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Emily LakdawallaAugust 6, 2014

"We're at the comet!" Rosetta has arrived at comet 67P

After a journey of more than a decade, Rosetta has finally arrived at comet 67P Churyumov-Gerasimenko. Confirmation of the successful rocket firing came at about 9:30 UTC via a webcast from ESA's Operations Centre in Darmstadt, Germany. Congratulations to ESA, to the scientists and engineers on the mission, and all the people of all of ESA's member nations!

To celebrate the arrival, they released this photo of the comet taken three days ago, from a distance of 285 kilometers. The spacecraft is now three times closer, on an odd triangle-shaped orbit, so even better photos are yet to come. I have been adding new images and information to this post all morning. A more detailed report on the day's press events by Daniel Fischer will be posted later today.

OSIRIS view of comet Churyumov-Gerasimenko on August 3, 2014

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

OSIRIS view of comet Churyumov-Gerasimenko on August 3, 2014
Rosetta captured this view of comet Churyumov-Gerasimenko on August 3, 2014, three days before entering orbit, from a distance of 285 kilometers. The image resolution is 5.3 meters per pixel.

First signal received upon @ESA_Rosetta 's arrival at #Comet #67P as seen in #ESOC's Main Control Room

— ESA Operations (@esaoperations) August 6, 2014

Another newly released photo shows cometary activity. It's tempting to look at this and assume the jets are coming from the neck, but foreshortening could be confusing things.

Cometary activity on Churyumov-Gerasimenko, August 2, 2014

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

Cometary activity on Churyumov-Gerasimenko, August 2, 2014
Rosetta took a long-exposure image with its wide-angle camera on August 2, 2014, to observe jets of dust escaping from the comet. The photo was taken from a distance of 550 kilometers.

They also released an animation of 86 NavCam frames of the comet taken over the first few days of August. I separated some of the best ones out for your enjoyment:

Navcam views of comet Churyumov-Gerasimenko, August 4-6, 2014

ESA / Rosetta / NavCam / Emily Lakdawalla

Navcam views of comet Churyumov-Gerasimenko, August 4-6, 2014
This composite of Navcam images captures slightly more than two full rotations of comet Churyumov-Gerasimenko during Rosetta's final approach to its August 6, 2014 arrival. The comet rotates once every 12.4 hours. The images were taken from a longer animation; in the first four rows, the frames were probably taken an hour apart.

And here is an animation from the German space agency, DLR, which shows possible landing sites for Philae (I think they are the green dots).

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

Possible landing sites for Philae on Churuymov-Gerasimenko
The shape model shows how much illumination the comet surface receives over the course of its day (red is brighter, blue is darker) and possible locations for the landing of Philae on the comet (green spots) as of August 6, 2014. Philae will make the first-ever landing attempt on a comet on November 11, 2014.

Here's a Flickr photo album of the happy mission personnel and visitors at the European Space Operations Centre.

After the arrival, the OSIRIS team shared these two detail views cropped from their images:

OSIRIS image of Churyumov-Gerasimenko taken upon arrival (detail 1)

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

OSIRIS image of Churyumov-Gerasimenko taken upon arrival (detail 1)
The image shows the comet’s ‘head’ at the left of the frame, which is casting shadow onto the ‘neck’ and ‘body’ to the right. The image was taken from a distance of 120 km and the image resolution is 2.2 meters per pixel.
OSIRIS image of Churyumov-Gerasimenko taken upon arrival (detail 2)

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

OSIRIS image of Churyumov-Gerasimenko taken upon arrival (detail 2)
A smooth region on the ‘base’ of the ‘body’ section of comet 67P/Churyumov-Gerasimenko. The image was taken from a distance of 130 km and the image resolution is 2.4 meters per pixel.

And a processing feat by Daniel Macháček: a 3D view of the comet. He had to synthesize the right-eye image by warping the OSIRIS image (the left eye) to the shape of a NavCam image (the right eye).

Comet Churyumov-Gerasimenko in 3D

ESA / Rosetta / NavCam / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA / Daniel Macháček

Comet Churyumov-Gerasimenko in 3D

A 3D view of the comet composed from images taken by the OSIRIS camera and NavCam. The resolution of the two cameras is quite different, so it took some processing to make it work as a stereo pair. The left-eye image is the original OSIRIS photo; the right-eye image is a synthetic one made by warping the OSIRIS photo to the shapes of features visible in the NavCam photo. More formats: Left stereo | Right stereo | Flicker gif

Here is the full text of the press release from ESA about the arrival:

Paris, 6 August 2014

Rosetta arrives at comet destination

After a decade-long journey chasing its target, ESA's Rosetta has today become the first spacecraft to rendezvous with a comet, opening a new chapter in Solar System exploration.

