Research outcomes

As of 2007, there is no direct evidence of extraterrestrial life.[16] Although examination of the ALH84001 meteorites, which were recovered in Antarctica and are thought to have originated from the planet Mars have provided what some scientists suggested to be microfossils of extraterrestrial life, the interpretation is disputed.[17] In 2004, the spectral signature of methane was detected in the Martian atmosphere by both Earth-based telescopes as well as by the Mars Express probe. Methane is predicted to have a relatively short half-life in the Martian atmosphere, so the gas must be actively replenished. Since one possible source, active volcanism, has thus far not been detected on Mars, this has led scientists to speculate that the source could be (microbial) life - as terrestrial methanogens are known to produce methane as a metabolic byproduct.

Missions to other planetary bodies, such as Mars Science Laboratory, ExoMars, Beagle 2: Evolution to Mars, the Cassini probe to Saturn's moon Titan), and the "Ice Clipper" mission to Jupiter's moon Europa hope to further explore the possibilities of life on other planets in our solar system.

Efforts to answer secondary questions, such as the abundance of potentially habitable planets in habitable zones and chemical precursors, have had much success. Numerous extrasolar planets have been detected using the "wobble method" and transit method, showing that planets around other stars are more diverse than previously postulated. The first Earth-like extrasolar planet to be discovered within its star's habitable zone is Gliese 581 c, which was found using radial velocity.[18]

Due to technological limitations, most of the planets so far discovered have been hot gas giants, thought to be inhospitable to any life. It is possible that some of these planets may have moons with solid surfaces or oceans that are more hospitable. It is not yet known whether our solar system, with rocky, metal-rich inner planets ideal for life, is of an aberrant composition. Improved detection methods and increased observing time will undoubtedly discover more planetary systems, and possibly some more like ours. For example, NASA's Kepler Mission seeks to discover Earth-sized planets around other stars, by measuring minute changes in the star's light curve as the planet passes between the star and the spacecraft. Research into the environmental limits of life and the workings of extreme ecosystems is also ongoing, enabling researchers to predict what planetary environments might be most likely to harbor life.

Progress in infrared astronomy and submillimeter astronomy has revealed the constituents of other star systems. Infrared searches have detected belts of dust and asteroids around distant stars, underpinning the formation of planets. Some infrared images purportedly contain direct images of planets, though this is disputed. Infrared and submillimeter spectroscopy has identified a growing number of chemicals around stars which underpin the origin or maintenance of life.