Tour: Coming in Hot: NASA's Chandra Checks Habitability of Exoplanets

Using NASA’s Chandra X-ray Observatory and ESA’s XMM-Newton, astronomers are testing how habitable exoplanets are based on whether they receive lethal radiation from the stars they orbit. This type of research will help guide observations with the next generation of telescopes aiming to make the first images of planets like Earth.

A team of researchers examined stars that are close enough to Earth that telescopes set to begin operating in the next decade or two could take images of planets in their so-called habitable zones, defined as orbits where the planets could have liquid water on their surfaces.

Any images of planets will be single points of light and will not directly show surface features like clouds, continents and oceans. However, their spectra — the amount of light at different wavelengths — will reveal information about the planet’s surface composition and atmosphere.

There are several other factors influencing what could make a planet suitable for life as we know it. One of those factors is the amount of harmful X-rays and ultraviolet light they receive, which can damage or even strip away the planet’s atmosphere.

A team of astronomers began with a list of stars that are close enough to Earth that future ground and space-based telescopes could make images of planets in their habitable zone. These future telescopes include the Habitable Worlds Observatory and ground-based Extremely Large Telescopes.

Based on X-ray observations of some of these stars using data from Chandra and XMM-Newton, the researchers examined which stars could have hospitable conditions on orbiting planets for life to form and prosper.

The team studied how bright the stars are in X-rays, how energetic the X-rays are, and how much and how quickly they change in X-ray output, for example, due to flares. Brighter and more energetic X-rays can cause more damage to the atmospheres of orbiting planets.

They identified stars where the habitable zone’s X-ray radiation environment is similar to or even milder than the one in which Earth evolved. Such conditions may play a key role in sustaining a rich atmosphere like the one found on Earth.

Observing time on the next generation of telescopes will be precious and extremely difficult to obtain. These X-ray data are helping to refine and prioritize the list of targets and may allow the first image of a planet like the Earth to be obtained more quickly.