Boozy Comet’s Mysterious Heat Source Offers Clues to How Planets Like Earth Obtain Water

To study comets, scientists only have a small window of time to observe their glowing glory as they zip closely past the sun. In December 2018, one peculiar comet made its closest approach to Earth in centuries with a dramatic flyby bright enough to be seen with the naked eye.

Dubbed the "Christmas Comet" for its visibility during the holiday season and its greenish gleam, the celestial object flew within 7.4 million miles of Earth, which is about 30 times the distance of the moon. Now, researchers who observed the comet at the time are finding it's quite a bit more odd than previously thought—and these oddities may reveal how molecules were distributed when our solar system first formed, according to a new study published in The Planetary Science Journal in March 2021.

The comet, technically called Comet 46P/Wirtanen, had an unexpectedly high temperature as it whipped past the sun while spewing an abnormally high amount of the alcohol, methanol, reports Ed Browne for Newsweek.

"46P/Wirtanen has one of the highest alcohol-to-aldehyde ratios measured in any comet to date," study author Neil Dello Russo, a cometary scientist at Johns Hopkins University, says in a statement. "This tells us information about how carbon, oxygen, and hydrogen molecules were distributed in the early solar system where Wirtanen formed."

Astronomers used the newly upgraded Near-Infrared Spectrograph (NIRSPEC) at Hawaiʻi's Keck Observatory to analyze what chemical building blocks made up the comet. While other instruments less sensitive than NIRSPEC would take hours to detect the compounds, the Keck Observatory instrument completed the task within 10 to 20 minutes, reports Dan Robitzski for Futurism. NIRSPEC collects data about the amount of sunlight that shines through the comet's coma, or tail-like trail of gas and debris, reports Michelle Starr for Science Alert. The research team identified acetylene, ammonia, ethane, formaldehyde, hydrogen cyanide, water, and high amounts of methanol in the comet.

Simply put, comets are sort of like dirty snowballs, or icy chunks of dust and rock leftover from when the solar system formed. Only visible when swinging close by the sun, their icy centers called a nucleus heat up and spew gas and dust, developing a hazy tail of debris called a coma. As the sun heats the comet, the coma expands and can extend to hundreds of thousands of kilometers in length. The entire coma envelopes the comet and trails behind as it moves through space. The coma usually cools down as it goes further away from the comets center. However, Comet 46/P Wirtanen's coma did not decrease in temperature as it progressively extended further away from its nucleus.

"We found that the temperature measured for water gas in the coma did not decrease significantly with distance from the nucleus, which implies a heating mechanism," study author Erika Gibb, a University of Missouri-St. Louis astronomer, says in a statement.

While the research team does not know what may be causing the ice ball's heating mechanism, they have a few suspicions. The solar radiation may ionize some of the molecules in the comet's coma, resulting in energetic electrons colliding with other molecules and releasing heat, Science Alert reports. Or it's possible that chunks of ice are falling off the comet's nucleus, and as they fall, they turn into gas, releasing more energy further out into the coma, IFLScience reports.

When analyzing the coma, researchers found higher portions of water in the outer coma, which is consistent with this hypothesis, reports Science Alert. Chunks of ice falling from hyperactive comets may explain how water planets formed. Scientists suggest Earth's oceans could have came from water-carrying comets that crashed into the planet.

"Comet studies like this are exciting because they serve as a launchpad for answering the million-dollar question – are we alone?" said Greg Doppmann, an astronomer at the Keck Observatory, in a statement. "The organic compounds on comets tell us what ingredients formed our solar system and served as precursors to life. We can then look for these same prebiotic molecules in other planetary systems, which opens an exciting door to the very real possibility of finding microbial life beyond Earth – not in our kids' lifetimes, but our own lifetime."

The team of astronomers plan to continue analyzing the data to see if a future space mission will be needed to collect more insights about the comet and the early solar system.

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.