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It's Showtime! Philae Probe Revs Up for Historic Comet Landing

A boxy spacecraft is on its way to make the first-ever controlled landing on a comet — and you can watch the drama unfold on the Web.
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An electronics-filled box about the size of a washing machine is gearing up to make the first-ever controlled landing on a comet — and you can watch the drama unfold on the Web.

The Philae lander has been riding piggyback on the European Space Agency's Rosetta spacecraft for more than 4 billion miles (6 billion kilometers), during a decade-long, $1.3 billion mission to catch up and hang around a rubber-ducky-shaped agglomeration of ice and dust known as Comet 67P/Churyumov-Gerasimenko. Rosetta made its rendezvous in August, and now it's time for the box-shaped Philae lander to go its own way.

After a momentary hiccup in the procedure for "waking up" Philae's instruments on Tuesday, ESA has given the probe the first of several "go for landing" commands.

Philae — which is named after an island in the River Nile that figures in the story of the Rosetta Stone — is due to separate from Rosetta at 3:35 a.m. ET Wednesday. Confirmation is expected to be received at 4:03 a.m., due to the light-travel time between the comet and Earth. Touchdown on the comet's surface, 14 miles (22.5 kilometers) below Rosetta, is scheduled seven hours later at 11:03 a.m. ET.

Like archaeology's Rosetta Stone, Philae and Rosetta are expected to provide data that will help experts decipher a longstanding mystery — in the Rosetta mission's case, the mix of materials from which the solar system was made.

Comet Churyumov-Gerasimenko is considered one of the leftovers from the solar system's formation 4.5 billion years ago, and thus preserves the stuff that was shaped under other circumstances into Earth and the other planets.

Rosetta's readings already have provided some interesting twists. For example, the volatile chemicals on the comet's surface would probably smell like a mixture of rotten eggs, embalming fluid and horse urine. It also turns out that the comet is dirtier than expected around the landing site, which has been named Agilkia.

"It's a more dusty surface material, somewhere between hard-packed snow and cigarette ash," Rosetta project scientist Matt Taylor said Monday during a news briefing at the European Space Operations Center in Darmstadt, Germany.

Image: Philae
An artist's conception shows the European Space Agency's Philae lander anchored to Comet 67P/Churyumov-Gerasimenko.ESA / ATG Medialab

Going deeper

But the secrets of a comet go beneath the surface, and that's where Philae comes in. The lander is designed to drift onto the surface, anchor itself with a couple of harpoons and drill into the ice. Samples will be extracted and then analyzed with an assortment of cameras, spectrometers and gas chromatographs. Sounding devices will probe the comet's deep interior, and a magnetometer will measure magnetic fields.

All those readings will be beamed up to Rosetta and relayed back to Earth, over the course of as little as a week or as long as many months.

Mission planners estimate Philae's chances of success at about 75 percent. Touchdown would make Comet Cheryumov-Gerasimenko the first comet and the seventh solar system object beyond Earth to be the locale for a soft landing. The other celestial objects include Earth's moon, Venus, Mars, the Saturnian moon Titan and the asteroids Eros and Itokawa. NASA's Deep Impact probe blasted a projectile into Comet Tempel 1 in 2005, but that hardly qualifies as a soft landing.

Even if Philae misses its mark or crashes, ESA says the broader Rosetta mission is still likely to meet most of its science objectives. The Rosetta spacecraft is due to shadow Comet Cheryumov-Gerasimenko as it approaches and rounds the sun over the course of the next year.

Follow the mission

Whether it's a hit or a miss, Philae's journey is easy to follow on the Web. Here's where to look: