Suffice it to say, if the Milky Way contains 100 billion Earth-like planets, and there’s somewhere in the region of 500 billion galaxies, then there’s an extremely high chance of other planets harboring life. As for how we’ll get to those planets, though — or, alternatively, how the residents of those planets will get to us — remains a very big question. The nearest probably-habitable planet is Tau Ceti e, which is 11.9 light years from Earth. The fastest spacecraft ever, Helios II, traveled at 43 miles per second (70km/s), or 0.000234c (the speed of light). At that speed it would take 51,000 years for a spacecraft to reach Tau Ceti e.
It gets worse: Helios II was only travelling that fast because it was orbiting close to the Sun; Voyager, for example, travels at just 8 miles per second (so, about 200,000 years to reach Tau Ceti e). To reach another star within a reasonable time period (say, 50-100 years) we would need a propulsion system that’s capable of around 0.1c (10% light speed). There are a few proposed methods for reaching such insane speeds (antimatter rockets, fusion rockets), but nothing that’s being immediately (and seriously) considered for interstellar travel. Who knows, maybe NASA’s warp drivewill pan out? If they can work out the whole annihilating-the-star-system-upon-arrival issue, that is…
Research paper: doi: 10.1093/mnras/stt318 – “Extending the planetary mass function to Earth mass by microlensing at moderately high magnification”
[The image at the top of the story is an infrared image of the core of the Milky Way, captured by NASA’s Spitzer space telescope. Infrared imaging allows you to see many stars which are normally obscured by intergalactic dust.]
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