In the movie Avatar, this is exactly what has happened, and one of the large gas giant planets orbiting Alpha Centauri A has a moon named Pandora that is inhabited by the mysterious blue creatures named Na’vi.
Next out is Barnard’s Star, named for Edward Barnard of Lick Observatory in California, who discovered it in 1916. It is a dim, cool star like Proxima Centauri and is the closest nearby star that can be seen from the northern hemisphere, in the constellation Ophiuchus. Although it is about six light years away, it’s getting closer to us, zipping through the galaxy at such a rate that it will come closer than Proxima Centauri in about 11,000 years, then move off again into deep space!
Wolf 359 is yet another small red star, this time in the constellation Leo. German astronomer Max Wolf measured its movement and listed it in a catalogue in 1917. More than seven light years away, it’s very faint and is actually one of the coolest stars known. Any planet orbiting this star would have to be very close to it in order to get enough heat and light to support any kind of life.
OUR NEAREST NEIGHBOURS
1. Proxima Centauri
2. Alpha Centauri A
3. Alpha Centauri B
4. Barnard’s Star
5. Wolf 359
6. Lalande 21185
7. Sirius A
8. Sirius B
9. Luyten 726-8 A
10. Luyten 726-8 B
11. Ross 154
Other planetary systems may have more than one sun in the sky. This artist’s conception shows what the sky might look like on a planet orbiting within a three-star system. Could such a planet support life?
Lalande 21185 is in Ursa Major, better known as the Big Dipper. It was first catalogued by French astronomer Jerome Lalande in 1801. Although it’s much brighter and hotter than the previous few stars in our list, it’s not as warm as our Sun. Even though it is a bit more than eight light years away, astronomers have been able to detect a planet around it and it may have more. Could life have formed here?
Sirius, the Dog Star, is in the constellation Canis Major, more than eight-and-a-half light years from us. It is the brightest star in our sky, blue-white in colour and very noticeable when it is shining in the night, often casting shadows on Earth. It’s about twice the size of our sun but much, much hotter. It might be possible for life to form on a planet in orbit around it, but it would complicated by Sirius’ companion star, Sirius B, which is a much smaller star — a dwarf star — that is only about the size of Earth but is made of very dense matter. A milk jug filled with this kind of matter would weigh as much as a four-story building on Earth. Could life form in this two-star system?
Luyten 726-8 A and B are two small stars in the constellation Cetus, and are nearly nine light years away from Earth. They were discovered by Willem Luyten, a Dutch astronomer, in 1948. They are also “red dwarf” stars but have a distinctive characteristic that may make them unfit for sustaining life: they flare up occasionally, sending streams of energy into space. These flares are similar to those that shoot out from our own Sun, sometimes causing electrical blackouts on Earth. However, the flares on the Luyten stars are much more powerful and have greater energy.
UFOS AND ALIENS IN LITERATURE
One of the first stories to describe an alien visiting Earth is the classic literary work Micromegas, by the French satirist Voltaire. Written in 1752, the story tells of how someone from a planet orbiting Sirius travelled to Earth in the company of a Saturnian. These beings were supreme in many ways, least of all their size; one was 120,000 feet tall! The story was essentially a way to poke fun at French society at the time, so was quite fanciful, with the giants plucking ships out of the water and scorning the little Earthmen who thought themselves superior to others. In the story, the alien visitors marveled at our primitive and illogical society.
Ross 154 is another red dwarf star in the constellation Sagittarius, and is more than nine light years from Earth. It also flares, with outbursts every few days.
Some other relatively nearby stars, such as Tau Ceti and Epsilon Eridani, were the targets of an attempt to establish radio contact with extraterrestrial beings in the 1960s. Our messages apparently were not answered, so they don’t feel like answering, they weren’t listening, or they’re not there to begin with.
The nearest star that is most like the sun is Tau Ceti, in the constellation Cetus. It’s only 12 light years away and does not exhibit flaring like other near stars, so it has a better likelihood of having planets with life. This is why it has been the target of searches for extraterrestrial life. No planets have been located in orbit around it, although Tau Ceti is known to have a disc of debris surrounding it, meaning that any planets there would have been bombarded with asteroids, perhaps wiping out life that may have started to form. Still, it may be one of the best local prospects for our finding alien life. No radio signals have been detected emanating from the Tau Ceti system, but scientists have not given up hope. Tau Ceti is one of five “best bets” that are being considered for new searches by dedicated instruments looking for signs of extraterrestrial life.
Another one of the “best bets” is Epsilon Eridani, a star similar in composition to the Sun. It’s less than 11 light years away from Earth, but because it is relatively close, some direct astronomical measurements of it are possible, and it is known to have at least one large planet plus a ring of rocky debris. As long ago as 1960, a radio listening program called Project Ozma targeted both Tau Ceti and Epsilon Eridani, with no success. Recent observations have likewise not yielded any signs of life. However, because its temperature and size are like the Sun, it is the nearest star thought to be capable of having planets that could have life.
For this reason, many science fiction works have involved Epsilon Eridani: the space station Babylon 5 orbited a planet around Epsilon Eridani; Isaac Asimov’s Foundation series is set partly in the Epsilon Eridani system; and the popular video game Halo has the planet Reach as a military base that saw much fighting over two game visualizations, with other planets of Epsilon Eridani part of the action as well.
Recently, astronomical techniques and imaging have advanced so much, it has been possible to detect planets around some stars. More than 400 extrasolar planets have been found using high-powered telescopes and spectral analyses of starlight. Because of their incredible distances, nearly all of these planets are much bigger than Earth, and in many cases, far bigger than Jupiter, the largest planet in our own Solar System.
In January 2010, astronomers discovered a planet only about four times as massive as Earth. What’s more, it is only about 80 light years away from us, in the constellation Hercules. However, this relatively small exoplanet is very close to its star (named HD156668) and is therefore far too hot to sustain life as we know it.
In 2004, astronomers detected a large planet orbiting the star Gliese 436, a dim red dwarf only 33 light years from Earth. It is about the size of Neptune, smaller than Jupiter but much larger than Earth. In 2008, astronomers announced they had found a second planet inside the orbit of the first one, possibly less than twice the size of Earth. This very hot planet zips very quickly around its parent star, only a fraction of the distance from it that Mercury orbits our Sun, and we know that the surface of Mercury is hot enough to melt lead! In addition, other astronomers believe there may be other planets in this