(ORDO NEWS) — So far, astronomers have discovered over 5,000 confirmed exoplanets, with thousands more awaiting confirmation, and many billions more awaiting discovery.
These exoplanets come in a huge variety of sizes, compositions, orbital periods, and just about every other feature that can be measured.
The study of exoplanets has also made it possible to learn more about the solar system. We used to think of it as an archetypal arrangement of planets, but now we know why we don’t have a Super-Earth.
Super-Earths are a class of planets that are common around other stars.
They are determined only by mass, from 2 to 10 masses of the Earth. Even though planet hunters have discovered over 1,500 of them, there are none in the solar system.
Professor of planetary astrophysics Stephen Kane from the University of California decided to find out what would happen if a super-Earth appeared in our solar system.
How will this change our solar system? Will a Super-Earth bring our solar system more in line with some of the other systems we see in the Milky Way? Will the solar system be recognizable at all?
To find out, he created a simulated Super-Earth in a simulation of our solar system.
The paper resulting from the study “Dynamical Consequences of the Super-Earth in the Solar System”, for which Kane is the sole author, has not yet been peer-reviewed.
In his paper, Kane points out the gap between the size and mass of the planets in our solar system and what that means for researchers.
Computer models and simulations are now an important part of astronomy, and over time they are becoming more detailed and powerful.
The researchers change the input data to see how objects such as solar systems and planets form and behave under different conditions.
In this work, Kane placed a Super-Earth in the solar system to see what would happen.
Kane added planets with masses between 1 and 10 Earth masses in increments of 1 Earth mass. He placed the planet in different starting positions in circular orbits.
The orbits were coplanar with Earth’s, and the semi-major axis ranged from 2 to 4 astronomical units (AU) in 0.01 AU increments.
Simulations showed that the inner planets were more prone to instability due to the addition of Super-Earth than the outer planets.
“A wide area of 2-4 a.u. contains many MMR (mean motion resonance) sites with inner planets that further enhance the chaotic evolution of the inner solar system,” the paper says.
“Chaotic evolution” is putting it mildly. The addition of a Super-Earth changes the relationships between the planets and changes the entire architecture of the inner solar system.
Poor Mars only got halfway through the simulation and then got thrown out.
Mercury only made it one third of the way through the simulation before interactions with Venus and Earth and their increasing eccentricities imparted a torque to Mercury’s orbit, pushing it away.
In another simulation run, Kane placed an 8-Earth-mass Super-Earth at a distance of 3.7 AU.
This resulted in a slight initial increase in the eccentricities of Earth and Venus, which then, combined with the influence of Jupiter, changed Mercury’s orbit so much that it was quickly ejected again.
The catastrophic removal of Mercury then changed the Earth and Venus, giving them angular momentum in their orbits.
“This leads to a significant periodic evolution of their orbits, with both high-frequency and low-frequency changes in their eccentricities,” writes Kane.
Mars’ orbit is relatively unaffected in this scenario, although its eccentricity is “subject to high frequency oscillations due to interactions with the outer planets.”
The outer part of the solar system has also changed, although not as much. When the simulations placed the 7 Earth mass planet at 3.79 AU, little happened at first. But in the end, there are drastic changes.
The orbit of the Super-Earth is changing, and its semi-major axis reaches 30 AU. In about 4 million years, Super-Earth will be ejected from the system.
Its ejection conveys angular momentum, and this has “a significant effect on the eccentricities of Saturn, Uranus and Neptune,” Kane explains.
In another simulation, the introduced Super-Earth also had 7 Earth masses, and the AU changed only slightly, from 3.79 to 3.8.
The super-Earth was ejected again, and Jupiter and Saturn experienced increased eccentricity. A small change also resulted in the loss of Uranus.
Kane performed several thousand simulation runs, and depending on the parameters, some of the inner planets were ejected, as was the Super-Earth implanted in the system.
In other architectures, ice giants were also thrown out. But outlier is only one outcome, albeit the most extreme.
Simulations have shown that the presence of a Super-Earth can make the orbits of other planets more eccentric.
This could wreak havoc on the planet’s climate, as temperatures fluctuate greatly depending on where the planet is in its eccentric orbit.
“These interactions lead to large amplitude oscillations in the orbital eccentricities of Venus and Earth, creating Milankovitch cycles that could potentially affect the long-term climate of these planets,” Kane concludes.
There are many super-Earths, and it remains an open question how much their presence affects habitability in other systems.
“The dependence of planetary climate on orbital interactions with Super-Earths will require additional atmospheric data and modeling to determine whether the presence of such planets (or their absence) may predominantly lead to climate effects due to eccentricity,” explains the author.
Kane calls the lack of a Super-Earth a “double-edged sword”. On the one hand, we don’t have the ability to study Super-Earth as closely as we can study terrestrial planets, gas giants, or ice giants.
But the presence of a Super-Earth could completely change the solar system and potentially have catastrophic consequences for life.
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