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From a press release of the European Space Agency (ESA), September 5, 2016:

Less than a month before the end of the mission, the Rosetta orbiter’s high-resolution camera has revealed the Philae lander wedged into a dark crack on Comet 67P/Churyumov-Gerasimenko.

philae_found

Credit: ESA/Rosetta/MPS for OSIRIS Team

The images were taken on September 2 by the OSIRIS narrow-angle camera as the orbiter came within 2.7 km of the surface and show the main body of the lander, along with two of its three legs.

The images also provide proof of Philae’s orientation, making it clear why establishing communications was so difficult following its landing on November 12, 2014.

The discovery comes less than a month before Rosetta descends to the comet’s surface. On September 30, the orbiter will be sent on a final one-way mission to investigate the comet from close up, including the open pits in the Ma’at region, where it is hoped that critical observations will help to reveal secrets of the body’s interior structure.

Link: full Rosetta mission press release, including further images and explanations.

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From a JPL news release, February 10, 2015:

Astronomers tinkering with ice and organics in the lab may have discovered why comets are encased in a hard, outer crust. Using an icebox-like instrument nicknamed Himalaya, the researchers show that fluffy ice on the surface of a comet would crystalize and harden as the comet heads toward the Sun and warms up. As the water-ice crystals form, becoming denser and more ordered, other molecules containing carbon would be expelled to the comet’s surface. The result is a crunchy comet crust sprinkled with organic dust, like a deep-fried ice cream: the crust is made of crystalline ice, while the interior is colder and more porous. The organics are like a final layer of chocolate on top.

comet-ice-cream-670x440-150210-jpg

Credit: ESA/Rosetta/NAVCAM

The composition of comets is important to understanding how they might have delivered water and organics to our nascent, bubbling-hot Earth. New results from the Rosetta mission show that asteroids may have been the primary carriers of life’s ingredients; however, the debate is ongoing and comets may have played a role.

Links: JPL news article; Rosetta home.

From a press release of the Max Planck Institute for Solar System Research, July 17, 2014:
As ESA’s spacecraft Rosetta is slowly approaching its destination, Comet 67P/Churyumov-Gerasimenko (see p. 213) is again proving to be full of surprises. New images obtained by OSIRIS, the onboard scientific imaging system, confirm the body’s peculiar shape that earlier pictures had hinted at. 67P is obviously quite unlike any other comet visited so far. (See also previous post.)

“The distance still separating Rosetta from 67P is now far from astronomical,” says OSIRIS principal investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. “It’s a trip of less than 12,000 kilometers. That’s comparable to travelling from Germany to Hawaii.”

However, while taking a snapshot of Mauna Kea, Hawaii’s highest mountain, from Germany is an impossible feat, Rosetta’s camera OSIRIS is doing a great job at catching ever clearer glimpses of its similarly sized destination. Images obtained on July 14th clearly show a tantalizing shape. The comet’s nucleus consists of two distinctly separated parts.

Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

“This is unlike any other comet we have ever seen before,” says OSIRIS project manager Carsten Güttler from the MPS. “The images faintly remind me of a rubber ducky with a body and a head,” he adds with a laugh. How 67P received this duck-like shape is still unclear. “At this point we know too little about 67P to allow for more than an educated guess,” says Sierks. In the next months, the scientists hope to determine more of the comet’s physical and mineralogical properties. These could help decide, whether the comet’s body and head were formerly two individual bodies.

In order to get an idea of what seems to be a very unique body, the observed image data can be interpolated to create a smoother shape. “There is, of course, still uncertainty in these processed, filtered images and the surface will not be as smooth as it now appears,” Güttler points out. “But they help us the get a first idea.”

Links: the original MPS press release and media files; an interactive movie (requires a Flash player) depicting Rosetta’s journey through the Solar System to reach Comet 67/P C-G.

Adapted from an ESA press release, July 17, 2014:
New images of Comet 67P/Churyumov-Gerasimenko reveal an extraordinarily irregular shape (see p. 213). It has become clear that this is no ordinary comet. Like its name, it seems that comet 67P/C-G is in two parts.

Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

ESA scientists have made this movie, using a sequence of 36 interpolated images each separated by 20 minutes, providing a truly stunning 360-degree preview of the overall complex shape of the comet. It supports the presence of two definite components – one segment seems to be rather elongated, while the other appears more bulbous. Indeed, some people have already likened the shape to a duck, with a distinct body and head. Note that the comet’s surface features won’t be as smooth as these processed images imply.

Dual objects like this – known as ‘contact binaries’ in comet and asteroid terminology – are not uncommon. Indeed, Comet 8P/Tuttle is thought to be such a contact binary; radio imaging by the ground-based Arecibo telescope in Puerto Rico in 2008 suggested that it comprises two sphere-like objects. Meanwhile, the bone-shaped Comet 103P/Hartley 2, imaged during NASA’s EPOXI flyby in 2011, revealed a comet with two distinct halves separated by a smooth region. In addition, observations of asteroid 25143 Itokawa by JAXA’s Hayabusa mission, combined with ground-based data, suggest an asteroid comprising two sections of highly contrasting densities.

Is Rosetta en-route to rendezvous with a similar breed of comet? The scientific rewards of studying such a comet would be high, as a number of possibilities exist as to how they form.

Links and further resources: the full ESA press release; link to unprocessed (still) image; link to movie.

Only a small bit of the sun-grazing Comet ISON has apparently survived its perihelion passage on Thanksgiving Day (November 28th), so no grand display of a comet with a tail visible to the naked eye will be seen.  Still, the comet has given a lot of scientific data through spectra from ground-based telescopes and views from a variety of spacecraft. (See Section 8.3)

Comet ISON, which has orbited the Sun among the objects of the Oort cloud for almost 4.5 billion years, perhaps as much as a light-year away from the inner Solar System, has remained largely untouched since the time of the Solar System’s formation. Since it was first detected nearly a year ago, astronomers hoped that its passage would offer a unique glimpse of the state of our Solar System in its earliest moments.

Links: Updates from Sky & Telescope magazine; ISON movie from SOHO’s coronagraph; ISON image gallery from Spaceweather.com; NASA Comet ISON Observing Campaign website.