Tag: Comet 67P/C-G

Philae might have bounced

4:07 pm

Data from the Philae lander suggests that, when the spacecraft’s harpoons failed to fire, the probe might have bounced and then settled to the surface.

[T]elemetry from the craft suggested it might have drifted off the surface after landing and started to turn. This subsequently came to an end, which the German Space Agency official interpreted as a possible “second landing” on Comet 67P. This “bounce” was always a possibility, but had been made more likely by the failure of the harpoons to deploy, and the failure of a thruster intended to push the robot into the surface.

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A comet picture taken by Philae on the way down

1:06 pm

Comet 67P/C-G as seen by Philae during its descent

I am not sure if the actual landing site is visible in this image. I don’t think so as nothing seems to match what was on the earlier close-up. Moreover, the Rosetta website does not say.

No images on the surface have yet been released. There are also issues that could prevent a full success.

However, while the lander has touched down on the comet using its harpoons, scientists said that it had not yet deployed its anchors which meant that it was not completely attached to the surface. The surface was much softer than they expected, so there were some concerns that it was not securely fixed on the comet – although from a software point of view things seemed to be fine. Engineers will attempt to fire the anchors again soon in order to keep Philae attached to the surface of the comet.

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Philae has landed successfully!

9:14 am

Philae has landed successfully on Comet 67P/C-G.

Philae is on the surface, its harpoons have fired and the landing gear has been moved inside, and Philae is in contact. It’s incredible! Massive smiles on everyone’s faces. The room went mad. Twice — when we first had the hint, and then when Stephan Ulamec and Andrea Accomazzo confirmed it. Unbelievable.

More information and data will be coming in a few hours. Stay tuned.

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Philae is go for separation, despite problem

12:25 am

Engineers have given a go for the separation of the Philae lander from Rosetta, despite the failure of a thruster to operate.

During checks on the lander’s health, it was discovered that the active descent system, which provides a thrust upwards to avoid rebound at the moment of touchdown, cannot be activated.

At touchdown, landing gear will absorb the forces of the landing while ice screws in each of the probe’s feet and a harpoon system will lock Philae to the surface. At the same time, the thruster on top of the lander is supposed to push it down to counteract the impulse of the harpoon imparted in the opposite direction. “The cold gas thruster on top of the lander does not appear to be working so we will have to rely fully on the harpoons at touchdown,”says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center. “We’ll need some luck not to land on a boulder or a steep slope.”

Update: Separation has occurred and signal reacquired from Philae. We wait for landing.

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Close-up image of Philae’s landing site

9:32 am


Agilkia landing site for Philae

Inset of landing site

In the preparation to Wednesday’s landing of Philae on Comet 67P/C-G, Rosetta’s science team has released a great image of the landing site, shown above. To the right is a higher resolution inset of the site itself, with the smallest object visible about 8.5 feet across.

Looking at this inset, there are some obvious worries that we all should be aware of prior to the landing attempt. Though the Agilkia landing site is generally more smooth than most of the comet’s surface, it still has significant hazards. The lower part is strewn with boulders and rocks, many of which are quite large. Any one of these could do serious harm to Philae should it land on them.

Even more interesting is the upper part of the landing site. Though very smooth, the image suggests to me that this is a very thick pile of softly packed material. Philae might land there and quickly sink below the surface, where its cameras will be able to see nothing.

Nonetheless, the science team has also released this outline of Philae’s science timeline after landing. The lander will also be taking images of both Rosetta and the comet during its descent, so even if the landing is a failure we will still get some worthwhile data.

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The November 12 timeline of events for Philae’s landing on a comet

10:16 am

ESA has released a detailed timeline of events on November 11-12, when Rosetta’s Philae lander will be released and land on Comet 67P/C-G. They have also released a much more readable summary of the most critical events, describing what will be happening.

For Americans, these events will be occurring from around 3 pm (Eastern) November 11, when the process begins, to 12 pm (Eastern) November 12, when Philae will send back the first signals after landing. Much of the most critical events will take place in the wee hours of the morning.

Meanwhile, one of Rosetta’s instruments has confirmed the presence of water vapor and carbon dioxide in the jets seen near the comet’s narrow neck.

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Rosetta gets in position to release Phalae

9:36 am

Rosetta has successfully maneuvered into position prior to releasing Philae on November 12 for landing on Comet 67P/C-G.

The thruster burn took place starting at 02:09:55 UTC (03:09:55 CET), ran for 90 seconds and, based on an initial analysis of spacecraft radiometric data, delivered a delta-v – change in speed – of 9.3 cm/sec, as confirmed by the Rosetta Flight Dynamics team. It was the second and final of two ‘deterministic’ (i.e. direction and thrust are prepared in advance) manoeuvres that moved Rosetta onto the planned lander delivery orbit, now at a height of about 30 km, which will be maintained right up until the pre-delivery manoeuvre at two hours before separation at 08:35 UTC (09:35 CET) on the morning of 12 November.

