye. Image via Constellation of Words

The Summer Triangle

The constellation Cygnus lies within a larger star pattern known as the Summer Triangle. See the three bright stars here: Vega, Deneb and Altair? See how the pattern of the cross (Cygnus the Swan) likes inside the triangle made by those three stars? More about the Summer Triangle here.

The two stars of Albireo constitute a true binary star system. In other words, its two stars aren’t merely a chance alignment as seen from Earth. Instead, they revolve around a common center of mass.

These two stars lie quite far apart, however, and might take as long as 100,000 years to orbit one another. Even though these two stars appear close together in a telescope, keep in mind that you’re looking at a system that’s 430 light-years away.

By the way, the brighter of the two stars in the Albireo system has been found with advanced telescopic techniques to be two stars as well. Thus there are at least three stars in this system.

Ian Anthony - a member of the EarthSky Photo community on G+ - posted this beautiful shot of Albireo in May 2013.

Ian Anthony shared this beautiful telescopic shot of Albireo. Notice the color contrast between the two stars.

Bottom line: The star Albireo – also known as Beta Cygni – in the constellation Cygnus, is a famous double star. A small telescope reveals that one star is blue and the other is gold.



from EarthSky https://ift.tt/33aDQB6
Image via Tom Wildoner

Albireo, one star blue and the other golden. Photo via Tom Wildoner.

Albireo – also called Beta Cygni – isn’t the brightest star in the sky. It looks like an ordinary single star to the eye. But peer at it through a telescope, you’ll learn why stargazers love Albireo. With a telescope, you’ll easily see Albireo as a beautiful double star, with the brighter star gold and the dimmer star blue.

How can you see Albireo as two stars? They are best viewed at 30X (“30 power” or a magnification of 30). Unless you have exceedingly powerful binoculars, mounted on a tripod, binoculars won’t show you Albireo as two stars, but any small telescope will. When you do see Albireo as two stars, notice the striking color contrast between the two.

How can you spot Albireo in the night sky? It’s easy to find, if you can located Cygnus the Swan. Cygnus has an easy-to-recognize shape, that of a cross, and the constellation is also known as the Northern Cross. The brightest star in Cygnus, called Deneb, marks the head of the Cross or the Tail of the Swan. Albireo marks the base of the Cross or the Head of Cygnus.

The constellation Cygnus the Swan. The bright star Deneb is in the Tail of Cygnus. Image via Constellation of Words

The constellation Cygnus the Swan. The bright star Deneb is in the Tail of Cygnus, while Albireo is at the Head of the Swan. Albireo represents the Swan’s Beak or Eye. Image via Constellation of Words

The Summer Triangle

The constellation Cygnus lies within a larger star pattern known as the Summer Triangle. See the three bright stars here: Vega, Deneb and Altair? See how the pattern of the cross (Cygnus the Swan) likes inside the triangle made by those three stars? More about the Summer Triangle here.

The two stars of Albireo constitute a true binary star system. In other words, its two stars aren’t merely a chance alignment as seen from Earth. Instead, they revolve around a common center of mass.

These two stars lie quite far apart, however, and might take as long as 100,000 years to orbit one another. Even though these two stars appear close together in a telescope, keep in mind that you’re looking at a system that’s 430 light-years away.

By the way, the brighter of the two stars in the Albireo system has been found with advanced telescopic techniques to be two stars as well. Thus there are at least three stars in this system.

Ian Anthony - a member of the EarthSky Photo community on G+ - posted this beautiful shot of Albireo in May 2013.

Ian Anthony shared this beautiful telescopic shot of Albireo. Notice the color contrast between the two stars.

Bottom line: The star Albireo – also known as Beta Cygni – in the constellation Cygnus, is a famous double star. A small telescope reveals that one star is blue and the other is gold.



from EarthSky https://ift.tt/33aDQB6

These 2 dead stars whip around each other in minutes

Two dead stars have been spotted whipping around each other every seven minutes. The newfound dynamic duo, officially known as ZTF J1539+5027, is the second-fastest pair of orbiting dead stars, called white dwarfs, yet discovered.

The pair, located nearly 8,000 light-years away in the Boötes constellation, is also the fastest eclipsing binary system, meaning that one white dwarf repeatedly crosses in front of the other from our point of view.

Astronomers at Palomar Observatory, near San Diego, California, found the pair of stars using Caltech’s Zwicky Transient Facility (ZTF), a state-of-the-art sky survey that rapidly scans the night skies looking for anything that moves, blinks, or otherwise varies in brightness.

The newly-discovered star pair orbit each other roughly every seven minutes. When the larger, cooler star passes in front of, or eclipses, the smaller, hotter star, the light of the smaller star is blocked. To astronomers observing the system, the pair appears to vanish for around 30 seconds during the eclipsing phase of their orbit.

Large bluish sphere and smaller white sphere with concentric orbits marked with green lines.

Artist’s concept of the pair of orbiting white dwarfs, called ZTF J1530+5027. Image via Caltech/IPAC/R. Hurt.

According to the astronomers’ observations, each of the newfound white dwarfs is roughly the size of Earth, with one being a bit smaller and brighter than the other, and together they weigh as much as our sun. The two objects orbit very closely to each other, at one-fifth the distance between Earth and the moon; in fact, the orbiting stars would fit inside the planet Saturn. And they whip around each other every seven minutes at speeds of hundreds of kilometers per second.

Caltech graduate student Kevin Burdge is lead author of a study about the stars, published July 25, 2019 in the journal Nature. Burdge said in a statement:

As the dimmer star passes in front of the brighter one, it blocks most of the light, resulting in the seven-minute blinking pattern we see in the ZTF data. Matter is getting ready to spill off of the bigger and lighter white dwarf onto the smaller and heavier one, which will eventually completely subsume its lighter companion. We’ve seen many examples of a type of system where one white dwarf has been mostly cannibalized by its companion, but we rarely catch these systems as they are still merging like this one.

