What would happen if we had an extra planet in our solar system? Not marginally like the hypothetical planet nine far behind Pluto but right in the middle of Mars and Jupiter?
Such a world would devastate the orbits of most planets, according to new research simulating a super earth — a term used for worlds more massive than Earth but lighter than gas giants — and chronicled the fates of all eight planets. The results show that minute changes in the orbit of Jupiter, which is more massive than all other planets combined, have profound and devastating effects on the finely balanced orbits of other planets.
“Everything works like complicated clockwork,” said Stephen Kane, an astronomer at the University of California at Riverside and the study’s sole author, in a opinion (opens in new tab). “Throw more gears into the mix and it all collapses.”
Related: Super-Earths: Exoplanets close to the size of Earth
For a long time, our solar system was considered the template for all planetary systems. However, over the past 25 years, it has quickly and firmly become an outlier for not having a super-Earth of its own.
NASA exoplanet hunting missions such as Kepler and Transiting Exoplanet Survey Satellite (TESS) have led astronomers to realize that such planets are surprisingly common in the Milky Way: a third of all exoplanets are super-Earths. They think our solar system doesn’t have a super earth because Jupiter its emergence suppressed when it moved significantly towards the asteroid belt and back again during which it Posted much material on the sun. As such, they find it difficult to understand such worlds, which are common in other solar systems, lacking local data that would otherwise help them model compositions and other properties.
This “has been a source of frequent frustration” in the exoplanet community, Kane told Space.com in an email. “My study was therefore intended to answer the question: What if your wish came true?”
The inner four planets are particularly vulnerable
Super-Earths can be anywhere from two to ten times that size as big as our planet, so Kane simulated planets of different masses and placed them at several distances in the main asteroid belt between Mars and Jupiter. He started with a super-Earth at twice the distance between the Earth and the Sun, or 2 astronomical units (AU; 185 million miles or 297 million km) and increased the distance to the outer edge of the asteroid belt to 4 AU (371 million miles or 597 million km). This led to thousands of simulations, each starting in the present day and ending 10 million years later. Every 100 years, Kane recorded the consequences for each of the eight planets in the solar system.
These results showed that all four inner planets – Mercury, Venus, Mars and Earth – are particularly susceptible to changes in orbit; In many cases, some or all four planets have been ejected from the solar system. None of the thousands of simulations showed the departure of Jupiter or Saturn. But in some cases, the two gas giants have dumped other planets, including the newly added super-Earth itself as well as Uranus, wreaking havoc among its moons.
“I wouldn’t get too much hope that the moons will stay in stable orbits around the planet when it’s ejected from the solar system,” Kane said.
When a planet is seven times the mass of Earth Gliese 163c placed slightly behind Mars, the simulation showed that the orbits of all four inner planets became unstable. The orbits of Earth and Venus became eccentric or ovoid enough that they had “catastrophic close encounters”. The change in their orbits then released energy that was transferred to Mercury and ejected shortly thereafter. Mars survived only halfway, and Earth and Venus made their way about eight million years ago.
Gas giants can hold their own
Unlike terrestrial planets, gas giants, particularly Jupiter and Saturn, were less affected by the additional planet. Their orbits were only slightly unstable at mean-motion-resonance (MMR) locations — specific locations where two planets have orbital periods that are a simple integer ratio to each other. (For example, an object in a 3:1 MMR with Jupiter orbits the Sun exactly three times for each Jupiter orbit.)
So immediately placed with Kane Gliese 163c-like Super-Earth in the outer reaches of the asteroid belt at 3.8 AU, it ended up in an 8:5 MMR with Jupiter and a 4:1 MMR with Saturn. As a result, the orbits of both gas giants become more ovoid, so much so that they first removed super-Earth and later Uranus. Kane’s study found that in this case even the smallest change in the outer solar system greatly affected the inner planets; For example, Mars was ejected a few million years after Uranus.
“What surprised me most about the study was the sensitivity of the entire Solar System architecture to Jupiter’s resonances,” Kane said in an email to Space.com.
The addition of a super-Earth is least messy, according to the study, when the planet is placed at the end of the asteroid belt near 3 AU (278 million miles or 447 million km). Here it would interact minimally with giant planets and hardly disturb the solar system, argues Kane.
In this case, “a major gap that needs further exploration is the stability of the solar system on longer timescales (let’s say 1 billion years),” Manasvi Lingam, an astronomer at the Florida Institute of Technology who was not involved in the study , Space.com said in an email.
Overall, the study shows “how important Jupiter is to the dynamics of the solar system,” Kane told Space.com, “and that even relatively small changes can make a huge difference in the stability of our system.”
Super-Earths may be common in most solar systems because giant planets like Jupiter are rare: only 10 percent of Sun-like stars harbor giant planets at distances from the Sun like ours, and the number drops even further for older stars.
According to Kane, researchers have often speculated whether our solar system could safely harbor another planet between Mars and Jupiter, and the answer seems to be a resounding no.
“If you’re an exoplanet human and you find a genie in a bottle, please don’t wish the solar system had a super-Earth,” Kane said tweeted (opens in new tab). “You could inadvertently destabilize the solar system!”
The research is described in a Paper (opens in new tab) published February 28 in Planetary Science Journal.
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