Cool, Planet-like Y Dwarf Started Life as a Fiery, Hot Star

Can you imagine a planet beginning its life as a star? Astronomers have spotted an extremely cool, planet-like object that probably spent much of its youth as hot as a star.

Called WISE J0304-2705, the object was first spotted with the WISE observatory. It's part of a group of cosmic objects called the "Y dwarf" class, which is the coolest stellar temperature class yet defined.

The current temperature on this cosmic object is about 200 to 300 degrees Fahrenheit, a temperature that's in between that of Earth and of Venus. Yet because this object has a possible ancient origin, it's likely that a large change in temperature took place.

"Our measurements suggest that this Y dwarf may have a composition and/or age characteristic of one of the Galaxy's older members," said David Pinfield, one of the researchers, in a news release. "This would mean its temperature evolution could have been rather extreme."

If this Y dwarf is indeed an ancient object, then it would have gone through several stages of temperature evolution. During its first 20 million years, it would have been about 5,100 degrees Fahrenheit, the same as a red dwarf stars. Then, after 100 million years, it would have cooled to 2,700 degrees with silicate clouds condensing on its atmosphere. At a billion years of age, it would have cooled further to about 1,800 degrees, which is so cool that methane gas and water vapor would have dominated its appearance. The finally, it would continue its cooling to what it is today.

That said, the researchers are still investigating this object. They hope to learn a bit more about an object that appears to have passed from star-like temperatures to planet-like temperatures.

"The discovery of WISE J0304-2705, with its peculiar light spectrum, poses ongoing challenges for the most powerful modern telescopes that are being used for its detailed study," said Maria Teresa Ruiz, a team member involved in the study.

The findings are published in the journal Monthly Notices of the Royal Astronomical Society.