Scientists build spectral library to identify water on exoplanets
by Clarence Oxford
Los Angeles CA (SPX) Nov 15, 2024
Cornell University researchers are constructing a library of basalt-based spectral signatures, examining chemical processes from Earth’s hot mantle. This compilation aims to shed light on the composition of planets outside our solar system and potentially reveal water’s presence on those exoplanets.
“When the Earth’s mantle melts, it produces basalts,” explained Esteban Gazel, professor of engineering. Basalt, a prevalent volcanic rock in our solar system, serves as an essential recorder of geological history, he added.
“When the Martian mantle melted, it also produced basalts. The moon is mostly basaltic,” Gazel said. “We’re testing basaltic materials here on Earth to eventually elucidate the composition of exoplanets through the James Webb Space Telescope data.”
Gazel, along with Emily First, a former Cornell postdoctoral researcher and now assistant professor at Macalester College, co-authored the paper “Mid-infrared Spectra for Basaltic Rocky Exoplanets,” which was published in ‘Nature Astronomy’.
Understanding how minerals reflect the processes forming these rocks and their spectral characteristics is crucial for developing this library, Gazel noted.
“We know that the majority of exoplanets will produce basalts, given that their host star’s metallicity will lead to mantle minerals (iron-magnesium silicates) that, when melted, predict the formation of basaltic lavas,” Gazel said. “This trend will likely be consistent not only within our solar system but across the galaxy.”
First recorded the emissivity of 15 basalt samples to identify their spectral signatures, which may correspond to detections by the space telescope’s mid-infrared spectrometer.
Once basaltic material erupts on an exoplanet and solidifies, it forms lava. If water is present, the interaction produces hydrated minerals, visible in the infrared spectrum. These can include amphibole or serpentine, which have distinct appearances and compositions.
Small spectral variances in basalt samples could, in theory, indicate whether an exoplanet had surface or internal water, said Gazel.
However, identifying water signatures is complex and would require the James Webb Space Telescope – located about a million miles from Earth – to spend extensive time observing a single system, followed by thorough data analysis.
The research team, examining these spectral signatures, used data from super Earth exoplanet LHS 3844b, located around 48 light-years away and orbiting a red dwarf star.
Ishan Mishra, from Nikole Lewis’s laboratory at Cornell, created code to model First’s spectral data, simulating potential exoplanet surfaces observable by JWST.
Lewis explained, “Ishan’s coding tools were initially developed for studying icy moons in our solar system. We are now applying these insights to exoplanets.”
First noted that the study’s goal was not specific to LHS 3844b but aimed at understanding a variety of basaltic exoplanets that JWST and other future observatories might observe.
Exploring rocky exoplanet surfaces has typically focused on identifying single chemical markers. With JWST’s advanced capabilities, scientists are transitioning to analyzing multiple components, enhancing understanding of these celestial bodies’ mineralogy and chemical makeup.
“On Earth, basalts erupting from deep-sea mid-ocean ridges differ in composition from those at volcanic islands like Hawaii,” First said. “Even rocks with similar bulk chemistry may host distinct minerals, making it crucial to study both characteristics.”
This research received support from the National Science Foundation, the National Institute of Standards and Technology, and the Heising-Simons Foundation’s 51 Pegasi b Fellowship.
Research Report:Potential for observing geological diversity from mid-infrared spectra of rocky exoplanets
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