ESA Rosetta Comet 67/P Mission: Rosetta Team Uncovers More Secrets

A colour image of Comet 67P/Churyumov-Gerasimenko composed of three images taken by Rosetta’s scientific imaging system OSIRIS in the red, green and blue filters; the images were taken on August 6, 2014 from a distance of 120 km from the comet. 

Image credit: ESA / Rosetta / MPS / OSIRIS Team / UPD /LAM / IAA / SSO / INTA / UPM / DASP / IDA.

The familiar shape of the comet has now had many of its vital statistics measured: the small lobe measures 2.6 × 2.3 × 1.8 km and the large lobe 4.1 × 3.3 × 1.8 km.

The total volume of the comet is 21.4 km3. Rosetta’s Radio Science Instrument has measured its mass to be 10 billion tons, yielding a density of 470 kg/m3.

By assuming an overall composition dominated by water ice and dust with a density of 1,500–2,000 kg/m3, Rosetta scientists show that the comet has a very high porosity of 70–80 percent, with the interior structure likely comprising weakly bonded ice-dust clumps with small void spaces between them.

The OSIRIS instrument has imaged some 70 percent of the surface to date: the remaining unseen area lies in the southern hemisphere that has not yet been fully illuminated since Rosetta’s arrival.

The scientists have so far identified 19 regions separated by distinct boundaries and, following the ancient Egyptian theme of the Rosetta mission, these regions are named for Egyptian deities, and are grouped according to the type of terrain dominant within.

The 19 regions identified on 67P/Churyumov–Gerasimenko are separated by distinct geomorphological boundaries; they are grouped according to the type of terrain dominant within each region. 

Five basic categories of terrain type have been determined: dust-covered (Ma’at, Ash and Babi); brittle materials with pits and circular structures (Seth); large-scale depressions (Hatmehit, Nut and Aten); smooth terrains (Hapi, Imhotep and Anubis), and exposed, more consolidated surfaces (Maftet, Bastet, Serqet, Hathor, Anuket, Khepry, Aker, Atum and Apis). 

Image credit: ESA / Rosetta / MPS / OSIRIS Team / UPD /LAM / IAA / SSO / INTA / UPM / DASP / IDA.

Five basic, but diverse, categories of terrain type have been determined: dust-covered; brittle materials with pits and circular structures; large-scale depressions; smooth terrains; and exposed more consolidated surfaces.

Much of the northern hemisphere is covered in dust. As the comet is heated, ice turns directly into gas that escapes to form the atmosphere or coma.

Dust is dragged along with the gas at slower speeds, and particles that are not traveling fast enough to overcome the weak gravity fall back to the surface instead.

Some sources of discrete jets of activity have also been identified. While a significant proportion of activity emanates from the smooth neck region, jets have also been spotted rising from pits.

The gases that escape from the surface have also been seen to play an important role in transporting dust across the surface, producing dune-like ripples, and boulders with ‘wind-tails,’ the boulders act as natural obstacles to the direction of the gas flow, creating streaks of material ‘downwind’ of them.

“Because comets have very little gravity, dust and gas flow freely into space. But 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,” said Dr Dennis Bodewits of the University of Maryland.

The scientists were able to make this discovery thanks to OSIRIS’ very sensitive cameras.

“Each pixel is about 30 cm. You couldn’t see a coffee cup, but you could see a large lunchbox. The resolution is about 10 times higher than Google Earth.”

According to the team, 67P/Churyumov-Gerasimenko was releasing the earthly equivalent of 1.2 liters of water into space every second at the end of August 2014.

MIRO (Microwave Instrument for the Rosetta Orbiter)

Credit: ESA

“In observations, made by the Microwave Instrument for Rosetta Orbiter (MIRO), over a period of three months, the amount of water in vapor form that the comet was dumping into space grew about tenfold,” said Dr Sam Gulkis of NASA’s Jet Propulsion Laboratory in Pasadena.

