The search for new solar systems has become the new exciting game with the recent discovery of the fifth planet around a distant star 55 Cancri, by astronomers working at the world famous W M Keck Observatory on Mauna Kea in Hawaii. The star 55 Cancri, located 41 light years away in the constellation of Cancer, having almost the same mass and age as our own Sun, is only the second star discovered so far, having a planetary system of its own like our Sun.

Even though nearly 230 individual exo-solar planets have been discovered during the last 15 years, the only other star with a planetary system discovered to date is mu Ara in the Southern Sky, which has four planets circling round it. It has taken over 15 years of painstaking and systematic observations of more than 2000 nearby stars by some of the most sophisticated telescopes such as Shane Telescope of Lick Observatory in San Francisco and Keck Observatory in Hawaii to put together the true picture of the 55 Cancri exo-solar planetary system. The fact that we have started discovering other stars having a rich variety of planetary systems like our own Sun has made planetary hunt a most exciting game. 

Speculation regarding the existence of life elsewhere in the universe and search for Extraterrestrial Intelligence (SETI) have been the subject of intense interest with scientists and philosophers, since the time of Anaximander, who first elaborated on the existence of other worlds around 500 B C. The classification of main sequence active stars based on their temperature derived from the epoch making discovery of  Meghnad Saha, provided the key to unlocking the mystery of stellar evolution. It was clear that neither the hottest massive stars which burn out quickly with a lifetime of a few million years nor the smaller cool stars are likely to have planets capable of supporting life, which requires billions of years to evolve.

However, based on probabilistic calculations, most of the scientists believe that the majority of billions and billions of stars resembling our Sun, both within our own galaxy and other galaxies exceeding ten billion, could have earth like rocky planets where life and in some cases even intelligent technological civilisations could have evolved. 

In spite of the sound logic behind our argument that our solar system with eight planets and evolution of life and intelligence on planet Earth, is neither unique nor purely accidental and there must be many other similar solar systems which should have evolved like our own, astronomers had not even detected exo-solar planets let alone planetary systems and presence of life till recently.  This was primarily due to the poor sensitivity of our telescopes and large distances involved in locating planets around other stars.

It is only during the last 15 years with the intensive search of the skies, both from the ground and space, using highly sensitive telescopes, that about 230 exo-solar planets have been discovered. It is hoped that the 27 cm diameter telescope named COROT (Convection Rotation and Planetary Transits) launched on December 27, 2006 would discover many more planets, some of which will no doubt be Earth like rocky planets. While practically all the exo-solar planets discovered so far are individual planets orbiting around massive neutron stars, this is the first time discovery of planetary systems is being reported. 

The newly discovered planet, which is probably like Saturn, is the fourth planet from the centre of 55 Cancri star. It is 45 times as heavy as earth and orbits around 55 Cancri in 260 days in a circular orbit at a distance of 72.5 million miles from the star. The inner most planet of 55 Cancri is about the size of Neptune located just at a distance of only 3.5 million miles from the parent star and orbiting around it in less than 3 days. The second planet is slightly smaller than Jupiter circling round every 15 days at 11.2 miles from the star, and the third is as massive as Saturn which orbits round 55 Cancri every 44 days at a distance of 22.3 million miles. The most distant fifth planet located 539.1 miles away from 55 Cancri has a mass of about four times Jupiter and completes its orbit around 55 Cancri every 14 years.  

Scientists have yet to discover a twin of our solar system with at least one earth like planet. Even though intensive planetary hunt during the last 15 years has so far led to the discovery of just two full-fledged solar planetary systems outside our Sun, it gives us the hope that the exciting discovery of a few solar systems like our own is not far behind. The discovery of Earth like habitable planets, having physical conditions hospitable for the evolution of life and intelligence, is the first step towards the discovery of alien life, which, if and when discovered, will undoubtedly go down in the history of science as the crowning glory of humanity.
(The writer is Chairman, PRL-Council, Department of Space.)