European astronomers said Tuesday that they had discovered the smallest planet yet found orbiting another star. The planet could be as little as only 1.9 times as massive as the Earth and belongs to a dim red star known as Gliese 581, which lies about 20 light-years from Earth in the constellation Libra.

The star was already know to harbor at least three more massive planets. The new planet, known as Gliese 581e, is probably rocky like the Earth, but it lies in such a close orbit  only three million miles from its star  that it is surely blasted with too much radiation and heat to be livable.

Michel Mayor, of Geneva Observatory, and his colleagues announced their results at a conference at the University of Hertfordshire in Britain and in a paper submitted to the journal Astronomy and Astrophysics.

Astronomers said the discovery was more encouragement that the galaxy was full of small-mass planets and that with more time and improved instruments like the Kepler satellite, recently launched by NASA, they would eventually find Earth-like planets in orbits suitable for life around other stars.