Peering through Alien Atmospheres
By Skylar Xu ’24
Jonathan Gomez Barrientos ’22 at Cornell University was first drawn to astronomy by Curiosity, the Mars rover that the National Aeronautics and Space Administration (NASA) launched in 2011. He wanted to learn more about the instruments on board the rover. While taking introductory astronomy classes during his first two years at Cornell, he found that he was passionate about astronomy and all it had to offer.
Barrientos now explores the possibility of life on Earth-like planets beyond our solar system, called exoplanets, under the direction of Lisa Kaltenegger, an associate professor in astronomy in the College of Arts & Sciences at Cornell, the director of Cornell’s interdisciplinary Carl Sagan Institute.
“By Earth-like exoplanets we really mean rocky exoplanets that orbit in this region called the habitable zone, which is a region in space where the conditions are just right for liquid water to potentially exist on the surface of the exoplanet,” explains Barrientos. Although current technology cannot find life on exoplanets, the recently launched James Webb Space Telescope (JWST) will for the first time be able to search for biosignatures — such as the presence of oxygen in combination with a reducing gas like methane — that might indicate life on other worlds.
Extending the Reach of Reflection Spectroscopy
Barrientos uses computer models that simulate data generated by reflection spectroscopy, a technique that analyzes the light reflected by exoplanets.
In reflection spectroscopy, the light reflected off an exoplanet is broken down into its constituent wavelengths, which is to say the complete spectrum of colors in the light, and plotted as a line graph on a chart. Brightness is plotted on the vertical axis and wavelength on the horizontal axis. Spikes and dips mark the magnitude of light reflected at that wavelength. Dips at particular wavelengths are caused by atoms and molecules that are present in the planet’s atmosphere and that absorb light at those wavelengths, whereas spikes indicate that the planet is reflecting light at those wavelengths. Because various chemical elements absorb light in identifiable ways, researchers can infer from the reflected light certain physical and chemical properties of the planet, such as the composition of its atmosphere and how it might be changing.
According to Barrientos, reflection spectroscopy can tell us about more than just the atmosphere of an exoplanet. Some of the light reflected from an exoplanet reaches the planet’s surface before passing back out through the planet’s atmosphere. Taking advantage of this fact, Barrientos has demonstrated that the same light astronomers use to decipher the composition of an exoplanet’s atmosphere might contain clues about its surface, too.
Light reflected off Earth’s surface, for example, spikes near the infrared portion of the spectrum because of vegetation. Chlorophyll, the green pigment found in all plants, is transparent at near-infrared wavelengths. Since near-infrared light is not absorbed by chlorophyll, the light registers as a spike on a spectrograph.
“Just by doing the simulation, I demonstrated that we’ll be able to learn about the surface of a distant planet [using reflection spectroscopy].”
Features on an exoplanet’s surface may similarly leave their mark on the reflected light spectrum. But Barrientos cautions against the claim that a similar feature on exoplanets alone could be indicative of life. “We don’t know if alien plants have the same red edge as earth plants, for instance. We don’t know if they reflect light at the same wavelength.”
Preparing for a Future Space Telescope
In April 2022 Barrientos was excited to see the National Academies of Science, Engineering and Medicine (NASEM) propose a transformative telescope to be launched in the 2040s. The telescope would cost an estimated 11 billion dollars and would make observations from space of Earth-like exoplanets orbiting Sun-like stars, offering a new perspective on humans’ place in the universe. “Detecting and learning about Earth-like exoplanets is one of the major directions astronomy will be heading in,” explains Barrientos. “It proved to be a big deal in the astronomy community.”
In collaboration with Nikole K. Lewis, an assistant professor of astronomy and the deputy director of the Carl Sagan Institute in the College of Arts and Sciences, the deputy director of the Carl Sagan Institute, and Ryan MacDonald, a research associate in astronomy who is also at the Carl Sagan Institute, Barrientos has developed a tool that extracts properties of exoplanets from simulated data collected by a telescope like the one proposed by NASEM. Simulations are important, according to Barrientos, because no telescope has yet captured information about the atmospheres of Earth-like exoplanets orbiting Sun-like stars. Telescopes and other technology are integral to astronomical research and data collection, and when the technology is not yet available, models can guide researchers’ decisions about what data they should try to collect. Models can also provide powerful outlooks on what astronomy research could do in the future. “Just by doing the simulation, I demonstrated that we’ll be able to learn about the surface of a distant planet [using reflection spectroscopy],” Barrientos says.
On the Cusp of Further Discovery
In his graduate work, Barrientos hopes to analyze observed data gathered by the newly launched JWST and other telescopes designed to collect data from distant planets. Compared to the Hubble Space Telescope, the JWST’s larger size combined with its improved infrared resolution and sensitivity make it possible to collect more light from rocky exoplanets that are orbiting small stars, rendering a whole new portion of the universe accessible.
“I feel like we’re at a certain point in history where we have the tools to answer the question of whether there’s life on other planets,” relates Barrientos. “I think the time is now.” In terms of extraterrestrial life, Barrientos is optimistic that it’s out there. “If it happened once, why not twice?” he says.
Barrientos, who graduates in May 2022, will continue his astronomy research in graduate school at the California Institute of Technology. “It’s an exciting time because of JWST,” Barrientos says. Pursuing a PhD is especially meaningful to Barrientos because he came to Cornell as a first-generation college student. “It’s very significant for my family…going all the way to PhD is very exciting for me.”
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