Tag: Comet 67P/Churyumov-Gerasimenko

The Rosetta science team has prepared a FAQ outlining what we should expect next month as Comet 67P/C-G reaches and passes its closest point to the Sun, with Rosetta (and hopefully Philae) there to watch.

The most interesting detail they note is this:

Will the comet break apart during perihelion?

The comet has not broken apart during its many previous orbits, so it is not expected to do so this time, but it cannot be ruled out. Scientists are keen to watch the possible evolution of a 500 m-long fracture that runs along the surface of the neck on the comet during the peak activity.

You can see an image from Rosetta that shows this fracture here. As I wrote then,

The biggest fracture line appears to be a meandering line that is traveling from the image’s top center to its mid-right. There also appear to be parallel lines below it. As we are looking at the nucleus’s neck, these lines suggest that the connection between the two large lobes is somewhat strained, and that it is not unlikely that these two sections will break apart at some time in the future. Though there is no way to predict at this time when that will happen, it will be truly exciting if it happens when Rosetta is in the neighborhood.

More on the comet sinkholes! New data from Rosetta has now confirmed that some of the plumes or jets that the spacecraft has seen emanating from Comet 67P/C-G come directly from the sinkholes that they have discovered on the nucleus.

In a study reported today in the science journal Nature, 18 quasi-circular pits have been identified in the northern hemisphere of the comet, some of which are the source of continuing activity. The pits are a few tens to a few hundreds of metres in diameter and extend up to 210 m below the surface to a smooth dust-covered floor. Material is seen to be streaming from the most active pits. “We see jets arising from the fractured areas of the walls inside the pits. These fractures mean that volatiles trapped under the surface can be warmed more easily and subsequently escape into space,” says Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research, lead author of the study.

Time for many cool images! The Rosetta science team has just released to the public another batch of images from its navigational camera.

The 1776 images cover the period between 23 September and 21 November 2014, corresponding to Rosetta’s close study of the comet down to distances of just 10 km from the comet centre – 8 km from the surface – and the images taken during and immediately following the landing of Philae on the comet.

You can browse through them at your leisure, making your own discoveries if you have a sharp eye and know something about planetary geology.

The science team for Rosetta’s navigation camera have released to the public 1297 images taken of Comet 67P/C-G as the spacecraft began its approach on August 1, 2014 through September 23, 2014.

The release also included a video assembled from these images, showing the comet nucleus as Rosetta approached from August 1 to August 22. I have embedded that video below. As you watch, you will think, “How does this thing stay together?” Though the video shows the nucleus’ rotation at a highly accelerated rate, which exaggerates the stresses on the object, the question is a good one, and in fact, is actually predicting the future. Eventually, this nucleus will break up.

During its most recent close fly-by of Comet 67P/C-G Rosetta had a number of issues that caused the spacecraft to go into safe mode.

During the most recent flyby, a number of issues were reported, starting with the primary star tracker encountering difficulties in locking on to stars on the way in towards closest approach. Attempts were made to regain tracking capabilities, but there was too much background noise due to activity close to the comet nucleus: hundreds of ‘false stars’ [from comet debris] were registered and it took almost 24 hours before tracking was properly re-established.

In the meantime, a spacecraft attitude error had built up, resulting in the high gain antenna off-pointing from the Earth. Indeed, a significant drop in the radio signal received by ground stations on Earth was registered. Following recovery of the star tracker system, the off-pointing was immediately automatically corrected and the operations team subsequently saw a return to a full strength signal from the spacecraft.

However, issues with false stars were still occurring. Cross comparisons with other navigation mechanisms showed inconsistencies with the star trackers and some on board reconfigurations occurred. While attempting to reconfigure those, the same error occurred again leading this time to an automatic safe mode on Sunday afternoon. Safe modes occur when certain spacecraft parameters fall out of their normal operating ranges and the spacecraft automatically takes measures to preserve its safety. This also includes switching off the science instruments to protect them.

Rosetta is operating nominally now, but these issues are going to get more serious in the coming months, as the comet gets more active. Rosetta’s engineering team is going to have to come up with a method for the spacecraft’s star trackers to distinguish between stars and the debris in the comet’s coma. If they don’t it is likely that they will have to reduce the close fly-bys significantly.

Rosetta’s high resolution camera has taken a color image of Comet 67P/C-G’s narrow neck, the area where the most plume activity has taken place.

When seen with the human eye, comet 67P/Churyumov-Gerasimenko is grey – all over. With its color filters Rosetta’s scientific imaging system OSIRIS, however, can discern tiny differences in reflectivity. To this effect, scientists from the OSIRIS team image the same region on the comet’s surface using different color filters. If, for example, the region appears especially bright in one of these images, it reflects light of this wavelength especially well.

“Even though the color variations on 67P’s surface are minute, they can give us important clues”, says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. In a recent analysis performed by the OSIRIS team, the Hapi region clearly stands out from the rest of the comet: while most parts of 67P display a slightly reddish reflectivity spectrum as is common for cometary nuclei and other primitive bodies, the reflection of red light is somewhat lower in this region.

They as yet do not know exactly why the smooth area at the neck has a very slight blueish tinge, though they suspect it is because of the presence of a higher percentage of frozen water.

More cool images! Rosetta’s navigation camera has taken another very amazing close-up of Comet 67P/C-G, snapped during the February 14 fly-by.

The cropped section above focuses on the transition between two regions, the generally smooth area called Imhotep on the right and the more mountainous and rugged area called Khepry on the left. Go to the link for the full image, which also includes an interesting description of the engineering problems of doing these close fly-bys.