Starship Asterisk*

Rosetta's Farewell

Explanation: After closely following comet 67P/Churyumov-Gerasimenko for 786 days as it rounded the Sun, the Rosetta spacecraft's controlled impact with the comet's surface was confirmed by the loss of signal from the spacecraft on September 30, 2016. One the images taken during its final descent, this high resolution view looks across the comet's stark landscape. The scene spans just over 600 meters (2,000 feet), captured when Rosetta was about 16 kilometers from the comet's surface. Rosetta's descent to the comet brought to an end the operational phase of an inspirational mission of space exploration. Rosetta deployed a lander to the surface of one of the Solar System's most primordial worlds and witnessed first hand how a comet changes when subject to the increasing intensity of the Sun's radiation. The decision to end the mission on the surface is a result of the comet's orbit now taking it to the dim reaches beyond Jupiter where there would be a lack of power to operate the spacecraft. Mission operators also faced an approaching period where the Sun would be close to line-of-sight between Earth and Rosetta, making radio communications increasingly difficult.

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Wonderful but strangely sad ending to these two explorers

Adieu, Rosetta and Philae...Adieu...

At least they rest and travel the Solar System together, after a largely successful "life"...a person couldn't ask for much more.... and in space, they don't rust or corrode, or grow much older in appearance....

And what a view they have...

Bon Voyage.
:--[===] *

What are those many white spots?

What an extraordinary similarity this, and so may other Rosetta pictures have to planetary 'geo'logy!

The crag above appears to have strata, to be a sedimentary rock, the scree slope below is graded with small stuff at the top, boulders 'below' with the largest scattered onto the 'alluvial' 'land' beyond that. It could be any eroded alpine valley! I KNOW this isn't so, but can/will any geologist discuss this similarity, please? Is just that rocks are rocks, and even in microgravity they behave the same?

JOhn

JohnD wrote:What an extraordinary similarity this, and so may other Rosetta pictures have to planetary 'geo'logy!

The crag above appears to have strata, to be a sedimentary rock, the scree slope below is graded with small stuff at the top, boulders 'below' with the largest scattered onto the 'alluvial' 'land' beyond that. It could be any eroded alpine valley! I KNOW this isn't so, but can/will any geologist discuss this similarity, please? Is just that rocks are rocks, and even in microgravity they behave the same?

JOhn

It almost looks as the the lower areas appear to have been liquid and that some sort of low-G flow has occurred.

Indeed, which is why I described that area as 'alluvial', shaped and deposited by non-marine water.
But it isn't! It can't be!

Why is it so familiar looking, as if it were a photo of a scene in the desert? If it has so little gravity then how can it be stratified and how can it have talus slopes? I guess I expected an amalgum of space rock held together by what - ice of some kind? Of all the photos I've seen of other planets and moons this is the most unexpected.

My brain just can't help but interpret this as a picture taken from the surface. Features on the ground appear progressively bigger in angular size towards the picture bottom, as one would expect in such case.

rj rl wrote:My brain just can't help but interpret this as a picture taken from the surface. Features on the ground appear progressively bigger in angular size towards the picture bottom, as one would expect in such case.

Rosetta’s OSIRIS narrow-angle camera captured this image of Comet 67P/Churyumov-Gerasimenko at 01:20 GMT from an altitude of about 16 km above the surface during the spacecraft’s final descent on 30 September.

The image scale is about 30 cm/pixel and the image measures about 614 m across.

source: http://rosetta.jpl.nasa.gov/gallery/ima ... omet-16-km

PS: My first search result lead me to JPL and not to ESA

Woodworker Will wrote:Why is it so familiar looking, as if it were a photo of a scene in the desert? If it has so little gravity then how can it be stratified and how can it have talus slopes? I guess I expected an amalgum of space rock held together by what - ice of some kind? Of all the photos I've seen of other planets and moons this is the most unexpected.

The picture was taken at 16 km of height. So the mountains in the background must have a height of 30 or 40 km - possible only with low gravity I think.

PS: Hmm ... maybe I am wrong

16 km above the surface, 600 m across ... maybe the dimension of the background mountain is much smaller because it's a narrow angle photo ...

