Science: Comet Collision

How Hawai‘i had a front-row seat for the hit of the year.

"This is really a trip into the unknown," said Frederic Chaffee, director of the W.M. Keck Observatory on the Big Island.

It was July 3, the night that both of the Keck telescopes atop Mauna Kea were pointed, like virtually every other telescope on the planet and above it, at the Tempel 1 comet.

Chaffee was down the mountain at Keck headquarters in Waimea, talking to a standing room only crowd waiting to see Earth's first intentional celestial car wreck-an 800-pound, coffee-table-size probe trying to crash into a comet half the size of Manhattan.

Only about 250 people got inside the lecture hall. The talkative group ranged from serious space geeks, who asked questions like whether impact was timed for "perihelion" (closest proximity to the sun), to normal folks, who, when they hear the word "comet," normally think of a heavenly cleanser.

Everyone gawked at three large screens. One screen showed the NASA feed constantly switching between the mission control room full of nervous scientists chattering into headsets, the view of the comet from the impactor in its last minutes before getting run over at 23,000 miles per hour, and the comet from the mothership about 300 miles away. A second screen looked over the shoulders of three Keck astronomers in the glow of their computer monitors. The center screen was from one of the Keck telescopes, showing a small cluster of black pixels (easier to see in negative) that would later be spectrographically analyzed to reveal the chemical composition of the comet. This information would give astronomers a glimpse of the solar system's origins, which was the whole purpose of the mission.

An artist’s rendering of the Deep Impact probe striking the comet, Tempel 1. Photo: NASA/JPL/UMD

As all these images changed upon the lecture hall wall, the audience got play-by-play color commentary from Chaffee and Heidi Hammel, a University of Hawai'i alum, who is co-director of research at The Space Institute in Boulder, Colo.

As the minutes ticked away until impact, a voice from the NASA control room reported a 44-second burn, which would steer the impactor perfectly into position to be smashed to smithereens. Hammel was getting excited: "So they're firing the rockets right now. Feel it?"

"Yes!" shouted someone about to go into orbit.

Chaffee, silhouetted against a huge picture of the comet just taken by the impactor, said to the room: "If you aren't amazed that we can time a probe within seconds of something 80 million miles away, you should be." Everyone laughed.

Then stopped.

A NASA guy could be heard asking about a red warning light on his console. Chaffee's eyes widened until another NASA guy said to chill, the warning light was expected.

And then, a couple minutes later, there was a cheer from everyone who was seeing the first image of a comet becoming one with a spacecraft from Earth. The union spread a wide, white splash of ice and dust out into the blackness of space.

Keck astronomers were already "busily taking fingerprints of this comet," said Chaffee, adding that, to scientists everywhere (not to mention the rest of us), "this is an extraordinarily exciting night."

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