No, Scientists Did Not Find 10 Billion Earth-Like Planets In The Galaxy - Forbes

Artist's impression of sunset on the super-Earth world Gliese 667 Cc (Credit: ESO)

The science news headlines are buzzing today with the results of a new study by astronomers from the High Accuracy Radial velocity Planet Searcher (HARPS). You might have seen them already, because they're pretty exciting. "10 Billion Earth-Like Planets May Exist in Our Galaxy" reads one.  "'Billions' of habitable worlds in our own Milky Way galaxy?" reads another.

So did scientists really find billions of Earth-like planets in our Galaxy, teeming with alien races ready to trade, conquer, and/or say hi to us? Unfortunately, no, that's what this discovery is about.

That said, the scientists at HARPS have absolutely made a fascinating discovery.  This team focused their search for exoplanets on red dwarfs – which are the most common stars in the Galaxy. Over the course of six years, they examined 102 such red dwarfs, and found 9 planets which are called "super-Earths" – rocky planets that have between 1-10 times the mass of our own planet. Two of those planets were found within the "habitable zone" of the star – meaning that the temperatures on those planets would allow liquid water to flow on the surface.

Based on their findings, they were able to extrapolate that more of the stars also probably had super-Earths, based on gravitational analyses, though the planets were not definitively detected. They were also able to extrapolate whether those super-Earths were likely to be orbiting in the habitable zone around the star.

"Our new observations with HARPS mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet," says Xavier Bonfils, the leader of the team in a press release. "Because red dwarfs are so common — there are about 160 billion of them in the Milky Way — this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone."

However, just because these planets exist in the habitable zones around the stars doesn't mean that they're "Earth-like" – as some of the news reports are claiming. The surface of these planets would be quite different, due to the light from the red dwarf. The mass on a lot of these planets is also a lot more than Earth. Which means that life from here on Earth might have a difficult – if not impossible – time surviving on one of them. That said, the presence of liquid water could mean that these planets could evolve life of their own. However, the likelihood of such life developing is lower than that of a planet that could be considered more Earth-like.

"The habitable zone around a red dwarf, where the temperature is suitable for liquid water to exist on the surface, is much closer to the star than the Earth is to the Sun," says Stéphane Udry, another member of the team. "But red dwarfs are known to be subject to stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely."

However, this doesn't mean that life can't evolve on those planets, and as astronomers learn more about these planets, looking for signs of life is the next logical step. What's more, even though these planets aren't Earth-like, it's encouraging to see how common planets with liquid water could potentially be in our galaxy. This finding encourages the possibility that habitable planets are likely to be found around stars resembling our own Sun's – which means that the discovery of truly Earth-like planets could be right around the corner.

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