An extrasolar planet, or exoplanet, is a planet that exists beyond our own solar system, orbiting a distant star other than our sun. So far, more than 800 planets have been located and confirmed by means of the wobble they induce in the star around which they are orbiting, or by the dip in light output from their star as they pass in front of it.
For centuries, extrasolar planets were merely a subject of speculation, a common element in science fiction stories such as Star Trek. Although astronomers generally supposed that some existed, it was a complete mystery how common they were and how similar they were to the planets of our solar system.
The first confirmed detections of exoplanets were finally made in the 1990s. Based on current findings, astronomers now estimate that at least 20 percent of all stars have planets.
In the fictional world of Star Trek, the name Eridani has been mentioned in relation to the homeworld of the Vulcans. One of two stars, either Epsilon Eridani or Eridani 40 had been suggested as the home sun of Mr. Spock. In 2006, NASA announced that a planet had been found circling Epsilon Eridani, which is only ten and a half light years from Earth.
As with many of the planets thus far discovered orbiting stars other than our own sun, telescopes on Earth were able to notice the wobble induced by the gravity of the planet, swinging its star back and forth the same way an ice skater twirling his partner might be pulled first one way and then the other.
The planet thus discerned swinging about Epsilon Eridani weighs in at about the same mass as Jupiter, with an orbital period of nearly seven years. Thus, the Jupiter-like world around Epsilon Eridani sits a bit closer to its sun than our Jupiter, which takes nearly twelve years to orbit our sun. If the Epsilon Eridani gas giant were to appear within our solar system, it would be on the outer edge of our asteroid belt, the rubble pile lying between Mars and Jupiter.
Bottom line in all of this: the solar system of Epsilon Eridani seems remarkably similar to our own. Based on what scientists think they understand about how planet formation works, in order to have a planet like ours, not too warm and not too cool, and not too big or small, something like Jupiter needs to be going around a star about the same place Jupiter is. Until Kepler was launched in 2009, planets as small as Earth were just too tiny to be discernable by any of our then current detection techniques. That has now changed thanks to the Kepler Space Telescope. As of December 2011, Kepler has found a total of 2,326 candidates (a few hundred of which have been confirmed, with the rest awaiting confirmation. It is estimated that about 90 per cent are real and not noise in the data). Of these candidate worlds, 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. What is of greatest interest is that 48 of these planet candidates are circling in the habitable zones of their stars.
But finding a Jupiter-like planet in a Jupiter-like place at Eridani is pretty good; and it suggests that something very interesting might be hiding around this star. Kepler, unfortunately, is not aimed toward Epsilon Eridani.
The discovery of extrasolar planets naturally raises the question of whether some might support extraterrestrial life. The short answer is that we simply don’t know yet. But given the size of the universe and the high percentage of sun-like stars that demonstrably have planets, it seems that if you’re in a betting mood, betting that life is out there is the way to go. In fact, thanks to Kepler it is beginning to look as if the overwhelming majority of all stars, regardless of size, have planets. So consider: a galaxy like our home galaxy, the Milky Way, has 400 billion stars. If only one percent of those have planets (an unrealistically low percentage), that’s still four billion solar systems. Recently, scientists at JPL have pointed out that there are at least 50 billion galaxies like the Milky Way in the universe. Based on the data gathered thus far by Kepler, they estimate that there are at least one sextillion Earth-like planets in the universe. Does it really seem reasonable to believe that only one planet out of all those would have life of some sort on it?
The issue of whether any of that life is intelligent life is a secondary question, of course. But personally, I would be surprised if human beings are the only ones who have looked at the stars at night and wondered if anyone else is up there. However, if any of them have green blood and pointy ears and live on a planet called Vulcan orbiting Epsilon Eridani, I’d be flabergasted.