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What if Earth were a super-Earth?

What would happen to life on Earth if the planet were supersized?
(Image: © Shutterstock)

For nearly four years, NASA's Kepler spacecraft whisked through space, surveying our corner of the galaxy. It monitored more than 150,000 stars, looking for planets about the size of Earth that belonged to other solar systems. The mission didn't disappoint; Kepler found countless examples of a type of planet known as a super-Earth

These faraway planets might remind you of home — they're rocky, smaller than gas giants, located near their star and sport a relatively thin atmosphere. But they're way larger than the blue marble: These super-Earths are a honking two to 10 times bigger in mass than our Earth. 

Because there are so many super-Earths out there, it begs the question: What would happen to our planet if it were two or even 10 times the size it is now? 

Related: What if the Earth was flat?

It's possible that Earth and the other inner planets of our solar system were headed in that direction, Mickey Rosenthal, a doctoral candidate studying planet formation at the University of California, Santa Cruz, told Live Science. One theory is that the gargantuan planet Jupiter became so large that it cut off access to cosmic building blocks needed to make the inner planets bigger — effectively starving them, Rosenthal said. 

No matter the reason for Earth's current size, there's no way to truly know what would happen to Earth if it were super. But scientists have some ideas based on what they've learned about our faraway cousins.

For starters, you'd be shorter — you, Mount Everest and every tree in California's Sequoia National Park — because if you increase the size of a planet and keep everything else identical, gravity increases, too. If Earth were twice its size, you'd be heavier, because the force of gravity increases as the planet's density and radius increase. It would take more energy to resist gravitational pull, so the structures we have today wouldn't be strong enough to stand as tall as they do now. 

With a larger planet and stronger gravitational field, Earth would also experience more collisions, Rory Barnes, a theorist who studies planet habitability at the University of Washington, told Live Science. As a superplanet, Earth's greater gravitational pull would effectively attract more and larger asteroids, so "Armageddon-type" collisions would become more of a concern than they are now, Barnes said. 

If the hypothetical super-Earth were even bigger, say, 10 times its current mass, dramatic changes could start happening in Earth's interior. The iron core and liquid mantle would also be 10 times larger, and with more gravity acting on a larger mass, the pressure beneath Earth's surface would increase. This high pressure could cause the iron core to solidify, Barnes said. 

As of now, convection currents in our partially liquid core generate Earth's magnetic field. But if the core solidified, the currents would stop and the magnetic field could be weakened or eliminated, Barnes said. If our magnetic field faded or disappeared, it would be very bad for life on Earth, Barnes said. 

Our magnetic field "shields life on the planet from the nastiness of space," Barnes noted. Without it, charged particles flying through space, also called solar storms, could slam into Earth. And these tiny particles can cause all kinds of problems, including breaking up DNA and increasing the risk of cancer, he said.

Barnes also pointed out that a larger interior could make super-Earth more volcanically active than it is now. As the radius of the planet increases, there's more energy inside and fewer places for that energy to escape. More volcanic eruptions wouldn't be surprising, he said. Plate tectonics, too, would be different on a super-Earth. But the exact effect is still an open question. A larger mantle would also be hotter, possibly causing more vigorous convection currents that would push plates around more. In contrast, it's possible that under the high pressure, the crust would be totally fused together and plate tectonics wouldn't exist at all.

Based on the super-Earths that scientists have found so far, we can't really be certain Earth would even be habitable if it were a super-Earth. The Kepler space telescope was best at detecting planets close to their star — much closer than Earth is to the sun. Most super-Earths known to science are almost as close to their star as Mercury is to our sun. 

For Earth to be comparable, it would need to have an orbit of about 100 days, said Hilke Schlichting, an associate professor of astrophysics at the University of California, Los Angeles. That orbit might be habitable in systems with a star smaller than the sun, but if our Earth were that close to our sun, all of the water on the planet would vaporize, Schlichting said. 

In other words, Earth would be out of the habitable zone and, in essence, would become a steam planet, she said.

Surprisingly, many of the super-Earths discovered so far seem to be water rich, like entire water worlds, Rodrigo Luger, the Flatiron Research Fellow at the Simon Foundation's Center for Computational Astrophysics in New York City, said in an interview. It's possible that these planets formed from large pieces of ice and then later migrated close to their stars, which prompted their ice to melt, he said. 

However, these planets might not be habitable, since their deep oceans plummet to a solid ice layer. This ice is not formed by low temperatures, but by the intense pressure of the super-deep ocean, which forces water molecules into a solid state. This ice layer blocks any interaction between the atmosphere and the planet's interior, meaning there is no carbon cycle (a process in which carbon cycled through the atmosphere, ocean, and crust) or no mineral exchange (which regulates Earth's long term temperature via an interaction between atmosphere and the mantle), according to Luger. That doesn't promote habitability — at least for life as we know it. 

The reality is that scientists have more questions about super-Earths than they have answers. And we don't fully understand the physics of our own interior, much less that of a planet many solar systems away, Luger said. We don't know what would happen if Earth were supersized or closer to the sun. But, so far, it seems very fortunate that we aren't living on a planet that's any of those things.

