Sep 08 2009


Published by under Astronomy
Comments: 6

There has been much talk in recent years about the ongoing discovery of exoplanets – planets around suns other than our own. The technology to detect these distant objects has been increasing recently. There are two primary methods for detecting exoplanets: One method is to look for the wobble in the parent star caused by the gravity of the planet. The planet and its star revolve around their center of gravity, which will not be in the dead center of the star itself, but off center, causing a wobble.

earth-saturn-sThe second method is called the transit method in which we look for alterations in the amount of light we can see from a star because of a planet that moves in front of it.  This requires that the view of this system from the earth is roughly in the plane the planet is orbiting – the planet has to move in front of (transit) the star from our perspective. The new Kepler telescope is designed to detect light from many stars with sufficient sensitivity that it can find small (earth-size) planetary transits.

With all the talk about exoplanets, there has been, until now, little talk of exomoons – moons around planets around other stars. Until Kepler it has simply not been possible to detect exomoons. David Kipping of University College London has now published a paper in which he says that this is feasible.

This is exciting. While the whole exoplanet exercise is fascinating and is giving us the ability to have some data about the constitution of other stellar systems, interest is highest in earth-like planets – planets around the same size and temperature as earth, specifically able to have liquid water. This, of course, is because we want to know how many planets out there might be capable of harboring life. This will enable us to get a better handle on at least one component of the famous Drake equation that can be used to calculate the likely number of alien civilizations out there.

It is likely, however, that earth-sized moons of larger gas giants could have conditions suitable for organic life. Even smaller moons could be candidates. In our own system, Jupiter’s moon Europa likely has a liquid water ocean under its surface ice crust – complete with alien creatures swimming around. In fact, life-bearing moons may vastly outnumber life-bearing planets.

Kipping thinks that Kepler is sensitive enough to detect the wobble in a large and light planet (like Saturn) caused by an earth-sized moon. We are just gearing up for the flood of new exoplanets Kepler will discover over the coming years, and now Kipping adds exomoons to the buffet (how’s that for mixing metaphors).

Kepler has already passed a test of its ability to detect exoplanets (by detecting planets we already knew were there). At present Kipping’s paper just deals with the mathematical plausibility of exomoons. We don’t know yet of any exomoons so this ability cannot be tested as it was for detecting exoplanets. It seems that we just have to wait and see – when Kepler detects new explanets will their transits wobble due to the presence of large moons. NASA could also point Kepler at known exoplanets of a size and mass that would make them good candidates for detecting their moons.

If this scheme works, then the number of possible candidates for exobodies that might contain life that we detect in the near future may significantly increase. Cool.

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