Berkeley
IF YOU want to boost your chances of finding extraterrestrial
intelligence, point your telescope at a star in the constellation of Scorpius,
say astronomers in Brazil. They have found that this star resembles our Sun more
closely than any other investigated.
Although the Sun is often dismissed as just an average star, it actually
outshines most of its peers. It is also one of only 4 per cent of stars in our
Galaxy known as G-type main-sequence stars鈥攜ellow stars that burn hydrogen
into helium at their centres. Sun-like stars are the obvious targets in the
search for life elsewhere.
Advertisement
Now Gustavo Porto de Mello of the Federal University in Rio de Janeiro and
Licio da Silva of the National Observatory have found that the yellow star 18
Scorpii is a virtual carbon copy of the Sun. The star lies 46 light years from
Earth and is dimly visible to the naked eye.
The astronomers used telescopes in Chile and Brazil to obtain high-resolution
spectra of several Sun-like stars, including 18 Scorpii. Using a precise
distance to the star measured by the Hipparcos satellite launched in 1989, they
determined very accurately how much light the star emits.
After analysing the data, the researchers conclude that 18 Scorpii 鈥渟urpasses
all previously claimed solar twins in likeness to the Sun鈥�. As far as they can
tell, the star鈥檚 mass, temperature, colour, surface gravity, rotation speed,
surface activity and iron abundance match the Sun鈥檚. Only the luminosity and age
differ modestly: 18 Scorpii emits 5 per cent more light than the Sun and it is
slightly older.
The Sun鈥檚 most famous near-twin is Alpha Centauri A, a yellow star just 4.35
light years away. But compared with 18 Scorpii, Alpha Centauri A is a distant
cousin: it emits 52 per cent more light than the Sun and has 60 per cent more
iron. Furthermore, Alpha Centauri A has two companion stars, whereas 18 Scorpii
and the Sun are single. Single stars such as 18 Scorpii offer the best prospects
for having planets with stable orbits.
鈥淲e recommend that it be considered for strong priority in the ongoing planet
searching programmes as well as in SETI surveys,鈥� say the astronomers. They will
publish the results in the 10 June issue of Astrophysical Journal
Letters.
Ed Guinan of Villanova University in Pennsylvania says that observations of
18 Scorpii could shed some light on climate change: 鈥淪olar twins can tell us
about the Sun, which is the main driver of Earth鈥檚 climate.鈥