Astronomers have discovered a small, compact source embedded in a gap in the disk surrounding a young star. They believe it is a baby planet in the process of growth.
Protoplanetary systems offer rare insights into the evolutionary history of solar systems like our own. We already know from extensive observations and theories that solar systems begin as huge clouds of interstellar gas that then compress and begin to rotate. Eventually this spinning gas flattens out into a disk and planets begin to form around a central core.
While we understand the general picture very well, we don’t understand the details of planet formation, particularly the differences between inner rocky planets and outer giant worlds. So the more directly we can observe protoplanetary systems, the better our understanding can be.
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Unfortunately, the process of planet formation takes place over millions of years, so we can’t just stare at a system and watch it evolve before our eyes.
Or can we?
A team of astronomers has released a series of observations of the system, called HD169142, going back almost a decade. This system has a very fortunate orientation as it appears from the front of our field of view, giving us a full view of the entire system. The system itself is a disk forming planets.
A planet cuts a gap in a protoplanetary disk in the system HD 169142. (Image credit: Hammond et al.)
Previous observations had already identified an annular gap in the disk, located about 37 AU from the central star. Subsequent observations discovered a small object embedded in this gap. The team made repeated observations over several years and found that the small, compact object was moving.
The team argues that they are watching a baby planet move around a star. They believe it is a planet because the bright source’s motion coincides with the typical Keplerian motion of a planet around a star. Second, the edges of the gap are very bright, which is expected from theoretical simulations where a planet’s gravity has carved a gap in the disk.
Eventually, the team observed spiraling structures in the disk emanating from the gap. This is also expected from theoretical calculations based on the planet’s gravitational influence on the rest of the disk.
They believe this protoplanet is about the mass of Jupiter and is still in the process of formation. It has already accumulated a lot of gas and is removing that gas from its ring, and more gas is likely being channeled from the surrounding disk onto the planet. We don’t yet have the observational capabilities to determine if other planets are forming within the disk, but continued study of this baby system may shed light on how planets like our own Jupiter form.
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