Can We Land On a Comet?

by Nancy Atkinson on February 3, 2012

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The Rosetta mission will do something never before attempted: land on a comet. The spacecraft is now on its way to intercept comet 67P/Churyumov-Gerasimenko in January 2014 and land a probe on it for what promises to be an amazing view. But what we know of comets so far comes from a few flyby missions. So, with surface composition and conditions largely a mystery, so how did engineers prepare to land on something that could be either solid ice or rock, or a powdery snow or regolith – or something in between?

They had to design the Philae lander so it could land equally well on any surface. In the tiny gravitational field of a comet, landing on hard icy surface might cause Philae to bounce off again. Alternatively, hitting a soft snowy one could result in it sinking. To cope with either possibility, Philae will touch as softly as possible. In fact, engineers have likened it more to docking in space.

Philae will fire harpoons to secure itself to the comet; additionally, the landing gear is equipped with large pads to spread its weight across a broad area (kind of like snowshoes.)

While landing on a comet will certainly be nail-biting, having a front row seat for when the comet gets closer to the Sun is the most highly anticipated part of the mission.

An artist concept of the Philae lander on comet 67P/Churyumov-Gerasimenko. Credit: Astrium - E. Viktor/ESA

“In some ways, a flyby is just a tantalizing glimpse of a comet at one stage in its evolution,” says Claudia Alexander, project scientist for the U.S. Rosetta Project at JPL. “Rosetta is different. It will orbit 67P for 17 months. We’ll see this comet evolve right before our eyes as we accompany it toward the Sun and back out again.”

We’ll be able to watch as it becomes “something poetic and beautiful, trailing a vast tail,” said Alexander. For once, we’ll be able to watch the surface of a comet transform in front of our eyes instead of relying on artist concept drawings! Additionally, the Rosetta spacecraft up above will be busy mapping the comet’s surface and magnetic field, monitoring the comet’s erupting jets and geysers, measuring outflow rates, and much more. Together, the orbiter and lander will build up the first 3-D picture of the layers and pockets under the surface of a comet.

Comets are considered a gold mine for astronomers who want to know what conditions were like back in the early days of our Solar System. And the data and images from this mission promises to be some of the most stunning we’ve yet seen.

Find out more about the Rosetta mission in the accompanying video, or see the ESA Rosetta website.

Source: Science@NASA

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

Aerandir90 February 4, 2012 at 3:31 AM

Imagine a time-lapse video of the sun getting nearer from the comet’s perspective, I’m sure it’ll go viral..

Rob Hemmings February 5, 2012 at 12:58 PM

Extremely unlikely. Most if not all comets will be rotating (tumbling) in a complex way, so there would be nowhere to place a camera which stays pointed at the Sun. Images or even video of the comet surface during outgassing would be interesting though. Data from Deep Impact/Hartley2 revealed large jets of cyanide gas being released, but without dust being blown with it, a process amongst many that isn’t understood.

Aerandir90 February 5, 2012 at 3:24 PM

Yea I didn’t think about that, but then again the camera wouldn’t have to stay pointed at the sun, as long as it sees the sun every once in a while, a time-lapse could still be made. The effects of disorientation would be interesting too, at least for me.

Anonymous February 4, 2012 at 4:23 AM

Awesome, I can hardly wait. What happens after the 17 months? Does it run out of fuel and just keep orbiting the comet forever anyway? What is the periodicy of this comet? Is it headed back to the Oort cloud afterwards?

Torbjörn Larsson February 4, 2012 at 11:41 AM

Your Wikipedia service is now open for business:

short-period, ~ 7 years, aphelion ~ 6 au or just outside Jupiter’s aphelion.

Bill Lanier February 4, 2012 at 7:00 AM

trip to the outer solarsystem or is it a small orbit around the large planets. Think about it. free ride to the ort cloud. And fast.

Guest February 5, 2012 at 8:07 PM

This particular comet barely reaches any further out than Earth does (1.3 AU).

In any case, no comet or asteroid ever provides a “free ride” to anywhere – in order to land on a spacerock, a spacecraft has to match its velocity, and once its done that, the spacerock might as well not exist: the spacecraft is already on the trajectory that the spacerock was going to make anyway.

Torbjörn Larsson February 4, 2012 at 11:38 AM

The comet is “letting her hair down for us“. (“c.1200, from O.Fr. comete (12c., Mod.Fr. comète), from L. cometa, from Gk. (aster) kometes, lit. “long-haired (star),” from kome “hair of the head” (cf. koman “let the hair grow long”), of unknown origin.”)

Seems we have an eventful period of years ahead, 2012 – 2017 sees probes, rovers, commercial cargo, suborbital and orbital tourism, ISS, VASIMR and manned missions (China, perhaps US). “Only” JWST is missing (launching 2018 earliest; but don’t count on it).

Bummer, all this and so little large missions on exoplanets.

Mihir Panchal February 4, 2012 at 12:34 PM

Building up on this mission, can we select some comet having a very large elliptical orbit which goes to the Oort cloud and back.. piggy back some instruments on it? It will need no propulsion energy saving energy to power instruments that can keep relaying data for hundreds of years!

ikma February 4, 2012 at 2:37 PM

I’ve always been curious about that idea. I’m no astrophysicist (by a long shot), but if we’re going to land a probe on a long period comet like that and hitch a ride out to the Oort cloud, don’t we have to match the probe’s velocity and location to that of the comet? Which would mean (I think) that we would pretty much have to match the probe with the comet’s orbit around the sun. And if we’re going to match the comet’s orbit, why does the comet even have to be there? I guess it seems to me trying to hitch a ride on a long period comet wouldn’t save any energy, when we would spend the same amount of energy just putting the probe itself into a highly elliptical orbit.

Can anybody who knows more about this confirm that for me, or if not explain why I’m wrong?

Ethan Walker February 4, 2012 at 8:24 PM

Right, unless you want to match velocities by “impact acceleration”.

Ethan Walker February 4, 2012 at 9:12 PM

dammit disqus

Ethan Walker February 4, 2012 at 8:59 PM

Right, unless you want to match velocities by “impact acceleration”.

Anonymous February 4, 2012 at 10:53 PM

I completely agree, unless you have a big rubber band, harpoon the comet when it passes and hopes that the rubber band will buffer the speed difference.

Anonymous February 4, 2012 at 6:04 PM

I guess you could avoid the use of some propulsion energy, but there’s no friction in space, so you won’t get as much savings as you seem to think. However, such a mission could be used in order to perform an extended mission.

Anonymous February 4, 2012 at 7:27 PM

Won’t work, you need the same energy to get to that comet as to travel yourself without a comet.

Anonymous February 5, 2012 at 9:05 AM

Indeed a very exciting prospect which will hopefully bring the solar system more into the public consciousness.

Anonymous February 5, 2012 at 3:43 PM

I like this idea.. just wish that lander had a fully instrumented package that would transmit data back to Earth and last for decades! Instrumentation AND advanced antenna for VLBI

Muhammad Azhar February 6, 2012 at 1:06 PM

Of course it would require same energy to land on a comet for matching velocity as to travel there without it. But it would be for only once. If we land a robot on a a comet which visits Oort Cloud and has been around for a while, our lander would be spending no fuel for drifting across long distances or orbiting around Sun again and again but just to communicate with us and sending data while staying on it. Possibilities for exploration are many.

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