It is not surprising, and it was just a matter of time, but it appears that scientists have now found a fairly reasonable candidate for a place which could support life outside our solar system.  http://www.bbc.co.uk/news/science-environment-16040655?mid=5475  See article below.

With fantastic advances in the ability of astronomers to see distant objects it became clear a few years ago that it was just a matter of time before they would be able to see earth-like planets.  This is a very exciting time for astronomy and cosmology.  The technology is interesting.  Planets have been detected by more than one means.  It is worth noting that scientists have not actually seen any planets outside our solar system yet.  Even the brightest of planets cannot be detected by the most powerful telescopes, although this, too, might become possible eventually.

There are at least two methods scientists have used to detect distant planets.  The first is by observing the very slow wobble of distant stars.  When a gas giant like Jupiter orbits a star, the mutual pull of the planet and the star for one another creates a very slight wobble in the visible position of the star.  Stars with gas giants even larger than Jupiter, with the planets closer to their star than Jupiter is to ours have been detected this way.  This method has not yet been used to detect earth-like planets.  It is the other method which is most interesting for us. 

The second method for detecting a planet is when the planet passes in front of the star from the perspective of observers on the earth.  This creates a partial eclipse of that star.  The decrease in light from the star is very slight–much less than 1%.  Yet, with close neighbor stars, and with astronomer’s ability to study thousands of stars simultaneously, they have been able to detect planets by this method.  From the amount of light occlusion and from the period of orbit, scientists are able to estimate both the distance and the size of these planets. 

The recent announcement of the discovery of Kepler 22-b is just such a success.  Kepler 22-b is a little bit more than twice the diameter of the earth and is within the theoretical "zone of inhabitability" for planets on that star.  The zone of inhabitibility is given this name because for any star there is a range of distances from the star over which it is reasonable to assume that water on that star could be in a liquid state, allowing for the theoretical possibility that life analogous to what is found on the earth could subsist on that planet.  The estimated average temperature for the planet in question is about 20 degrees centigrade.  This is a very rough estimate because the actual temperature on a planet will depend heavily on the content of the atmosphere–something which we are observing on our home planet as global warming occurs due to the rise in carbon dioxide and methane in our own atmosphere.

While the discovery is 1. Not terribly surprising, as all scientists would have predicted the existence of such a planet  and    2. Nevertheless exciting as it is the first such confirmed discovery   we should be careful to oversell the discovery.  First of all, this method of discovery, unlike the wobble method described above, does not give the mass and therefore does not give the density of the planet.  For this reason, we do not even know for sure if it is a rocky planet.  Quite likely it is, but it is not clear that the current method will even be able to establish this most basic property.  Besides, in order for a planet to support significant life, it must have a very large iron content in order to protect against the solar "wind" coming from its star.  Even if Kepler 22-b is rocky, we will not easily know if it is made of mostly iron as our earth is.  Then, of course, there is the question of whether this planet actually supports life.  It is difficult to conceive how this can be answered without actually traveling to the planet.  So, as exciting and fun as the discovery of Kepler 22-b is, we should bear in mind the limitations of the implication of this accomplishment.

John Oakes