In the fictional universe of "Star Trek," the alien Spock comes from a world called Vulcan in the triple-star system 40 Eridani. Vulcan was destroyed in a previous movie, forcing Spock's race to immigrate to a planet called New Vulcan.
While Vulcan is one of the most well-known worlds in science fiction, the planet is entirely fictional. However, the star system it belongs to in "Star Trek" is for real. And scientists haven't ruled out Earth-like planets in that system, 40 Eridani, which is 16.5 light-years from Earth.
"Could there be an Earth-like planet in this system? We have no way of knowing that now," Karl Stapelfeldt, chief scientist of NASA's Exoplanet Exploration Program, said in a statement.
If an Earth-like world does exist, he added, "we don't yet have a way to detect it, but NASA is working on the technology to make it possible."
NASA principally searches for Earth-like worlds using the Kepler space telescope. The telescope, however, focuses on looking for planets that are very far away from Earth. NASA's planned orbiting observatory TESS (Transiting Exoplanet Survey Satellite), which will launch next year, can look at closer worlds around brighter stars — but NASA has not made it clear whether TESS can search for a planet like Vulcan.
When Spock was growing up, he would have been treated to triple sunsets on his home planet. The star his planet orbited, 40 Eridani A, is a dwarf star that is a short distance from the other stars in the system, a binary pair including 40 Eridani B (a white dwarf) and 40 Eridani C (a red dwarf).
Dwarf stars emit less energy than our own sun. So for Vulcan to be habitable, it would need to huddle closer to 40 Eridani A than Earth does to the sun. Scientists define a "habitable zone" as the region around a star where a planet could have liquid water. If the planet is too close, it loses most of its water (like Mercury). If it's too far, the water freezes out (like Pluto).
There are other factors as well that affect a planet's habitability, such as its atmosphere. Venus and Mars are pretty close to the sun's habitable zone. But Venus has a very thick atmosphere — probably enough to crush life-forms on the surface — while Mars' is wispy thin. There could be microbes on Mars, but any unprotected Vulcan on its surface would suffocate immediately.
Vulcan was actually not as temperate as Earth is, according to "Star Trek." Because it was on the inner edge of the habitable zone, the planet was more desert-like than our own planet. While the planet was destroyed in the 2009 "Star Trek" movie, in the original series and other "Star Trek" shows it remained a friendly location for the USS Enterprise to visit.