Back in 1995, astronomers had detected a planet orbiting around a Sun-like star. This was a huge deal. And today, we have discovered more than 4000 extrasolar planets. They come in a wide variety of sizes and characteristics. By the most optimistic projections, only about 50 are habitable, and only 20 have Earth-like temperatures. So, if we were to send off a probe to explore some of these worlds, what would be the top 5 nearest choices to visit?
5) Gleise 832c
Gleise 832 is a red dwarf star some 16 light-years away. It has one habitable planet. Whenever we’re talking about exoplanets there’s always that letter following the star’s name or number. The first letter (a) stands for the star itself, each subsequent letter stands for the planet in order of discovery. So, Gleise 832a stands for the star. The letter (b) in this case stands for the first planet discovered orbiting around Gleise 832, a gas giant much further out than (c), taking 9 years to orbit the star. Gleise 832c is actually the most similar to Earth out of all the discovered exoplanets. However, it orbits its star every 36 days. This may seem fast but Gleise 832 is a red dwarf star, much dimmer and cooler than our sun. So, Gleise 832c receives about as much stellar energy as we receive from our own sun, even though Gleise 832c orbits so much closer to its star.
4) Wolf 1061c
Wolf 1061 is another red dwarf star and almost as far away as Gleise 832 at just 14 light-years away. Its one habitable planet, Wolf 1061c was discovered in 2015. There are three planets discovered around Wolf 1061 and each of these is considered to be rocky, like Earth. However, the closest planet orbiting the Wolf 1061 is much too close, and the furthest planet out is thought to be too cold. This means Wolf 1061c is right in that “Goldilocks” zone. Wolf 1061c orbits its star every 18 days, meaning its much closer to its star than we are to ours. However, Wolf 1061 is a red dwarf star and much cooler than the Sun. Because it’s so close to Wolf 1061, it is believed that Wolf 1061c is tidally locked to its star, meaning one side of the planet always faces the star. This is problematic for life to arise on the planet since one side of the planet is very hot and one side is very cold.
3) Tau Ceti e
Tau Ceti is just 12 light-years away from us and is a yellow dwarf star. It’s one habitable planet, (e), is four times more massive than our own planet Earth. In fact, all five Tau Ceti worlds are much larger than Earth. At one point, it was believed that a second planet, (f) was also in the habitable zone of the star. However, we now know that (f) only recently joined the habitable zone due to Tau Ceti becoming more luminous over the years. Tau Ceti f has spent only 1 billion years in its habitable zone. This may sound like a long time but it’s believed that Earth took 2 billion years to first produce biosignatures in its atmosphere after the first organisms came to evolve. This means, if there is life on Tau Ceti f, it will be very hard to detect.
2) Barnard’s Star b
Six light-years away there is Barnard’s Star, a red dwarf with one habitable planet. Barnard’s Star b appears to be a super-Earth–larger than Earth but smaller than Uranus or Neptune. Its mass is 3.2 times that of Earth and orbits its star every 233 days. At that distance, because the star is smaller and cooler than our sun, the planet is colder than Earth, with an estimated surface temperature of -238 degrees Fahrenheit. This makes it unlikely to be habitable, although little is known still about specific conditions on the planet.
1) Proxima Centauri b
And finally, we have Proxima Centauri b, a planet orbiting around a red dwarf star at only 4 light-years away. Even though Proxima Centauri b appears to orbit in its star’s habitable zone, nobody knows for sure if it’s actually capable of supporting life. Researchers don’t know for sure if the planet has an atmosphere, or whether that atmosphere could allow for liquid water to exist on Proxima b’s surface. The planet’s surface temperature is unknown because it depends heavily on atmospheric characteristics. Much research is still due, but the studies conclude that the presence of liquid water on the surface today cannot be ruled out and thus Proxima b can be considered a viable candidate habitable planet.