Ohio State assistant professor of astronomy Ji Wang has been conducting research to advance the ability of detecting signs of life on exoplanets.
Wang’s goal is to study the traits of exoplanets, which are planets that orbit around stars outside of our solar system, in order to determine which have the most potential of containing life.
“In terms of determining what would make an exoplanet capable of holding life, the first thing is to determine whether it’s capable of having liquid water on its surface,” said Marshall Johnson, Columbus Prize Postdoctoral Fellow in the Department of Astronomy. “We need to know whether a planet is the right size and the right distance from its host star.”
If a planet is too big, it would have a crushing atmosphere that would make it too hot on the surface for life, if there is a surface at all, Johnson said. If a planet is too small, it would not be able to hang on to enough atmosphere.
“An atmosphere we all live in, the atmosphere in which we can breathe oxygen and the water can precipitate down, all of this [is a] kind of continuous cycle that supports life on Earth,” Wang said.
Wang noted that it’s easy to “appreciate the atmosphere of our own,” but said it can be challenging to study another planet’s atmosphere when astronomers can’t see it. That’s where a technique called spectroscopy comes in, Wang said.
Wang and a team of astronomers have been using spectroscopy, a ground-based telescope technique, to analyze the atmosphere of an exoplanet called HR 8799 c. Spectroscopy detects molecular compounds in the exoplanet’s atmosphere.
“Related to this research, we’re very interested in methane and water, and methane and water have their own distinguished spectroscopy features,” Wang said. “So, that’s what we’re looking for. We’re looking for the absorption features of water and methane.”
Location plays a role in a planet’s ability to carry life, as well. Too far from a star, and it would be too cold, causing water to freeze, Johnson said. Too close, and it would be too hot, causing the water to turn into steam.
Johnson said Wang’s work to measure water and methane in the atmosphere of exoplanets such as HR 8799 c, which is more of a Jupiter-like planet, is the first step toward being able to analyze more challenging, Earth-like planets.
“It’s low-hanging fruit,” Wang said. “It’s easy to start. It’s much bigger and brighter than the Earth, so if you want to really achieve the very ambitious goal of studying an Earth-like planet, we have to have some stepping stones, and HR 8799 c is one of those stepping stones.”
Wang said many of the techniques he is using can be transferrable or translatable to studying Earth-like planets in the future.
Wang is the lead author of this research, which was recently selected for publication in “The Astronomical Journal,” with co-authors from the California Institute of Technology; the University of California, Santa Cruz; Harvard University; and the University of Montreal.
Now that this research has effectively analyzed HR 8799 c’s atmosphere, it can be applied to other exoplanets, as well.
A new generation of ground-based telescopes is currently being built, and the telescopes will be three times larger.
“In the next decade, we are hoping that we can reach the sensitivity to see true Earth-like planets,” Wang said. “And at that time, we’ll have other techniques ready for all the issues, and the technical difficulties [will be] resolved, because of the effort that we are taking on. And hopefully by then it’s just a continuous effort to study the atmosphere of Earth-like planets.”