APOD: Rosetta's Rendezvous (2014 Aug 07)

[APOD Robot]

Rosetta's Rendezvous

Explanation: On August 3rd, the Rosetta spacecraft's narrow angle camera captured this stunning image of the nucleus of Comet 67P/Churyumov-Gerasimenko. After 10 years and 6.5 billion kilometers of travel along gravity assist trajectories looping through interplanetary space, Rosetta had approached to within 285 kilometers of its target. The curious double-lobed shape of the nucleus is revealed in amazing detail at an image resolution of 5.3 meters per pixel. About 4 kilometers across, the comet nucleus is presently just over 400 million kilometers from Earth, between the orbits of Jupiter and Mars. Now the first spacecraft to achieve a delicate orbit around a comet, Rosetta will swing to within 50 kilometers and closer in the coming weeks, identifiying candidate sites for landing its probe Philae later this year.

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[Ann]

I think it looks as if the comet is covered in snow. Maybe it is, too. Surely it has had at least one outburst recently? Couldn't it have covered itself in its own snow?

Ann

[Nitpicker]

The amazingly loopy, gravity assist trajectories are shown in the video on the page:
http://www.esa.int/spaceinvideos/Videos ... y_in_space

So that's how one sneaks up gently on a comet from behind, as it hurtles inwards to the Sun. And I suppose that's the easy bit ... I wonder what odds the landing team are giving themselves.

[SouthEastAsia]

The world would be justified to pause for a moment and more humbly appreciate as a wider humankind/race what this Rosetta mission is bringing to our collective scientific amazement and learning curve in both a more general and spcified field.

Bravo to Rosetta and ESA on this mission. Thank you from planet Earth as you bring us even more...

[geckzilla]

I like to compare Rosetta's approach to this comet to New Horizon's Pluto approach. It happened fast, didn't it? Rosetta has the advantage of achieving orbit around this tiny body. New Horizons will zoom by Pluto and probably leave us yearning for more data.

[metamorphmuses]

Compared to most asteroids I've seen images of (except for Itokawa, the "rubble pile"), the surface has a varied, interesting texture -- to me, it looks like parts have been melted. Maybe it's just because I have been prompted to think that way, with everything I have read about comets in general, but that suggests to me that the comet a big ball of icy mud, with areas that look half-melted and "gooey" and others where sublimation has left a sort of pitted surface.

[Paddy SA]

Incredible picture. But it needs a scale! I thought the BBC report showing its size relative to London was quite revealing (http://www.bbc.com/news/science-environment-28659783)
That surface looks like it has regmaglypts - which I thought were attributed to a meteorite's passage through the atmosphere. Does this imply that 67P Churyumov–Gerasimenko may have had a really close encounter in the past? And if so, with what; a planet or micro-planet, or maybe it was the sun?
Alternatively, could it be telling us that regmaglypts can be formed by the action of "solar wind" or other space processes?

[distefanom]

Simply fantastic and breathtaking image!
Whoa! mother nature is surprising, even on a "rubble pile of stones" like this one!
I never seen a surface like that one, even if I already seen surfaces of other asteroids.
What is astonishing, is the appearance, the so many steeples, and the
Incredibly smooth surfaces, between boulders and craters and impossible steep slopes here and there...
in the right lobe, right on the top, there is a wide depression where I can imagine the outgassing came out once.
Even thou, in the so-white rosetta image of August, 2 it appears that the main jet comes out from the "neck" of the comet...
At first impression I get, is the DOUGH you get when you knead the flour and it is still wet and not well worked...
It's incredible that only 4 days ago some jets where coming out violently from this thing, I really hope ESA could be smart enough together with some luck, not to be "aimed" by these jets, in a way that could damage the spacecraft....
Go on, ROSETTA ! ! !

[neufer]

[b][color=#0000FF]Comet Hartley 2 from close approach by EPOXI mission[/color][/b]

---

I think it looks as if the comet is covered in snow. Maybe it is, too. Surely it has had at least one outburst recently? Couldn't it have covered itself in its own snow?

After looking at Comet Hartley 2 it seemed to me that outgassing of carbon dioxide & water vapor mostly occurred at the spinning ends of this dipole comet (where the escape velocity is minimal).

What material doesn't escape falls/condenses mostly around the central neck (where the escape velocity is maximal).

Electostatics may play a big role here

[distefanom]

After looking at Comet Hartley 2 it seemed to me that outgassing of carbon dioxide & water vapor mostly occurred at the spinning ends of this dipole comet (where the escape velocity is minimal).

What material doesn't escape falls/condenses mostly around the central neck (where the escape velocity is maximal).

It seems that this comet behaves differently than Comet Hartley 2.
Here is an image of this comet, last 2 of august :
http://www.esa.int/spaceinimages/Images ... ugust_2014

here outgassing appears to flow out from the "neck"

[BDanielMayfield]

I wonder what the mass of this thing is. Have new mass estimates been released yet?

[Tszabeau]

I hope someone remembered to bring the salt shaker.

[Joules]

I wonder what the mass of this thing is. Have new mass estimates been released yet?

