Red Dwarf Stars May Turn Mini-Neptunes in Exo-earths

red dwarf

Astronomers have found that violent red dwarf stars may be the key to turn miniature planets that resemble Neptune, into exo-Earths. Stars with a relatively low mass are seen by astronomers as the last place to look for habitable planets like the Earth. Though, new studies suggest that these violent leviathans of stars may turn lifeless “mini-Neptunes” into life-bearing, habitable places like Earth.
Astrophysicists have concluded that M-type red dwarf stars have two definitive characteristics. They are much too harsh to allow for the conditions on a planet to harbor life because of violent cosmic weather and extreme tides.

Since the Sun is so large, the Earth must be far away to receive the heat needed to sustain life. However, it must not be located too close that the Sun would cook the Earth into a burnt crisp of a planet – much like Mercury. As the size of the star decreases, the size of the habitable zone decreases. Therefore, planets must be orbiting very close to a red dwarf star to have the ability to sustain life.
However, there are problems with orbiting too close. Even though the planet may receive an ample amount of heat, orbiting so close would cause extreme tidal fluctuations, which would render much of the planet dry and lifeless.

Rodrigo Luger, an astronomer at the University of Washington, explained that the reasons there are tides on Earth is because the gravity of both the moon and the Sun tug on the oceans. This is why the ocean bulges at high tide. Furthermore, he stated that the people on Earth are lucky that the tides only distort the oceans and only by a few feet.

The extreme tides on an exoplanet around a red dwarf star could actually warp the surface of the planet – like a constant earthquake. Extreme tides on land could trigger unbelievably strong tectonic plate activity and the ignition of volcanoes over the entirety of the planet. This would put in motion an extreme effect on the atmosphere and lead to a runaway greenhouse effect that would vaporized any and all surface water. As well, tidal locking, which happens when a single hemisphere continuously faces the star, would be problematic.

M-type red dwarfs usually have extreme cosmic weather. Therefore, the planets orbiting close to the star, within the habitable zone, would experience the force of powerful stellar winds and harmful stellar flares. If the planet possesses only a thin atmosphere, the surface would be exposed and would ultimately waste away the important lower atmosphere and eject it out into space. Though, what is bad for an Earth-like exoplanet may actually be what is needed to sustain life on a Neptune-like planet which possesses a very thick atmosphere.

Mini-Neptunes would begin to form much further away from a star, outside the normal habitable zone. A University of Washington press release stated that when ice molecules form with Hydrogen and Helium gases coming from the host star, they form rocky and icy cores that are surrounded by a thick, protective atmosphere.

Extreme tides would not be problematic due to the distance from the host star. Luger also explained that once some of the atmosphere erodes, ice can be turned into liquid water to create an abundance of surface water.

The debate still remains open on whether such a planet could sustain life, or be a lifeless, barren world. Astronomers state that if the planet is tidal locked, one side of the planet could the baked and eroded much like the planet Mercury, but the side facing away could potentially harbor life in minimal places.

Currently, the sheer possibility that life may exist on these exotic exoplanets is pure speculation. Though, very advanced telescopes can be used to detect the composition of a distant atmospheres by using stellar spectroscopy. Red dwarfs are very abundant in our galaxy and other galaxies in the Universe. Therefore, finding these mini-Neptunes around red dwarfs may lead astronomers to believe that they will be soon called exo-Earths.

By Alex Lemieux

Sources:
Daily Mail
Discovery
Tech Times

Picture: NASA/ESA/G. Bacon (STScI)Flickr License

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