…[T]he next planned orbit-changing manoeuvres will occur on the 12th at (a) 2 hours before separation and (b) about 40 minutes after, in between which Philae will be released. The pre-delivery manoeuvre will shift Rosetta’s trajectory so that the orbiter would be on a path so as to pass over the comet at a distance of 5 km, while the separation will occur at 08:35 UTC on board the spacecraft about 22 km (the confirmation signal will arrive on Earth at 09:03 UTC).

Since Philae is a passive lander, firing no thrusters but simply being thrown gently at the comet by Rosetta, the last two burns are crucial. The first literally puts Rosetta on the same collision course as Philae so that when the lander is released it is on a course to hit the comet. The second takes Rosetta out of that collision course, since no one wants it to hit the comet also.

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First chemical results from Rosetta

9:24 am

Spectroscopy from Rosetta has identified the make-up of a single dust grain captured by the spacecraft.

For the convenience of communications the science team had dubbed this single grain “Boris.”

[T]hese first results show that among the grain’s components are magnesium and sodium. Since 95 percent of the known observed minerals in comets resemble olivine and pyroxenes – containing a lot of magnesium – the detection of this element is not a big surprise. But, finding sodium in the dust grain, in a refractory mineral phase, has sparked our interest considerably.

The coma and tails of other comets are already known to contain sodium; it was observed in the dust samples returned from Comet Wild 2 by NASA’s Stardust mission, and a prominent example was also the sodium tail of Comet Hale-Bopp that flew past the Sun in April 1997 and which could be seen in the night sky for many weeks. However, by contrast, neither sodium nor magnesium were observed in Comet 67P/C-G dust grains before sampling the inner coma dust. But our dust grain Boris has showed off with clear sodium and magnesium mass peaks in the secondary ion mass spectra that we obtained.

Their next goal is to identify where on the surface of Comet 67P/C-G this sodium came from.

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Comet 67P/C-G smells!

5:07 pm

Instruments on Rosetta have determined that the various molecules coming off Comet 67P/C-G have a strong aroma.

You might expect a rock that spends all its time in a vacuum to be fairly inoffensive, but in fact exposure to sunlight is causing it to give off quite an aroma: hydrogen sulfide, ammonia, formaldehyde, hydrogen cyanide, and other caustic gases would make it smell “suffocating,” like a cross between a filthy barn, an embalming room, and a rotten egg.

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Increasing activity at Comet 67P/C-G

8:49 am

Data from Rosetta in the past month has been showing a steady and gradual increase in dust emissions from the surface.

While images obtained a few months ago showed distinct jets of dust leaving the comet, these were limited to the ‘neck’ region. More recently, images obtained by Rosetta’s scientific imaging system, OSIRIS, show that dust is being emitted along almost the whole body of the comet. Jets have also been detected on the smaller lobe of the comet. “At this point, we believe that a large fraction of the illuminated comet’s surface is displaying some level of activity,” says OSIRIS scientist Jean-Baptiste Vincent from the Max Planck Institute for Solar System Research (MPS) in Germany.

The last two images at the link compare the same location with one image overexposed to make the jets visible. What is interesting is that the source of the jet is not evident in the other normally exposed image. It is almost as if surface material is simply heating up and then using that extra energy to simply throw itself off the surface. Why that then forms jets however is puzzling.

More info here.

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Comet 67P/C-G at 2 feet per pixel

9:58 am

New images from Rosetta, now about 6 miles from the surface of Comet 67P/C-G, show details as small as 2 feet across.

Go to the link to see some images. If you were hiking there, these images would see you.

In related news, the Rosetta team is asking the public to help name the landing site for its Philae lander.

As the location of the first soft landing of a human-made object on a comet, the site, currently identified as Site J, deserves a meaningful and memorable name that captures the significance of the occasion. The rules are simple: any name can be proposed, but it must not be the name of a person. The name must be accompanied by a short description (up to 200 words) explaining why this would make the ideal name for such an historic location. A jury comprising members of the Philae Steering Committee will select the best name from the entries, and the winning proposer will be invited to follow the landing in person from ESA’s mission control centre in Darmstadt, Germany on 12 November.

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Giant boulders on Comet 67P/C-G

9:42 am

Giant boulders on Comet 67P/C-G

As Rosetta has moved in on Comet 67P/C-G, engineers have focused in on its most interesting surface features, such as the nucleus’s neck as well as a collection of very large boulders on a relatively smooth area on the nucleus’s larger lobe. The biggest boulder, seen as the middlemost rock in the photo above, they have named Cheops. It is estimated to be 150 feet across with a height of about 80 feet.

It should be emphasized that calling these features boulders might actually be premature at this time.
» Read more

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Rosetta gets the go to descend to six miles

8:42 am

After spending a week circling Comet 67P/C-G at a distance of about 12 miles, engineers have now decided they can move Rosetta in to only six miles.

A series of manoeuvres will reduce Rosetta’s distance from its current 18.6 km orbit (taking 7 days) to an intermediate orbit approximately 18.6 x 9.8 km (with a period of about 5 days). From there the orbit will be circularised at about 9.8 km radius, with a period of approximately 66 hours on 15 October, and the mission will enter the “Close Observation Phase” (COP). This will provide even higher resolution images of the landing site in order to best prepare for Philae’s challenging touch-down. The new orbit will also allow a number of Rosetta’s science instruments to collect dust and measure the composition of gases closer to the nucleus.

