One of the best things about the sheer number of exoplanets that astronomers are currently finding is how some are just very different. Those differences can sometimes undermine standing theories, and prompt scientists to start considering new theories that account for the new information. That is undoubtedly what will happen to accommodate a new massive planet found by a team led by Dutch scientists. This planet is unique in one very special way – it is about 110 times farther away from its star than the Earth is from the sun.
The star and accompanying planet are located in the southern constellation Musca about 360 light years away from Earth. Known as YSES 2b, the planet was found by the Young Suns Exoplanet Survey (YSES) which uses data from the Very Large Telescope to search for young stars. The one YSES 2b is orbiting is only 14 million years old, but resembles what our own sun would have looked like at that age.
There is no planet like YSES 2b around our current sun though, and its existence has some interesting implications for models of the early solar system. Three potential explanations were put forward as to how such a massive planet could form so far out from the star.
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First would be that it simply grew out of the protoplanetary disc, which is the most common method of planetary formation. However, models of those early stage discs suggest that not enough material would be available in the disc to form a planet six times the size of Jupiter that far away from the parent star.
Another possible explanation is that there was some gravitational instability in the planetary disc, causing material to collect at the planet’s distant location. For that to be the cause, there would have to be lots of material out in that space in order to cause the instability. Right now there doesn’t appear to be enough of it to do so.
The final explanation is that the planet formed much closer to the star, and then migrated out to its extreme distance over the last few million years. A similar thing is posited to have happened with the gas giants in our own solar system known as the Grand Tack Hypothesis. Scientists would expect some other force to cause that migration though. Most usually that force would be caused by a second planet, but scientists don’t see one that could have caused the gravitational disturbance to send the planet out far enough to end up where it is now.
While all three processes have arguments against them, it is still possible that one or more did in fact create YSES 2b. But a more interesting prospect is that there was some other process that created it, and which would be new to science. More study is needed, including seeing if the planet is indeed moving or potentially increasing in mass, which could shed more light on the finding. Until then astronomers, including the ones running the YSES survey, will continue to search out wonderfully bizarre exoplanets.
Astronomie.nl – Giant planet at large distance from sun-like star puzzles astronomers
Astronomy & Astrophysics – Discovery of a directly imaged planet to the young solar analog YSES 2
Daily Galaxy – Exoplanet Mystery –”The Gas Giant That Should Not Exist”
Sci-news.com – Astronomers Directly Image Giant Planet around Young Sun-Like Star
Bad Astronomy – Astronomers Find An Exoplanet Where An Exoplanet Shouldn’t Be
Direct image of the planet YSES 2b (bottom right) and its start, which is being blocked by a coronagraph in the center of the image.
Credit: ESO / SPHERE / VLT / Bohn et all