March 17, 2008 -- Astronomers have come up with an ambitious, brute-force observational technique to detect Earth-sized and perhaps habitable planets orbiting one of our nearest neighbor stars.
No stranger to science fiction fans, the triple-star system called Alpha Centauri is a tad more than four light-years away. The reality is that one or more Earth-like planets are thought likely to exist around one of the system's two small, almost sun-like stars: Alpha Centauri B.
"You can have planets orbiting each star if [the stars in the multiple star system] are far apart," explains astronomer Javiera Guedes of the University of California at Santa Cruz. Guedes is the lead author on a paper to appear in Astrophysical Journal about not only how to find those planets, but why they are thought to exist there.
Guedes and her colleagues ran and re-ran computer simulations to recreate the Alpha Centauri system over its early planet-birthing period of 200 million years.
No matter the initial conditions, the simulations all led to the formation of different planetary systems. All of them contained at least one Earth-sized planet, some of which formed inside the habitable, liquid-water zone around Alpha Centauri B.
The next challenge for the researchers is how to detect any such planets. The traditional approach is to look for a subtle wobble to the star, which indicates that it has planets swinging around it. The problem is that small, rocky planets are not heavy enough to produce large, easily detectable wobbles.
To get around that limitation, Guedes and her colleagues plan to use relatively small, ground-based telescopes to make more than 90,000 observations of Alpha Centauri B over five years.
With that number of observations, their hope is that any wobbling can be spotted and separated from the background noise of other stars. The technique is unusual, and only makes sense when the star and its planets are near Earth.
"What I wonder is why didn't someone think to do it before," said Guedes. "The answer is that it takes 90,000 observations."
All those observations are expected to serve another function as well. Stellar scientists hope to find a window into the star's interior by searching the noise for p-modes (p for pressure) of sound waves inside Alpha Centauri B.
"P-mode...frequency is determined by the structure of the star," said stellar researcher Sarbani Basu of Yale University. The signals could reveal such details as how much helium the star contains and the temperature of its core.
"In the case of the sun, p modes have been used very, very successfully to determine solar structure and dynamics to an amazing degree of precision," said Basu. "For stars other than the sun, we do not expect such precise results, but nevertheless, the frequencies of these modes will enable us to build up a picture of the interior of these stars and allow us to check if we had been modeling these correctly."
Related Links:
Irene Klotz's blog: Space Diary
Larry O'Hanlon's blog: Earth Impacts