Washington, December 22 : A new study has figured out what astronomers on Earth and possible aliens in other parts of the universe may learn about a planet from very distant observations, with the help of telescopes much more powerful than the ones that are currently in use.
The research team, which includes a professor from MIT, says among other things, the telescope could probably tell aliens that the surface of Earth is divided between oceans and continents.
The analysis says that such telescopes may also be helpful in learning a little bit about the dynamics of the weather systems on the planet.
"Maybe somebody's looking at us right now, finding out what our rotation rate is - that is, the length of our day," says Sara Seager, associate professor of physics and the Ellen Swallow Richards Associate Professor of Planetary Sciences at MIT.
Most of the planets astronomers have discovered beyond the Solar System have not actually been seen. They have instead been indirectly observed by looking at the influence they exert on stars they orbit.
It is believed that even with the most advanced telescopes planned by Earth's astronomers for use over the next several years, a planet orbiting another star would only appear as a single point of light. Except its brightness and colour, the planet will not provide any other detail.
However, the latest analysis suggests that a great deal of information about a planet can be gleaned from a single pixel, and the way it changes over time.
"The goal of (our) project was to see how much information you can extract" from very limited data, Seager says.
She says that the way of analysing the data the she and her co-authors studied would work for any world that has continents, bodies of liquid on its surface, and clouds in its atmosphere, even if those were made of very different materials on an alien world.
After studying data from Earth's weather satellites, the astronomers learnt that while clouds vary from day to day, there are overall patterns that stay relatively constant, associated with where arid or rainy landmasses are.
They say that detecting such repeating patterns may allow distant astronomers to figure out the planet's rotation period because a brightening associated with clouds above a particular continent would show up regularly once each "day," whatever the length of that day might be.
According to them, once the day's length is determined, any variations in that period would reveal the changing weather, such as clouds in a different place than the average.
No telescope currently in use is capable of making the measurements that Seager and her team analysed. However, it is believed that planned telescopes such as NASA's Kepler, set for launch in 2009, would be able to discover dozens or hundreds of Earth-like worlds.
Then, says Seager, even more advanced space observatories being considered, such as NASA's Terrestrial Planet Finder, would allow the follow-up studies to learn about these planets' rotation and weather, and the composition of their atmospheres.
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