The team of astronomers spotted the white dwarf pair with ZTF’s large 576-megapixel camera, which rapidly scans the entire sky every three nights, and the bulk of the plane of the Milky Way every night. Burdge found ZTF J1539+5027 by running a computer program that tracked 10 million cosmic objects, looking for changes over a three-month span. He said:

This pair really stuck out because the signal repeats so often and in such a predictable way.People haven’t been able to systematically search for things that change on minute-time scales before. ZTF lets us do this because its camera is huge and it can easily take pictures across the sky and then come back and repeat.

Burke said that the white dwarfs began their lives as stars like our sun, except they were bound together as a tight-knit pair. As the stars aged, they swelled up into red giants, one after the other. Over time, the swollen stars shed their outer layers, leaving behind two dead stars – the white dwarfs.

Study co-author Jim Fuller is an assistant professor of theoretical astrophysics at Caltech. He said:

Sometimes these binary white dwarfs merge into one star, and other times the orbit widens as the lighter white dwarf is gradually shredded by the heavier one. We’re not sure what will happen in this case, but finding more such systems will tell us how often these stars survive their close encounters.

The team says that the white-dwarf duo should keep blinking in the night sky for a hundred thousand years to come. Amateur astronomers may be able to even see the pair as one spot on the sky, flashing every seven minutes, with the help of a telescope at least one meter in size.

Bottom line: Astronomers have spotted a pair of white dwarfs- called ZTF J1539+5027 – orbit each other every 7 minutes. It’s the 2nd fastest pair of orbiting dead stars spotted so far.

Source: General relativistic orbital decay in a seven-minute-orbital-period eclipsing binary system

Via Caltech



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

Two dead stars have been spotted whipping around each other every seven minutes. The newfound dynamic duo, officially known as ZTF J1539+5027, is the second-fastest pair of orbiting dead stars, called white dwarfs, yet discovered.

The pair, located nearly 8,000 light-years away in the Boötes constellation, is also the fastest eclipsing binary system, meaning that one white dwarf repeatedly crosses in front of the other from our point of view.

Astronomers at Palomar Observatory, near San Diego, California, found the pair of stars using Caltech’s Zwicky Transient Facility (ZTF), a state-of-the-art sky survey that rapidly scans the night skies looking for anything that moves, blinks, or otherwise varies in brightness.

The newly-discovered star pair orbit each other roughly every seven minutes. When the larger, cooler star passes in front of, or eclipses, the smaller, hotter star, the light of the smaller star is blocked. To astronomers observing the system, the pair appears to vanish for around 30 seconds during the eclipsing phase of their orbit.

Large bluish sphere and smaller white sphere with concentric orbits marked with green lines.

Artist’s concept of the pair of orbiting white dwarfs, called ZTF J1530+5027. Image via Caltech/IPAC/R. Hurt.

According to the astronomers’ observations, each of the newfound white dwarfs is roughly the size of Earth, with one being a bit smaller and brighter than the other, and together they weigh as much as our sun. The two objects orbit very closely to each other, at one-fifth the distance between Earth and the moon; in fact, the orbiting stars would fit inside the planet Saturn. And they whip around each other every seven minutes at speeds of hundreds of kilometers per second.

Caltech graduate student Kevin Burdge is lead author of a study about the stars, published July 25, 2019 in the journal Nature. Burdge said in a statement:

As the dimmer star passes in front of the brighter one, it blocks most of the light, resulting in the seven-minute blinking pattern we see in the ZTF data. Matter is getting ready to spill off of the bigger and lighter white dwarf onto the smaller and heavier one, which will eventually completely subsume its lighter companion. We’ve seen many examples of a type of system where one white dwarf has been mostly cannibalized by its companion, but we rarely catch these systems as they are still merging like this one.

The team of astronomers spotted the white dwarf pair with ZTF’s large 576-megapixel camera, which rapidly scans the entire sky every three nights, and the bulk of the plane of the Milky Way every night. Burdge found ZTF J1539+5027 by running a computer program that tracked 10 million cosmic objects, looking for changes over a three-month span. He said:

This pair really stuck out because the signal repeats so often and in such a predictable way.People haven’t been able to systematically search for things that change on minute-time scales before. ZTF lets us do this because its camera is huge and it can easily take pictures across the sky and then come back and repeat.

Burke said that the white dwarfs began their lives as stars like our sun, except they were bound together as a tight-knit pair. As the stars aged, they swelled up into red giants, one after the other. Over time, the swollen stars shed their outer layers, leaving behind two dead stars – the white dwarfs.

Study co-author Jim Fuller is an assistant professor of theoretical astrophysics at Caltech. He said:

Sometimes these binary white dwarfs merge into one star, and other times the orbit widens as the lighter white dwarf is gradually shredded by the heavier one. We’re not sure what will happen in this case, but finding more such systems will tell us how often these stars survive their close encounters.

The team says that the white-dwarf duo should keep blinking in the night sky for a hundred thousand years to come. Amateur astronomers may be able to even see the pair as one spot on the sky, flashing every seven minutes, with the help of a telescope at least one meter in size.

Bottom line: Astronomers have spotted a pair of white dwarfs- called ZTF J1539+5027 – orbit each other every 7 minutes. It’s the 2nd fastest pair of orbiting dead stars spotted so far.

Source: General relativistic orbital decay in a seven-minute-orbital-period eclipsing binary system

Via Caltech



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

adds 2