A (hypothetical) planet to end life on Earth
End life on Earth with a planet?
If a planet had formed between Mars and Jupiter, where the asteroid belt now reigns, it might have meant the end of life on Earth. That’s the conclusion of a researcher at the University of California, Riverside, who said on March 7, 2023, that he has now looked closely at this realm of our solar system. He said his computer simulations suggest that an Earth-like planet – orbiting between Mars and Jupiter – would have pushed Earth out of the solar system and wiped out life on this planet.
Astrophysicist Stephen Kane is the sole author on the peer-reviewed study, which attempts to understand two different sorts of “gaps.” The Planetary Science Journal published Kane’s study on February 28, 2023.
Last chance to get a moon phase calendar! Only a few left. On sale now.
Understanding gap #1
The first gap Kane wanted to understand is a gap in distance between the four small rocky planets in our solar system (Mercury, Venus, Earth and Mars) and the four large gas giant planets (Jupiter, Saturn, Uranus, Neptune).
The regular placement of planets in our sun’s family – known about and described since the 1700s by what astronomers call Bode’s Law – suggests there should be a planet between Mars and Jupiter. But no planet exists there.
Instead, that gap in space contains the asteroids, or what we today call the asteroid belt. Could the asteroid belt once have been a planet? It’s likely the final verdict on this question isn’t in yet. But, over time, we’ve learned that if all the mass in the asteroid belt came together to form one body, it wouldn’t be much of a planet. In fact, it’d contain barely half the mass of the dwarf planet Pluto.
Understanding gap #2
The second gap addressed by Kane’s study is a gap in size, or, more accurately, in mass. Earth is the most massive of the four terrestrial planets. And Neptune is the least massive of the four gas giant planets. Yet Neptune is 17 times more massive than Earth (it’s also four times wider).
Meanwhile, among the 5,000-plus exoplanets astronomers have discovered so far, orbiting other stars, we know plenty of planets with masses between that of Earth and Neptune. So why doesn’t our solar system have planets in that mass range? As Kane said:
In other star systems there are many planets with masses in that gap. We call them super-Earths.
Simulating a non-existent planet
These two sorts of “gaps” – the gap in distance and the gap in size – prompted Kane to do what astronomers often do when perplexed by an outer space mystery. He ran computer simulations. In other words, with a computer, he placed hypothetical planets of various masses – including those that would be considered super-Earths – into the area of space between Mars and Jupiter.
Then he ran the simulation forward in time, and watched what happened. The results were disastrous, for our sun’s third planet … and for the sun’s first and second planets, too.
Giant Jupiter’s imaginary field day
Consider that the hypothetical super-Earth was being inserted – via computer simulation – between Mars and Jupiter. And now consider Jupiter’s mass. It’s our solar system’s most massive planet, with more than twice the mass of all the rest of our sun’s planets combined. Since gravity and mass are linked, Jupiter has an out-sized gravitational influence as well. If a hypothetical super-Earth had existed in the realm of today’s asteroid belt, it would have disturbed Jupiter’s orbit.
Then, in turn, Jupiter would have disturbed the orbits of all the other planets. As Kane’s statement from UC Riverside explained:
Depending on the mass and exact location of a super-Earth, its presence could ultimately eject Mercury and Venus as well as Earth from the solar system.
It could also destabilize the orbits of Uranus and Neptune, tossing them into outer space as well.
The super-Earth would change the shape of this Earth’s orbit, making it far less habitable than it is today, if not ending life entirely.
Only when Kane shrunk the imaginary planet down and put it directly between Mars and Jupiter did it achieve a stable orbit in his simulations. However, small nudges one way or another would again throw off our solar system as we know it. Kane said:
This fictional planet gives a nudge to Jupiter that is just enough to destabilize everything else.
So, he commented, it’s a good thing the super-Earth isn’t there!
Life in other solar systems
Kane’s experiment might shed light on the ability of life to flourish (or not) on planets in other solar systems. A gas giant planet (say, with the mass of Jupiter) near neighboring Earth-like planets or super-Earths might decide the fate of the orbits of those distant worlds … and the potential for life to evolve.
Of the systems discovered so far, planets with the mass of Jupiter tend to orbit closer than our Jupiter to their stars. Astronomers have found gas giants far from their stars, like Jupiter, in only about 10% of distant solar systems.
Kane said his study caused him to reflect on our own solar system’s framework. He said:
Our solar system is more finely tuned than I appreciated before. It all works like intricate clock gears. Throw more gears into the mix and it all breaks.
Bottom line: Is there a planet that could end life on Earth? Not that we know of. But computer simulations by a scientist at the University of California, Riverside suggest that a hypothetical super-Earth orbiting in the space between Mars and Jupiter would be bad news for Earth and earthly life.
Source: The Dynamical Consequences of a Super-Earth in the Solar System