The mission
Rosetta is the first mission designed to orbit and
landing on it, Rosetta will allow us to reconstruct
land on a comet. It consists of an orbiter, carrying
the history of our own neighbourhood in space.
11 science experiments, and a lander, called
Rosetta will also help to discover whether comets
‘Philae’, carrying 10 additional instruments, for the
contributed to the beginnings of life on Earth. Comets
most detailed study of a comet ever attempted.
are carriers of complex organic molecules, delivered
Rosetta gets its name from the famous Rosetta
to Earth through impacts, and perhaps played a role
stone that led to the deciphering of Egyptian
in the origin of life. Moreover, volatile light elements
hieroglyphics almost 200 years ago. Similarly,
car ried by comets may also have played an important
scientists hope that Rosetta will unlock the
role in forming Earth’s oceans and atmosphere.
mysteries of how the Solar System evolved.
During its long journey, Rosetta was scheduled to have
Rosetta’s launch was originally scheduled for January two close encounters with asteroids of the main asteroid
2003 on an Ariane-5 rocket. Rosetta’s target at that time belt that lies between the orbits of Mars and Jupiter. The
was Comet 46P/Wirtanen, with the encounter planned
first was with (2867) Steins, a rare E-type asteroid. The
for 2011. However, following the failure of the first Ariane
flyby started on 4 August 2008 with optical navigation of
ECA rocket, in December 2002, ESA and Arianespace
the asteroid itself – a technique never before used in ESA
took the joint decision
spacecraft operations.
not to launch Rosetta
The closest approach
during its January
was on 5 September
2003 launch window.
2008, 18:58:19 UTC,
This meant that
when (2867) Steins
Rosetta’s intended
was 2.14 AU from the
mission to Comet
Sun and 2.41 AU from
46P/Wirtanen had
Earth. The encounter
to be abandoned.
occurred with a
relative velocity of 8.62
In May 2003, a
km/s and reached
new target comet
a minimum distance
and launch date
of 802.6 km. The flyby
for Rosetta were
took place on the Sun
selected: the
side of the asteroid in
spacecraft was
the plane defined by
launched in March
the relative velocity
2004 and arrived
and the Sun direction.
at its new target,
The flyby strategy
67P/ChuryumovStill image from animation of Philae separating from Rosetta and descending to the surface
allowed continuous
Gerasimenko,
of comet 67P/Churyumov-Gerasimenko in November 2014. Credit: ESA/ATG medialab
observations of the
earlier this year.
asteroid before,
during and after closest approach as well as passing
Objectives
through phase angle zero. To keep the asteroid in the
ESA’s comet-chaser will be the first to undertake
field of view of the scientific instruments during the
a lengthy exploration of a comet at close quarters.
closest approach phase, the spacecraft had to target
After entering orbit around Comet 67P/Churyumovwith an accuracy of better than 2 km and to perform
Gerasimenko in 2014, Rosetta will release its
an attitude flip manoeuvre lasting 20 minutes, after
Philae small lander onto the icy nucleus.
which autonomous tracking of the asteroid started.
Rosetta will orbit the comet for about a year as
On 10 July 2010 Rosetta had its second asteroid close
they head towards the Sun. Once they have passed
encounter, this time with (21) Lutetia, a large asteroid
perihelion (closest distance to the Sun), Rosetta will
(dimensions: 126 km x 103 km x 95 km – about 10 times
keep orbiting the comet for another half year, while the
bigger than Steins). The flyby was a spectacular success
comet moves back out towards the orbit of Jupiter.
with Rosetta performing faultlessly, passing the asteroid
As the most primitive objects in the Solar System,
at 15 km/s. The spacecraft had its closest approach at
comets carry essential information about our origins.
15:44:57 UTC, at a distance of 3162 km. The cameras
Their chemical compositions have not changed
and other instruments had been working for hours and
much since their formation, therefore reflecting that
in some cases days before and after closest approach
of the Solar System when it was very young and still
providing important new insights about the nature of
‘unfinished’, more than 4600 million years ago. By
this heavily cratered asteroid that has suffered many
orbiting Comet 67P/Churyumov-Gerasimenko and
impacts during its 4.5 billion years of existence.
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