Scientists may be one step closer to finding another Earth-like planet, thanks to Yale astronomers who have come up with a new way to analyze stars outside of Earth’s solar system.
Postdoctoral researcher John Brewer and astronomy professor Debra Fischer developed a new computational technique for determining the chemical composition of nearby stars. Knowing the chemistry of these stars provides important clues for characterizing their orbiting exoplanets. This in turn provides researchers with a more effective way of pinpointing potentially habitable planets. Brewer and Fischer’s study was accepted by the Astrophysical Journal and will be published in the coming weeks.
“We’ve really fallen short of detecting planets like Earth for years,” Fischer said. “Only now are we on the threshold of being able to detect real analogs of our own world — that’s where we have the best chances of finding life that we recognize.”
For this study, Brewer improved the accuracy and scope of a technique Fischer had previously developed. They used a spectrograph — an instrument that splits light into different wavelengths — to analyze 849 nearby stars. Atoms in the atmosphere of a star absorb light at specific wavelengths, Fischer said, so the resulting spectrum can be a “compositional fingerprint” of what the star is made of.
Analyzing these absorption features can lend insight into many different characteristics of stars, including temperature, surface gravity and chemical composition, she added. Because planets are formed from the dust and gas that surround a newly formed star, they are composed of the same elements present in the star’s atmosphere.
“What’s exciting about this work is that we’re not just able to speculate, but we’re starting to get hard evidence about how the composition of stars affects the composition of the planets that orbit them,” said astronomy professor Greg Laughlin, who was not affiliated with the study. “They’ve made an interesting discovery and it’s going to be even more interesting to see what comes next.”
In their research, Brewer and Fischer focused on the carbon-to-oxygen and magnesium-to-silicon ratios, which can determine whether a planet has the potential to support life. For example, a low carbon-to-oxygen ratio implies that more oxygen is available to bind with magnesium and silicon, which would form a crust and mantle similar to that of the Earth. According to Brewer, an optimal magnesium-to-silicon ratio can result in the formation of plate tectonics and relatively mild volcanoes, which are both “critical pieces in regulating our climate through the carbon cycle on long timescales.”
Although astronomers started identifying exoplanets in the 1990s, obtaining reliable data on these new planets’ compositions is a difficult task, said Johanna Teske, a postdoctoral fellow at the Carnegie Institution for Science who researches the chemical conditions for planet formation. Brewer and Fischer’s sample is an “important step forward” for prioritizing which stars to characterize, added Teske, who was not affiliated with the study.
In addition, Brewer also explored the concept of diamond planets — planets with carbon-rich interiors that form crystal structures when compressed under enormous pressure. Concrete evidence of diamond planets would imply there exists a new class of previously uncharacterized planets. Several Yale astronomers, including Fischer, have previously worked on studies involving diamond planets.
However, Brewer found no carbon-rich stars in his sample of 849 stars, which means that diamond planets are likely “exceedingly rare.”
Brewer said he hopes to further improve the precision of his analysis technique, and he looks forward to using his methods to continue his study of planet formation. Fischer is also leading an instrumentation team with the hopes of detecting other Earth-like planets around nearby stars.
“I think we’re really right on the edge right now of being able to find a whole lot of habitable planets,” Brewer said. “Already from both the Kepler spacecraft and from the ground, we’re finding an amazing number of rocky planets, and we’re finding smaller and smaller planets.”
As of last month, researchers had discovered 3,375 exoplanets, according to the National Aeronautics and Space Administration’s Exoplanet Science Institute.