Are you looking for a second Earth? We need to – humanity is on the fast track to ruining our one.
Of course it’s not an easy task. A planet discovered the other week with the help of Kiwi astronomers underlines the problems. Four astronomers here in New Zealand contributed data to the OGLE microlensing follow-up network program in 2012. The results were published recently – and the good news is, OGLE found a planet.
OGLE, incidentally, stands for ‘Optical Gravitational Lensing Experiment’. An apt acronym. It works by exploiting a quirk of Einstein’s theory of relativity – that mass distorts space-time. Massive stars bend light around themselves, acting as ‘lenses’ and enabling us to point a telescope at the massive star, and so detect faint objects passing directly between us and them, that we wouldn’t otherwise be able to observe. The gravity lens around the distant star is known as an ‘Einstein Ring’, and the method is usually used to pick up planets orbiting in the ‘halo’ of a star – the debris orbiting it, like our Oort Cloud. These are known as Massive Compact Halo Objects (MACHOS). Cool or what?
Anyhow, back to the news. The planet is called OGLE-2013-BLG-0341LBb, and it’s about 3000 light years away in the constellation Cassiopeia.
The good news?
- It orbits its sun at 0.8 AU – nearly the distance of Earth (yay!)
- It’s about Earth sized – mass is thought to be only twice ours (yay!)
- That doesn’t imply twice our surface gravity (yay!) [I can't calculate it unless I know the radius and density of the planet, which I don't, but if density is the same as Earth, average 5.5 g cm <exp>3, then the surface gravity won't be double because surface gravity is also proportional to the radius. Just saying.]
- It’s orbiting just one star in a binary pair (Tattooine, sort of – yay!)
So is this Earth 2? Well, if I were you I’d take warm clothes. The bad news is that the star is a red dwarf, 400 times less energetic than the Sun, so the planet has a surface temperature of 60 degrees Kelvin – in centigrade, a chilly -210 degrees. (Booooo!)
The search for Earth-like planets has got exciting lately as we’ve developed the tech to discover them. Problem is, the gear is not good enough to image them directly. We can’t learn much other than the size and orbital distance – from which we can derive its year, mass and temperature. If we’re lucky, we might also get a handle on its atmospheric makeup, via spectrography as it transits its sun.
For these reasons, usually when we detect a planet that’s otherwise in the ‘goldilocks’ zone, we don’t know whether it’s actually like Earth. It might be like Venus - runaway greenhouse with sulphuric acid, crushing atmosphere and oven-like temperatures. We don’t know. Don’t forget, if astronomers 3000 light years away were using the same techniques to analyse our solar system, they might conclude there were two Earths here from the planetary mass and orbital data.
The way things are going, of course, we’re likely to end up with two Venuses. Venuses? Venii? You know what I mean.
And it’s a worry.
Copyright © Matthew Wright 2014