A Comet’s Coma: Rosetta Studies Space Shield

Comets are usually treated as if they’re meaningless balls of worthless snow, ice, and dirty snow, rightfully bereft of any greater fate than a long and futile battle with the sun, who perniciously enjoys himself as he strips them bare over millions, or billions, of years.

However helpless one might think comets are in their hapless existence, Rosetta studied that comets have an external shield, and scientists recently measured this comet-shield encapsulating the most famous comets in our solar system: Comet 67p/Churyumov-Gerasimenko.

And if this isn’t enough to sate your scientific appetite, scientists have also learned what sorts of materials litter the surface of Comet 67p’s surface, and what they’re finding is chock full of surprises.


Solar wind, a never-ending wave of highly charged invisible particles known as plasma, passes through the solar system, on its way away from the sun. Radioactive and malicious, solar wind travels millions of miles out into deep space, bombarding comets with high energy particles. But when this happens, the way the energy interacts with the water vapor surrounding an asteroid is called the comet’s coma.

This coma is given form by the heat of the sun, which heats surface ice to a temperature high enough for it to sublimate into gas, expand, and collect into a gaseous shield around the comet. This tree-sap-like reaction to solar wind actually deflects further solar damage in a way analogous to a windshield protecting the interior of a car from rain.


Astronomers have actually known about comets’ vaporous atmospheres since the late 1980’s, but the technology required to study the comas simply did not exist for scientists’ use until the last few years. Last year, astronomers used the world’s most expensive land telescope — the Atacama Large Millimeter/Submillimeter Array — to detect the very first traces of hydrogen and carbon compounds in two disparate comets’ comas (neither were Comet 67P).


When it comes to studying comets’ comas–it doesn’t matter how much money you have going into it. Just like real estate, it’s all about location, location, location. This is why the European Space Agency sent the Rosetta spacecraft to go and actually land on Comet 67P, and because of this keen insight, we are learning more about comas using a few simple instruments on board the Rosetta than we would with billions from the ground.

Upon Rosetta’s arrival, it began to orbit comet 67P and used its Plasma Consortium Ion and Electron Sensor (on board) to count how many particles were bombarding the craft, in essence mapping the difference in solar wind between outside and inside the comet’s coma.


The blue you see behind a comet is actually an ion tail, and this is formed by the solar wind’s interaction with water vapor present in the coma. This strips electrons from water molecules, producing water ions, and the comet moves on through space, leaving a trail of ionized gas. Scientists assume every comet has such a tail.

As the comet grows closer to the sun, the coma will intensify into a shield allowing absolutely no particles from the solar wind through, and this stronger shield will help to protect the hapless comet as it slingshots around the sun at a minimum distance of 111 million miles, ETA less than two weeks.


You don’t need shields if you can be as slick as Susan on this: