Scarcely had the electrons dried on my last post about extrasolar planets than some pretty dramatic news hit the wires: discovery of the most Earthlike extrasolar planet yet, orbiting the star Gleise 581, about 20 light years away. The star is a dim red dwarf - though quite close as stars go you would need a telescope to see it - and it was already known to have two other planets.
Earthlike is a relative term - I wouldn't recommend buying real estate there yet, even if we had a way to get there. The planet is at least eight times Earth's mass, thus probably about twice its size - possibly rather more, if it is largely made of less dense stuff than rock, as big planets usually are. All we know about it is its distance from the parent star, 0.073 AU* (about 10 million km), and its minimum mass - the mass may be greater, for reasons I'll go into if someone wants me to.
* An AU, "astronomical unit," is the average distance from the Earth to the Sun - about 150 million kilometers, or 93 million miles for those of us in countries where they still use medieval units. Get used to it, because I will be using AUs a lot here.We also know how bright the star is - not very (about 1/200 as bright as the Sun) - from which we can determine how much sunlight, or Gleise 581-light, it gets. Even this little bit of information, however, is enough to take a fair first guess at the planet's temperature, which comes to about 0-40 degrees C (32-104 F) - a temperature that permits liquid water, the most basic stuff of life. It could be colder if it is covered with ice that reflects away most of the light that otherwise would warm it, or much hotter if it has a dense greenhouse atmosphere like Venus. Still, it is at the right distance to have liquid water, which is a very good start. Conceivably - pure speculation here - it could have a lot of liquid water, perhaps a hydrosphere several thousand kilometers deep, making Earth's oceans look like a thin muddy film by comparison.
This discovery isn't just cool - it is awesome.