M-dwarfs, or small stars about half the size of our sun, are the most popular stars in the Milky Way: our galaxy has nearly 150 billion of them. A team of European astronomers recently looked at 102 M-dwarfs and found two planets orbiting inside what is called the "Goldilocks" region – the region where temperatures are not too hot or cold for liquid water. In theory, that means there are tens of billions of Goldilocks planets in the Milky Way. If there's water, there could be life, says School of Earth and Atmospheric Sciences Associate Professor James Wray.
For those who seek life on other worlds, it is fantastic news that habitable planets may be common around M dwarfs, the most abundant stars in the galaxy. But "habitable" here simply means that we expect liquid water would be stable on their surfaces, based on guesses about the planets' atmospheres. To test this, we must isolate each planet's light from that of its star, and collect a spectrum, thereby measuring the abundance of various atmospheric gases. If we find an oxygen-rich atmosphere, especially in combination with organic molecule(s), then life may be the most probable explanation.
But definitive life detection will come only from direct probing, and this will take many years even if we can send a probe at near-light speed. Fortunately, M dwarfs are so common that they represent most of the nearest stars! Still, we living astronomers must hope for rapid medical advances if we wish to see the results from interstellar probes within our lifetimes.
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