NASA’s Kepler mission
NASA is searching for Earth-like planets in a specific area of the Milky Way galaxy, the galaxy to which we belong. This is being done by putting a spacecraft outside the atmosphere of the Earth. Even as you are reading this, the Kepler spacecraft is collecting brightness information from about 100,000 stars. This information will then be analysed to find out if there are any planets orbiting it.
The technique used is explained in this animation. What they do is essentially this. They continuously observe the brightness of the stars. If a planet moves across a star (called a transit) then the planet will block some of the light that comes out from the star and hence the brightness will go down. After the planet has passed, the brightness will come back to its normal level. It is these drops in brightness that will tell us that some planet is rotating the star being observed.
Of course a solitary drop in brightness does not suggest a planet. A planet is confirmed only if there are multiple transits, each having the same amount of drop in brightness, the same duration of drop, and a constant interval between the drops.
But the reason why I am writing this post is to show you the picture below. Click on it. The enlarged picture is worth spending some time looking at.
These are the 1235 candidate planets that were identified till March 2011. The second row gives a picture of the Earth so that the rest can be seen relatively. But if you thought that the picture was the Earth, then join the club. No, the picture is that of the Sun. As discussed above planets are observed in transit against the background of their stars. Here, the bright disk is the Sun. Do you see a dark dot in that disk? If it is not very clearly visible click on that picture and look at the full size pic. Now the dot is visible, right? That dot is…
No, neither is that the Earth. That is Jupiter, the biggest planet of our solar system. If you really want to see the Earth, download this full resolution picture that NASA has uploaded to flickr. It is 9.3 MB in size. But me being the large hearted soul, I have downloaded it and cut out that part alone for you to see it below.
Do you see the Earth now? I still recommend that you download that full resolution picture. It is fun.
Now, coming back to the Kepler mission. One interesting point about this is that the drop in brightness can be observed only if the orbit of that planet is aligned along our line of sight. If not the planet will not obstruct our view of that star and hence no drop in brightness will be observed.
I will let the Kepler FAQ take over here.
For Kepler to detect a transiting planet, its orbit plane must be lined up with our line of sight. Most of the time, the extrasolar planets’ orbital planes do not line up. For Earth-size planets around Sun-like stars, the chances of randomly oriented orbital planes being in the correct orientation for Kepler to see a transit is about 0.5%. That is why the design of Kepler called for a very wide field telescope to be able to observe more than 100,000 stars. If all those stars had Earth-size planets, about 500 (100,000 x .005) would be in the correct orientation to transit. Statistically, we can infer that every planet Kepler detects represents hundreds more planets that are out there but not detectable due to inopportune orbital orientation.
Thus, if we have discovered 1235 planets, then there must, about 245,675 undetected planets out there. There are many more such interesting pieces of information on their FAQ page. Spend some time there to see what humankind is trying to do.
But if any of you reading this is thinking of moving to one of these planets once we exhaust our energy supplies here and pollute it sufficiently enough to render it useless for human habitation I am sorry to say that there is bad news.
The stars that Kepler is observing are in the range of a few hundred to a few thousand light-years away. One light year is about 6 trillion (6,000,000,000,000) miles.
In plain English, the theoretical minimum to reach even the closest of these stars is a few hundred years. There you go (pun half intended).