Editor's note: This story was updated to note that if Earth were twice its mass, gravity would increase, but not by twice as much. Also, to clarify that super-Earths are planets that are between two and 10 times the mass of our planet.

Originally published on Live Science.

  • Edward
    The author did not spent too much time on examining the science of this article. For example when size is mentioned, say, 2x to 10x that of earths, what does that mean? Is it radius or mass? The mass increases with the cube of the radius so a planet of 2 times earths radius would have a mass of 2³ = 8 times our mass, other things being equal which they aren't density being the primary variable. And surface area varies as the square of radius so 2 x the diameter would give 4 x the surface area. This is an awful lot bigger planet than that of earth and leaves lots of extra area for meteors to fall on maybe!

    Gravity is not a linear function either since it depends on the mass of a sphere which is not a linear function of radius, as I mentioned above. Your weight will decrease by the square of the distance from the centre of a planet according to the formula F ~ Mm/r², where M = the mass of the planet and m = your mass, divided by the square of the distance from you to the centre of the planet. For your consideration, if you had two planets of equal mass but one was lower density then you would weigh less on the larger planet (the low density one) because you are farther from its centre.

    This is not complex math but the article was way too simple and therefore wrong.
    Reply
  • Edward
    From the article "If the hypothetical super-Earth were even bigger, say, 10 times its current size, dramatic changes could start happening in Earth's interior. The iron core and liquid mantle would also be 10 times larger, "

    This is also quite wrong. First, the problem of size. Again what does 10 x larger mean? If size were radius the core would be 10 times the radius all other things being equal again. But mass is proportional to the cube of radius as I mentioned in my first reply. This means the core would be 10³ = 1000 times more massive not 10! No small difference.
    Reply
  • Pensive1
    It would be more revenue for the ill greed 1%.
    Reply
  • Pensive1
    As Edward pinpoints to the greater difference in mass, additionally it woud mean a greater gravity which would affect just about everything including the retention of poisonous gases like CO2, ammonia, sulfur and the likes. Ife would just not be supported at all! This planet exhibits precise specifications that supports life and evidences a Highly intelligence at work.
    Reply
  • William Pennat
    Edward said:
    The author did not spent too much time on examining the science of this article. For example when size is mentioned, say, 2x to 10x that of earths, what does that mean? Is it radius or mass? The mass increases with the cube of the radius so a planet of 2 times earths radius would have a mass of 2³ = 8 times our mass, other things being equal which they aren't density being the primary variable. And surface area varies as the square of radius so 2 x the diameter would give 4 x the surface area. This is an awful lot bigger planet than that of earth and leaves lots of extra area for meteors to fall on maybe!

    Gravity is not a linear function either since it depends on the mass of a sphere which is not a linear function of radius, as I mentioned above. Your weight will decrease by the square of the distance from the centre of a planet according to the formula F ~ Mm/r², where M = the mass of the planet and m = your mass, divided by the square of the distance from you to the centre of the planet. For your consideration, if you had two planets of equal mass but one was lower density then you would weigh less on the larger planet (the low density one) because you are farther from its centre.

    This is not complex math but the article was way too simple and therefore wrong.
    Agreed. When you say two times larger, you have to specify whether you mean diameter or volume. Since the article also says you would be two times heavier, I assume it means twice the diameter. This is the interesting thing about gravity. Other things being equal (like density), the surface gravity of a planet is linear with respect to radius -- it increases in direct proportion to its radius. So even though a so-called "super Earth" that is twice Earth's diameter would have eight times its mass (2^3), it's surface gravity would "only" be twice Earth's.
    Reply
  • uswine
    Edward said:
    From the article "If the hypothetical super-Earth were even bigger, say, 10 times its current size, dramatic changes could start happening in Earth's interior. The iron core and liquid mantle would also be 10 times larger, "

    This is also quite wrong. First, the problem of size. Again what does 10 x larger mean? If size were radius the core would be 10 times the radius all other things being equal again. But mass is proportional to the cube of radius as I mentioned in my first reply. This means the core would be 10³ = 1000 times more massive not 10! No small difference.


    Yes this isn't clear at all in what they wrote. The composition of a planet controls its maximum size but what you will find is that as planets become more massive, the tendency towards gravitational compression increases until eventually, at a mass roughly 1.7 times that of Jupiter or 540 Earth masses, you reach a critical point where the planet stops getting larger. Beyond this critical point, adding more mass to a planet actually makes it smaller because the compression created by the extra mass is greater than the volume of the extra mass.

    For rocky planets like the earth the size limit is about 3 earth radii
    Reply
  • VennieThompson
    Pensive1 said:
    As Edward pinpoints to the greater difference in mass, additionally it woud mean a greater gravity which would affect just about everything including the retention of poisonous gases like CO2, ammonia, sulfur and the likes. Ife would just not be supported at all! This planet exhibits precise specifications that supports life and evidences a Highly intelligence at work.
    Galaxies like grains of sand on a beach, random nonintelligent variation in planets is sufficient to explain a rare but present incidence of a planet like Earth. It's perhaps the astonishment of being a Being on such a rarity would create the tendency of a sentient on such an object to hypothecate an intelligence of enormous powers as necessary to it's existence. I too am a sentient impressed by the wonder of it all. This only peripherally skirts G.R.A.P.E.S.
    Reply