An international team of astronomers from the United States, Australia, and Brazil has identified 121 giant exoplanets in the habitable zones of their respective stars, with each expected to be orbited by several terrestrial (rocky) moons. Their work is published in the Astrophysical Journal.
Artist’s impression of a potentially habitable exomoon orbiting a giant planet. Image credit: Sci-News.com.
Since the 2009 launch of NASA’s Kepler telescope, astronomers have identified over 2,000 planets around other stars.
A primary goal of the Kepler mission is to identify planets that are in the habitable zones of their stars, meaning it’s neither too hot nor too cold for liquid water — and potentially life — to exist.
Terrestrial planets are prime targets in the quest to find life because some of them might be geologically and atmospherically similar to Earth. Another place to look is gas giants identified during the Kepler mission.
While not a candidate for life themselves, gaseous exoplanets in the habitable zone may harbor rocky moons that could sustain life.
“There are currently 175 known moons orbiting the eight planets in our Solar System,” said co-author Dr. Stephen Kane, a researcher at the University of Southern Queensland and the University of California, Riverside.
“While most of these moons orbit Saturn and Jupiter, which are outside the Sun’s habitable zone, that may not be the case in other solar systems. Including rocky exomoons in our search for life in space will greatly expand the places we can look.”
“Rather than looking to new exoplanets in the ongoing pursuit to find life outside of Earth, the new tactic instead looked at whether these giant exoplanets had large rocky moons,” added lead author Michelle Hill, an undergraduate student at the University of Southern Queensland.
“There are potentially a lot more moons than there are Earth-size planets, so this research means there could be double the number of possibly habitable worlds out there in the habitable zone.”
“What that means is that Earth-like planets might not be the first place we find signs of life.”
Dr. Kane, Hill and their colleagues identified 121 giant planets that have orbits within the habitable zones of their stars.
At more than three times the radii of the Earth, these gas giants are less common than terrestrial planets, but each is expected to host several large exomoons.
“Now that we have created a database of the known giant planets in the habitable zone of their star, observations of the best candidates for hosting potential exomoons will be made to help refine the expected exomoon properties,” Hill said.
“Our follow-up studies will help inform future telescope design so that we can detect these exomoons, study their properties, and look for signs of life.”
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Michelle L. Hill et al. 2018. Exploring Kepler Giant Planets in the Habitable Zone. ApJ 860, 67; doi: 10.3847/1538-4357/aac384
