Scientists develop new technology to detect water on exoplanets using basalt spectroscopy

Researchers are using basalt spectroscopy to study exoplanets and using the James Webb Space Telescope to search for water. By studying chemical processes in Earth's hot mantle, Cornell University scientists are building a library based on the spectral signatures of basalt. This research aims to determine the composition of exoplanets and provide evidence for water on these exoplanets.

Engineering professor Esteban Gazel said: "When the Earth's mantle melts, it produces basalt. Basalt is a gray-black volcanic rock that is found throughout the solar system and is an important recorder of geological history. When the mantle of Mars melts, it also produces basalt. The moon is mostly basalt," he said. "We are testing basaltic materials on Earth to ultimately elucidate the composition of exoplanets using data from the James Webb Space Telescope."

Gazel and Emily First, a former postdoctoral researcher at Cornell University and now an assistant professor at Macalester College in Minnesota, are the authors of a study recently published in Nature Astronomy.

Gazel said understanding how minerals record the processes that formed these rocks, and what their spectral signatures are, is the first step in developing a library of them: "We know that most exoplanets produce basalts because the metallicity of their host stars leads to mantle minerals (iron-magnesium silicates) so that when they melt, the phase equilibrium (the balance between two states of matter) predicts that the resulting lava will be basalt. It will not only prevail in our solar system, but throughout the Milky Way."

First, 15 basalt samples were measured for their emissivity, which refers to the extent to which a surface radiates energy encountered, which can help search for spectral signatures that the space telescope's mid-infrared spectrometer might detect.

Once basalt melt erupts on an exoplanet and cools, the basalt hardens into a solid rock, known as lava on Earth. If water is present, the rock will interact with the water to form new hydrated minerals, which are easily detected in infrared spectra. These altered minerals may become amphibole (a hydrated silicate) or serpentine (another hydrated silicate that looks like snakeskin).

By studying tiny spectral differences between basalt samples, scientists could theoretically determine whether exoplanets once had flowing surface or interior water, Gazelle said.

Evidence of water would not be immediately apparent and further work would be needed before this detection method could be adopted. The James Webb Space Telescope (JWST) is about 1 million miles from Earth, and it takes dozens to hundreds of hours to focus on a system a light-year away, and then even more time to analyze the data.

The research team used data from the super-Earth exoplanet LHS 3844b when looking for a rocky exoplanet to simulate their hypothesis and consider 15 different characteristics.

Ishan Mishra, who works in the laboratory of Nikole Lewis, associate professor of astronomy, wrote computer code to model First's spectral data to simulate how different exoplanet surfaces would behave on JWST.

Lewis said the modeling tools were originally intended for other applications. "Ishan's coding tools were originally developed to study icy moons in the solar system," she said. "We are now finally translating what we have learned in the solar system to exoplanets."

"Our goal was not to evaluate LHS 3844b specifically," First said, "but to consider a reasonable range of basaltic exoplanets that JWST and other observatories might observe in the coming years."

When it comes to exoplanets, exploration of rocky surfaces has been mostly limited to single data points - only finding evidence of chemical types in the scientific literature - but that is shifting to multi-component as observers take advantage of JWST, the researchers said.

By trying to find characteristics related to the mineralogy and chemical composition of the bulk -- for example, how much silicon, aluminum and magnesium is in the rock -- geologists can learn more about the conditions under which the rock formed, geologists said.

"On Earth, if you have basalts erupting from the ocean floor deep in mid-ocean ridges, and those basalts are erupting on oceanic islands like Hawaii, you'll find some differences in the bulk chemistry of those rocks," First said. "But even bulk rocks with similar chemical compositions may contain different minerals, so those are important features to study."

Compiled from /ScitechDaily