Terrestrial Planet Finder
Terrestrial Planet Finder comprises two complementary observatories: a visible-light coronagraph (above), to launch first, and a formation-flying infrared interferometer (below), to launch several years later.
Terrestrial Planet Finder infrared interferometer.
The Terrestrial Planet Finder (TPF) is a suite of two complementary observatories to study all aspects of planets outside our solar system: from their formation and development in disks of dust and gas around newly forming stars to the presence and features of those planets orbiting the nearest stars; from the numbers at various sizes and places to their suitability as an abode for life.
By combining the high sensitivity of space telescopes with revolutionary imaging technologies, the TPF observatories will measure the size, temperature, and placement of planets as small as the Earth in the habitable zones of distant solar systems. In addition, TPF's spectroscopy will allow atmospheric chemists and biologists to use the relative amounts of gases like carbon dioxide, water vapor, ozone and methane to find whether a planet someday could or even now does support life (see biospheres, recognition of).
Our understanding of the properties of terrestrial planets will be scientifically most valuable within a broader framework that includes the properties of all planetary system constituents, including both gas giant and terrestrial planets and debris disks. Some of this information, such as the properties of debris disks and the masses and orbital properties of gas giant planets, will become available with currently planned space or ground-based facilities. However, the spectral characterization of most giant planets will require observations with TPF. TPF's ability to carry out a program of comparative planet studies across a range of planetary masses and orbital locations in a large number of new solar systems is by itself an important scientific motivation for the mission. However, TPF's mission will not be limited to the detection and study of distant planets. An observatory with the power to detect an Earth orbiting a nearby star will also be able to collect important new data on many targets of general astrophysical interest.
The TPF observatories
TPF will take the form of two separate and complementary observatories: a coronagraph operating at visible wavelengths and a large-baseline interferometer operating in the infrared. During almost 20 years of study, design concepts have alternated between interferometeric arrays and coronagraphs. In recent years alternative architectures have emerged with the potential to achieve similar science goals. These opened up the possibility of new mission concepts and additional precursor missions.
Prior to NASA budget cuts to its science program announced in early 2006, mission planners had been expecting to launch the TPF coronagraph observatory in 2014 followed by the infrared interferometer sometime before 2020. However, because of diversion of funds to support the Space Shuttle and International Space Station, the Terrestrial Planet Finder is now on indefinite hold.