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NASA’s Chandra X-ray space telescope has created a three-dimensional map of stars close to the sun that could help astronomers search for alien planets that could host life.
The map created by Chandra – which is celebrating 25 years in orbit but is facing a troubling budget crunch – could inform scientists about exoplanets to guide future telescopes to search for habitable conditions.
The stars mapped by the telescope are arranged in concentric rings around the sun, at distances between 16.3 light years and 49 light years. This is close enough that telescopes could collect wavelengths of light or “spectra” from planets in the habitable zones of these stars. The habitable zone or “Goldilocks zone” is a region around a star that is neither too hot nor too cold to allow liquid water to reach Earth’s surface.
The spectrum from these planets created as starlight shines through the air could reveal surface features such as continents and oceans, and atmospheric features such as clouds and chemical content.
Related: Happy 25th anniversary, Chandra! NASA celebrates with 25 stunning images from its flagship X-ray observatory
Chandra’s X-ray capability is key to selecting the planets to investigate for possible habitability. High-energy light such as X-rays and ultraviolet radiation can destroy a planet’s atmosphere and also break down the complex molecules needed as the building blocks of living things, destroying their habitability.
So, if Chandra sees a planet under heavy X-ray bombardment, scientists can conclude that it is not the best world to study in their search for alien life.
“Without X-ray characterization from their host star, we would be missing a key element of whether or not a planet is truly habitable,” said Breanna Binder of California State Polytechnic University, the team leader behind of the new map. statement. “We need to look at what kind of X-ray doses these planets get.”
X-rays are bad news for life, even in Goldilocks zones
Binder and colleagues built their map by first starting with a list of 57 stars that are close enough to our solar system that future telescopes in space, like the Habitable Earth Observatory, and on terra firma, like the Very Large Telescope ( ELT), imaging planets. orbiting in their Goldilocks zones.
Being in the habitable zone is no guarantee that a planet will be hospitable, however. Venus and Mars are both in the sun’s habitable zone, on either side of Earth, but the surface of Mars seems unsuitable for life as we know it, and superheated Venus is hostile to it.
So, to narrow down their list, the team used data from 10 days of Chandra observations and 26 observing days of the European Space Agency’s (ESA) XMM-Newton space telescope to determine how bright the stars in X-rays. Then, they determined how energetic these X-rays are and how quickly the star’s X-ray emission changes.
The scientists claimed that the brighter and more energetic the X-rays, the more likely any orbiting exoplanets have seriously damaged their atmospheres or lost them entirely.
“We have identified stars in which the X-ray radiation environment of the habitable zone is similar to or even milder than the one in which the Earth developed,” explained team member Sarah Peacock, from the University of Maryland. “Such conditions may play a key role in sustaining a rich atmosphere similar to that found on Earth.”
Some of the stars the team examined are already known to be orbited by exoplanets with masses and sizes similar to solar system giants Jupiter, Saturn, Neptune, and Uranus, with a handful of candidates under about half the mass of Earth.
These systems may also contain planets with masses and sizes more compatible with Earth’s planets that have not yet been discovered.
Earth planets in these systems may have been missed by the most reliable method of exoplanet detection, the transit method. This technique relies on a planet crossing or “shifting” the face of its star, causing a slight drop in the star’s light output in the process.
This depends on a planet coming between its star and Earth, which means that some systems are not properly oriented to see Earth with the transit method. The technique is best for seeing giant planets close to their star, so smaller worlds orbiting far away could be missed.
The other primary exoplanet detection technique, the radial velocity method, relies on the “wobble” caused by seeing a planet as it orbits its star and is pulled by its gravitational pull. Again, this method favors massive planets close to their stars, generating a more pronounced wobble.
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“We don’t know how many Earth-like planets will be found in images with the next generation of telescopes, but we know that it will be valuable and very difficult to spend the time to see them,” team member and University of California, Riverside researcher Edward Schwieterman concluded. “This X-ray data helps to refine and prioritize the target list and may lead to faster acquisition of the first image of an Earth-like planet.”
The team’s research was presented at the 244th meeting of the American Astronomical Society meeting in Madison, Wisconsin.
