Planets that orbit stars other than the Sun are called exosolar planets. As of December 10, 2009, according to the Extrasolar Planets Encyclopaedia, 407 of these exosolar planets, also called exoplanets, have been discovered.
Most of these exoplanets are much larger than the Earth. However, a few are Earth-like, being of a similar size and mass to the Earth.
Astronomers are especially interested in these exoplanets that are Earth-like and orbiting stars that are Sun-like because they feel that the potential for life on these planets is higher than other exoplanets that are many times larger than Earth.
Star: 61 Virginis
The first three planets are orbiting the star 61 Virginis (61 Vir), which is within the constellation Virgo. The star is being called “virtually a twin of the Sun.” [Telegraph.co.uk: “Discovery of new planets raises hopes of other life in universe”]
These three newly discovered planets range in mass from 5.3 to 24.9 times the mass of the Earth, whose mass is approximately 5.9736 Ã— 1024 kilograms. [Statistics provided by the NASA Goddard Space Flight Center (GSFC)]
61 Virginis is about 27.8 light-years away from Earth.
Page two talks about the second star that was found to have a planet orbiting about it.
The second star to have a planet recently discovered to be orbiting about it is this one.
The fourth planet to be discovered by this international team is orbiting the star 23 Librae, which is within the constellation Libra. It is about 83.7 light-years away from Earth.
23 Librae is a yellow dwarf star, with a mass just over the mass of the Sun (1.05 Sun-mass) and a radius of 1.25 times that of the Sun.
The planet has a mass similar to the planet Jupiter, which has a mass of 1.8986 Ã— 1027 kilograms, which is about 317.8 times the mass of Earth. [Statistics provided by the NASA Goddard Space Flight Center (GSFC)]
The planet orbits its star in a 14-year orbit. As a comparison, Jupiter orbits the Sun in 12 years.
Dr Simon O'Toole, of the Anglo-Australian Observatory, stated: "… what we detect from this star system is very like what we'd detect from our own Solar System if we were observing it from a distance, because Jupiter has the strongest gravitational effect of all our Sun's planets." [Telegraph.co.uk]
The discoveries (of the planets orbiting around 23 Librae and 61 Virginis) were made by an international team of astronomers using data collected over several years from the Anglo-Australian Telescope in New South Wales and the W.M. Keck Telescope in Hawaii.
The lead scientists of the team included R. Paul Butler, of the Department of Terrestrial Magnetism at Carnegie Institution, and Steven S. Vogt, of the Department of Astronomy and Astrophysics at the University of California, Santa Cruz.
They detected the new planets by observing the "wobbling" of the stars caused by the planets' gravitational pull.
Page three talks about a third star found to contain a planet orbiting it.
Astronomers are not sure, yet, but at least one planet and possibly another one or two planets could be orbiting about it.
In related news, the discovery of three planets around the star HD 1461, by the Keck telescope, has also been announced by the same international team of scientists.
See the 12-14-2009 University of New South Wales article “New planets around sun-like stars.”
According to the 12-14-2009 EurekAlert article New planet discoveries suggest low-mass planets are common around nearby stars, the “… system found by the team features a 7.5-Earth-mass planet orbiting HD 1461, another near-perfect twin of the Sun located 76 light-years away."
"At least one and possibly two additional planets also orbit the star. Lying in the constellation Cetus, HD 1461 can be seen with the naked eye in the early evening under good dark-sky conditions.”
And, “The 7.5-Earth-mass planet, assigned the name HD 1461b, has a mass nearly midway between the masses of Earth and Uranus."
"The researchers said they cannot tell yet if HD 1461b is a scaled-up version of Earth, composed largely of rock and iron, or whether, like Uranus and Neptune, it is composed mostly of water.”
These astronomers, and other ones also searching for explanets, are hopeful that Earth-like planets are plentiful around Sun-like stars, and that they only have to continue to search for them in order to find them in our Milky Way galaxy.