Up until the last few decades ago, our picture of what might be the distant stars, which is the only one of the planets, moons, asteroids, and other bodies in our own solar system. But the discovery of thousands of exoplanets has dramatically improved our picture of what's out there in terms of large bodies. Comets and asteroids, by contrast, are undoubtedly in the future.
Moons, however, are awkwardly in between. It should be possible to image them as their gravitational influence. And we might as well get a more direct indication of their presence.
But now scientists are suggesting that they have been examined the making. By looking at some planets forming a young star, they think they have spotted a disk around one of the planets.
Moon formation, in theory
The formation of moons is thought to be tied up in the formation of planets Themselves. Young stars are surrounded by a disk of material, including gas, dust, and ice at various distances from the star. Once planets begin to condense from this material and grow above a critical mass, they'll clear out of space within their orbit within the disk.
But the disk is dynamic, so some of the material within this gap will eventually flow into it, falling under the planet's gravitational influence. (Technically, the planet grabs something passing through its hill radius.) This will form a disk similar to the one orbiting the star. Some of its material wants to flow into the planet, increasing its mass. But some of the material will stay in orbit, where it can form moons. [circumplanetary disks] The birthplace of satellites is the main moons of Jupiter and Saturn. "
A small international team of astronomers decided to It is centered on a young star that is somewhat smaller than Earth, with a large disc that includes a suspicious gap. Two likely planets are present in the gap, with one being the first exoplanet ever to have been imaged directly.
This combination of features-planets has created a gap in the star's planet-forming disk-design moons could form. Conveniently, the researchers did not even have any new observations to look at. It has been published observations done with the ALMA telescope.
Rings and things
The ALMA images show a large disk orbiting the star but a good short of it. There's also a faint inner disk that is itself embedded in. ALMA so picks up the two known bodies in the gap, termed PDS 70b and PDS 70c. The latter is right near the inner edge of the disk and difficult to resolve from it.
Things get a bit weird, however, when you compare those images with infrared data on the same system. But they also suggest the outside planet is hauling material out of the nearby area. Meanwhile, at PDS 70b (the inner planet), there's a blob of dust nearby-but it does not seem to be centered on the planet.
The authors interpret these images as showing that PDS 70c is forming a proto-lunar disk as it's funneling additional materials into the planet itself.
Meanwhile, things at PDS 70b are even stranger, given where it appears to be a circumplanetary disk-but it's not located where the planet is. "We do not currently have any robust interpretation," the authors acknowledge. Orbital location called a Lagrange point. We just can not tell at this stage.
All of this provides evidence that our models of moon formation are probably on the right track. And, if they do form these plans, it's going to be most impressive. Due to its large mass and current heat content, PDS 70c is estimated to be about three times the size of Jupiter; the disk that surrounds it is to extend to the distance between the Earth and the Sun. Even if it does form a large collection of moons, however, they will remain difficult to image, as the planet's orbital plan would prevent them from using either method.
Astrophysical Journal Letters 201