Rosetta mission data reveals how comets evolve

A team of researchers has unveiled closest-ever details about the evolution of a comet that was in headlines last year when the European Space Agency's Rosetta mission helped its Philae lander touch down on the surface of 67P/Churyumov-Gerasimenko (C-G).

The study helps scientists better understand 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).

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.

A 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 Aug 13, 2015 after which it will head away from the Sun once again.

The series of papers appeared in a special issue of the journal Science.