terrestrial planet finder
•  a Space telescope to find planets outside from our solar-system as small as Earth • 

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At this moment, the TPF program has been postponed indefinitely.

Still, the are two proposed architecture concepts for TPF. The TPF-C and TPF-I. Launch of TPF-C had been anticipated to occur around year 2014, and TPF-I possibly by 2020.
Short Introduction:

The Terrestrial Planet Finder (TPF) uses a small collection of high sensitivity telescopes (probably 4 large 3.5-meter telescopes) with revolutionary imaging technologies. It will measure the temperature, size, and the orbital parameters of planets as small as our Earth in the habitable zones of distant solar systems. Also, TPF's spectroscopy will allow atmospheric chemists and biologists to use the relative amounts of gases like carbon dioxide, water vapor, methane and ozone to find whether a planet might support life. The launch was to be anticipated between 2012-2015 until NASA's budget cuts.

"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."
- National Research Council

One great challenge is how to detect planets against the blinding glare of their parent star. TPF with 4 big telescopes, will reduce the glare of parent stars to see planetary systems up to 50 light-years away.

Infrared interferometer concept for Terrestrial Planet Finder
Earth-like planets:

An Earth-like planet is a rocky planet. Such planets will be found quite close to their star, where the temperatures are too high for the planet to be mainly made of ice. We will determine the amount of heat on a planet by its distance from its star, and we will confirm the temperatures by the broad overall shape of its spectrum. Cool planets will be brighter at the long wavelength end of their spectrum; hot planets will be brighter at the short wavelength end.

A small object such as our Moon has too little gravity to hold an atmosphere. However, an object this small could be detected in a nearby system because it would be only 12 times fainter than Earth. It could be recognized because it would show no atmospheric absorption features in its spectrum.

The smallest Earth-like planet we know is Mars (it's about half the diameter of Earth & weighs about 9 times less), which has about one-tenth as much matter as Earth. If a Mars-size planet had the same temperature as Earth, it would be three and a half times fainter. Mars presently has a rather minimal atmosphere, but there is evidence that a thicker atmosphere with water vapor existed in the distant past.

If a terrestrial planet is too close to its star, it loses water from its atmosphere and surface. We believe this is what happened to Venus (Venus is about 1.22 times less massive than Earth, and has a 1.05 times smaller polar radius).

If the planet is too hot, the water becomes vapor, and is lost from the atmosphere. If the planet is too cold, the water freezes. Either of these conditions would make a planet very inhospitable for life.

... continue to page 2 (Mission Goal)

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