The Terrestrial Planet Finder (TPF) concept, currently under study by NASA, comprises a suite of two complementary observatories that would 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.
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.
An accepted scientific priority
The search for habitable planets and life has received strong support within the scientific community. The 2001 decadal review of astronomy and astrophysics, "Astronomy and Astrophysics in the New Millennium," prepared by the National Research Council, stated that:
"The discovery of life on another planet is potentially one of the most important scientific advances of this century, let alone this decade, and it would have enormous philosophical implications."
The decadal committee recommended that NASA go ahead with TPF, but with the caveat that precursor missions should confirm the expectation that terrestrial planets are common around solar-type stars. The committee also recommended that in the mission should give comparable weight to the broader science goals of studying planetary systems and the structure of astronomical sources imaged at high angular resolution.
The survey also noted the importance and challenges of building a Terrestrial Planet Finder, and noted that the success of precursor missions and technology must first be demonstrated.
What will TPF look like?
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.
In May of 2004, NASA announced it would fly two separate missions with distinct and complementary architectures to fully realize the goals of Terrestrial Planet Finder. These goals are explicit in the nation's new vision for space, which directs NASA to "conduct advanced telescope searches for Earth-like planets and habitable environments around other stars."
More information:
Astronomy and Astrophysics in the New Millennium
TPF Book (PDF files)
High-res TPF artwork
