Tag: comets

Many cool images! The Rosetta team has released a bunch of very nice images taken of Comet 67P/C-G during August when the spacecraft was flying in close. The image on the right, cropped and reduced in resolution to post here, shows the comet’s large lobe, with the narrow neck to the left. Make sure you check out the full resolution image. It was taken on August 10, 2016 from about 8 miles away, and has a resolution of less than four feet per pixel. If a person was standing there you could just see them!

What I find most fascinating is the incredible curvature of the comet’s surface. The smooth area on the left, dubbed Imhotep (images of which have been posted here previously), has several big boulders on its flat surface. If you stood there, the ground would be down and horizontal. Walk only a short distance and you quickly reach the curving horizon and that flat area would look like a steep slope dropping down behind you. Yet, the boulders do not roll down hill! Walk a short distance more and you begin to enter the neck region, with giant walls rising above you, until you start to walk up them and they become the floor!

The scientists running Rosetta are asking the public to help them pour through the more than 20,000 images of Comet 67P/C-G to identify any changes the comet has undergone since the spacecraft’s arrival.

Because Rosetta’s star tracker became confused by dust particles, the spacecraft lost contact with Earth, went into safe mode, and required the entire weekend for engineers to regain control.

“We lost contact with the spacecraft on Saturday evening for nearly 24 hours,” says Patrick Martin, ESA’s Rosetta mission manager. “Preliminary analysis by our flight dynamics team suggests that the star trackers locked on to a false star – that is, they were confused by comet dust close to the comet, as has been experienced before in the mission.” This led to spacecraft pointing errors, which triggered the safe mode. Unfortunately the star trackers then got hung in a particular sub mode requiring specific action from Earth to recover the spacecraft.

“It was an extremely dramatic weekend,” says Sylvain Lodiot, ESA’s Rosetta spacecraft operations manager.”

The spacecraft has been diving to within only a few miles of the surface of Comet 67P/C-G, which means it is flying close to the comet’s coma. The increased dust in that region has confused the star tracker in the past, but this appears to have been the most serious event yet.

Data from Rosetta has found that Comet 67P/C-G has changed color and brightness since the spacecraft’s arrival.

Even when Rosetta first rendezvoused with the comet far from the Sun, ices hidden below the surface were being gently warmed, sublimating into gas, and escaping, lifting some of the surface dust away and contributing to the comet’s coma and tail. VIRTIS shows that as the ‘old’ dust layers were slowly ejected, fresher material was gradually exposed. This new surface was both more reflective, making the comet brighter, and richer in ice, resulting in bluer measurements.

On average, the comet’s brightness changed by about 34%. In the Imhotep region, it increased from 6.4% to 9.7% over the three months of observations

The changes are similar to those found on the Moon when the surface there is disturbed. The old surface is very dark. When hit by a meteorite or scrapped by an astronaut’s foot, it brightens. In the case of Comet 67P, the underlying ice pushes outward when heated, the dust is removed, and the surface gets brighter.

Cool image time! As part of its research plan, Rosetta has been moved outward from Comet 67P/C-G for the next few weeks in order to better study its coma and tail. In this new position, engineers were able to maneuver the spacecraft so that it was flying about 600 miles farther from the Sun and could look back and see the Sun being eclipsed by the comet.

Thanks to the combination of a long, four-second exposure, no attenuation filter and a low-gain setting on the analogue signal processor of NAVCAM (a setting that is used to image bright targets), the image reveals the bright environment of the comet, displaying beautiful outflows of activity streaming away from the nucleus in various directions. It is interesting to note hints of the shadow cast by the nucleus on the coma below it, as well as a number of background stars sprinkled across the image.

In the next week the spacecraft will move back in close to the comet.

Cool image time! As Rosetta completes a several weeks of in-close observations it took the above oblique view (cropped and reduced to show here) of Comet 67P/C-G. The image was taken from about 7.5 miles with a resolution of about 3 feet per pixel. It shows the Imhotep flat area with the large 80-foot-high Cheops boulder in the center. It is worthwhile to compare this image with one taken in January.. Though the angle is far different, you can recognize the same areas in Imhotep where some of the surface has apparently evaporated away.

What I especially like about today’s image is that it really gives one a feel for what it would be like to stand on the surface here. The light gravity allows some strange rock configurations, such as that giant weird balancing outcrop on the horizon. If you were standing in Imhotep that outcrop would hang above you threateningly.

The spacecraft is now moving away from the comet for the next few weeks

Following the brief encounter at these close distances, Rosetta is now heading out on an anti-sunward excursion to around 1000 km to investigate the comet’s wider coma, tail and plasma environment. Today, 24 March, Rosetta is already over 200 km away from the comet. The current plan is for Rosetta to make a 30 km zero phase flyby around 9 April, before entering back into closer bound orbits by 21 April.

Cool image time! As Comet 67P/C-G moves away from the sun and cools down, the Rosetta science team has been able to move the spacecraft back in close to the comet. The image on the right was taken on March 5 from only 12.6 miles above the comet’s surface, and has a resolution of 14 inches per pixel.

I have brightened the image and cropped it to show it here. At this scale, if they managed to photograph the location where Philae sits we would see it with no problem at all. As it is, the detail is remarkable. For example, look at the slope below the cliff in the lower right. You can see what look like a very faint series of terraces, suggesting the existence of onion-like layers below the surface.

Go to the link. There is a second high resolution image there that is as amazing.

Scientists using Rosetta have finally detected the expected bubble or region surrounding Comet 67P/C-G where there is no magnetic field and the Sun’s solar wind does not enter.

The bubble is caused by the material being ejected from the comet. Scientists had detected the same thing around Halley’s Comet back in 1986, but it turns out the bubble around Comet 67P/C-G is larger than expected based on those previous measurements, and also fluctuates in size more than predicted.

The Rosetta science team has determined that Comet 67P/C-G has no voids or large caverns in its interior, and that its low density is because its dust and water ice have mixed to produce a “fluffy” density.

In a new study, published in this week’s issue of the journal Nature, a team led by Martin Pätzold, from Rheinische Institut für Umweltforschung an der Universität zu Köln, Germany, have shown that Comet 67P/Churyumov-Gerasimenko is also a low-density object, but they have also been able to rule out a cavernous interior. This result is consistent with earlier results from Rosetta’s CONSERT radar experiment showing that the double-lobed comet’s ‘head’ is fairly homogenous on spatial scales of a few tens of metres.

The most reasonable explanation then is that the comet’s porosity must be an intrinsic property of dust particles mixed with the ice that make up the interior. In fact, earlier spacecraft measurements had shown that comet dust is typically not a compacted solid, but rather a ‘fluffy’ aggregate, giving the dust particles high porosity and low density, and Rosetta’s COSIMA and GIADA instruments have shown that the same kinds of dust grains are also found at 67P/Churyumov-Gerasimenko.