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Artist's rendering of the planet orbiting the star Gliese 436 (Lynette Cook/California & Carnegie Planet Search)

(PLANETQUEST) -- The race to find planets beyond our solar system heated up more than ever during the month of May, when astronomers announced 32 previously unknown planets orbiting nearby stars. The new findings increase the number of known "exoplanets" to 231.

At least four of the stars astronomers observed have multiple-planet solar systems, like our own. Three other stars are thought to contain the remains of failed stars, called "brown dwarfs," in addition to a planet.

One of the more exotic of the new discoveries is the planet HAT-P-2b, discovered by an international team using the Hungarian-made Automated Telescope (HAT). The planet is over eight times more massive than Jupiter despite being only slightly bigger around. It whips around its host star in just over five-and-a-half days. Another group of astronomers discovered a planet with an even shorter year: TrES-3, a planet a bit bigger than Jupiter and about twice as massive, takes about 31 hours to orbit its binary star host, one of the quickest orbits ever observed. The planet was discovered using a network of telescopes called the Trans-atlantic Exoplanet Survey (TrES).

Other planets found include XO-2 b, a planet the size of Jupiter and about half as massive, and CoRoT-Exo-1 b, another "hot Jupiter" with an orbital period of one-and-a-half Earth days. CoRoT-Exo-1 b is the first exoplanet discovered by the French planet-finding CoRoT satellite.

By far the biggest haul of new planets came from a joint effort between the California and Carnegie Planet Search and the Anglo-Australian Planet Search teams. Together, they discovered 28 new planets and four new multiple-planet solar systems in the month of May, announcing their findings at the semi-annual meeting of the American Astronomical Society in Honolulu.

Three of the new planets were found orbiting very large stars nearly twice the size of our sun. Typically, it's very difficult for astronomers to observe planets of massive stars because the stars spin very quickly and have pulsating atmospheres that can obscure or mimic planetary signals. In order to bypass this problem, the two teams have concentrated on retired "A" type stars - ones that have nearly completed their life cycle and stabilized temporarily. They have found that these larger stars tend to have larger planets - likely because these solar systems initially formed out of more raw material.

The team also found seven so-called "brown dwarfs," corpses of stars that were never big enough to maintain fusion, as well as two other objects that could either be massive planets or small brown dwarfs.

In addition to updating the roster of newly discovered planets, the California and Carnegie and Anglo-Australian teams made further observations of a planet orbiting the star Gliese 436. The planet, which is similar in size and density to Neptune, is thought to have a rocky core surrounded by water that has been compressed by temperature and pressure into a solid form. Its atmosphere may contain hydrogen and helium, which would give it a blue color as it reflects light from its host star, a red dwarf only 30 light-years from Earth.

With an orbit of just over two-and-a-half days, this "hot Neptune" lies extremely close to Gliese 436. It also has an unusually oblong orbital path that suggests the presence of another planet nearby, according to a press release by the astronomers.

This breakneck pace of discovery may be a sign of things to come, as astronomers' methods for spotting exoplanets become increasingly accurate. "We're just getting to the point where, if we were observing our own solar system from afar, we would be seeing Jupiter," Jason T. Wright, a member of the California and Carnegie Planet Search team, said in a statement.

Written by Joshua Rodriguez/PlanetQuest