The current state of knowledge suggests that the Earth formed within 100 million years of the birth of the Sun — but there’s been a lot of debate about this number, as well as questions over just how representative of other stars it may be. Theoretically, planetary formation should take place much more quickly — in less than 10 million years — but there’s been no observational support for this.
A team led by Johny Setiawan of the Max Planck Institute for Astronomy in Heidelberg, Germany has found a young planet around the star TW Hydrae. And I do mean young — the star itself is only about 10 million years old, so the planet must be of comparable (or younger) age. This is so young that the planet is still in the midst of the star’s protoplanetary disk. So other planets are likely still forming, at least until the star gets really active and blows all the small leftovers away, like a construction crew cleaning up at a worksite.
In a sense, the discoverers of this new world got lucky. They used the radial velocity approach to find it, looking for faint wobbles in the host star’s motion. So fortunately for them, the planet (given the not-so-endearing name of TW Hya b) is a whopper — between 5.5 and 13 times the mass of Jupiter! It’s also VERY close to its parent star, orbiting at about 1/10 the distance from its sun as Mercury does from ours. This means things happen very fast on the young planet, since its year is only 3.6 of our days long.
The original study will be published in Nature later today, so expect to see lots of commentary on this over the next few days. Over a longer span, this should really liven up the long-running debate over the myriad paths that planet formation can follow.
Meanwhile, here is some further reading for the astronomically inclined: