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Did a supernova cause the Devonian mass extinction event? – Universe Today

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359 million years ago the Earth suffered one of its worst extinction events, and a team of researchers at the University of Illinois think that it might be caused by a series of supernova explosions no more than 35 light years away.

Every once in a while something disastrous happens to life on Earth. The biggest episodes we call extinction events. The latest big one happened about 65 million years ago, and was a very rough time for dinosaurs but turned out pretty awesome for the mammals. But that extinction event was just the latest in a long series of interruptions in the multitude of life on the planet. One of the earliest extinction events happened at the boundary of the Devonian and Carboniferous periods about 359 million years ago.

We’re not exactly sure what triggered that extinction event. There’s no clear smoking gun like there is for the asteroid impact evidence of the one that killed most of the dinosaurs. But a team of researchers from the University of Illinois are proposing a radical and otherworldly explanation: supernovae.

An artist’s impression of Betelgeuse. Its surface is covered by large star spots, which reduce its brightness. During their pulsations, such stars regularly release gas into their surroundings, which condenses into dust. Image Credit: MPIA graphics department

The key piece of evidence leading to this hypothesis is the fact that fossils of plants remaining from that tumultuous era show signs of nasty sunburns: excess UV exposure. The ozone layer of the Earth does a fantastic job of blocking almost all the UV radiation from the sun, so the fact that these critters were getting an extra dose means that our ozone layer had to be depleted. There are a lot of potential geological processes that can scrub away our ozone layer, and there’s also one celestial one.

The intense radiation from a close enough supernova blast can strip away our ozone, leaving the surface of the Earth exposed to the UV onslaught from the sun. In general, intense UV radiation isn’t too great for living beings, hence an extinction event.

The researchers estimated that a single supernova blast within 65 light years could have been enough to suppress our ozone layer for about 100,000 years. The fossil record indicates that life was having a tough go at it for three times that length, however, so the researchers speculate that the supernova wasn’t alone. This isn’t a crazy idea, as stars do tend to cluster and big stars do tend to go off as supernova relatively close by.

But as of yet this is an untested hypothesis. The next step is to find evidence in those fossil layers of an excess of certain radioactive elements like plutonium-244. This element isn’t naturally produced on the Earth, and so the only way for it to exist in that layer of sediment is for it to have been put there as the shock-wave of the supernova washed over our planet.

If you’re worried about the next supernova blast, don’t stress out. The nearest supernova candidate to the Earth is the star Betelgeuse, which is located a safe 600 light years away.

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Salty ponds found on Mars suggest stronger prospect of life on red planet, scientists say – CBC.ca

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A network of salty ponds may be gurgling beneath the South Pole on Mars, alongside a large underground lake, raising the prospect of tiny, swimming Martian life.

Italian scientists reported their findings Monday, two years after identifying what they believed to be a large buried lake. They widened their coverage area by a couple hundred miles, using even more data from a radar sounder on the European Space Agency’s Mars Express orbiter.

In the latest study appearing in the journal Nature Astronomy, the scientists provide further evidence of this salty underground lake, estimated to be 20 to 30 kilometres across and buried 1.5 kilometres beneath the icy surface.

Even more tantalizing, they’ve also identified three smaller bodies of water surrounding the lake. These ponds appear to be of various sizes and are separate from the main lake.

Roughly four billion years ago, Mars was warm and wet, like Earth. But the red planet eventually morphed into the barren, dry world it is today.

The research team led by Roma Tre University’s Sebastian Emanuel Lauro used a method similar to those used on Earth to detect buried lakes in the Antarctic and Canadian Arctic. They based their findings on more than 100 radar observations by Mars Express from 2010 to 2019; the spacecraft was launched in 2003.

All this potential water raises the possibility of microbial life on — or inside — Mars. High concentrations of salt are likely keeping the water from freezing at this frigid location, the scientists noted. The surface temperature at the South Pole is an estimated -113 degrees C and gets gradually warmer with depth.

These bodies of water are potentially interesting biologically and the researchers wrote that “future missions to Mars should target this region.” 

Earlier this year, a new computer model by NASA scientists lent further support to the theory that the ocean beneath the thick, icy crust of Jupiter’s moon Europa could be habitable.

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Salty lake, ponds may be gurgling beneath South Pole on Mars – CP24 Toronto's Breaking News

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Marcia Dunn, The Associated Press


Published Monday, September 28, 2020 7:46PM EDT

CAPE CANAVERAL, Fla. – A network of salty ponds may be gurgling beneath Mars’ South Pole alongside a large underground lake, raising the prospect of tiny, swimming Martian life.

Italian scientists reported their findings Monday, two years after identifying what they believed to be a large buried lake. They widened their coverage area by a couple hundred miles, using even more data from a radar sounder on the European Space Agency’s Mars Express orbiter.

In the latest study appearing in the journal Nature Astronomy, the scientists provide further evidence of this salty underground lake, estimated to be 12 miles to 18 miles (20 kilometres to 30 kilometres) across and buried 1 mile (1.5 kilometres) beneath the icy surface.

Even more tantalizing, they’ve also identified three smaller bodies of water surrounding the lake. These ponds appear to be of various sizes and are separate from the main lake.

Roughly 4 billion years ago, Mars was warm and wet, like Earth. But the red planet eventually morphed into the barren, dry world it remains today.

