When you think about comets (you know, as often as you tend to do in your daily life…) you picture these cold, dusty, gaseous clumps of interplanetary rock which orbit through our solar system 18+ miles per second. Right?
The main image is of Comet Lovejoy, taken by NASA astronaut Dan Burbank while aboard the International Space Station as Commander in 2011. Other still images he captured can be viewed here.
Comets fall toward the sun. Most survive their trip, but the class that has achieved the most press are referred to as sungrazer comets (given the name due to their close approach to the sun). The sungrazers which happen to survive the harsh solar radiation and gravitational stress are slung back out unto the solar system, placed upon a new orbital path, only to return again on their next solar rendezvous (at perihelion) whence we are reminded to turn our eyes sky(universe)ward to observe them on their journey. Learn more from NASA Goddard on why we see so many sungrazing (Kreutz) comets.
Comet Hale-Bopp (credit: Jerry Lodriguss)
However, comets still remain quite a mystery to us. With the attention currently on our robotic emissaries Rosetta and Philae - the spacecraft/lander duo currently orbiting comet 67P/Churyumov-Gerasimenko (67P/C-G) - there’s still a grand amount of knowledge to be gained on these fragments of interplanetary material.
learn more about comet 67P(C-G)… (image credit: ESA)
Some of these sungrazers, for instance - whether they survive or not - offer insight into the comet and the sun itself:
Because the comet goes through a phase transition called sublimation - where the solid, frozen surface is boiled off in transition to a gas - this activity reveals the sun’s magnetic field lines as they effect the cometary “tail” of gasses being expelled.
the anatomy of a comet (credit: wiseGEEK)
This, of course, is why we are even able to observe a passing comet without the aid of binoculars or telescopes sometimes…due to their bright tails, which are the result of sublimation. With the aid of stellar space observatories like NASA’s SOHO/TRACE, SDO, STEREO, IBEX, and IRIS spacecraft, our understanding of the sun is improving; and subsequently, the sun’s influence on comets. Learn more about NASA’s Heliophysics Program.
More on NASA’s Heliophysics program (credit: NASA)
With such exquisite and meticulous spacecraft observing this sun/comet interaction, these once enigmatic bodies of planetary rock and dust have become a key component to understanding the early formation of our solar system. All of this brings into view NASA’s newly released 3-D maps to further identify and analyze the atmospheric composition of comets.
From a recent MOTHERBOARD piece:
“We achieved truly first-of-a-kind mapping of important molecules that help us understand the nature of comets,”
— Martin Cordiner, Lead Researcher; NASA Goddard Center for Astrobiology
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 Astronomers and astrophysicists 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.
3-D observations from the NASA study provide a view into the inner coma, along with mapping of the molecule HCN and formaldehyde. (Credit: VisualizeAstronomy)
The team focused on three molecular species, tracing whether they flow outward evenly in all directions or come off from the nucleus in clumps. 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.
“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…these observations open a new window on this poorly known component of cometary organics.”
— Michael Mumma, Co-author on the study and Director; Goddard Center for Astrobiology
We’ve observed comets since 239 B.C. Building on the knowledge we’ve gained, who could have imagined that these feared and awe-inspiring wonders from beyond deep space would reveal - to one curious species of intelligent life forms - the secrets of their solar system and quite possibly, the origin (or transportation) of life to their home planet itself.