NASA’s Chandra X-ray Space Telescope has created a three-dimensional map of stars near the Sun that could help astronomers search for planets that might host the Sun. alien life.
The Search for Alien Life
The map created by Chandra, which just celebrated 25 years in orbit but is facing a worrying budget crisis, could tell scientists which exoplanets to point future telescopes at to conduct research on conditions suitable for alien life.
The stars mapped by the telescope are arranged in concentric rings around the Sun, at distances ranging from 16.3 light-years to 49 light-years. This is close enough for telescopes to pick up 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 for liquid water to exist on a world’s surface.
The spectra of these planets created by starlight passing through their air could potentially reveal surface features such as continents and oceans, and atmospheric features such as clouds and chemical contents.
Chandra’s ability to use X-rays is critical to selecting which planets to examine for possible habitability. High-energy light such as X-rays and ultraviolet radiation can strip away a planet’s atmosphere and also break down complex molecules needed as building blocks for living things, ruining their habitability for alien life.
So if Chandra sees a planet undergoing intense X-ray bombardment, scientists can deduce that it is not the best world to study for alien life.
“Without characterizing the X-rays from its host star, we’re missing a key piece of information about whether a planet is truly habitable for alien life,” Breanna Binder of California State Polytechnic University, leader of the team behind the new map, said in a statement. “We need to look at what kind of X-ray doses these planets are receiving.”
Binder and colleagues built their map by initially starting with a list of 57 stars close enough to our solar system to allow future space-based telescopes, such as the Habitable Worlds Observatory, and ground-based telescopes, such as the Extremely Large Telescope (ELT), to image planets orbiting in their Goldilocks zone.
Just because a planet is in the habitable zone is no guarantee that it hosts alien life, however. Venus and Mars are both in the habitable zone of the sun, on either side of Earth, but the Martian surface appears to be unsuitable for alien life, and a superheated Venus is downright hostile to it.
So, to narrow down the list, the team used data from 10 days of observations from Chandra and 26 days of observations from the European Space Agency’s (ESA) XMM-Newton space telescope to see how bright the stars are in X-rays. They then determined how energetic these X-rays are and how rapidly the stars’ X-ray output is changing.
The scientists reasoned that the brighter and more energetic the X-rays, the more likely it was that the orbiting exoplanets had suffered severe damage to their atmospheres or lost them altogether. “We have identified stars where the X-ray radiation environment of the habitable zone for alien life is similar to or even milder than the one in which Earth evolved,” said team member Sarah Peacock of the University of Maryland. “Such conditions could play a key role in supporting a rich atmosphere like the one found on Earth.”
Some of the stars the team examined are already known to be orbited by exoplanets with masses and sizes similar to the solar system giants Jupiter, Saturn, Neptune and Uranus, with a handful of candidates having masses less than about half that of Earth.
There may also be planets in these systems with masses and sizes more compatible with those of Earth, currently unknown.
Earth-sized 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 “transiting” the face of its star, causing a small dip in starlight in the process.
This is due to a planet coming between its star and Earth, which means that some systems are not oriented correctly to see worlds with the transit method. The technique is best at spotting massive planets close to their star, so smaller worlds orbiting relatively far away may not be detected.
The other primary exoplanet detection technique, the radial velocity method, relies on detecting the “wobble” a planet causes as it orbits its star and tugs on it gravitationally. Again, this method favors massive planets close to their stars, which generate a more significant wobble.
“We don’t know how many Earth-like planets will be discovered in images with the next generation of telescopes, but we do know that observing time on them will be precious and extremely difficult to obtain,” concluded team member Edward Schwieterman, a researcher at the University of California, Riverside.
“These X-ray data are helping to refine and prioritize the target list and could enable the first image of an Earth-like planet to be obtained more quickly.” The team’s research was presented at 244th meeting of the American Astronomical Society in Madison, Wisconsin.
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