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 that attempted to land on the
nucleus of comet.
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