Astronomers may have found a moon orbiting a distant rogue planet. While the planet doesn鈥檛 orbit a star, its moon may be close to the size of Earth and warm enough to have liquid water on its surface, a feature necessary for life as we know it.
at Texas A&M University and her colleagues performed a series of calculations to try to determine whether rogue planets would be good places to look for moons beyond our solar system, called exomoons. While there have been several tentative detections of possible exomoons, none of them have been confirmed yet.
They found that it should be relatively easy to detect exomoons orbiting large rogue planets because there is no glare from a host star adding unwanted noise to the images. In such a system, the main source of light would be the planet itself, which would continue to glow with the heat generated in its formation, making it simpler to search for an orbiting moon. Up to 15 per cent of rogue planets are expected to have moons that pass between them and Earth, blocking out some of their light and allowing us to detect the moons.
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Over the course of their investigations, the researchers sorted through archival data from the Spitzer Space Telescope and were surprised to find an exomoon candidate around one of a pair of rogue planets we had already observed, a system called 2MASS J1119-1137 AB.
鈥淲e weren鈥檛 actually looking for moons,鈥� says Limbach. 鈥淭here are about a dozen of these free-floating planets that have been observed with Spitzer, and we were studying those to figure out the level of intrinsic variability we should expect from things like clouds.鈥�
This detection is still highly inconclusive, she says, but if there is an exomoon there, it is probably about 1.7 times the mass of Earth and circling a planet 3.7 to 9.2 times the mass of Jupiter. The potential moon receives roughly the same amount of radiation from its planet as Earth does from the sun. 鈥淔rom the surface of this object, the planet in the sky would be larger than the moon appears from Earth by a factor of 10 or 20, so it would be this giant ball of glowing red ember in the sky,鈥� says Limbach.
She and her team plan to make more observations with ground-based telescopes to double-check this detection. Their study found that more exomoons around rogue planets should be easily detectable with the James Webb Space Telescope, which is scheduled to launch in December.
The Astrophysical Journal Letters
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