Over the years, this technique has raised many false hopes, as when two companions were supposedly detected earlier in the century around Barnard's Star. They later proved to be artifacts of the telescope. Of course, detecting that a planet exists is only part of the problem. The next obstacle is determining whether this planet could support life. To do this, scientists use spectroscopy.
Spectroscopic observations allow astronomers to determine the chemical make-up of a planet.
With this information, they can detect water and oxygen, an indicator that biological activity could exist. Different chemicals absorb radiation at characteristic wavelengths, forming spectroscopic absorption bands. Conversely, when these absorption bands are observed, the presence of those chemicals may be inferred. It should prove to be our most powerful tool yet in the detection of extrasolar planets. This NASA Hubble Telescope near-infrared image of newborn binary stars reveals a long thin nebula pointing toward a faint companion object which could be the first extrasolar planet to be imaged directly.