We need to find another world where humanity can live on. And most likely, it will be a super-Earth, a rocky world larger than Earth. What if we lived there?
Super-Earths
Super-Earths are rocky planets that are larger than Earth-sized planets. Like Proxima Centauri b is Earth-sized, approximately 1.08 times as wide as Earth but it is sometimes called a super-Earth. But Kepler-22b is more than 2 times larger than Earth. That definitely means it is a super-Earth.
Super-Earths are among the most common type of planets in the Universe, whereas there is none in the Solar System. We only have small rocks and large balloons for the 8 planets here. There are 1296 super-Earths discovered according to NASA as of August 2020.
There are some very weird super-Earths, like other kinds of planets. For example, 55 Cancri e, is a planet with lots of lava and diamond, with sparkling skies. COROT-7b may be the leftover core of a gas giant. OGLE-2005-BLG-390Lb, a super cold super-Earth, is only -223 degrees celsius on its surface.
Image Source: exoplanets.nasa.gov and NASA’s Eyes
Why our Solar System has none
Why don’t our Solar System have a super-Earth, and join most of the stars? That is because of Jupiter’s trajectory in the newborn Solar System billions of years ago. When Jupiter migrated inward, it absorbed the ingredients of the rocky planets by its gravity.
Also, that can explain why Mars is so small too because Jupiter ate its food. This is also one of the reasons why Jupiter is so massive and evidence that Jupiter is the first planet formed in the Solar System.
If Earth was a super-Earth, what would change for life?
Well, super-Earths come in various sizes, from a little bigger than Earth-sized planets to more than twice as wide as Earth. If it was just a little larger, we might evolute as a different species or have different skills. We could have adapted a thicker atmosphere and increased weight. But things could get much, much worse if it was a lot larger than the current Earth.
The main concern is stronger gravity. When it happened, the pressure of Earth would be so high that it could not create a magnetic field anymore because the outer core would be solidified. It would pull a lot of gases and dust in, resulting in a very thick atmosphere. And don’t forget mass extinctions if life did somehow evolved. Asteroids would hit Earth more due to it pulling more in. So, although you may think a world twice larger is better, but it is much worse than you have ever thought before.
Then, what if Earth was a sub-Earth then?
Well, it would not be good either. The main concern is gravity, not stronger but weaker. Weaker gravity is also not good for life. Although asteroids wouldn’t hit it so much, its atmosphere would be too thin that organisms would have a hard time breathing. And we might not be able to hold a moon that is responsible for making Earth a more habitable place. Most terribly, in a thin atmosphere, water might evaporate because of the low pressure, without liquid water on its surface.
Because of these consequences, a potentially habitable exoplanet should be close to Earth in size and mass. Venus is a good example of that, but it is way to hot to host life. We must be happy that we are lucky to live in a planet that is just right to host life.