"It could happen almost any time now. We now have the technological capability to identify Earth-like planets around the smallest stars."
David Latham -Harvard-Smithsonian Center for Astrophysics
As astronomers become more adept at hunting for, and finding, exoplanets orbiting stars beyond the Solar System, international astronomers have figured out just what we should be looking for using the increasingly sophisticated technologies being developed.
Two exoplanets and an unknown celestial object, findings of the European Space Agency's COROT mission, an important stepping stones in the European effort to find habitable, Earth-like planets around other stars. These discoveries mean that the mission has now found a total of four new exoplanets.
COROT has now been operating for 510 days, and the mission started observations of its sixth star field at the beginning of May this year. During this observation phase, which will last 5 months, the spacecraft will simultaneously observe 12,000 stars.
Future telescopes such as NASA's Kepler, set for launch in 2009, would be able to discover dozens or hundreds of Earth-like worlds. The Space Interferometry Mission (SIM), to be launched early in the next decade, consists of multiple telescopes placed along a 30 foot structure. With an unprecedented resolution approaching the physical limits of optics, the SIM is so sensitive that it almost defies belief: orbiting the earth, it can detect the motion of a lantern being waved by an astronaut on Mars
The SIM, in turn, will pave the way for the Terrestrial Planet Finder, to be launched late in the next decade, which should identify even more earth-like planets. It will scan the brightest 1,000 stars within 50 light years of the earth and will focus on the 50 to 100 brightest planetary systems. The TPF will allow the follow-up studies to learn about these planets' rotation and weather, and the composition of their atmospheres.
All this, in turn, will stimulate an active effort to determine if any of them harbor life, perhaps some with civilizations more advanced than ours.
The two new planets discovered by COROT are gas giants of the hot Jupiter type, which orbit very close to their parent star and tend to have extensive atmospheres because heat from the nearby star gives them energy to expand.
“Scientists suspect that with the detection of COROT-exo-3b, they might just have discovered the missing link between stars and planets.”
In addition, an oddity dubbed ‘COROT-exo-3b’ has raised particular interest among astronomers. It appears to be something between a brown dwarf, a sub-stellar object without nuclear fusion at its core but with some stellar characteristics, and a planet. Its radius is too small for it to be a super-planet.
If it is a star, it would be among the smallest ever detected. Follow-up observations from the ground have pinned it at 20 Jupiter masses, which makes it twice as dense as the metal Platinum.
“COROT has also detected extremely faint signals that, if confirmed, could indicate the existence of another exoplanet, as small as 1.7 times Earth’s radius.”
COROT was launched atop the Soyuz from the Baikonour cosmodrome in Kazakhstan on 27 December 2006. Settled in its almost-circular polar orbit ranging between 895 and 906 km above Earth's surface, the spacecraft was first powered on 2 January 2007 and started its science observations on 3 February of the same year.
Exoplanets have rarely been seen; rather, they have been indirectly observed by looking at the influence they exert on stars they orbit. But 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 pixel. By comparison, a simple cellphone camera typically takes pictures with about a million pixels, or one megapixel. However, a great deal of information about a planet can be gleaned from that single pixel and the way it changes over time.
Analyzing the data would work for any world that has continents and bodies of liquid on its surface plus clouds in its atmosphere, even if those were made of very different materials on an alien world. For example, icy worlds with seas of liquid methane, like Saturn's moon Titan, or very hot worlds with oceans of molten silicate (which is solid rock on Earth), would show up similarly across the vastness of space.
However, the method depends on clouds covering only part of a planet's surface, regardless of what each world is made of. Saturn's Titan, for example, covered by perpetual global smog, would not give up the mysteries of its weather or rotation, nor would the boiling hot Venus, with its complete shroud of clouds.
The key, the astronomers learned after studying data from Earth's weather satellites, is that while clouds vary from day to day, there are overall patterns that stay relatively constant, associated with where arid or rainy landmasses are. Detecting those repeating patterns would 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. Once the day's length is determined, then any variations in that period would reveal the changing weather--that is, clouds in a different place than the average.
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 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.
"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.
Among other things alien astronomers could probably tell that our planet's surface is divided between oceans and continents, and learn a little bit about the dynamics of our weather systems and whether its a good day for a landing.
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