14-07-2007 Another Earth? (Article 94)

[Simon Kenny]

Another Earth? (Article 94)

The word Zodiac is derived from an ancient Greek phrase meaning “Circle of Animals”, yet the constellation of Libra, The Scales, is the only inanimate object contained within, a throw back to one of the many which the early Greeks inherited from the Babylonians. But it is older than that. In fact a Mesopotamian carving representing the celestial scales of justice, is dated at 2200 BC. This obscure region, west of Scorpius and on view during the summer months from Ireland, was brought into the scientific limelight last April, when astronomers discovered the first potentially Earth-like planet outside our Solar System. While there have been hundreds of exo-solar planets discovered thus far, this one stirred the hearts of astronomers due to its size and location in relation to its parent star. Most of the exo-planets are either Jupiter sized (Earth is approx 12000 km) or larger and either too far or too close from their respective suns, thus not particularly suitable for life, as we know it. Although preliminary news hit the world media in April, Shannonside Astronomy Club waited until further astronomical data was available, so we could print as always, the most accurate information we can.

The new planet orbits a faint star known by its unromantic catalogue number of Gliese 581. It whizzes round its parent sun every 13 days at a distance of only 11 million-km (compared to our own Earth-Sun distance of 150 million-km), and has a mass estimated at between 5 and 7 times that of the Earth. Combined with a diameter about 50% larger than Earth, its gravity would be about twice what we have here, (a 12 stone person would weigh 24 stone). But unlike our yellow Sun, Gliese 581 is a red dwarf, the most abundant type of star in our Galaxy. It is therefore much cooler, smaller and dimmer than our own Sun, which means the planet, named Gliese 581c (there are two other planets in the system) should be warm enough to sustain liquid water on its surface. The faintly glowing star — you need at least a 4 inch telescope to see it, though you will not see the planets — is at least 2 billion years old, 3 billion younger than our Sun. As it lies only 20.5 light years distant it is one of the 100 nearest stars.

The discovery team, based in Geneva, used a sophisticated planet hunting instrument on a 3.6m diameter telescope in Chile to ascertain the planet’s data, including a surface temperature between 0 and 40 degrees C, meaning it may have land and oceans. If the latter were correct, it could be the first discovered planet with suspected similar conditions to our own home. While we believe many of the 100s of billions of red dwarf stars have planets, statistically most of the planets around such stars will not be like Gliese 581c. Still, one could hypothesise walking around in ordinary clothes on this planet, but with difficulty under twice your own weight and that of your oxygen tank! Clear skies.