As astronomers look out across unfathomable distances and observe other solar systems, they often see so-called “super-Earths.” These worlds are rocky like Earth, but they can be several times more massive. They might also be our best hope of finding life outside our solar system. We’ll have to go to them, though. A new analysis of these exoplanets suggests any intelligent beings on these worlds might be stuck there due to the massive gravity on a super-Earth.
There are no super-Earths in our solar system, so scientists are forced to speculate about the actual conditions on such worlds. The consensus is that super-Earths would make a suitable home for life because their greater mass would encourage the retention of a thick atmosphere. That’s essential for protecting life from harsh radiation. Any life that developed there would, however, find chemical propulsion insufficient to break the bonds of gravity.
A super-Earth can have a mass as much as ten times that of Earth, and the corresponding 10x increase in gravity would make it hugely difficult to reach orbit, according to study author Michael Hippke of the Sonneberg Observatory in Germany. Launching a large payload like the upcoming James Webb Telescope on a Falcon Heavy-like rocket would require 60,000 tons (120 million pounds or 54 million kilograms) of fuel, significantly more than we need here on Earth. A larger Apollo-style mission would end up with a total mass of 440,000 tons because of fuel requirements. The Saturn V itself only weighed 3,270 tons.
Hippke suggests an alien race evolving on a super-Earth would be unable to reach space unless it became much more advanced or reckless than we are. In the “advanced” category, a space elevator could facilitate more efficient transport to space. A super-Earth species might begin with a tiny payload dragging a cable and progressively build up an orbital facility. However, this would require incredibly strong materials because of the high gravity, and even the best theoretical designs we have (based on carbon nanotubes) wouldn’t cut it.
If an alien species were sufficiently reckless, it could skip chemical propulsion entirely and use nuclear pulse engines. This form of propulsion detonates small atomic bombs to catapult the craft forward. The lifting power would be vastly higher and may be the only way for a civilization on a ten-Earth-mass planet to leave it. However, the risk of failure is significant (Hippke estimates 1 percent). A failed atomic rocket launch would be no different than nuking your own spaceport.
Perhaps, humanity is lucky to live on a small planet like Earth. Reaching orbit is still plenty challenging, but we might have an unusually good view of the universe if super-Earths are as numerous as it seems.
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