News Column

A date with a 4.6bn-year-old rock

January 20, 2014



After 10 years and 7 billion kilometres, the first spacecraft to try to land on a comet is close to its target provided the scientists can wake up the probe. If they succeed, the mission could provide vital clues soon to the origins of our own solar system, as James Langton reports

It has been slumbering for almost three years. But later today a signal from Earth will awaken the spacecraft Rosetta to begin one of the most complex and exciting missions in the exploration of our solar system.

The target is a four kilometre-wide comet heading towards the Sun. After its midday alarm call, Rosetta will start a 10-month chase at speeds of up 100,000kph that will end, if all goes well, with an audacious first landing on a comet.

The task has been compared with the film Armageddon, which featured Bruce Willis as the commander of a mission to intercept and destroy a gigantic asteroid on a collision course with Earth.

The path of comet Churyumov-Gerasimenko named after the Russian scientist who discovered it in 1969 is considerably less dramatic, with nothing worse than a close encounter with Jupiter.

Indeed, the Rosetta craft has been deemed more of a hazard than the comet it is chasing, after being mistakenly identified as a near-Earth asteroid by American astronomers after it swept past at a distance of just 5,700 kilometres seven years ago.

But the prospect of a successful landing on a comet is generating just as much excitement as the plot of a science fiction film, at least among the world's scientific community.

Rosetta, named after the ancient Egyptian stele that cracked the code of hieroglyphs, carries in its payload the landing module Philae, named after the Nile island where the Rosetta Stone was discovered in 1799.

Launched by the European Space Agency (ESA) from French Guiana in 2004, the twin craft are also seeking to crack a code in this case, unlocking the secrets of the solar system before its planets were formed.

Hence the decision to hunt down comet Churyumov-Gerasimenko, also known as comet 67P. Like all such bodies, it is a collection of dirt and ice that is thought to be a remnant of the birth of the solar system.

Mark McCaughrean, an astrophysicist and the ESA's director of science, describes 67P as a "time capsule" that has been locked away for 4.6 billion years: "It's time to unlock the treasure chest," he says.

Since its launch, Rosetta has flown around the Sun five times, making three fly-bys of Earth and one of Mars and travelling 7 billion km on its journey. It has used both planets' gravity to provide the acceleration to catch comet 67P.

In July 2010, the spaceship caught up with and photographed a 100km-diameter asteroid, Lutetia. Almost a year later, heading to the darkest region of the solar system, Rosetta was put into hibernation to conserve energy until the most crucial stage of the mission.

That begins today, by what the ESA calls "the most important alarm clock in the solar system", a computer on the spaceship.

Rosetta is now 673 million km from the Sun, and close enough for the rays of light to power its solar panels again. Until the reactivation, the craft has retained only enough power to keep its computer on standby and for three small heaters to stop it freezing solid. But for 31 months, the ESA has had no contact with the vessel.

At the mission control in Darmstadt, Germany, the first sign that all is still well will be a signal from Rosetta announcing it has woken up.

Before that, the spaceship will switch on its "star trackers", taking it out of its hibernation spin, checking its position and beginning the process of warming up other systems.

After firing thrusters the craft will have its solar arrays directly aligned with the Sun. It will next turn its antenna towards Earth to send a signal home. In all, it will take about six hours before scientists know all is well.

Because the distance is so enormous, the message will take nearly 45 minutes to reach Earth, with ESA relying on Nasa's help to boost the signal through its deep-space station in Goldstone, California.

In the next stage of the 1.3 billion (Dh7.8bn) mission, Rosetta will spend five months testing its systems during its journey through space.

This will include putting into place procedures to correct two small glitches that have occurred during the 10-year mission. One involves two of four "reaction wheels" that turn the ship, with the other a leak of helium for the thrusters.

All being well, Rosetta will gradually drawn alongside comet 67P in August at a distance of just 25km, initially taking photographs and identifying a possible landing site.

At present, scientists are divided over whether to pick one of three "live" sides, where material is being released into space, or another location less likely to damage the lander's instruments.

Finally, in November, Rosetta will be close enough to release Philae. Because of the comet's low gravity, the refrigerator-sized lander will fire a harpoon attached to a tether to stop itself drifting into space after the landing.

Once on the surface, Philae will start conducting a series of nine experiments, including a drill to extract material from the comet's interior.

While this stage of the mission is scheduled to last a week, there are hopes it will last much longer, with the rest of the mission scheduled to end in December next year.

For comet 67P, though, time is also running out. It is thought to have originated in the Kulper Belt, a reservoir of icy objects beyond Neptune. Collisions eventually eject some of these towards the Sun.

Comet 67P's trajectory will have taken it towards Jupiter, altering its orbit. Such bodies are known as short-period comets, as the heat of the Sun causes them to melt.

After so many billions of years, 67P will be lucky to survive another 20.

jlangton@thenational.ae


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Source: National, The (United Arab Emirates)


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