Super-Earths' powerful gravity could preclude alien civilizations from leaving their planets

Fuel requirement for launching from massive planets makes doing so extremely difficult and very expensive.
By Laurel Kornfeld | May 08, 2018
If alien civilizations exist on super-Earths, they may be unable to leave their home planets due to those planets' extremely powerful gravitational pulls, according to a new study submitted to the International Journal of Astrobiology.

Many super-Earths, exoplanets larger than Earth but smaller than Jupiter, have been discovered, with the average one being approximately 10 times larger than our planet.

Of all the exoplanets found to date, super-Earths are the most likely to harbor life as we know it. Because they are more massive than Earth, these worlds can hold thicker atmospheres, which protect life from cosmic rays but also increase the power needed to launch from their surfaces.

The planets' larger masses give them significantly stronger gravitational pulls, which could make it impossible for any intelligent civilizations on them to achieve escape velocity.

Launching a space mission comparable to the Apollo moon missions from a super-Earth would require so much fuel that the rocket would have to have a mass of 440,000 tons.

"On more-massive planets, spaceflight would be exponentially more expensive. Such civilizations would not have satellite TV, a moon mission, or a Hubble Space Telescope (HST)," study author Michael Hippke, an independent researcher affiliated with Germany's Sonneberg Observatory, told the website

Hippke calculated the size a rocket would have to be to escape a super-Earth such as Kepler-20b, which is located 950 light years away and is 70 percent wider than the Earth and 10 times more massive.

Escape velocity for a planet like Kepler-20b is about 2.4 times what it is for Earth. For planets with more than 10 Earth masses, chemical rockets are not powerful enough to achieve escape velocity, meaning any civilizations living on these worlds would have to pursue other methods of reaching space.

Other options such civilizations might consider are space elevators or nuclear-powered rockets though it is unclear whether the former would work for such massive worlds.

"Civilizations from super-Earths are much less likely to explore the stars. 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," Hippke said in an interview with the Daily Mail in the UK.



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