life on a rogue planet | Daily Planet

Work: NASA / JPL-Caltech

A “rogue” exoplanet with the preliminary name PSO J318.5-22 has been detected by a group of astronomers led by Michael Liu of the University of Hawaii at Manoa. By “rogue planet”, astronomers mean a planet that does not have a host star – it wanders alone in galactic space.

This particular world is a Jupiter-like gas giant, located about 80 light years from Earth in a collection of young stars (less than 50 million years old) of the Beta Pictoris moving group. With only about six times the mass of Jupiter, PSO J318.5-22 is one of the least massive rogue planets detected to date. It is an under-brown dwarf, even less massive than a brown dwarf (a gas giant that has failed to become a star).

Radiation levels in this type of planet are very high, with a seamless transition from gas to liquid in the deep atmosphere. Convection would move all organic compounds on the surface inward, where they would encounter extreme temperatures and pressures. Thus, life in a gas giant like PSO J318.5-22 should be considered extremely unlikely. But the rogue planet could be accompanied by a large moon, whose subsoil could be a potential abode of life.

The discovery gives credence to the idea that rogue planets could be very common. By some estimates, there could be as many as 100,000 of these nomads for every star in our galaxy!

According to current theories about the formation of the solar system, small rocky planets sometimes approach very large planets in the early chaotic stages before their orbits stabilize. Such close encounters could potentially drive the smaller planets out of the solar system altogether, leaving them to roam the galaxy as nomads. In fact, the Mars-sized object that collided or near-collided with early Earth (resulting in our unusually large Moon) would have become a rogue planet.

Any planet so detached from its original solar system could be very similar to Earth, and life could already have taken hold. Once ejected, the atmosphere would freeze on the surface. However, the heat from radioactivity in the core could provide enough energy to keep an ocean of water below the frozen surface. And it is quite possible that single-celled life and even subterranean life at hydrothermal vents is developing on this kind of “Steppenwolf planet”.

Under certain conditions, a cover of ice may not even be necessary. A thick atmosphere of molecular hydrogen could provide enough pressure and insulation to keep water liquid on the surface, if the atmosphere had 100 to 10,000 times the pressure of Earth and the planet was ejected quickly. In this case, again, the planet could retain some primitive life forms.

So even if a planet loses its star, it does not necessarily mean that it loses its inhabitants. There are many ways that life can persist.

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Arline J. Mercier

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