Meet Kenneth And Juliette, The Comet Carbon Duo

Optical image of two of the dust grains collected and analysed by COSIMA, named Kenneth and Juliette, which show the signature of carbon-based organics. They were collected in May and October 2015 respectively. Credits: ESA/Rosetta/MPS for COSIMA Team MPS/CSNSM/UNIBW/TUORLA/IWF/IAS/ESA/BUW/MPE/LPC2E/LCM/FMI/UTU/LISA/UOFC/vH&S/ Fray et al (2016)
These photos show two of the dust grains collected and analysed by COSIMA, named Kenneth and Juliette. They’re made of carbon-based, organic molecules collected from comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft. The scales show the particles’ size in mu microns. 100 μm = 0.1 mm, making Kenneth 0.3 mm long and Juliette 0.2 mm long. Although very tiny, both would be visible as specks with the naked eye. The smallest thing we can see is 0.1 mm (4/1000th inch) across. Credits: ESA/Rosetta/MPS for COSIMA Team et. all

Most of us really don’t care for dust. It’s something to blow off, swipe away with your hand or vacuum up. But dust is where it’s at when it comes to Rosetta’s Comet. By studying what’s in the tiny particles that vaporize off the comet, scientists have made a marvelous discovery. Two particles, playfully named Kenneth and Juliette, of the two hundred-plus grains analysed so far by the COSIMA instrument on the Rosetta spacecraft are composed of carbon compounds so complex, no one even has names of formulas for them yet.

Sure, the carbon is mixed with other previously reported elements such as sodium, magnesium, aluminium, silicon, calcium and iron, but it’s bound up in very large macromolecular compounds similar to the organic matter found in carbonaceous chondrite meteorites that have fallen to Earth. But the material is unique, at least to us earthlings because it contains much more hydrogen (the simplest element and what the sun is mostly made of) than in meteorites.

A slice of a CR carbonaceous chondrite, a type of meteorite known to posses complex organic compounds. Credit: Bob King
A slice of a CR carbonaceous chondrite, a type of meteorite known to posses complex organic compounds. Credit: Bob King

Keep in mind that nearly all meteorites come from asteroid collisions or spun-off material that eventually makes its way to Earth. Asteroids are “processed” rock, heated and compressed by gravity during their formation 4.5 billion years ago. It’s likely that hydrogen, the lightest gas, escaped during their formation. Heat will do that.

By contrast, comets must have avoided such significant heating to retain their hydrogen, and therefore must contain more primitive material. Primitive means the least processed and the closer to the original materials from which all the bodies of the solar system were created. From analyses of meteorites and laboratory simulations, the team was also expecting to find a wide diversity of organic material in Comet 67P/C-G, ranging from very small molecules to heavy organics.

As the sun's heat warms comet 67P/C-G, dust-laden gases are released into space. Rosetta and Philae sampled the dust to help determine what the comet's composed of. Credit: ESA/Rosetta
As the sun’s heat warms comet 67P/C-G, dust-laden gases are released into space. Rosetta and Philae sampled the dust and found carbon-containing organic material. Credit: ESA/Rosetta

They did find both but only very small motes were picked up by the several instruments on board Rosetta and the lander, Philae, while COSIMA  saw only very large carbon-bearing molecules in the dust particles, with nothing in between. This suggests a different source in the comet for each.

“These particles have remained pristine and untouched for billions of years until they were released in the days or weeks before being ‘caught’ by COSIMA,” said Martin Hilchenbach, principal investigator of COSIMA. “The results add to the growing picture that Comet 67P/C-G contains some of the most primitive material from our solar system’s early history.”

Like every bit of data gathered “in situ” or directly at the comet, we can see how well it fits with current theory or add to and alter the theory to better match the complex reality of what a comet is.