But the comet is 4km long (wide, rather), that's the thing.

rj rl wrote:But the comet is 4km long, that's the thing.

You are right, 4 km long and 40 km high is impossible ...

I strongly suspect that the 16 km figure in the description is wrong. Nothing about the picture makes sense with that figure. The comet is only 4 km on its longest dimension. Even an extremely narrow focus to cover such a relatively small area would flatten all features. This picture must have been taken at very close range

Looks like 16 METERS from the surface to me. Looks like the last frame seconds before impact, IMHO.

I'd imagine that our descendants will be extraordinarily interested in salvaging and examining this next time it circles back. Even wrecked, it will be a far better preserved example of 21st century tech than anything on earth. Imagine if the ancient Egyptians had crashed a spacecraft on a comet soon to circle back; we'd be extraordinarily excited to take a look!

So two questions:

1. When's the next approach to the inner solar system?

2. How badly did we crash it? I'm assuming, given weak gravity, that it wasn't totaled.

67P is considered a comet. I just can't believe how much snow and ice is present in this high-def close-up photo ! LOL

dmbeaster@aol.com wrote:I strongly suspect that the 16 km figure in the description is wrong. Nothing about the picture makes sense with that figure. The comet is only 4 km on its longest dimension. Even an extremely narrow focus to cover such a relatively small area would flatten all features. This picture must have been taken at very close range

Everything is consistent with the camera being 16 km from the comet. The camera has a 2.2° field, which means it's imaging a field about 600 meters across (as the source states) and (with a 2K square sensor) has a pixel scale of about 30 cm/pixel (also stated by the source). So those cliff-like structures with the "scree" below them are around 150 meters high- perfectly reasonable given the size of the comet.

Without a 3D pair (hopefully there are some image pairs in the dataset that can be used to generate one) it's very difficult to actually figure out what the 3D structure is in this image. Our brains try and turn it into something terrestrial, but it may be nothing of the sort given the very low gravity.

Jim Leff wrote:I'd imagine that our descendants will be extraordinarily interested in salvaging and examining this next time it circles back. Even wrecked, it will be a far better preserved example of 21st century tech than anything on earth. Imagine if the ancient Egyptians had crashed a spacecraft on a comet soon to circle back; we'd be extraordinarily excited to take a look!

So two questions:

1. When's the next approach to the inner solar system?

2. How badly did we crash it? I'm assuming, given weak gravity, that it wasn't totaled.

It comes around every 6.4 years. And the landing probably didn't do much damage- perhaps the solar panels were broken off. Nobody will be salvaging anything for at least some decades... and by then, the craft could be quite altered by the comet's activity. They did set it down in a region that showed signs of high activity.

Is there gravity on this comet? The pebbles and rocks look very stationary on the surface rather than floating off into space.

PeterL wrote:Is there gravity on this comet? The pebbles and rocks look very stationary on the surface rather than floating off into space.

The comet has mass, and therefore it has gravity. Indeed, it is gravity that holds it together. The surface gravity is around a ten-thousandth that of Earth, which means the comet has an escape velocity of about a meter per second. That's low enough that escaping gases can blow material away when the comet is near the Sun, but otherwise, what's laying there will keep laying there.

Wonder if CERES looks like that up close ?

How much mass does a body of rubble have to have before gravity becomes detectable ?

ta152h0 wrote:
How much mass does a body of rubble have to have before gravity becomes detectable ?

In so far as having gravity become the dominant factor in planetesimal growth

• —about 1 km in diameter:

https://en.wikipedia.org/wiki/Nebular_hypothesis#Rocky_planets wrote:
<<After small planetesimals—about 1 km in diameter—have formed by one way or another, runaway accretion begins. It is called runaway because the mass growth rate is proportional to R⁴~M^4/3, where R and M are the radius and mass of the growing body, respectively. It is obvious that the specific (divided by mass) growth accelerates as the mass increases. This leads to the preferential growth of larger bodies at the expense of smaller ones. The runaway accretion lasts between 10,000 and 100,000 years and ends when the largest bodies exceed approximately 1,000 km in diameter. Slowing of the accretion is caused by gravitational perturbations by large bodies on the remaining planetesimals. In addition, the influence of larger bodies stops further growth of smaller bodies.>>