George R. Ricker, senior research scientist at the Kavli Institute for Astrophysics and Space Research at MIT
Google has joined MIT scientists who are designing a satellite-based observatory -the Transiting Exoplanet Survey Satellite (TESS)- that they say could for the first time provide a sensitive survey of the entire sky to search for earth-like planets outside the solar system that appear to cross in front of bright stars. Google will fund development of the wide-field digital cameras needed for the satellite.
"Decades, or even centuries after the TESS survey is completed, the new planetary systems it discovers will continue to be studied because they are both nearby and bright," says George Ricker, leader of the project.
Most of the more than 200 extrasolar planets discovered so far have been much larger than Earth, similar in size to the solar system's giant planets (ranging from Jupiter to Neptune), or even larger. But to search for planets where there's a possibility of finding signs of living organisms, astronomers are much more interested in those that are similar to our own world.
Most searches so far depend on the gravitational attraction that planets exert on their stars in order to detect them, and therefore are best at finding large planets that orbit close to their stars. TESS, however, would search for stars whose orbits as seen from Earth carry them directly in front of the star, obscuring a tiny amount of starlight. Some ground-based searches have used this method and found about 20 planets so far, but a space-based search could detect much smaller, Earth-sized planets, as well as those with larger orbits.
This transit-detection method, by measuring the exact amount of light obscured by the planet, can pinpoint the planet's size. When combined with spectroscopic follow-up observations, it can determine the planet's temperature, probe the chemistry of its atmosphere, and perhaps even find signs of life, such as the presence of oxygen in the air.
The satellite will be equipped with six high-resolution, wide-field digital cameras, which are now under development. Two years after launch, the cameras--which have a total resolution of 192 megapixels--will cover the whole sky, getting precise brightness measurements of about two million stars in total.
Statistically, since the orientation of orbits is random, about one star out of a thousand will have its planets' orbits oriented perpendicular to Earth so that the planets will regularly cross in front of it, which is called a planetary transit. So, out of the two million stars observed, the new observatory should be able to find more than a thousand planetary systems within two years.
In fact, if a new estimate based on recent observations of dusty disks is confirmed, there might even be up to 10 times as many such planets.
Because the satellite will be repeatedly taking detailed pictures of the entire sky, the amount of data collected will be enormous. As a result, only selected portions will actually be transmitted back to Earth. But the remaining data will be stored on the satellite for about three months, so if astronomers want to check images in response to an unexpected event, such as a gamma-ray burst or supernova explosion, "they can send us the coordinates [of that event] and we could send them the information," Ricker says.
Because of the huge amount of data that will be generated by the satellite, which could launched as early as 2012, Google has an interest in working on the development of ways of process that data to find useful information.
Regardless of the funding for the satellite, the same wide-field cameras being developed for TESS could also be used for a planned ground-based search for dark matter in the universe--the invisible, unknown material that astronomers believe is more prevalent in space than the ordinary matter that we can see. Some of the unknown dark-matter particles must constantly be striking the Earth, and the plan is to train a bank of cameras inside tanks of fluid deep underground, to detect flashes of light produced by the impacts of these dark particles. Ricker's Kavli group is participating with MIT physics professor Peter Fisher's team in this new physics research initiative.
The electronic detectors for the new cameras are being developed in collaboration with MIT's Lincoln Laboratory. The lab's expertise in building large, highly sensitive detectors is a significant factor in making possible these unique cameras, which have no moving parts at all. If all goes well and funding is secured, the satellite could be launched in 2012 with NASA support, or even earlier with a private sponsor.
Posted by Casey Kazan. Adapted from an MIT release.