Super-Earth planets, or planets that are much larger than Earth, but fall within the "Goldilocks Zones" of nearby stars could harbor life, more so than Earth sized planets, but their size will make it difficult for aliens to leave their planet and explore the universe.
A planet's gravity literally imprisons all things on it, from the atmosphere to all living beings and non-living things. To explore the universe will mean fighting gravity and escaping its grasp. A report by Space.com mentions that to launch the equivalent of an Apollo mission on a super-Earth, the rocket alone must have a mass of about 400,000 tons because that much fuel will be required to reach escape velocity. To put that into perspective, the Great Pyramid at Giza has an estimated mass of 400,000 tons.
"On more-massive planets, spaceflight would be exponentially more expensive," said study author Michael Hippke, an independent researcher affiliated with the Sonneberg Observatory in Germany. "Such civilizations would not have satellite TV, a moon mission or a Hubble Space Telescope."
As researchers continue to search for and find alien stars with super-Earths orbiting them, one class of planets that can reach up to 10 times the mass of Earth is of particular interest, notes the report. These are also planets that lie within the habitable zones of their stars and can, in theory, hold liquid water, which also means life that humans can recognize.
While Earth-sized planets are a good spot to start life, research has proven that super-Earths are likely to be super-habitable. What this means is that they have greater mass, so their gravitational forces are considerably stronger, and as a result, their atmospheres can grow to be really thick. Thick atmospheres act as excellent protective shields from falling debris as well as cosmic rays and radiation from their stars.
Life on such planets could theoretically grow to become advanced civilizations that are certainly capable of spaceflight, notes the report. However, the strong gravity and thick atmosphere will also mean that it will be more difficult to blast off and reach escape velocity in time, making spaceflight a real issue.
Scientists calculated just how much force and power is needed from a rocket to blast off a super-Earth that is about 10 times as massive as Earth and 70 percent wider, like Kepler 20-b. This is a planet which is likely to host life and is about 950 light-years from Earth. On Kepler 20-b, the escape velocity has been estimated to be 2.4 times that of Earth's.
The stronger gravity pulls down on an object, in this case a space craft, the more energy it will require to lift off. More energy means more fuel, that in turn means larger rockets, which in turn means a heavier load to lift. Also, according to a report by Kurzgesagt, rockets can only get big to a certain size and weight after which it becomes impossible for it to lift itself off the ground. There is a definite point after which rockets cannot increase in size and mass.
"I am surprised to see how close we as humans are to end up on a planet which is still reasonably lightweight to conduct spaceflight," Hippke told Space.com. "Other civilizations, if they exist, might not be as lucky." Even if spacecrafts work as well as the Falcon Heavy, the report mentions that to just lift the upcoming James Webb Space Telescope, the rocket would need 55,000 tons of fuel.
"Civilizations from super-Earths are much less likely to explore the stars," Hippke said. "Instead, they would be to some extent arrested on their home planet and, for example, make more use of lasers or radio telescopes for interstellar communication instead of sending probes or spaceships."