Most Earth-Like Planet Found

April 26, 2007 — Leave a comment

I know this is literally yesterday’s news but here is my take on the story anyway. Researchers using the ESO 3.6m telescope in Chile have analysed the wobble of a star known as Gliese 581 (centre of starfield below). This star is about 20 light years away. Previously, a Neptune-like planet was found around this star by people using the HARPS data.

Gliese stars

Now the new research shows that there three planets, currently designated Gliese 581b, c and d (a is the star). The c planet is the Earth-like object. With a mass five time that of Earth and a diameter about 1.5 times. Using the fun AstroGrav software, which models masses such as solar systems as they interact via gravity, I made a mock up of the Gliese 581 system to help better visualise it using th data given in the paper.

Gliese system model

It should be stressed that there is no information given on many of the orbital parameters. That means that what I have modeled is not real and should be used only as a guide. I know the masses and orbital periods as well as the radius of the orbits and their eccentricities. I don’t know the inclination of each planet’s orbit to the plane of the system or the radii of the b and d planets.Even though the planet orbits very near to the central stars compared to the Earth, the star itself is much weaker. In fact the planet is believed to be in the habitable zone, a ring around the star in which a planets could support liquid water. In the image below (from ESA’s website) you can can see how the habitable zone moves outward as the star gets more powerful. Gliese 581c is more like the top scenario in this diagram.

Habitable Zone
So naturally the similarity in size and orbit, with the temperatures needed for liquid water (and thus life as we know it) has lead to much speculation on the news (bloody BBC Breakfast!) that this is our best best for life so far. Whilst this is true, it involves two large assumptions that are so far unfounded. There is no reason to think there is water on this planet. Not a single molecule of it necessarily exists and we will need to work very hard to detect it given its distance and that it sits in an (as far we know) three planet system.Secondly, we really don’t know anything about this little planet.

Yes, it is exciting that as our method improve we can find smaller and more Earth-like planets. However there is nothing to indicate that this planet looks anything like the Earth.Now don’t get me wrong, I am excited by this discovery. The indication, as I just said, that we might be able to pick out such tiny planets in the galaxy and relatively nearby is very exciting. This world has very strong gravity and a neighbour planet that flies through its sky every few days, possibly causing subtle eclipses and displaying rapidly changing phases like our Moon. Such an exotic world inspires the imagination and i hope that as we discover ever-more Earthy worlds we can see how our way of existing is just one of millions of possibilities in our galaxy alone.

So to conclude I shall change my tone. Yesterday we had news of the most Earth-like planet yet discovered. The cool thing though, is that we haven’t even begun our search for these terrestrial worlds really. The telescopes and techniques that are coming into use in the nest few years will completely bow away this amazing find. In about twenty or so year we might be lucky enough to even see a picture of one of these worlds. Maybe it will have continents and oceans like our own, maybe it will be more exotic than we had ever dreamed.

Maybe someone will be looking back.

Gliese Artists Impression

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