New close, Earth-like planet
Well, everyone’s blogging about it, so I have to chip in. Recently announced, scientists have found an Earth like planet only 20 light years away, and in the so-called “habitable zone” of its star.
Basically: By studying the motion of star Gliese 581 in the constellation Libra, astronomers were able to detect a planet with about 5 times the mass of Earth (about half as big again in diameter). Models suggest that it’s made of rock, quite similar to Earth. But most significantly, it’s at the right distance from the star for its surface temperature to be between 0-40 degrees - just the right temperature for liquid water, a requirement for life as we know it. Interestingly, the star is a red dwarf, a relatively cool slow burning star. This new planet is much closer in to its star than Earth is, but becase the sun is cooler, it doesn’t get fried. There’s no guarantee that the planet does have water, let along life, but at the very least it’s the first planet discovered which really ticks all the boxes.
I’ve got to say, I can’t help but be excited by this. There’s a potentially habitable planet among the 100 closest stars to Earth. Sure, it might just be chance - but if there really are lots of planets like this out there it really ups the argument for extraterrestrial life! It also means (and here I’ll be very speculative) that this planet could be the target of extra-solar exploration. Sure, this is a long way off (bets, anyone? I’d be surprised if it was within 100 years - maybe 200 as a ballpark figure?) and the logistics and travel time are enormous but 20 light years with a defined target makes it just a little more possible, I feel. Of course, I’d kind of like to get our own planet in order first…
Anyway, the book makers have already shortened the odds on alien life, so we must be getting closer!
If there are aliens there, they would be lucky.
Gliese 581 c is roughly 0.073 AU from its star (compared to 0.387 AU for Mercury), and Gliese 581 (the star) has a mass of 0.31 solar masses. Now, the precession of the planetery periapsis (equivalent to perihelion in the solar system) is proportional to M^{3/2}/r^(5/2). That means that the periapsis advance of Gliese 581 c is 11.16 times bigger than Mercury’s. Note that I didn’t take into account eccentricity (they seem to be similar, though: 0.16 for Gliese 581c and 0.2 for Mercury). The orbital radii I quoted are for the semi-major axis.
Imagine these aliens trying to develop a theory of planetary motion with such a large anomalous effect on their own planet. I wonder if it would be different to the way humans did it, with the evolution from Kepler’s laws to general relativity.