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The models, hypotheses and laboratory experiments of exoplanet researchers are a test bed to question what is possible.
Between searching for strange exoplanets, some so strange compared to our own solar system, many researchers focus on one key phrase: “potentially habitable.”
The exoplanets referred to as potentially habitable show no signs of life. It means that the planet is at the correct distance from its star, so that it is in the so-called Goldilocks zone, or habitable zone: not too hot, not too cold and just, within a possible surface temperature range where the Liquid water could exist on the planet’s surface. We equate liquid water with life on Earth, and it has also informed our quest for life beyond it.
But more research in recent years suggests that we are expanding our understanding of life and the conditions under which it might form.
Two new studies expand the range of conditions and locations of exoplanets that could potentially be habitable. Having that research in hand as new and advanced telescopes come online in the coming years and decades could help in the search for exoplanets that may not have been of interest before and provide targets for future studies.
Now, they just have to find these exoplanets.
Exoplanet atmospheres
The Hubble Space Telescope became the first to make direct detections of exoplanet atmospheres and study tHeir to the composition. Future telescopes, such as NASA’s James Webb Space Telescope to be launched next year, will be able to characterize exoplanet atmospheres in greater detail.
If we were to study Earth’s atmosphere that way, we would find that it is 78% nitrogen, 21% oxygen, 0.9% argon, and 0.03% carbon dioxide with trace elements from other gases.
Planetary astrophysicist and scientist Sara Seager and her colleagues published a new study this week examining how E. coli bacteria and yeasts, representatives of single-cell prokaryotes and eukaryotes, would react to a hydrogen atmosphere.
Laboratory experiments were based on the cultivation of E. coli and yeast in a 100% hydrogen atmosphere. Both reproduce normally, but at lower and slower speeds than in oxygenated air. For example, E. coli reproduced twice as slow and yeast was 2.5 times slower. The researchers believed This is due to a lack of oxygen.
But Seager and his colleagues wanted to see if the microorganisms would survive and reproduce, which they did. The researchers were not surprised because hydrogen is non-toxic, but their study acts as a proof-of-concept investigation for exoplanet scientists, Seager said.
Rocky exoplanets that are larger than Earth can hold large amounts of hydrogen in their atmospheres. These atmospheres would probably be larger and more extended because hydrogen is a light gas. And an extended atmosphere would be easier to detect for future telescopes, like Webb and others, Seager said.
“We hope to change the perspective of astronomers that life in general can survive in a type of atmosphere dominated by hydrogen or even in a wide variety,” Seager said in an email to CNN. “It will be difficult to find signs of life on rocky planets with atmospheres dominated by nitrogen or carbon dioxide. So I want astronomers and telescope allocation committees to be aware that there are other options to consider.”
While no rocky exoplanets with a hydrogen-dominated atmosphere are known yet, according to Seager, she has a proposal for the Webb telescope to identify rocky planets with hydrogen atmospheres.
Looking at other research on E. coli and yeast, Seager found something promising.
“We learned that simple E. coli [bacteria] “It produces a wide variety of gases, including many that have already been studied in computer simulations as potential bio-signature gases,” said Seager. “That such a simple life form has a diverse metabolic machinery to produce the diverse set of gases is encouraging – simple life elsewhere can do the same.”
Planets orbiting dead stars
Exoplanets have been found that orbit stars similar to our sun, or those with less mass, such as small red dwarf stars. They haven’t been found around the white dwarfs yet, or the remaining core of a star after it explodes.
But in a study published last week, the Carl Sagan Institute for Cornell University doctoral student Thea Kozakis and Director Lisa Kaltenegger compiled and published a guide to spot biosofirms within exoplanet atmospheres that could be in orbit around white dwarfs.
“The key question we asked is, if life existed on such a planet, could we detect it because it orbits around a dead star a long time ago? The answer is yes, if it is there, we could detect it,” Kaltenegger said in an email. to CNN. She is also an associate professor of astronomy at Cornell.
So how does a planet exist around a white dwarf star? Kozakis explained that planets could already exist in the star system before the star died.
“Or the planets would have to be from the original star system, although much farther from their star; anything close to a star would be destroyed during the red giant phase of stellar evolution,” Kozakis said in an email to CNN.
“But some studies have shown that planets or moons initially away from their host stars could migrate inward due to gravitational interactions with other planets in the system after the white dwarf formed. This would mean that these planets would have been very cold before its host became a white dwarf, although more than 99% of the water resides in our outer solar system, so they could be very interesting objects. “
When our sun turns into a red giant in 5 billion years, the expansion of the sun during this last phase before dying will destroy Mercury, Venus and Earth.
“The other possibility is that the planets could have formed after the white dwarf,” said Kozakis. “White dwarfs form after a star detaches from its outer layers as a ‘planetary nebula’, and some white dwarfs have been observed to have disks of material around them possibly due to these events. Similar to how planets form around new stars, perhaps planets could form from these new disks. “
So they could be first-generation planets in the outer part of the solar system, or second-generation planets that form from the star’s debris disk after it dies, Kaltenegger said.
“In both scenarios, the really interesting question would be where the water would come from,” he said. “If it’s a planet that was initially in the outer parts of the solar system, then it should have a large amount of ice, which would melt if it got close to the warm white dwarf.”
White dwarfs, which are slightly larger than Earth, begin to become very hot but cold over time. This means that the habitable zone shrinks around the star as it cools.
If a planet the size of Earth were to pass in front of the white dwarf, it would cause a 50% drop in brightness, as opposed to a 0.01% drop in brightness if Earth passed in front of the sun.
“This much more similar star planet size significantly improves the quality of the data we could obtain from a white dwarf planetary system, and would greatly decrease the observation time required to detect the composition of the atmosphere,” said Kozakis.
When the planet passes in front of the star, starlight illuminates the atmosphere.
“We are waiting and looking for that kind of transit,” said Kozakis. “By looking at such a planet’s transit, scientists can find out what’s in its atmosphere, refer to this document, compare it to spectral fingerprints, and look for signs of life. Publishing this type of guide lets observers know what to look for. “
Based on their models, Kozakis and Kaltenegger believed that “spectral fingerprints” like ozone, methane, and water could be seen in the atmosphere of planets orbiting white dwarfs with telescopes like Webb or the next extremely large Telescope being building in the Atacama desert in Chile.
These “fingerprints” can be indicators of life on a planet, so it is important that we understand how they are affected by the white dwarf, Kozakis said.
This is one aspect of finding so-called fingerprints for potentially habitable planets that Kaltenegger’s team is working on.
“Think of it as a large database of fingerprints so you can identify a fingerprint at the crime scene,” he said.
“Fingerprints” can be used to identify what is observed using Webb and other future telescopes.
“Once we look at the spectrum of these rocky worlds in the habitable zone of their stars, we want to know if what we are seeing are signs of life … to answer the fascinating question of whether we are alone in the universe.” Kaltenegger said.
