NASA Finds Comet 45P's Interior Has Both Carbon Monoxide, Methane

Comet 45P zoomed by Earth in early 2017, and researchers using NASA’s Infrared Telescope Facility (IRTF) in Hawaii helped study this cyclic visitor to gather more details on the celestial object.

Their study has shed light on the ices in Jupiter-family comets and has revealed that 45P doesn’t match any comet studied so far.

The team studied the levels of nine gases released from the icy nucleus into the comet’s thin atmosphere or coma.

The glowing air around a comet contains the atoms that helped build amino acids, sugars and other biologically relevant molecules in the solar system. The team found carbon monoxide and methane in the coma of 45P, a very rare detection in Jupiter-family comets.

The team found that the levels of carbon monoxide in the ices of the comet were completely depleted but methane levels were very high.

Gases originate around the center of a comet's interior where there are pockets of ices, rock and dust. Studying these ices can help understand the evolution of the comet over time and the comet’s history.

“Comets retain a record of conditions from the early solar system, but astronomers think some comets might preserve that history more completely than others,” said Michael DiSanti, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the new study in the Astronomical Journal, in a press release by NASA.

Using the iSHELL high-resolution spectroscopy of the IRTF, the team was able to detect many gases in the vaporized ices at once. This helped reduce uncertainty in readings where comparative study had to be done.

The team used readings from 45P’s closest pass to Earth early in 2017. They collected data on the amount of water, carbon monoxide, methane and six other native ices present in the comet. The researchers compared the levels of the ices on the sun-drenched side of the comet to the shaded side.

The results reveal that 45P is running so low on frozen carbon monoxide that it can be officially considered depleted.

When the carbon monoxide escapes because of heat from the sun, so should the methane. But the team found that 45P is rich in methane and is one of the rare comets that contain more methane than carbon monoxide ice.

The team feels that this is because the carbon monoxide in the comet might have reacted with hydrogen to form methanol, which explains its absence and the abundance of methane. This also explains the comet's larger-than-average share of frozen methanol.

Boncho Bonev, an astronomer at American University and the second author on the paper, said in the release that, “we want to distinguish comets as they formed from the processing they might have experienced, like separating historical relics from later contamination.”

“This broadens our knowledge of the mix of molecular species coexisting in the nuclei of Jovian-family comets, and the differences that exist after many trips around the Sun,” Faith Vilas, the solar and planetary research program director at the National Science Foundation, or NSF, which helped support the study, said in the report.

The comet — officially named 45P/Honda-Mrkos-Pajdušáková — belongs to the Jupiter family of comets, frequent orbiters that loop around the Sun about every five to seven years. Much less is known about native ices in this group than in the long-haul comets from the Oort Cloud.