Almost exactly 15 years ago, during the
night of 13/14 March 1986, ESA’s Giotto spacecraft
made history by obtaining the first close-up pictures
of a comet’s black, icy nucleus. After surviving a
battering from grains of comet dust, Giotto went on
to become the first spacecraft to visit a second
comet. The flyby of Comet Grigg-Skjellerup in July
1992 is still the closest encounter ever achieved
with one of these cosmic icebergs.

At a recent two-day
‘Giotto Heritage’
symposium held in
The Science
Museum, London,
scientists and engineers who worked on this
pioneering deep space mission came together to
reminisce about past triumphs and to look forward
to the next generation of comet explorers.

Knowledge gained from Giotto, ESA’s first ‘deep
space’ probe, is currently being used to develop the
Rosetta comet probe, which is scheduled for launch
in January 2003.

Project scientist Gerhard Schwehm, who also
played a leading role in the success of Giotto,
explained to the audience how Rosetta will make its
own unique contributions to Solar System
exploration. Most notably, it will become the first
spacecraft to orbit a comet at close quarters, and
the first to deploy a lander onto the surface of a
comet nucleus.

Dr Schwehm began by explaining a little of
Rosetta’s historical background. The mission was
born in Zurich on 22 May 1985, when it was
accepted as a Cornerstone science project by the
ESA Space Science Advisory Committee. It was
then known as the Comet Nucleus Sample Return
mission (CNSR) and was envisaged as a
collaboration with NASA. After a few years NASA’s
priorities changed, so the highly ambitious sample
return mission evolved into a slightly less complex
ESA-only mission dedicated to a comet rendezvous
and two asteroid flybys.

At the end of 1987, the project received the name
‘Rosetta’, after the famous Rosetta Stone that now
lies in the British Museum in London. In the same
way that the Rosetta Stone enabled historians to
decipher the mysterious hieroglyphic writing of
ancient Egypt, so Rosetta will enable scientists to
learn about the most primitive matter in the Solar
System – the building blocks from which the planets
were created.

“Comets are the messengers that give us access
to the early Solar System and the way it evolved,”
said Dr Schwehm. “They are believed to have
survived almost unaltered from the primitive
protosolar nebula. This, in turn, contained material
derived from the interstellar medium and giant
molecular clouds.”

So, 15 years after the Halley flyby, what is the
relevance of the Giotto mission for Rosetta?

“Rosetta was a logical progression from the initial
reconnaissance by Giotto,” explained Dr Schwehm.
“Giotto showed us for the first time what a comet
nucleus looked like. Now, instead of a short fly past
of the nucleus, Rosetta will be able to study the
comet from close range for more than one and a
half years and land a small spacecraft on its

In this way, Rosetta will not only tell us about the
origin and evolution of comets, but it may contribute
to the debate over the origins of planetary
atmospheres and the evolution of life.

Continuing on the theme of the Giotto heritage, Dr
Schwehm explained some of the similarities
between the two missions.

“Like Giotto, we have a fixed launch window – 20
days in the case of Rosetta,” he said. “If we miss
this, we will not be able to reach our target, Comet
Wirtanen, so we would have to wait one or two years
before another suitable comet came along.”

“We also know that we will have to put Rosetta into
hibernation for long periods during the eight-year
journey to Wirtanen,” he said, “but we are confident
that we can do this because of our previous
experience with Giotto.”

“The Giotto heritage is important in other ways,” he
added. “The community of planetary scientists in
Europe was quite small back in the eighties, so it is
not surprising that many of those who worked on
the earlier mission are also involved in Rosetta.
However, Giotto encouraged scientists from other
fields, such as plasma physics, into planetary

“Furthermore, the instruments on Rosetta have a lot
of common elements with their Giotto
predecessors,” he said. “And last but not least,
there is a European industrial heritage linking the
two generations of comet probe,” said Dr
Schwehm. “Despite corporate amalgamations and
changes of name, a similar industrial team has
been involved in both missions, since Astrium
includes many of the companies that worked on

“This broad heritage increases our confidence that
Rosetta will follow in Giotto’s footsteps and become
a tremendous success,” he concluded.