Rosetta's cometary goal now in sight

By Phil Plait

Rosetta is an amazing probe launched by the European Space Agency. In 2014 it will go into orbit around the comet 67P/Churyumov-Gerasimenko, and actually deploy a lander to sample the surface!

That rendezvous is still years away, but the target is now in sight: Rosetta has returned its first image of the comet.

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

Oh, very cool! The top image is the wide angle shot, showing a densely-populated star field toward the center of our galaxy; from Rosetta that's the direction to the comet. The second image zooms in a bit, and you can see some distant stars and nebulosity. The bottom one has been processed to remove the stars, and the nucleus of Churyumov-Gerasimenko stands out.

Note that this image was taken when Rosetta was still 163 million kilometers (100 million miles) from the comet -- that's more than the distance from the Earth to the Sun! That's why it took a total of 13 hours of exposure time to see the comet in these images; it's still extremely faint from that great distance.

These pictures are important for several reasons: they test the cameras, a critical event for the upcoming encounter; they provide navigation cues, allowing engineers to test if the position of the comet is where they expected it to be; and they give the scientists and engineers practice in dealing with the images from the probe.

Not that Rosetta has simply been coasting along; it's passed by the Earth, Mars, and even two asteroids -- Lutetia (see the gallery below of those spectacular images!) and Steins -- returning incredibly lovely pictures of these worlds.

Rosetta is already a very successful mission, and the best is yet to come.

Image credit: ESA 2011 MPS for OSIRIS-Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Image gallery of Rosetta's flyby of the asteroid Lutetia

Related posts:

- Ten Things You Don't Know About Comets
- Rosetta takes some home pictures
- Earth from Rosetta
- Rosetta swings by Mars

Bad Astronomy Gallery

(click any image to see it full size)

Lutetia up close and personal

On July 10, 2010, the European Space Agency probe Rosetta passed just 3162 km (1960 miles) from the asteroid Lutetia, a lumpy rock 130 km (81 miles) end-to-end.

This image, taken at closest approach, shows how battered and worn Lutetia is. Craters pockmark the surface, including several that are many kilometers across. Like the Martian moon Phobos, grooves line the surface, which may be from boulders rolling around, perhaps ejected from some of the craters when they were formed. They may alternatively be stress fractures from impacts; there is still a lively debate over what causes these features in small bodies.

Much of the surface appears smooth, indicating great age for this object. Over billions of years it's been assaulted by dust grains moving at incredible speeds, as well as the solar wind. This has essentially sandblasted the surface, taking - literally - the edge off of the rims of craters.

We have very few high-resolution images of asteroids, and the more we get, the more we learn about them. Given that every now and again we get hit by them, I'm a big fan of understanding them better.

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Approaching Lutetia

This series of pictures was taken as Rosetta approached Lutetia.

The first image in the upper left was taken about 9.5 hours before closest approach, when Rosetta was still 510,000 km (315,000 miles) from the asteroid - more distant than the Moon is from the Earth!

The last image (lower right) was obtained an hour and a half before the close encounter when the probe was still 81,000 km (50,000 miles) from Lutetia.

In the first image, details only about 20 km (12 miles) across can be seen, but that improves by almost a factor of 10 in the last image!

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Final approach sequence

This is the final sequence of images taken right at closest approach. The bottom right image was taken just at the moment that Rosetta passed Lutetia.

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Lutetia Closeup 1

For the first time ever, a spacecraft approached closely enough to the asteroid Lutetia to see its surface clearly. Craters dot the surface, as well as grooves. Note the elongated crater near the bottom (left of center); was that from a nearly horizontal impact? It's curious that it points almost directly to the crater to the left. That may just be coincidence; the surface is so cratered that some are bound to be in patterns just randomly.

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Lutetia Closeup 2

Another closeup of Lutetia's surface provided by Rosetta. In this shot, you can again see a variety of craters peppering the asteroid, as well as some grooves that follow the landscape. Those curves give a relative age for the grooves: they must have formed after the impact crater on the right, which distorted the landscape. Also, had they formed before, the impact would have eradicated them. Images like this can give scientists a vast amount of insight into the history of the asteroid.

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Crescent asteroid

After Rosetta passed Lutetia, its cameras were pointed back to the rock, and therefore back toward the inner solar system. That geometry gives us an amazing, brooding, and lovely view we never get from Earth: a crescent asteroid.

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA

Rock and rings

When Rosetta was still 36,000 km (22,000 miles) from Lutetia, it snapped this jaw-dropping shot of the asteroid with Saturn in the distant background. This means the spacecraft, the asteroid, and Saturn were almost exactly along the same line, a configuration that probably only lasted for a few seconds. It's remarkable that controllers on the ground were able to take this picture at just the right moment to obtain this amazing picture!

Credit: ESA 2010 MPS for OSIRIS Team. MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA