Searching for rocky planets, four light years away ...
Laughlin realized that by focusing observations on a single promising star, the signatures of smaller planets should gradually emerge. “Your signal, the mass of a planet in a given orbit, scales with the square root of the number of observations,” he said. “With four times as many observations, in theory you can detect planets that are half as massive. If you’re willing to average over not hundreds, but hundreds of thousands of measurements, you can probably detect planets with masses equal to or less than that of Mars”—that is, a tenth the mass of Earth.
The more Laughlin thought about it, the more foreordained Alpha Centauri appeared for such an extreme search strategy. It began to seem somehow destined. On human timescales, the stars appear fixed in the sky, but as our Sun moves through its 250-million-year orbit around the galactic center, it brings us to new neighbors. Every few hundred thousand years, the list of our nearest neighboring stars must be made anew.
“If we were plopped down at some random point in the galaxy, there’s only a 1 percent chance we’d find ourselves near stars so optimal for detecting small rocky planets like our own,” Laughlin said. “The hand of fate has dealt us a very interesting situation that has not existed for at least 99.9 percent of Earth’s history. It’s remarkable that Alpha Centauri is right next door just as humans emerge and develop the ability to make these measurements. I’m enamored with that coincidence.”
