As of September 2008 a total of 309 extrasolar planets have been discovered. So far only massive gas giants, like Jupiter, have been detected, although some as small as Neptune. No terrestrial, or earth like planets, have been discovered yet. This is because of the current limitations on the technology, or the method, used to detect planets. However, this will hopefully be changing soon.

Currently it is difficult to locate earth-sized planets because they are very small, and do not give off much reflected light from their stars. So far no planet has been bright enough on its own to be detected by our telescopes. We can only detect planets by the small gravitational effects these planets have on their host stars. Planets do not have much mass compared to stars but the little mass they have exerts a pull on their stars; it makes them wobble slightly. We can use the Doppler effect to measure this wobble. The Doppler effect makes it so that the light from the star is bluer when moving toward us, and redder when moving away from us. So when watching a star with a planet around it, the pull from the planet as it orbits the star causes this shift in the observed light from the star, thus we know the planet is there. However, the mass of earth-sized planets is too small to create any noticeable wobble.

However, progress is definitely being made. The Subaru Telescope, located atop mount Mauna Kea in Hawaii, has an 8.2-meter mirror and has recently started scanning nearby stars looking for planets. There are eight innovative cameras and spectrographs at Subaru optimized for various astronomical investigations in optical and near-infrared wavelengths. One of these cameras is called HiCIAO, or High Contrast Instrument for the Subaru Next Generation Adaptive Optics. It is designed to block out the harsh direct light from a star, so that nearby faint objects such as planets can be viewed. The new adaptive optics system uses 188 actuators behind a deformable mirror to remove the atmospheric distortion from its view, allowing Subaru Telescope to observe close to its theoretical performance limits. The Subaru Telescope hopes to be the first to directly observe a planet outside our solar system.

Now even though Subaru hopes to be the first to direct image a planet, it still cannot detect an earth-sized planet. NASA was planning on launching a space telescope for this purpose called the terrestrial planet finder. This would consist of two observatories planned to not only detect these types of planets but also even study their characteristics such as size, distance from star, and even atmospheric components. However, due to budget cuts at NASA the project has been postponed indefinitely. I think until this project, or a similar one is funded and launched, we will continue to be limited by our current earth-based telescopes, and earth-like planets will remain outside our view.