Dead stars will help astronomers find signs of life on exoplanets

Astronomers at Cornell University have developed a spectral field guide to help scientists understand the chemical signatures of exoplanets in the path of dead stars. These biosignatures will indicate whether life exists on these far-away rocky planets.

The next generation of space telescopes will be capable of scanning distant solar systems for signs of life. The research will be particularly focused on Earth-like exoplanets accompanied by burned-out stars known as white dwarfs.

“Rocky planets around white dwarfs are intriguing candidates to characterize because their hosts are not much bigger than Earth-size planets,” said study co-author Professor Lisa Kaltenegger.

The Extremely Large Telescope, currently under construction in northern Chile’s Atacama Desert, and the James Webb Space Telescope are scheduled to launch in 2021. These powerful tools will give astronomers a closer look at exoplanets.

“We show what the spectral fingerprints could be and what forthcoming space-based and large terrestrial telescopes can look out for,” said study lead author Thea Kozakis.

The key will be to capture images of an exoplanet in the brief time it crosses in front of a white dwarf – a small, dense star that has exhausted its energy.

“We are hoping for and looking for that kind of transit,” said Kozakis. “If we observe a transit of that kind of planet, scientists can find out what is in its atmosphere, refer back to this paper, match it to spectral fingerprints and look for signs of life. Publishing this kind of guide allows observers to know what to look for.”

The astronomers assembled spectral models for different atmospheres at different temperatures to create a template for possible biosignatures. The experts explained that catching exoplanets as they pass through the habitable zone of a white dwarf is challenging.

“We wanted to know if light from a white dwarf – a long-dead star – would allow us to spot life in a planet’s atmosphere if it were there,” said Professor Kaltenegger.

The research suggests that scientists will be able to recognize spectral biosignatures that are indicative of life, such as a combination of methane and ozone or nitrous oxide, if the chemical compounds are present. 

“If we would find signs of life on planets orbiting under the light of long-dead stars, the next intriguing question would be whether life survived the star’s death or started all over again – a second genesis, if you will,” said Professor Kaltenegger.

The study is published in Astrophysical Journal Letters.

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By Chrissy Sexton, Earth.com Staff Writer