The new observations from the Near-Infrared Spectrograph (NIRSpec) aboard the NASA/ESA/CSA James Webb Space Telescope show that the main-belt comet 238P/Read has a coma of water vapor, but lacks a significant carbon dioxide coma.
Comet 238P/Read was discovered on 24 October 2005 by the U.S. astronomer Michael T. Read using the Spacewatch telescope at Kitt Peak National Observatory.
Also known as P/2005 U1, it resides in the main asteroid belt but periodically displays a coma and a tail.
It has an orbital period of 5.63 years and a diameter of 600 m (2,000 feet).
“Main-belt comets themselves are a fairly new classification, and 238P/Read was one of the original three comets used to establish the category,” said Webb deputy project scientist for planetary science Dr. Stefanie Milam, an astronomer at NASA’s Goddard Space Flight Center, and her colleagues.
“Before that, comets were understood to reside in the Kuiper belt and Oort cloud, beyond the orbit of Neptune, where their ices could be preserved farther from the Sun.”
“Frozen material that vaporizes as they approach the Sun is what gives comets their distinctive coma and streaming tail, differentiating them from asteroids.”
Astronomers have long speculated that water ice could be preserved in the warmer asteroid belt, inside the orbit of Jupiter, but definitive proof was elusive — until Webb.
“In the past, we’ve seen objects in the main belt with all the characteristics of comets, but only with this precise spectral data from Webb can we say yes, it’s definitely water ice that is creating that effect,” said Dr. Michael Kelley, an astronomer at the University of Maryland.
“With Webb’s observations of 238P/Read, we can now demonstrate that water ice from the early Solar System can be preserved in the asteroid belt.”
According to the team, the missing carbon dioxide was a bigger surprise.
Typically, carbon dioxide makes up about 10% of the volatile material in a comet that can be…
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