Assessing the habitability of planets around old red dwarfs

A new study using data from NASA's Chandra X-ray Observatory and Hubble Space Telescope gives new insight into an important question: how habitable are planets that orbit the most common type of stars in the Galaxy? The target of the new study, as reported in our press release, is Barnard's Star, which is one of the closest stars to Earth at a distance of just 6 light years. Barnard's Star is a red dwarf, a small star that slowly burns through its fuel supply and can last much longer than medium-sized stars like our Sun. It is about 10 billion years old, making it twice the age of the Sun.

Credit: Chandra X-ray Center

The authors used Barnard's Star as a case study to learn how flares from an old red dwarf might affect any planets orbiting it. This artist's illustration depicts an old red dwarf like Barnard's Star (right) and an orbiting, rocky planet (left).

The research team's Chandra observations of Barnard's Star taken in June 2019 uncovered one X-ray flare (shown in the inset box) and their Hubble observations taken in March 2019 revealed two ultraviolet high-energy flares (shown in an additional graphic). Both observations were about seven hours long and both plots show X-ray or ultraviolet brightness extending down to zero. Based on the length of the flares and of the observations, the authors concluded that Barnard's Star unleashes potentially destructive flares about 25% of the time.

The team then studied what these results mean for rocky planets orbiting in the habitable zone—where liquid water could exist on their surface—around an old red dwarf like Barnard's Star. Any atmosphere formed early in the life of a habitable-zone planet was likely to have been eroded away by high-energy radiation from the star during its volatile youth. Later on, however, planet atmospheres might regenerate as the star becomes less active with age. This regeneration process may occur by gases released by impacts of solid material or gases being released by volcanic processes.

However, the onslaught of powerful flares like those reported here, repeatedly occurring over hundreds of millions of years, may erode any regenerated atmospheres on rocky planets in the habitable zone. The illustration shows the atmosphere of the rocky planet being swept away to the left by energetic radiation from flares produced by the red dwarf. This would reduce the chance of these worlds supporting life. The team is currently studying high-energy radiation from many more red dwarfs to determine whether Barnard's Star is typical.

A paper describing these results was published in The Astronomical Journal.

Source: NASA [October 30, 2020]

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Study shows comets impacted start of life on earth

The Big Bang may have started the universe, but it's likely that littler bangs played a key role in life on Earth, say Albion College Physics Professor Nicolle Zellner and Chemistry Professor Vanessa McCaffrey. They (along with former student Jayden Butler, '17) share their fascinating findings on the interspace dispersal of glycolaldehyde (GLA) in an article recently published by the journal Astrobiology.

An artist’s rendition of the comet exploding in Earth’s atmosphere
[Credit: Terry Bakker]

Their project, funded by NASA and conducted at the Experimental Impact Laboratory at Johnson Space Center, exposed GLA samples to impact pressures between 4.5 and 25 gigapascals—at the low end, forces far greater than the deepest ocean water pressures, or that of a piano dropped from hundreds of miles above the Earth. Albion's team discovered that GLA, a sugar important in the chemistry leading to ribose, can retain its integrity under such intense pressures.

"Experiments that simulate impacts have shown time and time again that biomolecules found on comets, asteroids, and meteorites are not completely destroyed," says Zellner. "The fact that GLA can remain intact under these kinds of pressures provides another piece of the puzzle in our understanding of how biomolecules survived impact delivery to an early Earth."

In addition to the GLA remaining unchanged throughout such intense conditions, McCaffrey noted that several new molecules were seen after impact and that some of these could have important biological implications.

Zellner notes that the Albion work predates recent observations by astronomers, who reported that GLA is present on several comets. These findings support the Albion team's assertion that GLA was likely dispersed throughout the solar system—and onto Earth—via comet impacts.

The project findings, says Zellner, add an important piece to the picture of how life began.

"Everybody assumed GLA was a starting molecule for ribose or amino acids, but little consideration was given as to its source," Zellner says. "We're showing what the source of that molecule could be."