Comet 67P/Churyumov-Gerasimenko and Rosetta now lie 405 million kilometres from Earth, about half way between the orbits of Jupiter and Mars, rushing towards the inner Solar System at nearly 55 000 kilometres per hour.

The comet is in an elliptical 6.5-year orbit that takes it from beyond Jupiter at its furthest point, to between the orbits of Mars and Earth at its closest to the Sun. Rosetta will accompany it for over a year as they swing around the Sun and back out towards Jupiter again.

Comets are considered to be primitive building blocks of the Solar System and may have helped to 'seed' Earth with water, perhaps even the ingredients for life. But many fundamental questions about these enigmatic objects remain, and through a comprehensive, in situ study of the comet, Rosetta aims to unlock the secrets within.

The journey to the comet was not straightforward. Since its launch in 2004, Rosetta had to make three gravity-assist flybys of Earth and one of Mars to help it on course to its rendezvous with the comet. This complex course also allowed Rosetta to pass by asteroids ?teins and Lutetia, obtaining unprecedented views and scientific data on these two objects.

"After ten years, five months and four days travelling towards our destination, looping around the Sun five times and clocking up 6.4 billion kilometres, we are delighted to announce finally 'we are here'," says Jean-Jacques Dordain, ESA's Director General.

"Europe's Rosetta is now the first spacecraft in history to rendezvous with a comet, a major highlight in exploring our origins. The discoveries can begin."

Today saw the last of a series of ten rendezvous manoeuvres that began in May to adjust Rosetta's speed and trajectory gradually to match those of the comet. If any of these manoeuvres had failed, the mission would have been lost, and the spacecraft would simply have flown by the comet.

"Today's achievement is a result of a huge international endeavour spanning several decades," says Alvaro Giménez, ESA's Director of Science and Robotic Exploration.

"We have come an extraordinarily long way since the mission concept was first discussed in the late 1970s and approved in 1993, and now we are ready to open a treasure chest of scientific discovery that is destined to rewrite the textbooks on comets for even more decades to come."

The comet began to reveal its personality while Rosetta was on its approach. Images taken by the OSIRIS camera between late April and early June showed that its activity was variable. The comet's 'coma' - an extended envelope of gas and dust - became rapidly brighter and then died down again over the course of those six weeks.

In the same period, first measurements from the Microwave Instrument for the Rosetta Orbiter, MIRO, suggested that the comet was emitting water vapour into space at about 300 millilitres per second.

Meanwhile, the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, measured the comet's average temperature to be about -70ºC, indicating that the surface is predominantly dark and dusty rather than clean and icy.

Then, stunning images taken from a distance of about 12 000 km began to reveal that the nucleus comprises two distinct segments joined by a 'neck', giving it a duck-like appearance. Subsequent images showed more and more detail - the most recent, highest-resolution image was downloaded from the spacecraft earlier today and will be available this afternoon.

"Our first clear views of the comet have given us plenty to think about," says Matt Taylor, ESA's Rosetta project scientist.

"Is this double-lobed structure built from two separate comets that came together in the Solar System's history, or is it one comet that has eroded dramatically and asymmetrically over time? Rosetta, by design, is in the best place to study one of these unique objects."

Today, Rosetta is just 100 km from the comet's surface, but it will edge closer still. Over the next six weeks, it will describe two triangular-shaped trajectories in front of the comet, first at a distance of 100 km and then at 50 km.

At the same time, more of the suite of instruments will provide a detailed scientific study of the comet, scrutinising the surface for a target site for the Philae lander.

Eventually, Rosetta will attempt a close, near-circular orbit at 30 km and, depending on the activity of the comet, perhaps come even closer.

"Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land," says Sylvain Lodiot, ESA's Rosetta spacecraft operations manager.

As many as five possible landing sites will be identified by late August, before the primary site is identified in mid-September. The final timeline for the sequence of events for deploying Philae - currently expected for 11 November - will be confirmed by the middle of October.

"Over the next few months, in addition to characterising the comet nucleus and setting the bar for the rest of the mission, we will begin final preparations for another space history first: landing on a comet," says Matt.

"After landing, Rosetta will continue to accompany the comet until its closest approach to the Sun in August 2015 and beyond, watching its behaviour from close quarters to give us a unique insight and realtime experience of how a comet works as it hurtles around the Sun."

Read more: Rosetta and Philae, pretty pictures, comets, mission status, comet Churyumov-Gerasimenko

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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