Now let's turn to what's interesting about these two systems. First, both stars are quite young (less than 100 Myr) - this means their planets are still hot from their formation, making them easier to detect. It also means that much of the debris from planet formation still remains in the system, in the form of dust rings surrounding the planets. These dust rings are much, much brighter than the planets themselves due to the much higher surface area available to radiate (look at the picture of Fomalhaut for a good idea of this), and this has lead many researchers to design ways to search for the presence of planets around young stars by looking for patterns in the dust created by their orbits. These new detections corroborate these techniques - patterns can be seen in the dust that can be directly attributed to the planet, and help constrain the mass of the planet.
The second (and I think more interesting) fact is that all the planets are at very large distances from their parent stars - the three planets around HR8799 are between 25 and 70 AU (astron. units - Earth-Sun distance), while the planet around Fomalhaut has an orbital radius of 100 AU!! For reference, the farthest giant planet in our own Solar System (Neptune) is thought to have formed at 15 AU from the Sun. How do these massive planets form so far out? Is it because the stars are larger? This seems like it might explain the planet at 25 AU, but the others are really pushing it. Do they form like stars - by collapsing out of the young protostellar cloud? These planets form the opposite endpoint of the "Hot Jupiter" planets first discovered by radial velocity surveys - and they look like they will have the same mind-blowing effect on the planet formation community.
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