Finding another Earth isn’t easy. Unfortunately.

Are you looking for a second Earth? We need to – humanity is on the fast track to ruining our one.

Simulated Exo-Earth. A picture I made. Apart from the fractal artefacts, does anybody notice what's wrong with it?
Simulated Exo-Earth. A picture I made. Apart from the fractal artefacts, does anybody notice the science issue that I didn’t correct?

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!)

Let me illustrate mass vs surface gravity. Although it has a mass 14.5 times that of Earth, 'surface gravity' on Uranus is just  89 percent that of Earth. That's because the radius is about 4 times Earth's. I made this picture with Celestia.
Let me use Uranus to illustrate mass vs surface gravity. Although it has a mass 14.5 times that of Earth, ‘surface gravity’ on Uranus is just 89 percent that of Earth. That’s because the radius is about 4 times Earth’s. I made this picture with Celestia.

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


9 thoughts on “Finding another Earth isn’t easy. Unfortunately.

  1. I’m confident there are other habitable planets out there — it’s just a matter of finding them. And it’s made harder by the fact that we can only see so far, so it’s possible there aren’t actually any habitable planets in our current vision range, but there might be some lurking just beyond.

    1. I’m inclined to agree. The impression I get is that other solar systems are way more weird and wonderful than we imagined. And ours is pretty boring and relatively uncommon by those standards. Maybe every planetary system is unique in its own way. That also suggests to me that the chance of finding another earth among the relative handful of stars that are local to us iow. But if we look far and hard enough I am in no doubt we will find one.

    1. For me the neatest part of the exoplanet hunt is the sheer coolness of tbe science and thinking that goes into it. An awesome application of satellite instruments, ground data and some pretty arcane physics.

    1. Science is filled with whimsy… And I can’t help thinking that physicists are pretty good at finding it. I’m sure they will find a habitable Earth type world before too long. The problem will be getting there at the speeds our rockets travel (bring a book…War and Peace recommended…).

  2. “OGLE.” Love it. That’s perfect. I’m just glad we’re looking. It’s stupid to put all your eggs in one basket. We’ve got to find another nest to insure our survival. It doesn’t matter that we can’t get there…yet. It’s going to take a while to find Earth 2, so we may as well get started now. Even when we find one in the Goldilocks zone, so many things could go wrong. Too much/too little gravity. Hostile bacteria, incompatible proteins, incompatible cellulose. Aggressive fauna. The list goes on. We’ll have to find many potential candidates to get the right one.

    Even before we head out to a promising planet, we need to learn how to live in a closed-cycle habitation, and get used to the idea. If we had half a brain, we’d already be trying this out in domes on the moon. If we can make it there, we can make it anywhere, so we may as well get started now.

    1. I agree. If we’re to do ‘space’ at all, we need to get experience – and a LOT of experience – at how living and travelling in it works in every detail. And where better to do that than our own back-door? The problem, I guess, will be paying for it – itself, not a problem providing there’s enough public enthusiasm. We gotta keep working on promoting space!

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