Rosetta, Philae, and the Comet Landing

Until recently comets have been part of many of our mysteries and superstitions, some societies even claimed them to be gods moving through the sky. Science viewed them as pristine remnants of our solar system that blazed a circuitous trail going back nearly 4.6 billion years. Comets with their rock and ice payload are credited with bringing water to our planet. Scientists have always been eager to study comets so we could learn more about the origins of the planets, solar system, and how life evolved.

This is what was fantastically accomplished recently by the lander Philae when it landed on the duck-shaped comet 67P/Churyumov-Gerasimenko and drilled into its crust. Rosetta became the first space craft ever to put itself in orbit around a comet and inject its lander payload Philae onto the comet’s surface.

Rosetta and Philae, a product of human ingenuity, started on this most improbable of journeys nearly a decade ago. The European Space Agency (ESA), embarked on this highly risky and supremely challenging mission of flying through our solar system, nearly six billion kilometre, at speeds as high as 135,000km/hr, chasing a three mile wide comet, and landing on it after 10 years of travel.

It has travelled through several fly-bys of the Sun and Earth, one of Mars, two trips through the asteroid belt and a long hibernation in the chilly void beyond Jupiter, before rendezvousing with the comet. The achievement is one giant step for mankind like the Apollo missions to the moon. ESA is collaboration across countries from the European Union (EU), non-EU, and several former soviet-union countries. The German space agency, a part of the ESA, operated the Philae for ESA. The projects budget of $1.75 billion adjusted to inflation amounts to about 3.5 billion euro.

The orbiter Rosetta is named after the Rosetta stone, a volcanic rock found in Egypt which was the key to unlocking the secrets of Egyptian hieroglyphics, and analogously Rosetta hopes to answer the fundamental questions surrounding our origins. The lander Philae was named after an island in the Nile River which contributed to deciphering the Rosetta stone.

The American space agency NASA has in the past sent probes to fly by comets. In 1986, NASA’s Ice mission flew through the tail of Halley’s Comet and in 2005 interacted with comet Temple 1. None of the earlier attempts were targeting landing on the comet though. Planets and moons that are large, that have atmosphere to slow the descent, and gravity strong enough to grab the probes, are fairly well understood and comfortable for space scientists to handle. Comets on the other hand are small, have very low gravity, and no atmosphere making things extremely difficult. In fact, the gravity is feeble enough that any object lifting from the surface at a low 1meter/second will escape entirely and drift off into space.

Landing a probe the size of a washing machine on the comet surface is thus a huge challenge especially since the composition of the comet’s crust was unknown. Philae took nearly seven hours to descend to the surface from its mother ship, the Rosetta. Upon contacting the comet’s unexpectedly hard surface Philae bounced back three times. The lander’s legs were able to absorb most of the impact energy but not enough to stop it from bouncing.

The first of the triple bounce was nearly 1km high which caused the lander to come to rest at nearly a km away from the intended landing location. It ended up with only two of its three legs on the surface, nearly vertical in posture, tipped against a boulder, and alongside a wall of rock. Unfortunately this location allowed only about an hour of sunlight to reach Philae instead of the desired 12 hours. This prevented the battery and its backup from recharging using the solar energy.

Giving the eventuality that Philae would run out of charge, scientists activated a series of automated experiments in a race against time to collect pristine data from the surface of a comet. Heroically, Philae finished its drilling, collected the data, and communicated it back to Earth before going into a long coma. The ten instruments on board ranging from a sample drill, grain impact analyses, dust accumulator, visible and thermal spectrometer, optical spectroscope, amongst others, were used to perform surface measurements, determine surface composition, and test for the presence of amino-acids and complex organic molecules.

The ESA has made us all proud by sending this amazing robot to the fossil of a comet so that the origins of our existence and the composition of the comets can be analysed and deliberated upon. Space research has been one of the best examples where peaceful international cooperation has allowed humans to conquer mind and matter and work towards a common goal. We are using up resources on earth and it become more imperative that agencies and countries work collaboratively on more ambitious projects to secure the future of mankind and benefit all of humanity.