Oddball Alien Planets Discovered Among Newfound Worlds
Artist's impression of the CoRoT satellite.
Credit: CNES/Active Design

This story was updated at 5:30 p.m. EDT.

Six new and diverse alien planets ? including a world twice as massive as Jupiter orbiting a rapidly spinning star ? have been discovered by a planet-hunting space observatory.

The newfound extrasolar planets were spotted by the European CoRoT satellite around different stars. They span a broad range of sizes and masses and exhibit an assortment of physical properties. The smallest, CoRoT-8b, is approximately 70 percent of Saturn's size and mass.

Since 1995, scientists have discovered over 450 total exoplanets.

"With the addition of this new batch, the number of exoplanets discovered by CoRoT has risen to 15," said Magali Deleuil from Laboratoire d'Astrophysique de Marseille in France, the head CoRoT's exoplanet program. "The increasing size of the census, which includes objects with very diverse characteristics, is of vital importance for better understanding of planetary systems other than our own."

The new collection of planets also includes larger worlds scientists are now calling CoRoT-10b, CoRoT-11b, CoRoT-12b, CoRoT-13b and CoRoT-14b. They belong to the planet class known as 'hot Jupiters.' [Photos: Strangest alien planets.]

The CoRoT satellite also spotted a brown dwarf (CoRoT-15b), which is an intermediate object between a planet and a star. CoRoT-15b is about 60 times as massive as Jupiter. ?

Oddball exoplanets

And there are other peculiarities among the newfound planets.

CoRoT-10b, for instance, has an extremely eccentric orbit that results in extreme variations in its surface temperature over the course of its year. The exoplanet's elongated orbit takes it very close to its host star,? and the substantial variation in the orbital distance results in a tenfold increase in the planet's exposure to stellar radiation.

Scientists estimate that the surface temperature of the planet may increase from 480 degrees to over 1,100 degrees Fahrenheit (250 to 600 degrees Celsius), in only 13 days, which is the length of a year on CoRoT-10b.

CoRoT-8b, whose internal structure should be similar to that of icy, giant planets like Uranus and Neptune, is the second smallest exoplanet discovered by the CoRoT team so far.

"The rich diversity emerging from this sample is a very interesting result, showing CoRoT's ability to detect exoplanets, which are rather different from each other," said Malcolm Fridlund, a project scientist for CoRoT at the European Space Agency (ESA). "Being able to study a wide variety of planets will provide important insights into the formation and evolution of planetary systems."

Additionally, CoRoT-11b's parent star spins around its axis at an extraordinarily fast rate. The rapidly rotating parent star makes it stand out from the others. The star spins around its axis in less than two days ? an exceptionally high speed. In comparison, our sun has a rotation period of about 26 days.

"This is the third exoplanet discovered around such a rapidly rotating star," said Davide Gandolfi, the ESA Research Fellow who led the study of CoRoT-11b. "Because of the fast rotation of its host star, such a planet could only have been discovered because it transits in front of it, thus only a transit-hunger, such as CoRoT, could have spotted it."

CoRoT-12b, 13b and 14b all orbit close to their host star, but each exhibit different properties. CoRoT-13b is smaller than Jupiter and twice as dense, suggesting a massive, rocky core inside the planet.

CoRoT-14b has a size similar to Jupiter, but, amazingly, is 7.5 times the mass and 6 times the density of our solar system's largest planet. Planets, such as CoRoT-14b, that are very massive and very hot are rare, and this exoplanet marks only the second of this type that has been discovered so far.

How CoRoT hunts alien planets

In its hunt for exoplanets, CoRoT (short for Convection Rotation and planetary Transits) ? which is operated by the French space agency CNES ? observes a large number of stars over a significant period of time, and tries to spot any subtle changes in luminosity of the stars' emitted light.

This 'dimming' could be an indicator that the star hosts a planet, which, at the point when the light changes, is transiting in front of the star and partially obscuring its light. This transit technique is one of several methods that are used to search for exoplanets. It is also the technique that enables astronomers to determine the radius of the alien planet ? by measuring the depth of the transit.

CoRoT does not work alone, however. Adequate follow-up observations are needed to confirm that the transiting body is indeed a planet, and not a cosmic body whose structure or behavior simply mimics the presence of a planet (such as one or more companion stars).

Once CoRoT detects a candidate planet-hosting star, some of the foremost ground-based observations then collect high-resolution images and spectra, which yield a wealth of additional information.

"This result anticipates what may be achieved by future space-based missions searching for exoplanets," said Fridlund.

CoRoT is a precursor for PLATO, a Cosmic Vision candidate mission that will be able to seek planetary transits over a much larger sample of stars due to its much wider field of view. PLATO will be equipped with 34 telescopes, and will study brighter stars than those that can be observed with CoRoT, making it possible to determine the age of the planet-hosting stars through astroseismology measurements.

These improvements, plus the ability to more accurately estimate exoplanet masses and sizes using PLATO, will provide an important step in the quest to understand the conditions that favor the formation of Earth-like planets.