A second look at a comet

On Valentine’s Day night, JPL employees forfeited any plans for romance in order to taste the fruits of a single celestial encounter. At a little before 9 p.m. Monday, NASA’s Stardust-NExT shuttle came within 125 miles of Tempel 1, a comet scientists have been tracking for years. The meeting, cheekily billed by NASA as “A Date with a Comet,” was more than five years, and hundreds of research hours, in the making.

This “date” brings with it a scientific first — until now, no comet has ever been visited more than once. In 2005, the vessel Deep Impact rendezvoused with the comet for the purpose of creating an impact crater that would reveal some of the comet’s sub-surface components. An 800-pound copper projectile successfully reached the surface, driving up ice particles and dust flecks that were observed and recorded by the craft.

Since that impact event, Tempel 1 has completed a five-year revolution around the sun. Its Valentine’s Day encounter with Stardust-NExT (New Exploration of Tempel 1) will allow researchers to see what changes have occurred since its last perihelion, or the orbital point closest to the sun.

“We want to see how much has changed in the last five years,” said Joe Ververka, principal investigator for Stardust-NExT at Cornell University, during a Monday night online broadcast of the event. “We know that comets change because there is ice, but where do those changes occur?”

The Stardust spacecraft was launched in 1999 to collect data and materials from Wilt II, a comet located near Jupiter’s orbit. In 2004, it reached its original destination, gathered particle samples and sent them by capsule to Earth. Those samples arrived in 2006 and are still being studied by NASA scientists, said Donald Sweetnam, deputy project manager for the Stardust-NExT mission.

Scientists saw that with some careful planning, the Stardust spacecraft might have just enough fuel to reach the Tempel 1. They meticulously recalculated its course, using the Earth’s gravitational pull to slingshot the vessel onto a path that would bring it near the comet. Predicting an encounter with an irregularly moving object years in advance was a difficult task, and as of early Monday, many Stardust team members were nervously expectant.

“We’re only in good picture-taking proximity to the comet for a few minutes,” Sweetnam said early Monday. “It’s a real trick to show up at the right instant where the features you want to see are visible.”

Stardust captured 72 high-resolution images of the comet, the first of which were released Tuesday afternoon. The success of the mission not only will inspire further discussion about comets and their inherent mystery, but also how NASA might double up on missions and spare considerable expenses in the future.

Ververka, who originally proposed repurposing Stardust for the Tempel 1 visit, estimated the cost of this mission to be about $29 million. That figure, he continued, is a far cry from the $500 million it would have cost NASA to build the mission from the ground up and reflects a new way of thinking on how space craft might be repurposed after their original missions have been completed. Stardust-NExT Project Manager Tim Larson agreed in a Tuesday news conference.

“This expansive mission, for one thing, is very low cost. It’s science at a really big discount,” Larson said.

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