The solar system may have ejected worlds the size of the moon and Mars into interstellar space


Previous research has found that when planetary systems form, a good number of worlds may not stay tied to their parent star, but instead be thrown into deep space. Astronomers have already discovered a handful of these floating worlds (sometimes referred to as “rogue planets”), such as 2MASS J1119-1137, which is four to eight times the mass of Jupiter and is about 95 light years from Earth.

Planets without stars may not be rarities. “A surprising result a few years ago was that there were as many as one or two Jupiter-sized floating planets per star,” says astrophysicist Thomas Barclay of the NASA Ames Research Center in California.

Until now, known orphan worlds have all been large enough that current observatories can discover them in the vast spaces between stars – gas giants like Jupiter and Saturn, instead of rocky planets like Earth and Mars. Still, the upcoming Wide Field Infrared Survey Telescope (WFIRST), an infrared space observatory that NASA plans to launch in the 2020s, “could find land mass and potentially Martian mass material,” Barclay said.

To see how many rocky nomadic worlds could exist, the researchers developed computer models simulating a star of the mass of the sun surrounded by 26 planetary embryos each about a tenth of the mass of the earth and 260 planetesimals each of about a hundredth of the sun. the mass of the Earth. (Mars is about 10.7% of Earth’s mass, while the Moon is about 1.2% of Earth’s mass.)

Scientists ran 150 simulations where planetary systems had two giant planets the mass of Jupiter and Saturn and 150 without these gas giants. These simulations each lasted 2 billion years, allowing all of these bodies to gravitationally attract each other and collide and stick to each other or come apart.

In simulated planetary systems without giant planets, “very little mass is ejected,” Barclay said. At most, bodies no bigger than a few times the mass of the moon would leave.

In contrast, when the stars had giant planets orbiting them, the powerful gravitational pulling forces of these massive worlds gave these planetary systems enough energy to project bodies up to three times the mass of Mars. outward to become rogue planets. Overall, these planetary systems ejected about five times the mass of Earth’s bodies, about half of which was the size of Mars or larger, while the other half was roughly the mass of the moon.

In simulated planetary systems with giant planets, there were two ejection epochs, Barclay said. The first epoch occurred during the first millions to tens of millions of years of the simulations, and projected relatively pristine primordial material. The second epoch occurred about 100 million years ago in the simulations, consisted of the results of impacts between bodies, and included larger bodies that formed from these collisions.

Overall, “we would expect to find something like seven or eight mass floating planets of Mars per star in the galaxy,” Barclay said. “If giant planets are common, we will find a lot of them; if giant planets are rare, we will find few. Our theoretical study has strong predictions that can be tested with future observations currently planned.”

However, “very few rogue planets had land mass,” Barclay said. This was mainly because most of the bodies were ejected before the time frame needed to develop a land mass world.

Although these simulations were run with stars similar to the Sun, “we wouldn’t expect to see very big differences for different types of stars,” Barclay said. “However, we want to run simulations to confirm this suspicion.”

Barclay warned that scientists “still don’t have a fantastic model of how the solar system was formed, let alone models of how other planetary systems were formed,” Barclay said. “Learning more about rogue planets could help us learn more about the formation of planetary systems – what is conserved and what is discarded. “

Barclay and his colleague Elisa Quintana detailed their findings Oct. 19 at the American Astronomical Society’s Division of Planetary Sciences and at the European Planetary Science Congress in Pasadena, California.


Arline J. Mercier