KEPLER-62F, A SUPER-EARTH-SIZE PLANET ORBITING A STAR SMALLER AND COOLER THAN THE SUN, ABOUT 1,200 LIGHT-YEARS FROM EARTH. (NASA AMES/JPL-CALTECH/TIM PYLE)
What if, without warning, a fortified Earth appeared between Mars and Jupiter? This mind-boggling topic is at the heart of a new study that investigates the potential impact of “super-Earths,” a type of planets that is surprisingly frequent in other star systems, on our solar neighborhood.
The discovery of an exoplanet in this region of our solar system poses a number of threats to life on Earth. These include direct impacts with the Sun and possible ejection from the solar system. Even larger planets, such as the ice giants Uranus or Neptune, might be thrown out of the solar system by super-Earths, which can be anywhere from 1.5 to 10 times as massive as Earth.
Even while it’s a lot of fun to speculate about how this might shake up our solar system, that’s not the only point of the thought experiment. In a broader sense, though, these hypothetical super-Earths can “provide important insights into the question of how typical our solar system architecture and evolution is compared with other planetary systems,” as one recent study in the Planetary Science Journal authored by University of California Riverside planetary astrophysics professor Stephen Kane put it.
“There are many planets in between the size of Earth and Neptune,” Kane told Motherboard in a phone interview. “something which is maybe twice the size of the Earth,” Neptune is around 2.4 times the size of Earth. As a result, “because we don’t have an analog to that kind of planet within our solar system, it has been a source of great lament amongst planetary scientists and exoplanet folks who wish that we did have a super-Earth, say between the orbits of Mars and Jupiter” that “we could study in detail.”
And because “wishing that we had a super-Earth within the solar system” is a topic that frequently arises in discussion, he said, “I really wanted to investigate this and say, ‘right, let’s just suppose our wish came true. How would that manifest itself? What would happen then, exactly?
Strange gravitational effects have been detected in the solar system’s extreme reaches, leading some scientists to speculate that there may be a planet lying roughly 20 times further from the Sun than Neptune. Planet Nine is a made-up planet whose existence is very debatable; it might be a massive super-Earth. Even if a super-Earth were concealed beyond the currently known planets, sending a space expedition to it would be extremely challenging.
The lack of a known super-Earth in our solar system is disappointing to those who research these unusual planets because of the numerous issues they raise that could be answered by a closer inspection. For example, it is unclear whether or not any super-Earths would be hospitable to life—potentially even more so than Earth-like planets—or at what point rocky planets like Earth transition into tiny gas giants like Neptune and Uranus.
Even while it seems that super-Earths are common in the Milky Way, and several have been discovered in the systems that are nearest to us, little is known about their habitats. Adding one to our solar system with the waving of a wand would allow us to examine it more closely.
When asked what the solution was, Kane stated, “we should be careful what we wish for,” citing the findings of his hundreds of simulations in which super-Earths of varying masses were added to our current system and the effects were simulated over a period of 10 million years.
These new worlds, according to Kane, are located between two and four au from the Sun (one au is the distance between the Sun and Earth). The super-Earths migrated to the main asteroid belt from this distance, filling the enormous void between the orbits of Mars and Jupiter. Mean motion resonances (MMRs) are correlations between the orbital frequencies of different planets that might affect their paths around a star, and they were usually triggered by the presence of these worlds in this area.