New 3D Maps Show How Comets Work in Incredible Detail

Comets are so much more than those cool, slowly melting balls of dirty ice and snow that trace wildly elliptical orbits through our solar system.

A recent study from a NASA-led team of scientists has created detailed 3-D maps of the atmospheres surrounding comets, identifying the myriad gasses that surround them. These gasses are important because some scientists posit that organic compounds might have arrived on Earth after hitching a ride on a comet.

"We achieved truly first-of-a-kind mapping of important molecules that help us understand the nature of comets," said Martin Cordiner, a researcher from NASA's Goddard Center for Astrobiology who led the international team.

The basis of the study was a series of observations done in 2013 on comets Lemmon and ISON using the Atacama Large Millimeter/submillimeter Array (ALMA) of high-precision antennas in Chile.

In both Lemmon and ISON, the team found that formaldehyde and HNC (which is made of one hydrogen, one nitrogen and one carbon atom) were both produced in the comets' comas.

The presence of formaldehyde confirmed existing theories about its presence in comets, but the HNC finding went one step beyond, settling a long-standing question about this material's source.

Scientists once thought HNC was pristine interstellar material coming from a comet's nucleus, but this doesn't appear to be the case. This latest study suggests HNC is made when large materials in the comet break down into organic dust in its atmosphere.

ALMA observations combine high-resolution two-dimensional images of a comet's gases with a detailed spectral image. This gives researchers a flat spread of the molecules present throughout the comet's atmosphere (or coma).

ALMA measurements also give researchers information about these molecules' velocities and direction relative to their observational line of sight, information that can turn the 2D map into a 3D one, essentially giving the coma depth.

This level of detail is almost unheard of when it comes to studying comets, and it's adding a whole new level to our understanding of these cosmic interlopers.

These kinds of detailed maps show what materials are lost from the comet's nucleus as it hurtles through space and what materials are formed within the coma. This helped the team identify the source of key organic molecules, the kind that are necessary for life as we know it.

The team focused on three molecular species, tracing whether they flow outward evenly in all directions or come off from the nucleus in clumps.

"Understanding organic dust is important, because such materials are more resistant to destruction during atmospheric entry, and some could have been delivered intact to early Earth, thereby fueling the emergence of life," said Michael Mumma, Director of the Goddard Center for Astrobiology, and a co-author on the study. "These observations open a new window on this poorly known component of cometary organics."

These new results don't answer the question of how life arose on Earth, whether our roots are in molecules that existed on the nascent planet, or whether vital building blocks arrived by chance from the Oort cloud. Still, it's a fascinating discovery, and one stepping stone towards future work that might answer those big questions.