Researchers examined stars close enough to Earth for future telescopes to capture images of planets in their habitable zones, where liquid water could exist.

While future images of planets will be single points of light, their spectra will provide information about surface composition and atmosphere.

Factors such as harmful X-rays and ultraviolet light from host stars, which can damage or strip away a planet's atmosphere, are crucial in determining habitability.

"Without characterizing X-rays from its host star, we would be missing a key element on whether a planet is truly habitable or not," said Breanna Binder of California State Polytechnic University in Pomona, who led the study. "We need to look at what kind of X-ray doses these planets are receiving."

Binder's team started with stars close enough to Earth for future telescopes, such as the Habitable Worlds Observatory and extremely large ground-based telescopes, to image planets in their habitable zones.

Using X-ray data from Chandra and XMM-Newton, the team assessed which stars could host planets with conditions suitable for life.

The study focused on stars' X-ray brightness, energy, and variability due to flares. High-energy X-rays can significantly harm planetary atmospheres.

"We have identified stars where the habitable zone's X-ray radiation environment is similar to or even milder than the one in which Earth evolved," said Sarah Peacock, a co-author from the University of Maryland, Baltimore County. "Such conditions may play a key role in sustaining a rich atmosphere like the one found on Earth."

The researchers analyzed X-ray data from nearly 10 days of Chandra observations and about 26 days of XMM observations of 57 nearby stars, some with known planets. Most of these are giant planets like Jupiter, Saturn, or Neptune, with a few potentially less than twice as massive as Earth.

There are likely more planets orbiting the sample stars, especially Earth-sized ones, that remain undetected. Transit studies, which detect tiny dips in light as planets pass in front of their stars, often miss planets due to the required special geometry. Only one exoplanet in the sample was detected by transits.

The wobbling of a star induced by orbiting planets is another detection method, primarily effective for finding giant planets close to their stars.

"We don't know how many planets similar to Earth 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," said co-author Edward Schwieterman of the University of California at Riverside. "These X-ray data are helping to refine and prioritize the list of targets and may allow the first image of a planet similar to Earth to be obtained more quickly."

These findings were presented at the 244th meeting of the American Astronomical Society in Madison, Wisconsin.

Related Links
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