New worlds, new vistas

This column usually focuses on terrestrial matters, but it is time to go extra-terrestrial for just one week. The space buff in me is simply at a loss for words to describe the feeling of euphoria after hearing the news that there are thousands of Earth-sized planets in our galaxy alone. Count the other galaxies in, and you probably have millions more Earth-like exoplanets (planets outside our solar system) to choose from in the whole universe.

This discovery has been made by NASA's Kepler Space Mission, the space observatory purpose built to discover Earth-like planets orbiting distant stars. Why is this discovery so exciting ?

Until now, information on the most exciting class of potential planet, more similar to the earth and less like the gas giants such as Jupiter, was sparse. We do not know, in the strictest sense of the word, whether many or all of them are Earth-like. Earth-sized is the more accurate description, but there are plenty of reasons to be happy about.

The first is that there are far more exoplanets out there than the number we already know. Most of the exoplanets that we already know about are giants, possibly Jupiter-like. Astronomers knew that smaller exoplanets exist, but this is the first time that they have been detected in large numbers. Of course, there should be more smaller planets than larger ones in the galaxy, judging just by the composition of our own solar system.

The most significant reason is that the discovery of the planets may help answer the question 'are we alone in the Universe ?'. It will take many more years of research and more space missions to answer this question, but the chances of answering it in the affirmative just received a boost. (There really are no 'pictures' of these planets. Kepler is a highly accurate photometer married to a powerful wide view telescope designed to detect minute changes in stellar brightness as planets cross in front of a parent star. And Kepler can look at around 100,000 stars at once).

If there are many more Earth-sized planets in the universe, at least some of them could be candidates for harbouring life, even intelligent life. That will fundamentally alter the way we look at ourselves.

Our planet, the Earth, is perfectly placed to host life. It is at just the right distance from a star (Sun), it has an atmosphere and water and it is not too large. There could be other planets in other 'solar' systems which have similar conditions. That could be a harbinger for life, at least of the microbial variety. Or they may be having the primordial conditions which led to the evolution of life here on Earth.

While these planets may share similar traits with the Earth, they could also be different and spectacularly so. They will be different in terms of terrain and life forms, if any. Astronomers use several terms - super-earths, water worlds, methane planets, gas dwarfs, and even carbon (think substances like diamond !) planets.

Super-earth refers to terrestrial planets -- icy, rocky, liquid, or gas dwarfs -- that are larger than Earth. A water world is exactly that - a planet made up mostly of water, a la Kevin Costner's Waterworld. On such a world the ocean would be hundreds to thousands of kilometres deep. Or it could be ice. In methane worlds, water is replaced by natural gas.

Carbon planets would be made up of carbon compounds and given the presence of water, would be candidates for life. That is the basis of life as we know it. But what about life 'as we do not know it' ? There could well be other compounds which may have given life to bizarre forms of life in these exoplanets.

Exoplanets apart, our own solar system may have a spark of life in bodies other than the Earth. There is a lot of speculation about Mars, but scientists are even more excited about the likes of Titan, the largest moon of Saturn. Some scientists believe that unusual creatures, capable of withstanding extreme temperatures can be found on Titan, which has a very dense atmosphere. Winds blow on Titan, which has methane rain, volcanoes and experiences earthquakes. The only difference is the temperature of minus 180 degree Celsius. The present Cassini probe and another probe scheduled to go there by 2017 will perhaps provide the answers. Titan could be a model for the exoplanets we may find.

While Titan is accessible for a robotic landing probe or even a manned probe, most of the exoplanets are hundreds of light years away. (A light year is the distance light travels in a year - around 10 trillion kilometers). Unless a now-unthinkable propulsion system (remember Star Trek ?) is invented in the far future, deep space travel will remain a dream. It might never be possible to actually physically search for life in exoplanets. The good news is that technology will most probably be available to get more detailed images of exoplanets over the next 20 years.

The next best thing is to wait for a signal from deep space, signifying intelligent life. Astronomers have been doing that for decades, with no success. We have also sent a physical message on spacecraft that are now in deep space and we are also broadcasting non-stop to space. Someone out there might respond or even visit us.

But are not aliens visiting us already ? There are many unexplained sightings of Unidentified Flying Objects, but no one has conclusively proven that alien spacecraft have landed on Earth. Such an encounter will, of course, change everything.

In the meantime, the implications of the Kepler discovery are nothing short of exciting: there are billions of stars in the Milky Way galaxy, many millions of them are as old as our sun. If Kepler's data are true, there are probably millions of earth-like planets that have been circling stars long enough for life to evolve, if the history of Earth itself is any indication. We may not be alone in the universe, after all. As Sir Arthur C Clarke said, "Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering".