Exoplanets

Planets, Planets, Planets…………. More planets

William Herschel discovered the planet Uranus on 13^th March 1781. Johann Gottfied Galle spotted the planet Neptune on 23^rd September 1846 right at the expected area. Clyde Tombaugh in the year 1930 on 18 ^th February identified a tiny spot to be a planet that we know as Pluto. The planets from Mercury to Saturn are known to us from ancient times as they are very much visible in the night skies, but the later three planets are so far from us that they are not visible without the aid of telescopes. Though Uranus sometimes can be seen through naked eyes also, but it will look no different than a faint star.

The quest of man to explore the Universe seems to be a never-ending quest. After having discovered three planets of our solar system, scientists felt the need to study them in detail. For that reason several unmanned spacecrafts were sent and are sent today to study and analyze these planets. To name a few of the spacecrafts, Voyager, Pioneer, Viking, Apollo, Cassini, Galileo, Mariner – all these spacecrafts has given mankind tremendous information.

While scientists study and update their knowledge of the planets of the solar system, a few institutes were busy studying the planets that are not of the solar system. The planets that do not go around our Sun but go around other stars are called Exoplanets: planets that do not belong to the solar system, they are external.

Our Sun is a star and all stars are suns. The Sun being closer to the earth seems to be bigger when compared with other stars. So if the observer goes far enough, he would see the Sun just like a star! If our Sun is also an ordinary star then why couldn't the stars that we see have planets too like our Sun?

Now the important point is to detect or identify the planets. Stars are so for away from is that even best telescopes show not much of details and Planets are much smaller then their parent star, the can be 5000 to 1,000 times smeller and plus they do not have their own light. The task of spotting planets around other stars is a years difficult one, but due to several advanced techniques we have detected 145 planets!

This May, at Baltimore. U.S, astronomers gathered to celebrate the tenth anniversary of the first planet discovered arrant a normal star other than the sun. Since 1995 up to now (2005), the number of planets that belong to other stars is 145. Majority of these planets are as massive as Jupiter, means they are gas giants. It is not that there are only gas giants in the universe, but they because of their more mass they can be detected easily.

Why are scientists searching for planets that are outside our solar system? The answer to this question lies in the following question: Does life exists elsewhere in the Universe? Life, if it exists elsewhere, it shall be found only at such a place where the condition is pleasant for the life to evolve, and such environment would be available on a planet, not on any star as they are too hot, heavy radiations, intense gravitational fields and magnetic fields, all these conditions are very unfavorable for life.

We have yet not succeeded in finding the existence of any sort of life anywhere else in the solar system (leaving earth). Yes, but we do speculate and hope that in the interiors of Mars there could be some life in the form of microorganisms, there could even be life in a particular atmospheric layer of Venus. There are even speculations being made about the existence of life on a few satellites of the planets like Saturn and Jupiter.

Our search of life is now extended to the planets of other stars. This new field is still in its early stage of growth, new techniques are being developed by which scientists will be able to detect terrestrial planets, where the chances of finding life is more.

One technique to detect a planet around the star is to track the motion of a star over period of 1 to 10 years. If the star is alone, then its motion will be non-disturbed one, means straight. But, if it is having a companion, then along its line of motion the star will be seen to wobble. This wobbling occurs because its companion gives a gravitational tug to its star. So the star will be seen deviating back and forth from its straight line of motion. The amount of deviation depends upon how heavy its companion is, usually the earth like planets will not be able to tug its star much and hence we will not be able to detect the existence of small planets around other stars.

Another technique used is to measure the luminosity of a star over a period of time. If no variations are noticed then it can be assumed that no (medium or large size) planet is eclipsing the star. The star under examination will show variations in its luminosity if a planet is going around it, the luminosity will decrease when the planet will come between us and the star and will again become normal when the planet is not in the straight line between us and the sun. The amount of variation and time interval between two variations will give enough data to expose the statistics of the planet that is going around the star. First we will know the time the planet takes to complete one revolution around the star, second a rough estimate of its angular diameter. It will also reveal its composition, that is we will come to know that does it have any atmosphere or not, and if it is having an atmosphere then what are its constituents. By knowing the constituents of a planet's atmosphere, we can also infer about the possibility of life or whether the conditions are favorable or not for the life to exist there.

51 Pegasi b is the first exoplanet discovered around a sun-like star outside of the solar system. It resembles Jupiter in terms of mass and size, i.e. it is a gas giant going around a star called 51 Pegasi in the Pegasus constellation. 51 Pegasi b is informally called as Bellerophon, a Greek hero (mythology). Michael Mayor and Didier Queloz discovered the planet on October 6, 1995. It is very close to its star (even closer than the Mercury planet) and circles its' star in a period of 4.23 earth days! Earth takes 365 days and Mercury takes 88 days to complete one revolution around the Sun. This will give idea of how close the planet must be to its star and also how fast it must be going around it.

There are peculiarities of every planet that are being discovered, some are too large, some have very elliptical orbits, some have higher concentrations of heavy elements. All theories that talk about the formation of planets and even stars needs a rethinking and this problem will keep the scientists busy for a few more decades.