Terrestrial Planet Finder is a device to find Earth-like planets.
We are looking for planets that are nearly twins of Earth, but some differences
are expected because of the planet's size, environment, and history.
We will recognize such a planet by its spectrum as shown here:
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 recognize 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 like the 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.
