Scientists have begun creating a database of spectral signatures based on basalt to explore chemical processes found in the Earth’s hot mantle. This initiative aims to uncover the makeup of planets beyond our solar system and potentially provide indications of water on those exoplanets.
Scientists have embarked on developing a collection of basalt-based spectral signatures by investigating the chemical processes in the Earth’s hot mantle. This project will not only help to identify the composition of exoplanets but may also offer clues about the presence of water on these planets outside our solar system.
Esteban Gazel, an engineering professor, explained, “When the Earth’s mantle melts, it forms basalts.” He noted that basalt, a dark gray volcanic rock found across the solar system, serves as an essential indicator of geological history.
“The melting of the Martian mantle produced basalts as well, and the moon primarily consists of basalt,” he added. “Our goal is to analyze basaltic materials on Earth to better understand the makeup of exoplanets using data from the James Webb Space Telescope.”
Gazel and Emily First, a former postdoctoral researcher at Cornell and now an assistant professor at Macalester College in Minnesota, authored a paper titled “Mid-infrared Spectra for Basaltic Rocky Exoplanets,” which was published on November 14 in Nature Astronomy.
According to Gazel, the initial step in constructing their database involves understanding how minerals document the processes responsible for forming these rocks and analyzing their spectroscopic signatures.
“We anticipate that most exoplanets will yield basalts. The metallicity of their host stars leads to mantle minerals (iron-magnesium silicates), and when these melt, the equilibrium predicts basaltic lavas,” Gazel stated. “This will be common not just in our solar system but throughout the galaxy.”
First conducted emissivity measurements—gauging how much energy a surface radiates—on 15 basaltic samples to identify potential spectral signatures detectable by the space telescope’s mid-infrared spectrometer.
When basaltic lava erupts on an exoplanet and solidifies, it forms rocks on Earth referred to as lava. If water is present, the rock can interact with it, leading to the formation of new hydrated minerals, which can be easily detected in infrared spectra. These altered minerals may manifest as amphibole (a hydrous silicate) or serpentine (another hydrous silicate, resembling snake skin).
By scrutinizing slight spectral variations between the basalt samples, scientists can theoretically discern whether an exoplanet once possessed surface water or had water within its interior, Gazel explained.
However, detecting evidence of water is not immediate, and additional research is required before such measurements can be utilized. The James Webb Space Telescope (JWST), positioned around 1 million miles from Earth, might take dozens to hundreds of hours to focus on a system light-years away, followed by more time to analyze the collected data.
In their search for a rocky exoplanet to test their hypotheses and analyze 15 distinct signatures, the research team used data from the super-Earth exoplanet LHS 3844b, located about 48 light-years from a red dwarf star.
Ishan Mishra, affiliated with Nikole Lewis, an associate professor of astronomy, developed computer code to model First’s spectral data to simulate how various exoplanet surfaces might appear to the JWST.
Lewis noted that these modeling tools were initially employed for different purposes. “Ishan’s coding tools were originally used for studying icy moons in our solar system,” she highlighted. “Now, we are attempting to translate what we’ve discovered in the solar system to exoplanets.”
“Our objective was not to examine planet LHS 3844b specifically,” First mentioned, “but to explore a viable range of basaltic rocky exoplanets that could be observed by the JWST and other observatories in the near future.”
The researchers observed that the exploration of rocky exoplanets has mostly been limited to analyzing single data points—detecting evidence of only one type of chemical—in scientific literature. This trend is shifting as astronomers increasingly utilize the JWST to study multiple components.
By working to identify signatures associated with mineralogy and overall chemical composition—such as the levels of silicon, aluminum, and magnesium in a rock—geologists can gain insights into the conditions under which the rock formed, they said.
First explained, “On Earth, comparing basaltic rocks from mid-ocean ridges deep in the ocean to those from island volcanic eruptions like in Hawaii reveals noticeable differences in their chemistry. However, rocks with similar elemental compositions can have distinct minerals, making both properties essential for analysis.”
Along with First, Gazel, Lewis, and Mishra, the co-authors include Jonathan Letai ’23 from Northeastern University and physicist Leonard Hanssen, Ph.D. ’85, who recently retired from the National Institute of Standards and Technology.
Lewis is a faculty fellow in Cornell’s Carl Sagan Institute.
This research was supported by the National Science Foundation, the National Institute of Standards and Technology, and the Heising-Simons Foundation/51 Pegasi b Fellowship.
