A huge, ultra-hot alien planet boasts surprising amounts of carbon, a new study reveals, suggesting that worlds beyond our own solar system may be far more diverse than scientists had imagined.
Researchers determined that large quantities of carbon swirl about in the atmosphere of the gas giant planet WASP-12b, making it the first carbon-rich world ever discovered.
The finding should change how astronomers think about planet diversity and formation, as well as the search for extraterrestrial life, researchers said. There may be carbon-rich rocky planets out there, for example, with mountains made of graphite or diamond. [Illustration of the carbon-rich alien planet]
"This study shows that there is this extreme diversity out there," study lead author Nikku Madhusudhan, now of Princeton University, told SPACE.com. "Fifteen years or so since the discovery of the first exoplanet, we're just beginning to appreciate how different they can be."
Reconstructing an alien atmosphere
WASP-12b, discovered in 2008, is about 1,200 light-years away, in the constellation Auriga. The alien planet is about 1.4 times as massive as Jupiter and sits just 2 percent as far from its parent star as the Earth is from the sun.
As a result of this extremely tight orbit, WASP-12b is a searingly hot world, with dayside temperatures reaching 4,200 degrees Fahrenheit (2,316 degrees Celsius) — hot enough to melt steel.
Madhusudhan and his colleagues analyzed light thrown off by WASP-12b at several different wavelengths, using new observations made by NASA's Spitzer Space Telescope as well as older data from the Canada-France-Hawaii Telescope in Hawaii.
By plugging this information into a computer model Madhusudhan developed, they were able to determine the most likely composition of the alien planet's atmosphere in great detail, and with a high degree of confidence.
"There is no room for significant uncertainty," said Madhusudhan, who performed the research while at MIT. "This model does not assume anything. It just runs through a huge parameter space."
The researchers found that WASP-12b is very different from other planets. Specifically, its atmosphere is far more carbon-rich.
An excess of carbon
"Carbon richness" is a measure of how much carbon a star or planet has, compared to its abundances of oxygen. The carbon-to-oxygen ratio of our sun is about 1-to-2, which means it has about twice as much oxygen as carbon.
No planets in our solar system are known to have more carbon than oxygen — though the ratio is unknown for Jupiter, Saturn, Uranus and Neptune, because water, the main oxygen carrier, is buried deep inside their atmospheres.
But WASP-12b has significantly more carbon than oxygen. It harbors less water vapor and much more carbon-containing methane than expected, researchers said.
The team reports its findings online Dec. 8 in the journal Nature.
A new type of planet
Because WASP-12b seems to be made of different stuff than planets in our own solar system, astronomers should open their minds when thinking about other alien planets, researchers said.
"This study shows for the first time that exoplanets can be very different," Madhusudhan said.
For example, small, rocky, carbon-rich planets could have rocks made of graphite or diamonds rather than the silica-based stuff we're used to here on Earth.
"This changes the landscape completely," Madhusudhan said. "It's nothing like we've ever imagined."
The study also suggests that the basic building blocks of planets can be diverse. The icy chunks of matter that came together to form the planets in our solar system, for example, likely bear little resemblance to the pieces that built WASP-12b.
"They could be made of tar, for example," Madhusudhan said. "That could be one explanation."
The new results also bear on the search for life beyond Earth, he added. If alien planets can be so different, scientists may have to open their minds to the varied forms life might be able to take.
For example, a rocky, carbon-rich planet with tarry seas — if one exists — may well harbor organisms with little resemblance to the water-requiring "life as we know it."
"What is the chemistry, and what sort of life-forms can sustain this chemistry?" Madhusudhan said. "This really opens our perspective."
This article was reprinted with permission from SPACE.com.
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