The little spot in this picture might be the main glance at first look at exomoons in the making


New telescope images may provide the primary view of moons forming outside the system .

The Atacama Large Millimeter/submillimeter Array in Chile glimpsed a dusty disk of probably moon-forming material around a baby exoplanet about 370 light-years from Earth. The Jupiter-like world is surrounded by enough material to form up to 2.5 Earth moons, researchers report online July 22 within the Astrophysical Journal Letters. Observations of this technique could offer new insight into how planets and moons are born around young stars.

ALMA observed two planets, dubbed PDS 70b and 70c, circling the star PDS 70 in July 2019. Unlike most other known exoplanets, these two Jupiter-like worlds are still forming — gobbling up material from the disk of gas and mud swirling around their star. During this formation process, planets are expected to wrap themselves in their own debris disks, which control how planets gain material and form moons.

Around PDS 70c, ALMA spotted a disk of dust about as wide as Earth’s orbit round the sun. With previously reported exomoon sightings still controversial, the new observations offer a number of the simplest evidence yet that planets orbiting other stars have moons.

Unlike PDS 70c, 70b doesn’t appear to possess a moon-forming disk. which will be because it’s a narrower orbit than PDS 70c, which is almost as faraway from its star as Pluto is from the sun. That puts PDS 70c closer to an outer disk of debris surrounding the star.

“C is getting all the fabric from the outer disk, and b is getting starved,” says study coauthor Jaehan Bae, an astrophysicist at the Carnegie Institution for Science in Washington, D.C.

“In the past, b must have gotten some material in its [disk], and it could have already formed moons,” Bae says. But to form the new images, ALMA observed wavelengths of sunshine emitted by sand-sized dust grains, not large objects, so those moons wouldn’t be visible.

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