Are There Any Planets Like Earth?

No, sensitivities must improve to detect smaller planets such as our own. The lightest of the 50 or so planets discovered through mid-2001 is still more than 150 times the mass of our Earth. This corresponds to a velocity induced on the light from the star of some 3m (10ft) per second, a brisk walk. The signal must first be processed to remove the effects of the much faster rotation of the Earth about the Sun, the solar systems' motion through space, and other effects. It may be difficult to improve enough to detect small planets, so astronomers are looking at another technique, where the planet crosses in front of the star, causing a 2% or less dip in the signal strength. This only works when the Earth is in or very near the exoplanet's orbital plane, so many more stars will have to be monitored; thousands in all. This will also require looking further afield, beyond present limits of instrumental sensitivity. It is currently expected that Earth-sized planets may become detectable in sufficient numbers for some statistical purposes by the year 2020, if space-borne instruments are funded.

Some Recently Discovered Extrasolar Planets

* Data for Jupiter, for comparison with extrasolar planets