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Monday, April 23, 2018

No Way Out? Aliens on 'Super-Earth' Planets May Be Trapped by Gravity

"Super-Earth" planets are giant-size versions of Earth, and some research has suggested that they're more likely to be habitable than Earth-size worlds. But a new study reveals how difficult it would be for any aliens on these exoplanets to explore space.

To launch the equivalent of an Apollo moon mission, a rocket on a super-Earth would need to have a mass of about 440,000 tons (400,000 metric tons), due to fuel requirements, the study said. That's on the order of the mass of the Great Pyramid of Giza in Egypt.

"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." [10 Exoplanets That Could Host Alien Life]

As researchers have discovered alien worlds around other stars, one class of exoplanets that popped up was the super-Earths, planets that can reach up to 10 times the mass of our own. A number of super-Earths apparently lie in the habitable zones of their stars, where temperatures can theoretically support liquid water on the planetary surface and thus, potentially, life as it is known on Earth.

Prior work suggested not only that worlds other than Earth-like ones could offer circumstances suitable for life, but also that some could be even more suitable than Earth-like planets. Super-Earths, researchers have suggested, might be "super-habitable" — their greater mass giving them stronger gravitational pulls, so they could hold thicker atmospheres to better shield life from harmful cosmic rays.

If life did evolve on a distant super-Earth, such aliens could have developed an advanced civilization capable of spaceflight. However, the strong gravitational pull of such planets could also make it more difficult for extraterrestrials to blast off their planets, Hippke said in the new study.

To see how difficult it might be for super-Earthlings to launch a conventional rocket, Hippke calculated the rocket sizes needed to escape a super-Earth 70 percent wider than our planet and 10 times more massive. Those are roughly the specs of the alien planet Kepler-20b, which lies about 950 light-years from Earth. On such a world, the escape velocity is about 2.4 times greater than on Earth.

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