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Philae’s landing site chosen

3:32 am

Philae's primary landing site

The Rosetta science team has chosen the primary landing site on Comet 67P/C-G for its Philae probe.

Site J is on the ‘head’ of the comet, an irregular shaped world that is just over 4 km across at its widest point. The decision to select Site J as the primary site was unanimous. The backup, Site C, is located on the ‘body’ of the comet. The 100 kg lander is planned to reach the surface on 11 November, where it will perform indepth measurements to characterise the nucleus in situ, in a totally unprecedented way.

This site is, located in the outside center of the nucleus’s smaller lobe, was picked unanimously because it appears to be the easiest to reach while also providing good science.

The descent to the comet is passive and it is only possible to predict that the landing point will place within a ‘landing ellipse’ typically a few hundred metres in size.

A one square kilometre area was assessed for each candidate site. At Site J, the majority of slopes are less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. Site J also appears to have relatively few boulders, and receives sufficient daily illumination to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase.

Provisional assessment of the trajectory to Site J found that the descent time of Philae to the surface would be about seven hours, a length that does not compromise the on-comet observations by using up too much of the battery during the descent.

I have put a close-up of the landing site below the fold.
» Read more

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Philae’s mission at Comet 67P/C-G

9:29 am

With the decision to pick a landing site for their Philae lander coming up this weekend, the Rosetta science team today released a press announcement describing in detail the lander’s mission.

The details are fascinating. Not only will Philae take images from the surface as well as get data of the surface and its surrounding environment, the probe will also literally pound the surface to measure its temperature as well as get seismic readings.

The MUPUS hammer is released and embeds itself into the ground so that it can measure the temperature at various depths in the subsurface. The acoustic signals of the vibrations of the hammer action will be detected by acoustic sensors in the feet of SESAME/CASSE and will be used to measure the mechanical properties of the nucleus.

If all goes well, they hope that Philae will remain operational on the surface through March.

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Playing with today’s Rosetta image of Comet 67P/C-G

12:04 am

Adjusted comet image

In releasing Wednesday’s image of Comet 67P/C-G, the Rosetta science team suggested that readers download it and play with the brightness and contrast settings to bring out some interesting details.

[I]f you adjust the contrast of the image you will see that there is a lot of ‘noise’ in the background. Some of this is simply detector noise and cosmic rays, but there seem to be a few bright objects that may be dust/ice particles between Rosetta and the comet.

In previous NAVCAM and OSIRIS images, we’ve already seen jets of gas laced with dust streaming away from the comet, and the instruments COSIMA and GIADA have started detecting dust, so it would be no surprise if these objects were also found to originate from the comet. In any case, it is a phenomenon that will clearly be studied in great detail at 67P/C-G over the coming weeks and months.

Another nice observation you might like to make while playing around with the contrast settings is that faint details can be brought out in the ‘neck’ region of 67P/C-G, which on first look is seemingly obscured by shadows. It appears as though the neck is being illuminated by the reflection of sunlight off the main body of the comet below.

The image on the left above is the image as released. The image on the right I have brightened considerably to bring out additional details. As they noted, you can see topographical details in the shadowed neck area. Also, the entire nucleus seems to be surrounded by faint dust streaming away in all directions.

It is going to be a great deal of fun to watch this comet change over the next year as it makes its journey around the Sun.

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Rosetta’s camera zooms in

9:10 am

67P/C-G on August 23, 2014
Comet 67P/C-G as seen on August 23, 2014 from 38 miles.
Click on image for uncropped version.

The Rosetta team has begun releasing more close-up images of Comet 67P/C-G taken by the spacecraft. The image to the right was taken by the navigation camera, but rather than capture the entire nucleus in a single image the camera is now zoomed in and taking a mosaic of four images. This picture is one quarter of that mosaic.

Note the boulders and the sharp peaks in the image. The boulders are important to map for planning Philae’s landing site. The sharp peaks suggest recent outgassing.

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Rosetta arrives

10:14 am

Rosetta has successfully achieved orbit around Comet 67P/C-G and has transmitted its first close up images. More information here and here about the rendezvous and what science the mission scientists plan to do as they orbit the comet.

The image below is looking down and past the comet’s smaller component as it casts a shadow on the neck and the larger component beyond. As with the earlier images, the comet’s pitted and corroded surface, lacking any obvious craters, is reminiscent to me of a pile of dirty snow that has been dissolving away. In fact, when I lived in New York I would see this kind of look every winter. When the city would get a big snowfall snowplows would push it into large mounds on the side of the road. As time passed these piles would get dirty from the city’s soot and grime, and also slowly melt away. After several weeks it would look almost exactly like the surface of Comet 67P/C-G.

The images and data that will come down from Rosetta over the next year and half as it orbits the comet in its journey around the Sun will be most fascinating. Stay tuned!

67P/C-G up close

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