This article may interest some of you.

Astronomers have come up with an ambitious observational technique to detect Earth-sized and perhaps habitable planets orbiting one of our nearest neighbour stars.

The triple-star system called Alpha Centauri is a tad more than four light-years away and is no stranger to science fiction fans.

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," says astronomer Javiera Guedes of the University of California at Santa Cruz.

Guedes is the lead author on a paper to appear in the 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.

Whatever the initial conditions, the simulations all led to the formation of different planetary systems.

All contained at least one Earth-sized planet, some of which formed inside the habitable, liquid-water zone around Alpha Centauri B.
How do we detect them?

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.

But small, rocky planets are not heavy enough to produce large, easily detectable wobbles.

To get around that, 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, they hope to spot any wobbling and separate it 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," says Guedes. "The answer is that it takes 90,000 observations."
Inside stars

These observations are also expected to serve another function.

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," says Professor Sarbani Basu, a stellar researcher at 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," says 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 modelling these correctly."

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I believe that the Earth alone has a mass of about 1/330,000 that of the Sun. Also I believe that the distance from the center of rotation is inversely proportional to the mass of each object. That would mean that, since 1/330,000 is about a third of a million and the Earth is about 93,000,000 miles out, that the Sun, just due to the Earth, revolves around the center of mass 3 * 93 = about 280 miles away. It covers one radian, 280 miles, in 1/(2 pi) years or about 280 miles / 1396 hours or 0.2 miles per hour (about 9 cm/sec). So the maximum variation of velocity is +- 9 cm/sec throughout the year, three parts in ten billion the speed of light, or 0.000,000,000,3 c. I believe that would be the red- or blueshift of the Sun caused by the orbital motion of the Earth, plus or minus. I don't know how sensitive our spectrometers are. That would correspond to frequency change of plus or minus about 0.43 Hz at 1.42 GHz.

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