Comet 67P/Churyumov-Gerasimenko by Rosetta’s OSIRIS narrow-angle camera
on 3 August from a distance of 285 km. The image resolution is 5.3
metres/pixel. Copyright: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA
After a decade-long journey chasing its target, ESA’s Rosetta has today
become the first spacecraft to rendezvous with a comet, opening a new
chapter in Solar System exploration.
Comet 67P/Churyumov–Gerasimenko and Rosetta now lie 405 million
kilometres from Earth, about half way between the orbits of Jupiter and
Mars, rushing towards the inner Solar System at nearly 55 000 kilometres
per hour.
The comet is in an elliptical 6.5-year orbit that takes it from beyond
Jupiter at its furthest point, to between the orbits of Mars and Earth
at its closest to the Sun. Rosetta will accompany it for over a year as
they swing around the Sun and back out towards Jupiter again.
Comets are considered to be primitive building blocks of the Solar
System and may have helped to ‘seed’ Earth with water, perhaps even the
ingredients for life. But many fundamental questions about these
enigmatic objects remain, and through a comprehensive,in situstudy of
the comet, Rosetta aims to unlock the secrets within.
Comet on 3 August 2014
The journey to the comet was not straightforward, however. Since its
launch in 2004, Rosetta had to make three gravity-assist flybys of Earth
and one of Mars to help it on course to its rendezvous with the comet.
This complex course also allowed Rosetta to pass by asteroids Šteins and
Lutetia, obtaining unprecedented views and scientific data on these two
objects.
“After ten years, five months and four days travelling towards our
destination, looping around the Sun five times and clocking up 6.4
billion kilometres, we are delighted to announce finally ‘we are here’,”
says Jean-Jacques Dordain, ESA’s Director General.
“Europe’s Rosetta is now the first spacecraft in history to rendezvous
with a comet, a major highlight in exploring our origins. Discoveries
can start.”
Today saw the last of a series of ten rendezvous manoeuvres that began
in May to adjust Rosetta’s speed and trajectory gradually to match those
of the comet. If any of these manoeuvres had failed, the mission would
have been lost, and the spacecraft would simply have flown by the comet.
“Today’s achievement is a result of a huge international endeavour
spanning several decades,” says Alvaro Giménez, ESA’s Director of
Science and Robotic Exploration.
“We have come an extraordinarily long way since the mission concept was
first discussed in the late 1970s and approved in 1993, and now we are
ready to open a treasure chest of scientific discovery that is destined
to rewrite the textbooks on comets for even more decades to come.”
Comet activity on 2 August 2014
6 August 2014 - The comet began to reveal its personality while Rosetta was on its
approach. Images taken by the OSIRIS camera between late April and early
June showed that its activity was variable. The comet’s ‘coma’ – an
extended envelope of gas and dust – became rapidly brighter and then
died down again over the course of those six weeks.
In the same period, first measurements from the Microwave Instrument for
the Rosetta Orbiter, MIRO, suggested that the comet was emitting water
vapour into space at about 300 millilitres per second.
Meanwhile, the Visible and Infrared Thermal Imaging Spectrometer,
VIRTIS, measured the comet’s average temperature to be about –70ºC,
indicating that the surface is predominantly dark and dusty rather than
clean and icy.
Then, stunning images taken from a distance of about 12 000 km began to
reveal that the nucleus comprises two distinct segments joined by a
‘neck’, giving it a duck-like appearance. Subsequent images showed more
and more detail – the most recent, highest-resolution image was
downloaded from the spacecraft earlier today and will be available this
afternoon.
“Our first clear views of the comet have given us plenty to think about,” says Matt Taylor, ESA’s Rosetta project scientist.
“Is this double-lobed structure built from two separate comets that came
together in the Solar System’s history, or is it one comet that has
eroded dramatically and asymmetrically over time? Rosetta, by design, is
in the best place to study one of these unique objects.”
Today, Rosetta is just 100 km from the comet’s surface, but it will edge
closer still. Over the next six weeks, it will describe two
triangular-shaped trajectories in front of the comet, first at a
distance of 100 km and then at 50 km.
At the same time, more of the suite of instruments will provide a
detailed scientific study of the comet, scrutinising the surface for a
target site for the Philae lander.
Eventually, Rosetta will attempt a close, near-circular orbit at 30 km
and, depending on the activity of the comet, perhaps come even closer.
“Arriving at the comet is really only just the beginning of an even
bigger adventure, with greater challenges still to come as we learn how
to operate in this unchartered environment, start to orbit and,
eventually, land,” says Sylvain Lodiot, ESA’s Rosetta spacecraft
operations manager.
Arriving at a comet
As many as five possible landing sites will be identified by late
August, before the primary site is identified in mid-September. The
final timeline for the sequence of events for deploying Philae –
currently expected for 11 November – will be confirmed by the middle of
October.
“Over the next few months, in addition to characterising the comet
nucleus and setting the bar for the rest of the mission, we will begin
final preparations for another space history first: landing on a comet,”
says Matt.
“After landing, Rosetta will continue to accompany the comet until its
closest approach to the Sun in August 2015 and beyond, watching its
behaviour from close quarters to give us a unique insight and realtime
experience of how a comet works as it hurtles around the Sun.”
Notes for Editors:
Rosetta woke up from deep space hibernation at 18:18 GMT on 20 January
2014, nine million kilometres from comet 67P/Churyumov–Gerasimenko.
Following wake-up, the orbiter’s 11 science instruments and 10 lander
instruments were reactivated and readied for science observations. Ten
orbital correction manoeuvres were carried out between 7 May and
6 August, reducing the spacecraft’s velocity with respect to the comet
from 775 m/s to 1 m/s, equivalent to walking pace. Each of these
manoeuvres was critical: if any had failed, no rendezvous would have
been possible. More information about these manoeuvres can be found on
the Rosetta blog.
The latest ‘arrival’ image will be presented in the science session of
today’s ‘Rosetta comet rendezvous’ event at ESA’s Space Operations
Centre, ESOC, in Darmstadt, Germany, and in parallel will be published
online on the ESA Portal.
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