The closest and most-detailed look at the evolution of a comet, that was in headlines a year ago when the European Space Agency’s Rosetta mission helped its Philae Lander touch the surface of 67P/Churyumov-Gerasimenko (C-G), have been revealed by a team of researchers .
The new comet findings detailed into how comets form in the first place, how their surfaces evolve over time and how to potentially predict their lifespans.
“We are trying to see how a comet evolves over time, and also through the course of its orbit. Gaining this detailed time series is what distinguishes Rosetta from other missions,” said Michael A’Hearn, distinguished university professor emeritus of astronomy at University of Maryland (UMD).
A’Hearn with UMD astronomer Dennis Bodewits co-authored three of the papers as members of the team for Rosetta’s Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS).
He served as principal investigator on the Deep Impact mission, which sent an impactor module to the surface of comet Tempel I in 2005. This mission was the first to remove material from the interior of a comet’s nucleus, the solid central lump of ice, dust and debris and compare it to the material at the surface.
One of the Rosetta papers uses OSIRIS images to analyse the structure of C-G. Described as roughly the shape of a rubber duck, it consists of two lobes connected by a thin “neck”.
The team found that the majority of outgassing activity from the comet is occurring at the neck, where the OSIRIS cameras have consistently seen jets of gas and debris.
The second paper describes the surface of the portion of C-G that is currently visible to Rosetta. This “northern” region is divided into 19 distinct regions, all named for ancient Egyptian deities in keeping with the nomenclature of the mission.
“Comets are effectively twice as black as coal, with a thick dust layer shrouding the surface,” said Bodewits, an assistant research scientist at UMD. “It’s important to look for sublimating gas. This is where there are cracks in the dust layer, which can help us find water ice and track small changes in the comet’s surface.”
However, the third paper combines data from OSIRIS and another instrument, the Grain Impact Analyser and Dust Accumulator (GIADA).
This study looks at C-G’s coma – the thick cloud of dust and gas that envelops the nucleus. Comets have very little gravity, dust and gas flow freely into the space.
“We were surprised to find a cloud of particles orbiting the comet that are large and heavy enough to defy the sun’s radiation pressure,” Bodewits said.
The comet will be most active when it reaches perihelion or the single point in C-G’s orbit that is the closest and most intensely affected by solar radiation.
It will reach this point on August 13, 2015 after which it will head away from the Sun once again.
The papers were appeared in a special issue of the journal Science.