By Lauren Gold
ITHACA, N.Y. — When it comes to sensational explosions, fireworks this July Fourth may face some competition.
The show will be a carefully orchestrated collision between a probe from NASA’s Deep Impact spacecraft and the comet Tempel 1, about 133 million kilometers (83 million miles) from Earth. What happens as a result of the crash, says Joe Veverka, chair of Cornell University’s astronomy department and a Deep Impact team member, could give scientists new clues about how the solar system formed.
On Monday, July 4, from midnight to 3 a.m., the Cornell Space Sciences Building will be open to the public for a live view of the collision, courtesy of NASA TV. Peter Thomas, a Deep Impact team member and Cornell senior researcher, will be among several experts on hand to offer commentary and answer questions. Veverka will be stationed at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif.
At 1:52 a.m., a projectile deployed from the Deep Impact spacecraft (launched in January 2005 from Cape Canaveral) will be run over by Tempel 1. The collision between the 1-meter-wide (39 inches) copper impactor and the Manhattan-sized comet is expected to release about 19 gigajoules of kinetic energy, or the amount of energy released by exploding 4.8 tons of TNT.
If all goes as planned, the Deep Impact spacecraft will miss the comet by about 500 km (311 miles) and transmit images of the collision back to Earth. Veverka and Thomas will analyze the images and use them to construct digital three-dimensional maps of the comet. Michael A’Hearn of the University of Maryland leads the mission.
Scientists are passionately interested in comets, which are mainly dust, rock and ice, for the clues they offer about the solar system very early in its existence. “If you look at the solar system, most of the sizeable objects beyond Uranus are cometlike,” said Veverka. “Most of them have been out there for a long time, and they haven’t changed very much. If you’re trying to get the building blocks of the solar system, you can’t ignore comets.”
Tempel 1, discovered in 1867 by artist, lithographer and self-taught astronomer Ernst Wilhelm Leberecht Tempel, orbits between Mars and Jupiter, circling the sun about every 5.5 years. Deep Impact is the fourth of NASA’s Discovery Program missions, a series of voyages to examine different aspects of comets.
“On previous missions we’ve seen the outside of a comet, but we’ve never seen the inside,” said Veverka. “Living on a planet like Earth, you can make a good argument that most of the volatile stuff on Earth came from comets. We know that comets contain very complicated molecules — the kinds of things that you could probably, in the right circumstances, make the basis of life.
“It has been argued that the chemical seeds of life on Earth were brought here by comets,” Veverka said. “We’re not there yet, but one day hopefully we will know if you and I were descended from comets.”
That question won’t be answered this July Fourth. “But just the pictures of the comet coming in, I think, will be neat to people,” Veverka said. “You’re getting a close look at something you’ve never seen, from an exploration point of view. It’s possible there will be a lot of dust and it could be spectacular,” he adds. “I honestly don’t know. I will be as surprised as you as to what we will actually see.”
In March, NASA reported that Deep Impact’s High Resolution Instrument, one of four data collection instruments on the spacecraft, appeared to be out of focus. Scientists plan to use data processing techniques to sharpen the images, and principal investigator A’Hearn has said he expects the images to be the best ever taken of a comet.
Still, the uncertainty — about the size of the impact crater, the consistency of the material ejected or what kinds of images will come back — is the cause of a few rumored wagers around the Space Sciences Building and JPL.
“There are lots of people with firm ideas [about what will happen] — but they diverge,” said Thomas. “This is neat from the standpoint that it’s an experiment: You push on something and see what happens. The reaction is unknown. We have no idea how big a hole we’re going to make or what we’re going to learn. It’s a more edge-of-the-seat mission. We have basically no clue what’s going to happen.”
Except, of course, for one certainty. There will be ice cream.
The Space Sciences Building will be well stocked with Cornell Comet Swirl, a caramel-and-chocolate Cornell Dairy Bar creation concocted in honor of the event.
But Thomas would be excited even without the promise of ice cream.
“This is exploration,” he says. “That’s the real fun.”
