Fireworks on horizon as NASA targets comet

NASA will mark Independence Day in the US with an audacious mission that will blast a stadium- sized hole in a comet half the size of Manhattan.

It would give astronomers their first peek at the inside of one of these heavenly bodies.

If all goes as planned, the Deep Impact spacecraft will release a wine barrel-sized probe on a suicide journey, hurtling toward the comet Tempel 1 - about 80 million miles away from Earth at the time of impact.

“It’s a bullet trying to hit a second bullet with a third bullet in the right place at the right time,” said Rick Grammier, project manager at NASA’s Jet Propulsion Laboratory in Pasadena.

Scientists hope the July 4 collision will gouge a crater in the comet’s surface large enough to reveal its pristine core and perhaps yield clues to the origin of the solar system.

NASA’s fleet of space-based observatories - including the Hubble, Spitzer and Chandra telescopes - along with an army of ground-based telescopes are expected to record the impact and resulting crater.

Very little is known about comets and even less is known about their primordial cores.

Scientists do not know what kind of fireworks sky-gazers expect to see, but if the probe hits the bull’s-eye, the impact could temporarily light up the comet up to 40 times brighter than normal, possibly making it visible to the naked eye in parts of the Western Hemisphere.

“We’re getting closer by the minute,” Andrew Dantzler, the director of NASA’s solar system division, said earlier this month.

“I’m looking forward to a great encounter on July 4,” he said. If the €274 million mission is successful, Deep Impact will be the first spacecraft to touch the surface of a comet. In 2004, NASA’s Stardust craft flew within 147 miles of Comet Wild 2 on its way back to Earth carrying interstellar dust samples.

Scientists say Deep Impact has real science value that will hopefully answer basic questions about the solar system’s birth. Comets are frozen balls of dirty ice, rocks and dust and are leftover building blocks of the solar system after a cloud of gas and dust condensed to form the sun and planets four-and-a-half billion years ago.

As comets arc around the sun, their surfaces heat up so that only their frozen interiors possess original space material. Scientists believe that the impact will form a circular depression that will eject a cone-shaped plume of debris into space.

NASA guarantees that its experiment will not significantly change the comet’s orbit nor will the debris put the comet or any remnants of it on a collision course with Earth.

Discovered in 1867, Tempel 1 is a short-period comet, meaning it moves around the sun in an elliptical orbit between Mars and Jupiter and can be sighted every six or so years.

The Deep Impact spacecraft shares the same name as a 1998 Hollywood disaster movie about a comet headed straight for Earth.

NASA says that the names for the space mission and blockbuster movie were arrived at independently around the same time and by pure coincidence. The €274m mission blasted off from Cape Canaveral, Florida in mid-January to make its six-month, 268 million-mile voyage. In March, scientists got a scare when test images from one of Deep Impact’s telescopes were slightly out of focus.

The problem was fixed, and a month later, Deep Impact took its first picture of Tempel 1 from 40 million miles away, revealing a big snowball of dirty ice and rock.

Last week, scientists processed the first images of the comet’s bright core taken from 20 million miles away, which should help the probe zero in on its target.

However, the real action starts in the early morning of July 3 when the spacecraft separates, releasing an 820lb copper probe called the “impactor” on a one-way trip straight into the path of the comet. During the next 22 hours, mission control at Jet Propulsion Lab in Pasadena will steer both craft toward Tempel 1.

Two hours before the July 4 encounter, the impactor kicks into autopilot, relying on its self-navigating software and thrusters for the rest of the journey to steer it toward the sunlit part of the comet’s nucleus. The collision is expected to occur around 1.52am eastern daylight time.

Meanwhile, the spacecraft - with its high-resolution camera ready - will veer out of harm’s way some 5,000 miles away, as it stakes out a ringside seat for recording the collision.

The spacecraft will make its closest flyby minutes after impact, approaching within 310 miles.