Our solar system is unique in more ways than we imagined. Of course, it’s the only one discovered so far that has life. But, there’s also a distinct lack of super-earths close to our sun.
“Now that we can look at our own solar system in the context of all these other planetary systems, one of the most interesting features is the absence of planets inside the orbit of Mercury,” said Gregory Laughlin, professor and chair of astronomy and astrophysics at UC Santa Cruz and coauthor of the paper. “The standard issue planetary system in our galaxy seems to be a set of super-Earths with alarmingly short orbital periods. Our solar system is looking increasingly like an oddball.”
Laughlin and his fellow researchers tackle this mystery and have found a culprit. Jupiter.
Blaming Jupiter isn’t new. A team of astronomers in 2011 also pointed the finger at Jupiter in a scenario known as the “Grand Tack.”
Grand Tack explains that before Jupiter reached the orbit it’s at today, it migrated towards the sun. It wouldn’t be until the formation of Saturn that it would migrate to its current orbit.
Konstantin Batygin, coauthor of the paper, performed a series of numerical calculations to see what would happen if a set of rocky planets were close to the sun when Jupiter migrated towards the sun.
As Jupiter edged closer to the sun, gravity from the gas giant would have pushed the inner planets into overlapping orbits. This would have set off a massive chain reaction of collisions.
Laughlin compares it to what would happen if satellites were destroyed in low-Earth orbit. “Their fragments would start smashing into other satellites and you’d risk a chain reaction of collisions. Our work indicates that Jupiter would have created just such a collisional cascade in the inner solar system,” Laughlin said.
What happened to all the debris? Most of it would have been pushed into the sun according to researchers.
Today’s innermost planets would have formed from whatever debris was left over. This lines up with evidence that the four planets closest to the sun are younger than the outer planets. Plus, they are less massive and have thinner atmospheres than other planetary systems according to Laughlin.
“One of the predictions of our theory is that truly Earth-like planets, with solid surfaces and modest atmospheric pressures, are rare.”
The press release goes into a bit more detail about Jupiter and its migration towards the inner system.
According to Laughlin, the formation of giant planets like Jupiter is somewhat rare, but when it occurs the giant planet usually migrates inward and ends up at an orbital distance similar to Earth’s. Only the formation of Saturn in our own solar system pulled Jupiter back out and allowed Mercury, Venus, Earth, and Mars to form. Therefore, another prediction of the paper is that systems with giant planets at orbital periods of more than about 100 days would be unlikely to host multiple close-in planets, Laughlin said.
Previous research supports the idea of Jupiter moving towards the sun and back out. The researchers’ paper looks at the consequences of a migrating Jupiter. “Jupiter’s ‘Grand Tack’ may well have been a ‘Grand Attack’ on the original inner solar system,” Laughlin said.
Obviously our solar system is an outlier. So far, life is only found on Earth. The research above shows even the layout of our solar system is rare. I want to see if their prediction of giant planets at orbital periods of more than about 100 days limiting multiple close-in planets holds up. If it does, it could give astronomers a new parameter when it comes to searching for planetary systems like ours.
The paper was published in the Proceedings of the National Academy of Sciences.