Comet 67P Transformed as It Approached the Sun

Comet 67P/Churyumov-Gerasimenko

underwent some fantastic transformations as it approached the Sun, according to a new study of Rosetta data published this week in Science. Fractures grew, cliffs collapsed, and boulders rolled on the comet, among other geologic happenings. 

At the 48th Lunar and Planetary Science Conference in The Woodlands, Texas, Ramy El-Maarry of the University of Colorado, Boulder, revealed stunning images of the comet’s transformation as it approached perihelion, or the closest it gets to the Sun during its orbit. This is the first time scientists have observed in detail the punishment comets sustain this close to the Sun.

“This is the first mission that we’ve been able to have such a huge set of high-resolution images while at the same time having the longevity of a mission where we were able to look at a comet and study how it evolved through more than two years as it journeyed through the inner solar system,” El-Maarry said at the conference. He is a member of the U.S. Rosetta science team and lead author of the study.

From August 2014 through September 2016, Rosetta orbited 67P, its scientific instruments trained on the comet. Then the team attempted to land—and most likely crashed—the orbiter into the comet. Rosetta's fate remains unknown. But the data it sent back to Earth is not.

For the current study, the researchers focused on observations made between December 2014 and June 2016. Among the most striking phenomena they found is a collapsed cliff face, whose volume is the equivalent of nine Olympic-sized swimming pools.

A cliff collapse the researchers observed. Image Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

 
It fell not in a few giant pieces, but essentially crumbled apart, much in the way the White Cliffs of Dover in the United Kingdom sometimes fall. “It would have been like watching a slow-motion video,” El-Maarry told mental_floss. “If you saw the cliff starting to fall, and you’re on the comet, you would have had time to take out your phone, open the camera, start the video and keep recording for 20 or 30 minutes as the event unfolds.”

The collapse revealed bright, fresh, icy comet interior. It's the first time we've observed this process.

At the comet’s nucleus, outbursts caused by increased sunlight moved a 282-million-pound, 100-foot-wide boulder the distance of one and a half football fields. In a cometary day on 67P, an hour and half of perpendicular illumination can cause chaos. In the span of 20 minutes, temperatures swing from -140°C to 50°C. Interior ice sublimates―changes from solid to gas without bothering to become water―and blasts into space. Increased temperatures as the comet approached the Sun also caused Empire State Building–sized fractures along the neck of the rubber duck–shaped body.

Two images showing the boulder's movement. In the right image, the dotted circle outlines the original location of the boulder for reference. Image Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

 
These Rosetta data are the first direct link between outbursts and crumbling cometary material, and suggest that thermal gradients are fundamental drivers of geologic processes on comets, which include weathering and erosion, sublimation of water ice, and mechanical stresses arising from the comet's spin.

If you were to stand on the surface of 67P and witness the cliff face collapse, it would be quite an experience. “If you’re in the northern hemisphere, it might be a lot of fun,” said El-Maarry. “You’re seeing a lot of things happening in slow motion. You might be able to see dust coming from the southern hemisphere and falling like volcanic ash on top of you in the north. It would have also had a spectacular view of space because you don’t have an atmosphere.”

In the extremely long term, the processes responsible for fractures on the duck’s neck will cause the comet to split in two―temporarily. “What we can say with a degree of certainty is that it’s not going to explode. It’s going to break,” he described. “And because it’s going to break and separate, the two bodies still have enough gravity to pull themselves together to reattach.”

The next step, El-Maarry says, is to locate more bodies just entering the solar system, as opposed to objects that have been here for dozens of orbits. “What our work implies is that most of the activity seems to happen just as you enter the inner solar system in an inner configuration,” he said. He is interested in the findings from the New Horizons mission after it visits an object in the Kuiper Belt on January 1, 2019. That region is a source of comets, and New Horizons offers a chance at a pristine body before being subjected to heat or sublimation.

“It will be really cool to see what is the topography you’re seeing there. Are you seeing something that’s just a ball of dust and ice as we thought of comets before going to 67P,” El-Maarry wondered, “or are we going to see all this complex geology? This is going to be really very exciting. When you look at New Horizons, no one really thought that Pluto would look as amazing as it did in picture. And that’s what happens with space missions. They just keep surprising us and opening up new frontiers.”