One for the History Books - Rosetta Mission Lands on Comet Tomorrow

Impression of Rosetta mission landing. Credit: ESA/ATG medialab; Comet image: ESA/Rosetta/Navcam

History will be made when Rosetta's lander Philae makes a soft touchdown on a comet tomorrow. ESA's Rosetta spacecraft first captured the world's imagination back in January when it reawakened from hibernation, and tomorrow's landing will mark the crowning achievement in an already scientifically-rewarding mission.

ESA has created a wonderfully cute video detailing Rosetta and Philae's current status.

Comets remain elusive, transient objects that streak through our solar system and across our skies before just as quickly disappearing back to the frosty depths from whence they came. But comets may be vitally important to how life on Earth first began and to understand this process, we need to get up close and personal with a comet.

Professor Ian Wright, an Open University scientist involved in the experiments onboard Philae, said in a August press release, "Once the Philae lander touches down on the comet, we will be looking for evidence recorded in remnants of debris that survived the processes of planet formation. This is not merely a period of pre-history, but one that pre-dates the origin of life itself. Our quest is to gain insights into this transitional era, which took place more than 4.5 billion years ago,"

Rosetta mission selfie. Credit: ESA/Rosetta/Philae/CIVA

Ever tried lassoing a comet though? These things move fast. The comet that Rosetta is now orbiting is hurtling at an astonishing 55,000 kilometers per hour towards the Sun. That is 45 times faster than the typical speed of a bullet! The Rosetta mission has spent the last ten years building speed and gradually closing in on its icy target, named 67P/Churyumov–Gerasimenko, or 67P for short.

Finally in August of this year, Rosetta caught up with comet 67P and entered orbit. Close up, the shape of the comet was quite a surprise. Rather than the ellipsoidal blob expected, 67P actually looks like two blobs smooshed together, perhaps from a previous comet collision out in the Kuiper belt beyond Neptune. The complex shape has been fondly termed the 'rubber duck' by ESA and members of the public alike.

A series of jaw-dropping photographs have emerged over the past few months as Rosetta has maneuvered closer and closer to the comet's surface. Even as an astronomer, I have been amazed by the sheer size of this comet, and the massive cliffs, valleys, and boulders that decorate its surface. No longer is a comet a 'dirty snowball' in my mind, but rather a world with its own unique and dynamic geology. What an amazing place to explore!

Cliffs and boulders on comet 67P/Churyumov–Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

And we are about to do just that. In the early hours of tomorrow, Rosetta will deploy its washing machine-sized lander, Philae, on a seven hour journey down to the 'head' of the comet. Its destination is a site named Agilkia by public competition, and by 11 a.m. EST (4 p.m. GMT) we should be receiving the 'all is well' signal from Philae.

The people actually in charge of landing Philae are trying not to think of all the things that might go wrong.

Ekkehard Kührt, of the German Aerospace Center (DLR), perhaps wishes the geology were a bit less interesting, saying in a recent DLR video "We don't want Philae to end up on its back like a beetle, or to crash. All these things are much easier to solve on a spherical target than on a very rugged surface with valleys, even canyons, cliffs and crevices. These are difficult conditions."

The gravity of comet 67P is so small that Philae is in danger of bouncing off into deep space should it miscalculate its landing speed and trajectory. To avoid this catastrophe, Philae comes equipped with ice screws and harpoons to secure itself to the surface as soon as it touches down.

How Philae will secure itself to the comet. Credit: ESA/ATG medialab

Following that nerve-wracking moment, it should be smooth sailing. Philae will be our proxy geologist and conduct a series of experiments to determine the conditions and composition of the comet's icy surface. All this data (and undoubtedly even more astonishing images) will be beamed back to Rosetta and then on to Earth. Philae will remain latched onto the comet as it zooms towards the sun, continuing to monitor how the comet transforms in the growing solar heat for as long as possible. Currently Rosetta and the comet are about 500 million kilometers away from Earth, speeding along between Mars and Jupiter.

Brigitte Pätz, DLR Lander Operations Manager for Philae, says "What will be interesting for the scientists will be to observe the changes — what the comet does as it approaches the sun, becomes increasingly active, and starts to outgas and form jets."

There's no guarantee how long Philae will survive attached to the comet. If a powerful jet outgasses underneath its landing site, all bets are off.

But first things first, Philae must make a successful landing tomorrow. You can follow all the action at ESA's live-streaming event. If nothing else, be sure to check in just before 11 a.m. EST to witness the next 'giant leap for mankind' event.

In the meantime, learn the answers to the top five questions being asked about the Rosetta landing, in video put together by the Open University team in charge of several lander experiments:

And finally, did you know that comets could make music? Neither did Rosetta’s Plasma Consortium team when they detected strange oscillations in the 40-50 millihertz range, boosted here so we can hear the heavenly music.

--
By Tamela Maciel, also known as "pendulum"