“To be up close and personal with a comet for an extended period of time has provided us with an unprecedented opportunity to see how comets transform from cold, icy bodies to active objects spewing out gas and dust as they get closer to the Sun.”

Greenpeace International: Uncovering the Arctic

Uncovering the Arctic | Greenpeace International

The Esperanza is currently at anchor just offshore from the town of Longyearbyen, in the Arctic islands of Svalbard, from where we’re about to depart on the next leg of the Arctic Under Pressure expedition.

There’s a sense of itchy anticipation and excitement on board; we’ll be heading to places that most people never go, and documenting things rarely seen both above and below the ocean surface.

We’ve have had to keep this eagerness in check for the last couple of days, as our remote-operated vehicle (ROV) has been held up due to a transport strike in Norway, and hasn’t yet arrived.

We’ll be using ROV, along with a “drop camera” to take a look at what dwells beneath the ocean floor north of Svalbard, including in areas that were once unreachable due to sea ice.

As the summer ice edge shifts north due to climate change, more of the Arctic Ocean is exposed. Once assumed to be devoid of life, the world below the sea ice it is an incredible font of biodiversity.

No one, including the scientific community, has yet had a real chance to study or understand these newly accessible marine habitats or the ocean floor below, yet they’re already under threat from the commercial fishing industry.

Vessels from Norway, Russia, Germany, the UK, France, Portugal and Iceland have realised that new waters are being exposed, and are sailing ever further north to reap the profits that can be gained from cod and haddock fishing.

We are going to be documenting and reporting on which countries have fishing vessels in these waters – all within the Svalbard Fisheries Protection zone, under Norwegian jurisdiction, and keeping a close eye on what they’re up to.

Our demand is simple, but achieving it won’t be easy – we want governments to come to together to declare a moratorium on all industrial activities, including destructive fishing practices within the Arctic Ocean that has been historically covered and protected year round by sea ice.

Unlike the Antarctic, the Arctic Ocean has never been protected by a treaty. We think that like our southern frozen continent, the Arctic Ocean should be a place free from industrial development, and instead designated as a place of peace and science. Does that sound unreasonable?

Before the Esperanza heads off into the wilderness, we’ve taken some new crew onboard, – Noriko from Japan, Jetkse from the Netherlands, Gavin from the UK, Elena from the Ukraine, Arne, our famous ice pilot from Denmark, Henning and Sven from Norway, and Audun, our Svalbard-based guide.

Some others have departed, gone south for the summer, including Janet and Martin, who wrote a couple of the earlier blogs; they were here for the ocean acidification work in Ny-Ålesund.

While the Esperanza spends June and early July exploring the oceans, the IFM-GEOMAR scientists remain in Ny-Ålesund with the mescosms, investigating the future acidification of our oceans.

We’ll be back to see them next those guys next month – if they haven’t been driven mad by the Arctic Terns in the meantime. The terns, having migrated all the way from the Antarctic – yes, they catch both summers – build their nests near the dog yard in Ny-Ålesund, which tends to help keep the local Arctic fox away.

Once the terns have laid their eggs, they become enthusiastic defenders, and will fly at the head of anyone who walks by. The trick, apparently, is to hold a stick above one’s head – and the terns attack the stick instead. As there are no trees in Svalbard, I’m intrigued as to how a stick can be procured.

Speaking of this Arctic fox, it lives under the Dutch research station at Ny-Ålesund, where it can be seen springing from and bouncing along the snow. By everybody but me, it seems.

I staked out the area several times, waiting my chance to see the fox, which is just starting to change from winter to summer coat. I had no luck, until the very early hours of Sunday morning, that is.

I was strolling towards the Esperanza, and for once I was not carrying my camera. I spotted something sitting on the small beach near the pier; it was the fox, staring intently at a pair of common eider ducks.

It turned, and trotted towards me, then sat on a rock about 5m away, studying me with mild interest. We spent around two minutes like that, before the fox evidently become bored, and trotted off along the beach in search of breakfast.