We just observed the first ‘lunar formation’ in an exoplanetary system.
This one image, above, is the first to show moons actively forming around a planet.
The system’s central star, PDS 70, lies ~400 light-years away on the edge of the constellation Centaurus.
Two planets have been found: PDS 70b and 70c.
The latter contains a circumplanetary disk, newly revealed for the first time ever.
In theory, planets only acquire moons through three main processes.
1.) The giant impact scenario: leading to debris clouds around rocky bodies.
That debris then coalesces into satellites: like Earth’s, Mars’s, and Pluto’s moons.
2.) Gravitational capture: explaining Saturn’s Phoebe and Neptune’s Triton.
3.) A circumplanetary disk: likely explaining most of the Universe’s moons.
Stars and planets form from a cloud of collapsing gas, leading first to a proto-star.
A disk of planet-forming material rapidly coalesces around it: a protoplanetary disk.
Infrared and radio observatories have revealed these gap-rich disks in detail.
Every gap contains planets, which capture/clear the surrounding material.
However, the largest planets accrete their own disks: forming moons.
This connection explains why Jovian moons resemble low-mass exoplanetary systems.
Only PDS 70c has a circumplanetary disk; the next step will measure internal gas motions.
Perhaps, soon, we’ll understand the specifics of the emerging lunar system.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.
Starts With A Bang is written by Ethan Siegel, Ph.D., author of Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.