12-year long Rosetta Mission comes to an end with Spacecraft diving into the Comet

Perhaps nothing can quench boundless human curiosity and enthusiasm other than the amazing feats of science that enamour inquisitive mind. The incredible power of science by bestowing wings to power of imagination and creativity of mankind ushered scientific ilk into a new world of exciting innovations and discoveries. The exhilarating, imagination defying feats of space explorations send shudders of excitement that enthral science enthusiasts and researchers as well. One such mission that marvelled the scientific community with phenomenal accomplishments was the Rosetta mission. On Sep 30th the $1.46 billion mission successfully ended its illustrious 12-year long journey in the space by diving into the Comet 67P as planned.

The Mission

The International Rosetta Mission was approved in November 1993 by the European Space Agency (ESA)’s Science Program Committee as part of Planetary Corner Stone Mission under its long term space Science Program. The mission was originally scheduled for a rendezvous with the comet 46 P/Wiratenin but due to postponement of launch of the spacecraft twice, the new target was comet 67 P/ Churyumov-Gerasimenko. Comet was named after the discoverers Klim Churyumov and Svetlana Gerasimenko who first identified it in September 1969. The mission was aptly named after Rosetta Stone, the slab of volcanic basalt that provided the key to unravel the Egyptian hieroglyphs. Similarly, Scientists hoped that Rosetta mission would unfold mysteries of oldest building blocks of solar system, the Comets.

Comet Exploration

Comets are small icy bodies which originate either in the Oort Cloud that exist far beyond the orbit of the Pluto or from the Kuiper Belt located beyond the orbit of Neptune and releases gas or dust. When comets pass close to the sun they get heated up and begin to outgas thus displaying visible atmosphere or Coma and sometimes a tail. Usually the dust consists of ice, carbon dioxide, ammonia, methane and more. Evolutionary biologists believed that numerous comets impounded the surface of fledging Earth 4.6 billion years ago bringing with them water and other organic compounds needed for generation of life on Earth. A critical analysis of the comet mass would help understand in detail the evolution of the solar system and presence of extraterrestrial life. Comet 67 P believed to have originated from Kuiper belt belongs to Jupiter Family Comets is controlled by Jupiter’s gravity. Due to collisions or gravitational perturbations these icy bodies are ejected from the Kuiper belt and fall towards sun.

Rosetta Space Craft

Rosetta is a robotic spacecraft launched on 2nd March 2004 by the Ariane V rocket. It has two main elements: The Rosetta Space probe orbiter with 12 scientific instruments and Philae, a robotic lander had additional 5 instruments. It was designed to both orbit and land on the comet for a detailed study of the comet. Before entering a phase of hibernation in June 2011 when the instruments on board were powered down to conserve energy, it made three flybys of Earth and one flyby of Mars in 2007. It had passed by two asteroids: 2867 Steins in 2008 and 21 Lutetia in 2010. It created a buzz in the scientific community by waking up to a pre-set alarm after 31 months of hibernation on January 20th 2014 to begin its rendezvous in space with the comet 67P. After 10 years, five months and four days it orbited around Sun for five times traversed a distance of 6 billion kilometres. Rosetta took 10 years to reach the Comet. Moreover, it was travelling at much faster speeds which couldn’t ever be reached by spacecrafts leaving the Earth. Hence since its launch in 2004, Rosetta used the gravity of Earth and Mars as a slingshot to pick up the acceleration needed to enter the Comet’s trajectory. All the operations are controlled from the European Space Operations Centre (ESOC) Darmstadt, Germany.

Philae’s touch down with the Comet

The succeeding events post-hibernation were meticulously planned wherein the robotic lander Philae of Rosetta was all set to land on the surface of the comet. Accordingly, Rosetta slowed down to enter an orbit around the Comet in May 2014.  Landing was planned from the sunward side of the orbit to encounter less dust and reduce impact of a hard collision on Philae. On 6th August 2014 Rosetta had rendezvous with Comet 67P and after closer study of surface properties of Comet, exact site of landing was decided. In August 2014, Rosetta became the first spacecraft to orbit around a comet. By September the distance between Comet and Rosetta was reduced by series of burns on its thrusters. As Rosetta was closing nearer to Comet another major challenge was communication. Since the radio transmission signals travelling at a speed of light took 45 minutes to reach the nearest Gold Stone radio dish in California.  It was also decided that Philae will touch down on the site Agilika, a place located on smaller lobe of Comet.

