burnt-out comet appears to be covered in talcum powder

Written by theregister.com on April 8, 2021. Posted in Current News

Image: The Telegraph

Not only did a telescope on Earth spot, for the first time in history, an extinct comet on a close fly-by of our home world but scientists now reckon the space rock is covered in a substance similar to talcum powder.

Night-sky watchers from the National Astronomical Observatory of Japan (NAOJ) and the Koyama Astronomical Observatory discovered Comet P/2016 BA₁₄ five years ago, and recorded it for 30 hours as it made its closest approach to Earth. They initially thought the rock was an asteroid, though the data showed it was an unusual comet.

Unlike most comets, P/2016 BA₁₄ was not shrouded in a halo of dust and ice. In fact, it is coated in large phyllosilicate grains, a substance more commonly used on Earth for talcum powder.

“This result provides us a precious clue to study the evolution of comets,” said Takafumi Ootsubo, the lead author of a study into the body and an astronomer at NAOJ, on Tuesday. “We believe that further observations of the comet nuclei will enable us to learn more about the evolution of comets.”

When comets are warmed by sunlight, they are typically wrapped in an envelope of gases that give it a fuzzy appearance. The gases are produced when the ice and dust on its surface sublimate, and as these objects streak across the sky sometimes the particles are compressed into a tail.

Comet P/2016 BA₁₄, however, emits very little of these gases or particles because the material on its surface has mostly disappeared. Observations made using the Subaru Telescope reveals that underneath what remains of the ice and dust is a generous coating of something close to talcum powder.

“The normalized emissivity spectrum of the comet exhibits absorption-like features that are not reproduced by the anhydrous minerals typically found in cometary dust coma, such as olivine and pyroxene,” the study, published in the journal Icarus, reads. “Instead, the spectral features suggest the presence of large grains of phyllosilicate minerals and organic materials. Thus, our observations indicate that an inactive small body covered with these processed materials is a possible end state of comets.”

It’s the first time scientists have found hydrous silicate materials in or on a comet. The team estimated that the 800-metre-wide specimen has been scorched to temperatures beyond 330°C, and was probably in an orbit that brought it closer to the Sun than its current path.

The observations were made on March 22, 2016 when the comet passed within 3.6 million kilometres of our home planet.

The team wants to figure out if the comet accrued the powder on its body or if the phyllosilicate was there from the start. Detecting more near-dead comets could help confirm whether these objects do, indeed, transform into dead husks of talcum powder after one too many trips around the Sun.

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