Author: Jake Weber | Source: Albion College [October 27, 2020]

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'Fireball' meteorite contains pristine extraterrestrial organic compounds

On the night of January 16, 2018, a fireball meteor streaked across the sky over the Midwest and Ontario before landing on a frozen lake in Michigan. Scientists used weather radar to find where the pieces landed and meteorite hunters were able to collect the meteorite quickly, before its chemical makeup got changed by exposure to liquid water. And, as a new paper in Meteoritics & Planetary Science shows, that gave scientists a glimpse of what space rocks are like when they're still in outer space--including a look at pristine organic compounds that could tell us about the origins of life.

The meteorite fragment that fell on Strawberry Lake which contains pristine
extraterrestrial organic compounds [Credit: Field Museum]

"This meteorite is special because it fell onto a frozen lake and was recovered quickly. It was very pristine. We could see the minerals weren't much altered and later found that it contained a rich inventory of extraterrestrial organic compounds," says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and lead author of the new paper. "These kinds of organic compounds were likely delivered to the early Earth by meteorites and might have contributed to the ingredients of life."

Meteorites, simply put, are space rocks that have fallen to Earth. When things like asteroids collide in outer space, fragments can break off. These pieces of rock, called meteoroids, continue floating through space, and sometimes, their new paths collide with moons or planets. When a meteoroid breaks through the Earth's atmosphere and we can see it as a fireball or shooting star, it's called a meteor. If pieces of that meteor survive the trip through the atmosphere, the bits that actually land on Earth are called meteorites.

When the fireball arrived in Michigan, scientists used NASA's weather radar to track where the pieces went. "Weather radar is meant to detect hail and rain," explains Heck. "These pieces of meteorite fell into that size range, and so weather radar helped show the position and velocity of the meteorite. That meant that we were able to find it very quickly."

Less than two days after it landed, meteorite hunter Robert Ward found the first piece of the meteorite on the frozen surface of Strawberry Lake, near Hamburg, Michigan. Ward worked with Terry Boudreaux to donate the meteorite to the Field Museum, where Heck and Jennika Greer, a graduate student at the Field and the University of Chicago and one of the paper's authors, began to study it.

"When the meteorite arrived at the Field, I spent the entire weekend analyzing it, because I was so excited to find out what kind of meteorite it was and what was in it," says Greer. "With every meteorite that falls, there's a chance that there's something completely new and totally unexpected."

The researchers quickly determined that the meteorite was an H4 chondrite--only 4% of all meteorites falling to Earth these days are of this type. But the real thing that makes the Hamburg meteorite exceptional is because of how quickly it was collected and how well-analyzed it is.

"This meteorite shows a high diversity of organics, in that if somebody was interested in studying organics, this is not normally the type of meteorite that they would ask to look at," says Greer. "But because there was so much excitement surrounding it, everybody wanted to apply their own technique to it, so we have an unusually comprehensive set of data for a single meteorite."

Scientists aren't sure how the organic (carbon-containing) compounds responsible for life on Earth got here; one theory is that they hitched their way here on meteorites. That doesn't mean that the meteorites themselves contain extraterrestrial life; rather, some of the organic compounds that help make up life might have first formed in an asteroid that later fell to Earth. (In short, sorry, we didn't find any aliens.)

"Scientists who study meteorites and space sometimes get asked, do you ever see signs of life? And I always answer, yes, every meteorite is full of life, but terrestrial, Earth life," says Heck. "As soon as the thing lands, it gets covered with microbes and life from Earth. We have meteorites with lichens growing on them. So the fact that this meteorite was collected so quickly after it fell, and that it landed on ice rather than in the dirt, helped keep it cleaner."

The buzz around the meteorite when it landed also helped scientists learn much more about it than many other meteorites of its kind--they used a wide variety of analytical techniques and studied samples from different parts of the meteorite to get a more complete picture of the minerals it contains. "You learn a lot more about a meteorite when you sample different pieces. It's like if you had a supreme pizza, if you only looked at one little section, you might think it was just pepperoni, but there might be mushrooms or peppers somewhere else," says Greer.

"This study is a demonstration of how we can work with specialists around the world to get most out of the small piece of raw, precious piece of rock," says Heck. "When a new meteorite falls onto a frozen lake, maybe even sometime this winter, we'll be ready. And that next fall might be something we have never seen before."

Source: Field Museum [October 27, 2020]

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