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Headshot of Emily Lakdawalla

Quick Rosetta update: Churyumov-Gerasimenko is a contact binary!

Posted by Emily Lakdawalla

15-07-2014 8:42 CDT

Topics: Rosetta and Philae, pretty pictures, comets, mission status, comet Churyumov-Gerasimenko

I'm just back from vacation and struggling to catch up but I could not wait to post these amazing new images of comet Churymov-Gerasimenko from Rosetta. The nucleus of the comet is clearly a contact binary -- two smaller (and unequally sized object) in close contact. The CNES page where this photo was released says the whole nucleus measures 4 by 3.5 kilometers, in good agreement with Hubble and Spitzer estimates. Philippe Lamy is quoted as estimating that the two components would have come into contact at a relative speed of about 3 meters per second in order to stick together in this way.

Comet Churyumov-Gerasimenko from Rosetta on July 11, 2014

ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

Comet Churyumov-Gerasimenko from Rosetta on July 11, 2014
As Rosetta approached its target comet, the shape of the nucleus was revealed to be a contact binary -- two unequal-sized objects in contact with each other. All together, the object is about 4 by 3.5 kilometers in size.

Wow, wow, wow. I can't wait to get closer!

This unusual shape could present a navigational challenge for the Philae lander team. The CNES release quotes Philae navigator Eric Jurado as saying that "navigation around such a body should not be much more complex than around a nucleus of irregular spherical type, but landing the Philae probe [scheduled for November 11], however, could be more difficult, as this form restricts potential landing zones."

I'm at the New Horizons science team meeting right now and have had great fun showing these pictures to gobsmacked space scientists. Naturally, they're all trying to figure out what to call its shape. Alex Parker came up with the clearly best answer:

See other posts from July 2014


Or read more blog entries about: Rosetta and Philae, pretty pictures, comets, mission status, comet Churyumov-Gerasimenko


Bob Ware: 07/15/2014 11:20 CDT

Alex - yeah! Rubber Duckie it is! Love it! : )

Stephen Uitti: 07/15/2014 12:02 CDT

Double name. Double nucleus. Makes sense to me.

Ethan Walker: 07/15/2014 01:05 CDT

While it's probably not a viable landing site, how wonderful would it be to have Philae land near the contact point? What a wonderful surreal landscape to look out over!

JOEL WILLITS: 07/15/2014 02:01 CDT


Nick Oberg: 07/15/2014 02:33 CDT

Now animated:

AJA : 07/15/2014 05:22 CDT

@Joel Interesting thought. But wouldn't asymmetric ablation (after accounting for attitude with respect to the sun) require heterogenous composition (for different sublimation temperatures)? IANAE, but I don't think that cometary bodies have such drastic changes in chemistry of the ices over such small distances. Even otherwise, even if these bodies DO have some sort of differentiation, I still think it's more likely that two different bodies (with relatively rockier centres) came into contact, and started shedding the icy layers around their individual peripheries. (Slower shedding near the interface region because one body shades the other from the sun). That said, I wonder if they're literally frozen together (like putting one ice-cube on top of another, maybe with some pressure), or if they're only gravitationally bound (albeit still in physical contact)

Arbitrary: 07/15/2014 06:05 CDT

Two comets! The science value of the Roesetta mission suddenly doubled. Any one comet could be a unique freak which teaches us little about most of them. But if this is two comets formed independently and have had different orbits during billions of years, I think that the sampling statistics suddenly improved by a factor alot. How cool it will be to see how the materials in these two comets develop differently as they get closer to the Sun.

Arbitrary: 07/15/2014 06:09 CDT

@Ethan Walker Maybe the contact point is a practical landing site. It is more shielded from sunlight and therefor maybe less active. And maybe more prestine and interesting for Philae to drill into.

Lindsay: 07/16/2014 12:20 CDT

Taking a very rough estimation of the dimensions of the twin nucleus as 4 x 3.5 x 2 km for the larger and a 2.6 km diameter for the smaller object and treating them as two co-orbiting point masses with the measured 12.76 hour rotation period I get a minimum bulk density of around 150kg per cubic meter needed to hold it all together as a contact binary… Very crude admittedly but at least it gives a ball park indication of the density of these objects which looks to be very low. As the spacecraft continues its approach and the image resolution continues to improve we will hopefully get to hear ever more precise estimates of some of the physical properties over the next few days and weeks.

pikarl: 07/16/2014 02:27 CDT

Emily, thanks for your posts about Rosetta. I think the mission will be great - but the ESA PR is not as good as it could be (as recently commented in your blog: We (some German space enthusiasts) sent an open letter to responsables at ESA and other science institutions in Europe: What we want is realtime image publication over the whole mission. ESA just published pictures *weekly* so far. Maybe we should also increase the pressure in the future by starting a bigger campaign.

Marco: 07/16/2014 07:25 CDT

I'm with Joel on this one. Saying it is a contact binary is jumping to conclusions as to the history of the semi-separate lobes. Hartley and Borrelly have separate lobes but don't appear to have been formed from separate bodies impacting.

Laurel Kornfeld: 07/16/2014 01:11 CDT

I'm participating remotely at the New Horizons science team meeting, and participants' reaction to these images was both fascinating and amusing. I look forward to learning how this discovery will influence the choice of a landing site for Rosetta.

ELI71: 07/16/2014 02:07 CDT

Guuaa, I am once again amazed of our universa. I can,t wait to see more.

Lindsay: 07/16/2014 02:11 CDT

Rosetta has just completed another “FAT” burn to slow its approach to the comet at somewhere around the 8000km distance mark. From the daily distance postings on the ESA webpage it was been travelling at about 56km per hour relative to the comet since the previous FAT burn. It looks as though it has now slowed to something close to 16km per hour. A human could run that fast. Has there ever been a spacecraft approach as slow as this? Even the ion propelled Dawn spacecraft would likely have had higher approach velocities at Vesta as that asteroid has a fair bit more mass to contend with. I suppose there was Hayabusa at asteroid Itokawa, NEAR Shoemaker at Eros and possibly the Soviet Phobos 2 probe before it was lost being the only other comparable missions.

Derek Sellers: 07/16/2014 03:21 CDT

I'm gonna go with Zweibach:

Jonathan Ursin: 07/16/2014 11:53 CDT

I am no expert here but I think contact binary implies two pieces in contact regardless of origin. I wonder if there is a way to determine whether C-G is an eroded contact binary or a collided contact binary? I am so excited!!!

jim oberg: 07/22/2014 07:47 CDT

I love to be surprised, but it would astonish me if these were unrelated cometary objects rather than two fragments of the same primordial one that came apart, independently orbited, got tidal locked, and eventually kissed and froze. If the prelude to the kiss involved momentum dissipation, would there be traces of the thermal stresses? Astonish us further!

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