The Wobbly Star

Article excerpt

Byline: Lawrence Krauss

Why we keep finding new planets.

I don't know which I find more remarkable, the fact that there appears to be a small rocky, Earth-mass planet orbiting the closest star to our sun, or the fact that astronomers were able to discover it.

The latter fact may seem surprising. After all, if the Alpha Centauri system of three stars is our closest neighbor, shouldn't it be the easiest place to find extra solar planets?

If it was a matter of merely seeing them, like we see stars, that might be the case, but planets don't, in general, shine (although they can reflect the light from their host stars, which is why we can see the planets in our own solar system). Astronomers at the University of Geneva and their colleagues used a much subtler technique they helped develop almost two decades ago to discover the first extra-solar planets.

As a planet orbits its host star, it tugs at it in different directions, causing the star to wobble ever so slightly. The more massive the planet, the greater the wobble. The closer the planet, the faster it orbits its star, and the faster the period of the wobble.

But what is most astounding about the purported new planet, discovered around Alpha Centauri B, is that it is so light that it barely tugs its star at all. As it orbits every 3.2 days around its star, it causes the star to move back and forth at a speed of just 50 centimeters a second! That is the speed at which you might take a leisurely walk in the park.

That astronomers can deduce this kind of motion in a star four light years from us is so amazing, in fact, that we should be cautious about accepting the validity of the new claim, which was published in Nature last week, until it is confirmed using another independent set of observations. …