No. Last I saw was in the 0.1 to 0.4 g per cubic cm range. Too insubstantial for even CO2 or nitrogen ice. Yet the thing is obviously rigid. Now that Rosetta's in orbit, it shouldn't be too long before a proper gravity map and mass value come out.

[MadMan]

Amazing! The surface reminds me of what I remember from the movie "Deep Impact". Looks like the high spots on the top half have been sanded down, maybe by the dust coming from the leading edge?

[Steve Dutch]

In fifty years of space exploration, this is the very first object that has the weird spiky appearance so beloved of special effects artists!

[BDanielMayfield]

I wonder what the mass of this thing is. Have new mass estimates been released yet?

No. last I saw was in the 0.1 to 0.4 g per cubic cm range. Too insubstantial for even CO2 or nitrogen ice. Yet the thing is obviously rigid. Now that Rosetta's in orbit, it shouldn't be too long before a proper gravity map, and mass value come out.

Thanks Joules. Yes, the most accurate way to "weigh" an astronomical body would be to see how long a known mass at a known distance takes to orbit it.

Electostatics may play a big role here

Like dust bunnies?

[neufer]

I wonder what the mass of this thing is. Have new mass estimates been released yet?

No. Last I saw was in the 0.1 to 0.4 g per cubic cm range. Too insubstantial for even CO2 or nitrogen ice. Yet the thing is obviously rigid. Now that Rosetta's in orbit, it shouldn't be too long before a proper gravity map and mass value come out.

Last of the FATties

<<With about 4500 km separating Rosetta from comet 67P/C-G, the spacecraft will conduct the last of four FAT – ‘Far Approach Trajectory’ – orbit correction manoeuvres later today. Mass is possibly the most uncertain of all the cometary parameters (because the density is extremely uncertain) yet is the single most important parameter to be estimated from the standpoint of early navigation activities at the comet. The latest science data – including recent images indicating the comet is a complex 'contact binary' – is enabling the mission team to refine models of the comet. Based on the best estimates of the comet size & shape available before the recent images, the mass is estimated at 3.14x10¹² kg [; i.e., π billion tonnes corresponding to a mean density of 102±9 kg/m³]. This will surely change as we learn more about this enigmatic object.>>

[neufer]

Click to play embedded YouTube video.

In fifty years of space exploration, this is the very first object that has the weird spiky appearance so beloved of special effects artists!

I hope ESA knows what it's doing

[Byork]

I have an alternative mission for Rosetta. Forget the rendezvous with comet 67P Churyimenko. Rosetta can shoot back to Mars and land on the larger moon Phobos for a front seat view of the Martian atmosphere. The Rosetta deployment on Phobos will help to determine the rate of meteoritic impact with the Martian surface.

[MargaritaMc]

http://asterisk.apod.com/viewtopic.php? ... 72#p230172
Rosetta arrival highlights

[Chris Peterson]

After looking at Comet Hartley 2 it seemed to me that outgassing of carbon dioxide & water vapor mostly occurred at the spinning ends of this dipole comet (where the escape velocity is minimal).

What material doesn't escape falls/condenses mostly around the central neck (where the escape velocity is maximal).

The outgassing and particle ejection models we use to describe comets put material ejection velocities several orders of magnitude above the comet escape velocity. It's unlikely that significant material settles back down due to gravity, or that gravity impacts where material is ejected from on an irregular nucleus.

Electostatics may play a big role here.

I think that's more likely to play a role in surface dust and ice than gravity.

[Psnarf]

What happened to my rubber duckie? Waah. This is the testbed for changing the orbit of a doomsday comet/asteroid. Acquisition: check. Orbit, determine best landing, land: WIP. The doomsday mover would have a lander that could push the object out of its collision window. Now we know we can do this early enough to work.
Once the sun starts boiling stuff off of the surface, I imagine the carrier rocket will be destroyed. The lander better have deep pointy feet so it can grab onto something that won't eject.
http://nssdc.gsfc.nasa.gov/nmc/spacecra ... ?id=PHILAE
Ahh, Philae has a harpoon to prevent it from bouncing off in the light gravity.

[julianm3]

Congratulations Rosetta team, great work! Hoping we'll get a movie of the rotation up close.

[ta152h0]

I agree , congratulations to the ROSETTA team. New Horizons was mentioned on the thread. I hope the spacecraft crashes into Pluto with the cameras rolling like the Rangers did on the moon. It would be fitting if Mr Tombaugh's ashes are on board.

[neufer]

I agree , congratulations to the ROSETTA team. New Horizons was mentioned on the thread. I hope the spacecraft crashes into Pluto with the cameras rolling like the Rangers did on the moon. It would be fitting if Mr Tombaugh's ashes are on board.

• Don't expect any "postcards" from New Horizons then:

<<New Horizons should perform a flyby of the Pluto system on 14 July 2015. Initial, highly-compressed images will be transmitted within days. Uncompressed images will take about nine months to transmit, depending on Deep Space Network traffic. It may turn out, however, that fewer months will be needed. The spacecraft link is proving stronger than expected, and it is possible that both downlink channels may be ganged together to nearly double the data rate.>>