The research team led by Roma Tre University’s Sebastian Emanuel Lauro used a method similar to what’s been used on Earth to detect buried lakes in the Antarctic and Canadian Arctic. They based their findings on more than 100 radar observations by Mars Express from 2010 to 2019; the spacecraft was launched in 2003.

All this potential water raises the possibility of microbial life on – or inside – Mars. High concentrations of salt are likely keeping the water from freezing at this frigid location, the scientists noted. The surface temperature at the South Pole is an estimated minus 172 degrees Fahrenheit (minus 113 degrees Celsius), and gets gradually warmer with depth.

These bodies of water are potentially interesting biologically and “future missions to Mars should target this region,” the researchers wrote.

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Another look at possible under-ice lakes on Mars: They’re still there – Ars Technica

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In recent decades, we’ve become aware of lots of water on Earth that’s deep under ice. In some cases, we’ve watched this water nervously, as it’s deep underneath ice sheets, where it could lubricate the sheets’ slide into the sea. But we’ve also discovered lakes that have been trapped under ice near the poles, possibly for millions of years, raising the prospect that they could harbor ancient ecosystems.

Now, researchers are applying some of the same techniques that we’ve used to find those under-ice lakes to data from Mars. And the results support an earlier claim that there are bodies of water trapped under the polar ice of the red planet.

Spotting liquids from orbit

Mars clearly has extensive water locked away in the forum of ice, and some of it cycles through the atmosphere as orbital cycles make one pole or the other a bit warmer. But there’s not going to be pure liquid water on Mars—the temperatures just aren’t high enough for very long, and the atmospheric pressures are far too low to keep any liquid water from boiling off into the atmosphere.

Calculations suggest, however, that liquid water is possible on Mars—just not on the surface. With enough dissolved salts, a water-rich brine could remain liquid at the temperatures prevalent on Mars—even in the polar areas. And if it’s trapped under the Martian surface, there might be enough pressure to keep it liquid despite the thin atmosphere. That surface could be Martian soil, and people are thinking about that possibility. But the surface could also be one of the ice sheets we’ve spotted on Mars.

That possibility helped motivate the design of the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on the Mars Express orbiter. MARSIS is a radar device that uses wavelengths that water ice is transparent to. As a result, most of the photons that come back to the instrument are reflected by the interface between ice and something else: the atmosphere, the underlying bedrock, and potentially any interface between the ice and a liquid brine underneath it.

And that’s what the original results, published in 2018, seemed to indicate. In an area called Ultimi Scopuli near Mars’ south pole. The researchers saw a bright reflection, distinct from the one caused by the underlying bedrock, at some specific locations under the ice. And they interpreted this as indicating a boundary between ice and some liquid brines.

Now with more data

Two things have changed since those earlier results were done. One is that Mars Express has continued to pass over Mars’ polar regions, generating even more data for analysis. The second is that studies of ice-covered lakes on Earth have also advanced, with new ones identified from orbit using similar data. So some of the team behind the original work decided it was time to revisit the ice sheets at Ultimi Scopuli.

The analysis involves looking at details of the photons reflected back to the MARSIS instrument from a 250 x 300 square kilometer area. One aspect of that is the basic reflectivity of the different layers that can be discerned from the data. Other aspects of the signal can tell us about how smooth the surface of the reflective boundaries are and whether the nature of the boundary changes suddenly.

For example, the transition from an ice-bedrock boundary to an ice-brine one would cause a sudden shift from a relatively weak, uneven signal to a brighter and smoother one.

The researchers generated separate maps of the intensity and the smoothness of the signal and found that the maps largely overlapped, giving them confidence that they were identifying real transitions in the surfaces. A separate measure of the material (called permittivity) showed that it was high in the same location.

Overall, the researchers found that the largest area that’s likely to have water under the ice as about 20 by 30 kilometers. And it’s separated by bedrock features from a number of similar but smaller bodies. Calling these bodies “lakes” is speculative, given that we have no idea how deep they are. But the data certainly is consistent with some sort of under-ice feature—even if we use the standards of detection that have been used for under-ice lakes on Earth.

How did that get there?

The obvious question following the assumption that these bodies are filled with a watery brine is how that much liquid ended up there. We know that these salty solutions can stay liquid at temperatures far below the freezing point. But the conditions on Mars are such that most of minimum temperatures for water to remain liquid are right at the edge of the possible conditions at the site of the polar ice sheets. So some people have suggested geological activity as a possible source of heat to keep things liquid.

That’s not necessarily as unlikely as it may sound. Some groups have proposed that some features indicate that there was magma on the surface of Mars as recently as recently as 2 million years ago. But the researchers here argue that if things are on the edge of working under current climate conditions, there’s no need to resort to anything exceptional.

Instead, they suggest that the sorts of salts we already know are present on Mars can absorb water vapor out of the thin Martian atmosphere. Once formed, these can remain liquid down to 150 Kelvin, when the local temperatures at Ultimi Scopuli are likely to be in the area of 160 Kelvin and increase with depth.

And if that’s true, there could be liquid in many more locations at Mars’ poles. Not all of them are as amenable to orbital imaging as Ultimi Scopuli, but it’s a safe bet that this team will try to find additional ones.

Nature Astronomy, 2020. DOI: 10.1038/s41550-020-1200-6 (About DOIs).

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