as it approaches the Sun, getting to
within 112 million miles (180 million kilometers) in summer next year, when
the comet will be expelling hundreds
of pounds of material every second.”
This mission has been one of ambition, science, and firsts. Rosetta is
the first spacecraft to rendezvous
with a comet, the first to orbit a
comet, and now the first to land
on a comet. So far we have seen
unprecedented views of a comet’s
surface, discovered what a comet
smells like, and even heard it “sing.”
Rosetta’s instruments have been
busy studying the comet from different angles, and taking images at different wavelengths. Using the VIRTIS
instrument, scientists were able to
take the comet’s temperature, de-
mission is a success, and the biggest
problem with success is that it looks
easy. This was not easy. It took a lot
of hard work and cooperation.”
Throughout history, comets have
fascinated us with their unpredictability. Even though we have a
better understanding of comets
behave, there is still much to discover. Earlier this year, researchers
observed a dramatic increase in the
comet’s activity, and at that time
Rosetta was too far from the comet
to determine the cause. In June, Rosetta’s MIRO instrument started detecting water outgassing from the
comet. At the time, Rosetta was
located at approximately the same
distance as the Earth is from the
Moon, from the comet, and MIRO
This four-image mosaic comprises images taken from a distance of 28.0 km from the centre of Comet 67P/
Churyumov-Gerasimenko on 31 January 2015. The image resolution is 2.4 m/pixel and the individual 1024
x 1024 frames measure 2.4 km across. The mosaic measures 4.6 x 4.3 km. Credit: ESA/Rosetta/NAVCAM
termining it is warmer than expected
and revealing the surface is actually
dark, dusty and porous instead of icy.
ESA Director General, JeanJacques Dordain had this to say
about the historic landing: “This is a
big step for human civilization. We
are the first to have landed on a
comet and that will stay forever. This
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observed 67P ‘sweat’ about 1 cup
(300 mL) of water per second – the
equivalent of two glasses. Ever since,
the activity has rapidly increased,
with peaks of 1.3 gallons (5 liters) of
water per second seen by MIRO.
Rosetta’s ROSINA instrument, also
known as the ‘comet sniffer’ detected a variety of molecules in the
coma of 67P, including water, carbon
monoxide, carbon dioxide, methane, and even a few nitrogen and
sulfur varieties. Translation: comet
67P smells like a combination of ammonia, urine, and rotten eggs. VITRIS
also detected both water and carbon dioxide in the comet’s coma,
backing up ROSINA’s findings.
The GIADA instrument, teaming
up with COSINA, has been busy
collecting dust particles, and measuring their velocities. After careful
analysis, COSINA determined that
at least one dust grain contains sodium and magnesium. This dust grain
sparked the researchers’ curiosity
so much, they named it Boris. Now,
both sodium and magnesium have
been detected in comets before.
However, in this case, the minerals
were detected in the comet’s inner coma and not the tail region.
Another question the Rosetta
mission hopes to answer is “Where
did Earth’s water come from?” Scientists have long hypothesized that
comets were responsible for supplying the infant Earth with water,
and ultimately life. Recently, ESA
announced that water vapor collected from the comet varies significantly from the water we find on
Earth, thus reigniting the debate on
where Earth’s water came from.
The Earth formed over 4.6 billion years ago, and in its infancy
was a much hotter world than we
know today. As such, any surface
water present would have boiled
off by the searing heat of an early
Earth. Today, our home planet is
very different, with two-thirds of
its surface covered by water. So
how did that water get here?
One hypothesis is that the water
was delivered to Earth after the planet significantly cooled, further on in its
development. The delivery method
was most likely via comet or asteroid
collision; however, this hypothesis is
strongly debated. How can we tell
where water came from? By analyzing the water and determining its
“flavor” or composition, researchers
can tell the proportion and variety
of hydrogen isotope present, thus
determining its origin. In the case of
comet 67P’s water, Rosetta’s analysis
discovered the water contained a
ratio of hydrogen to deuterium — a
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