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Astronomers Think They've Spotted a Moon Forming Around an Exoplanet

Scientists have detected a signal around an exoplanet that might be the signature of a circumplanetary disk—a disk of debris that could one day form into exomoons.

Astronomers theorize that in Jupiter and Saturn's early days, the massive planets would trap debris into these orbiting circumplanetary disks. The mass from the disks could then do one of two things: fall onto the planet or clump up into moons. New results from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile show off what might be evidence for one of these disks around a young exoplanet that's 370 light-years away from Earth.

The exoplanet at hand is called PDS 70c, the second-closest known exoplanet to the parent star PDS 70. It orbits far from its young (approximately 5 million-year-old) parent star, further than the distance between the Sun and Neptune and orbiting slightly closer than a vast ring of dust. Scientists first spotted evidence of PDS 70c earlier this year using the Very Large Telescope (VLT). The researchers interpreted their results not only to be the mark of an exoplanet but one that was gobbling up some of the gas and dust in its vicinity.

[...] The scientists claim that they have located a cloud of dust surrounding the large young planet, and inferred that the cloud was a circumplanetary disk. They estimated the disk's mass at between .002 to .0042 times the mass of the Earth, or somewhere around a quarter the mass of our own Moon.

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