On November 12th 2014, Rosetta accomplished scientifically challenging mission in the history of the space explorations so far. At nearly 500 million Kilometers distance from Earth, between Mars and Jupiter, 100kg Philae lander ejected from the spacecraft Rosetta and landed on the Comet surface. In common parlance, it was a process, wherein tried to transfer an object from one speeding bullet train to another. Both of them are flying at a speed of 65,000 km an hour. The task is onerous as crucial details like the densities, surface atmosphere of the Comet and other details of the landing site are not known. Moreover, the unusual double lobed shape of the Comet was not known until the rendezvous with the Comet.

Rosetta pictures indicated that surface of the comet was highly undulated with wicked slopes and elevated rocks. Comet was believed to be 4 kilometers wide, orbits around Sun in 6.6years with average temperature of -70C. Philae piggybacking on Rosetta separated from its mother, from a distance of 12 kilometers from comet with unfolded legs. To escape the weak gravity of comet Philae was endowed with Harpoons to anchor the Comet’s surface. Philae was designed to land on a slope of 30 degrees and once anchored it was supposed to transmit high-resolution pictures of the comet’s surface and perform analysis of Comet’s surface. The instruments on board can dig the surface and heat them to measure their properties. Unfortunately, the harpoons failed to fire upon landing so it bounced three times before settling down under a shadow of cliff in Abydos region. As a result, solar panels failed to provide enough energy for carrying out any analysis. Though Philae managed to send few images in the next days, it went silent on 14th November 2014. Fortunately, the lander was revived on June 13th 2015, when the Comet moved closer to Sun. It was observed that Philae had been collecting enough samples all the while but didn’t have enough power to send signals.

During this period Rosetta was tracking the Comet and conducting analyses of gases emitted by it, studying its atmosphere and gravity. Last month Rosetta again tracked Philae. Now with Comet heading towards Jupiter and Rosetta powered by Solar Panels wouldn’t have enough energy to keep up, scientists have decided to annul the program by allowing Rosetta to gently dive into the Comet.  Since comet surface is porous, Rosetta’s fall would be rather a slow-motion collision rather than a violent crash. Controlled impact gave scientists a chance to observe the surface properties of the Comet more clearly and till to the last minute, the spacecraft was sending back lots of images. The final landing place was a smooth patch in the head region of duck-shaped comet. The speed upon impact was close to walking speed pace. The end of the mission was signaled by blank computer screens and absence radio signal chatter.

Accomplishments of Rosetta Mission

Till now, Rosetta mission had successfully carried out its objectives of global characterization of asteroids, determination of their dynamic properties, surface morphology and composition. Analysis of data relayed by Rosetta, indicated that comets are not no longer dirty snowballs. But snowy dust ball, harboring organic compounds, carbon-based molecules the building blocks of life. The northern hemisphere of Comet’s nucleus was filled with dunes and ripples similar to that on Venus, Earth and Venus. It doesn’t have robust atmosphere and high gravity but has structures resembling sand dunes.

It was found that Comet 67P was darker than Charcoal without much water and ice. Northern hemisphere is relatively warm compared to southern hemisphere indicating existence of seasons. Researchers are currently busy analyzing the huge quantities of data collected by Rosetta and are hopeful of hitting at robust clues about the origins of Earth. Comets are basically the remnants of debris existing in space after creation of Solar System. Thus, this mission is extraordinary for its miraculous adventures in space and for overwhelming exhilaration it generated.


Earlier Cometary Explorations

Cometary explorations began in 1978 with the launch of NASA’s International Cometary Explorer. It passed the tail of Comet Giacoinni-Zinner and Comet Halley. It was followed by two Russian probes, Vega-1 and Vega-2 in 1984; Japanese twin spacecrafts Sakigake and Suisei (1985); ESA’s Giotto in 1985. NASA’s missions include- Deep Space 1(1998), Stardust (1999), Contour (2002), Deep Impact (2005) which was retired in 2010. Rosetta is the first mission ever  which attempted to land on the nucleus of comet.


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