Planets with volcanic activity are considered better candidates for life than worlds without such heated internal goings-on.

Now, graduate students at the ÌìÃÀÓ°ÊÓ´«Ã½ have found a way to detect volcanic activity in the atmospheres of exoplanets, or those outside our solar system, when they transit, or pass in front of their host stars.

Their , published in the June issue of the journal , could aid the process of choosing worlds to study for possible life and even one day help determine not only that a world is habitable, but in fact inhabited.

Volcanism is a key element in planetary habitability. That’s because volcanic outgassing helps a planet maintain moderate, life-inviting temperatures, regulating the atmosphere by cycling gases such as carbon dioxide between the atmosphere and the mantle.

Lead author , who has since graduated with a doctorate, said the project started in a UW astrobiology graduate seminar when a professor asked how one might detect — the grinding together and apart of huge slabs of a planet’s surface — on faraway worlds.

Plate tectonics is considered an aid to the origin of life because it allows for the recycling of materials from the atmosphere to the planetary interior. Some scientists have even proposed that life on Earth began at sites created by tectonic plates.

The students studied various models trying to predict whether an exoplanet might have plate tectonics, but found little in scientific literature on how to directly detect tectonic plates. So they started brainstorming.

“I came up with the idea of looking at explosive volcanic eruptions as a proxy, or stand-in, for plate tectonics,” Misra said. “I had done some work modeling aerosols produced by volcanic eruptions for other projects, so I started looking into how we might detect an eruption and what it would tell us.”

So the team used data from volcanic eruptions on Earth to predict what an Earth-like exoplanet might look like during such eruptions. The thinking, Misra said, was that explosive volcanic eruptions usually happen at the edges of tectonic plates, making them a good proxy indeed.

Gases released from smaller, nonexplosive volcanic eruptions tend to return quickly to the planet’s surface. Explosive eruptions, however, can send volcanic gases up into the stratosphere, where they “greatly affect the spectrum of the planet,” Misra said. The optical signature of the gases might be detectable by powerful telescopes such as the James Webb Space Telescope, scheduled for launch in 2018.

Co-authors are , and , all graduate students in the UW’s Department of Earth and Space Sciences and affiliated with the UW astrobiology program.

But while the connection between volcanic eruptions and tectonic plates is true on Earth, Misra said the team cannot say with certainty that the same is true throughout the cosmos. Still, he said, “An explosive eruption can probably be tied to volcanism if false positives such as dust storms can be ruled out.”

“These long-lasting, high-up aerosols can have a huge signal for an exoplanet, which is the key result for the paper,” Misra said. “What this means is that if we can detect a volcanic eruption on a planet, and if it meets other criteria like being in the habitable zone, that planet should move up our list of potential targets to search for life.”

The work may also someday help astronomers infer that a planet not only might have life, but actually does. Misra explained that while oxygen is thought an indicator of life, it’s also possible for oxygen to be produced abiotically, or by something other than biology.

Volcanism, Misra said, may help distinguish between oxygen that is produced by life or other planetary processes by helping astronomers better understand the planet’s environment.

“Volcanic gases often react with and destroy oxygen, and a detection of both oxygen and volcanism suggests that there is a source of oxygen in the planetary environment, which could be life,” Misra said.

The research was done through the , a UW-based interdisciplinary research group, and funded through the NASA Astrobiology Institute.

###

For more information, contact Misra at 440-554-6514 or amit0@astro.washington.edu. Cooperative agreement number NNA13AA93A.

Astronomers at the ÌìÃÀÓ°ÊÓ´«Ã½ have developed a new method of gauging the atmospheric pressure of exoplanets, or worlds beyond the solar system, by looking for a certain type of molecule.

And if there is life out in space, scientists may one day use this same technique to detect its biosignature — the telltale chemical signs of its presence — in the atmosphere of an alien world.

Understanding atmospheric pressure is key to knowing if conditions at the surface of a terrestrial, or rocky, exoplanet might allow liquid water, thus giving life a chance.

The method, devised by , a UW astronomy doctoral student, and co-authors, involves computer simulations of the chemistry of Earth’s own atmosphere that isolate what are called “dimer molecules” — pairs of molecules that tend to form at high pressures and densities in a planet’s atmosphere. There are many types of dimer molecules but this research focused only on those of oxygen.

Misra is first author of a published in the February issue of the journal Astrobiology.

The researchers ran simulations testing the spectrum of light in various wavelengths. Dimer molecules absorb light in a distinctive pattern, and the rate at which they form is sensitive to the pressure, or density, in the planet’s atmosphere.

“So the idea is that if we were able to do this for another planet, we could look for this characteristic pattern of absorption from dimer molecules to identify them,” Misra said. The presence of such molecules, he said, likely means the planet has at least one-quarter to one-third the pressure of Earth’s atmosphere.

Powerful telescopes soon to come online, such as the James Webb Space Telescope, scheduled for launch in 2018, may enable astronomers to use this method on distant exoplanets. With such enhanced tools, Misra said, astronomers might detect dimer molecules in actual exoplanet atmospheres, leading to a clear understanding of the planet’s atmosphere.

This research may also play a part in the greatest astronomical quest of all — the ongoing search for life in the cosmos.

That’s because the team realized along the way that oxygen dimer molecules are often more detectable in an atmosphere than other markers of oxygen. That’s important from a biological standpoint, Misra said.

“It’s tied to photosynthesis, and we have pretty good evidence that it’s hard to get a lot of oxygen in an atmosphere unless you have algae or plants that are producing it at a regular rate.

“So if we find a good target planet, and you could detect these dimer molecules — which might be possible within the next 10 to 15 years — that would not only tell you something about pressure, but actually tell you that there’s life on that planet.”

Misra’s UW co-author is , professor of astronomy; other co-authors are Mark Claire of Scotland’s University of St. Andrews and Dave Crisp of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

The research was performed through the UW-based and funded by NASA (Grant NNH05ZDA001C), as well as a grant from Advancing Science in America, Seattle chapter.

###

For more information, contact Misra at 440-554-6514 or amit0@uw.edu.