Whenever we think we’ve got a good grasp on how things work out in space something comes along and tells us otherwise. In this case it’s our models of how planets and star systems form. Astronomers in Chile recently discovered four enormous gas giants in a star system that should be far too young to have formed these massive planets.
CI Tau is a baby. It’s only two million years old and still surrounded by its protoplanetary disk, the swirling mass of dust that will eventually form into planets as gravity and time continue to work their weird magic on the system. The strange thing is that in this protoplanetary disk are conspicuous gaps, and in those gaps are already-formed massive gas giants. Scientists have no idea how they got there.
One of the planets, the closest to CI Tau was already known to astronomers. This monster of a planet—known as CI Tau b— is about 10 times the size of Jupiter and orbits CI Tau once every nine days. When astronomers discovered CI Tau b, it was the first so-called “hot Jupiter” ever discovered around such a young star. Hot Jupiters are gas giants that orbit their star at very close distances and very high speeds. CI Tau b is closer to its sun than Mercury is to ours. Hot Jupiters already seem to defy assumptions about how solar systems form, and finding one around such a young star was even stranger. The other hot Jupiters found belonged to star systems hundreds of times older than CI Tau b. Now it turns out that this anomaly of a planet has three other neighbors that are even more surprising and strange.
The discovery of the three new planets was detailed in a new paper published in The Astrophysical Journal Letters. The next planet out from CI Tau b is about the size of Jupiter, and orbits CI Tau at a distance of 13 AU (Astronomical Units, one AU is the distance from Earth to the sun, about 93 million miles or 150 million kilometers). Further out are the two most mysterious planets in the system. These are both about the size of Saturn and they orbit at distances of 39 and 100 AU. Yet another thing that makes this system so strange is that the outermost planet is 1000 times further away that the innermost planet, a variance in distance that is hardly ever seen in star systems. At such extreme distances it’s supposed to take a very long time for Saturn-sized planets to form. According to Professor Cathie Clark, lead author of the paper:
“Saturn mass planets are supposed to form by first accumulating a solid core and then pulling in a layer of gas on top, but these processes are supposed to be very slow at large distances from the star. Most models will struggle to make planets of this mass at this distance.”
More observations of these bizarre planets will be required to even being to make sense of how they formed. Regardless of what we find,it will likely further challenge our assumptions of how planets are formed. Especially if we find an alien planet manufacturing factory hiding in the protoplanetary disk. Likely? No, not at all. But it would be pretty cool.