Devangshu Datta: The Deep Impact probe

TECHNO BEAT

In the simplest possible terms, the Tempel I Deep Impact mission involved throwing a washing machine-sized, 350-kg "impactor" device at a Connaught Place-sized piece of real estate, seeing how large the bang was, and then picking through the debris.

The technical difficulty lay in the fact that the real estate in question was many, many millions of kilometres away from Connaught Place and moving at upwards of 23,000 kmph at the moment of collision.

It took the "washing machine" or rather, the mothership that delivered the impactor, almost six months to get there in a journey of more than 430 million kms.

There was a minor 7 km deviation in the original flight course but everything ended happily with a huge bang after two close-range course corrections brought things back on course. On July 4, the impactor smashed into Tempel I at a point some 135 million kms from Earth.

The mission itself was named in a nod of acknowledgement to the 1998 disaster movie, where a comet on collision course with Earth is diverted by chucking bombs at it.

The movie contributed to the worldwide excitement. The Nasa website recorded more than 80 million unique visitors in the 24 hours following the impact.

The real-life Nasa mission demonstrates the basic ability to hit a target moving at these speeds at these distances. However, that wasn't really the point of the exercise although it has interesting implications for protection from asteroids and comets.

Scientists have speculated for decades on the materials in comets "" the mysterious visitors that flame so spectacularly across the skies. A comet appears out of the frozen reaches of outer space as a ball of frozen ice and dust (known as the nucleus) traveling on a fast, highly eccentric orbit. It is believed that comets are very old, composed of material unchanged since the formation of the solar system.

When a comet approaches close enough to the sun, some of the material is ionised and vapourised and explodes out of the frozen nucleus. Some of this ionised vapour settles in a halo (called the "coma") surrounding the nucleus. The rest flows out into the flaming tail, which could stretch across the entire sky, if the respective angles of orbit of the Earth and the comet are correct.

Typically, a comet nucleus is between 10-50 kms in radius while the coma could form a gas-balloon of several thousand kms around the nucleus. The tail could stretch for up to 250 million kms "" that's the longest recorded so far.

By smashing a probe into Tempel I, Nasa got to examine the exact composition in greater detail than previously imaginable. The space agency directed its backup "eyes and ears" into the area to add to the observations. The Hubble Space Telescope, the Spitzer Space Telescope and the Chandra X-ray Observatory were all focused on Deep Impact.

Live telemetry continued with data transmission from the impactor until three seconds before impact. The last pictures from the impactor were taken from 30 kms above Tempel's surface. That means resolution down to less than 4 metres for the transmitted pictures.

The mothership recorded the impact, which vapourised the probe after driving it deep into the nucleus. The mothership incidentally, is fine and it might be used for yet another comet-busting mission some three-and-a-half years later.

For years, scientists have thought the basic amino acids that are at the basis of life might exist on comets. There are even theories that life on Earth was seeded by the tail of a comet passing close by, many eons ago. This probe will lead to many clarifications about the actual materials "" it will take months, if not years, before the scientists finish analysing the data.

The Deep Impact probe should also provide a glimpse beneath the surface of a comet, where material from the time of the solar system's formation remains unchanged.

Scientists even hope that this may provide clues to how the solar system was formed. Apparently, water vapour has already been detected in the spectrographic analysis of the debris and this is very promising indeed.