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Paris, 26 March 2003
Press Release
Nx 19-2003


ESA Studies Missions to Safeguard the Earth

Early on the morning of 30 June 1908, the vast forest of western
Siberia was illuminated by a strange apparition: an alien object
streaking across the cloudless sky.  White hot from its headlong
plunge into the Earth's atmosphere, the intruder exploded about 8 km
above the ground, flattening trees over an area of 2000 square
kilometres. 

Despite the huge detonation, equivalent to a 10 megaton nuclear
warhead (about 500 times the energy of the Hiroshima atomic bomb),
there were few if any casualties in the sparsely populated taiga.  If
the Tunguska object - probably an asteroid about twice the size of a
tennis court - had exploded over London or Paris, the list of
casualties would have run into millions.

Fortunately, cataclysmic events caused by incoming near-earth objects
(NEOs) are few and far between. Current estimates suggest that a 50
metre Tunguska-like object is likely to collide with the Earth once
every 100-300 years.  A 1 km object, which typically arrives every
few hundred thousand years, could wipe out an entire country.  An
impact in the ocean would be no better, generating enormous waves
(known as tsunamis) that would devastate coastal areas thousands of
kilometres away. 

An increasing awareness of the potentially disastrous consequences of
such impacts has driven recent efforts to detect and categorise the
larger Earth-threatening objects.  However, much more needs to be
done if the millions of Tunguska-like objects are to be found and
catalogued. Only then can advance warning of pending impacts be
provided and measures be taken to reduce the threat.

Despite the introduction of increasingly sophisticated search
programmes in various parts of the world, the search for objects
heading our way needs to expand into space.  Only space-based
observatories can provide the all-sky coverage required and detect
Earth-crossing objects that would normally be hidden in the glare of
the Sun. 

In July 2002 the general studies programme of the European Space
Agency (ESA) provided funding for preliminary studies on six space
missions that could make significant contributions to our knowledge
of NEOs. 

"The six proposals were selected because the mission concepts would
help to answer essential questions on the NEO threat, such as how
many there are, their size and mass, and whether they are compact
bodies or loose rock aggregates," said Andres Gálvez, head of the
Advanced Concepts Team at ESA's European Space Research Technology
Centre (ESTEC) in the Netherlands.

"This information, as well as other data, is needed before
appropriate mitigation procedures can be developed," he said.

"There are two broad categories.  The observatory missions are able
to detect and track many more NEOs than can be seen from the ground.
This enables astronomers to calculate their orbits and predict
whether they will offer a threat to the Earth far into the future."

"The flyby/rendezvous missions are designed to look at a small number
of NEOs in great detail, sending back information on their size,
composition, density, internal structure and so on.  This is
important because we need to know as much as possible about how they
will behave if we try to divert them from a collision course with
Earth." 

The six missions under study were:

ˇ Don Quijote:  This proposal involves the launch of two spacecraft
to test technologies required to deflect an asteroid heading towards
Earth. The 'Hidalgo' spacecraft will be targeted to impact a
500-metre-diameter asteroid at a relative speed of 10 km/s.  Its
companion, known as 'Sancho' will deliver a number of sensors to the
surface of the asteroid and observe from a safe distance what happens
during and after the high speed collision. This will provide valuable
information on the NEO's internal structure.

ˇ Earthguard 1: A proposal to mount a "hitchhiker" telescope on a
spacecraft en route to the inner Solar System, e.g. ESA's BepiColombo
Mercury orbiter. The telescope would detect Earth-crossing asteroids
larger than about 100 metres, which are very difficult or impossible
to detect with ground-based telescopes.

ˇ EUNEOS: A medium-sized telescope mounted on a dedicated spacecraft
platform that would search for the most dangerous NEOs from inside
the orbit of Venus. Its main goal is to detect 80% of the potentially
hazardous objects down to a few hundreds of metres in size. It is
estimated that this could be attained in 5 years. By systematic
re-detection of the objects, their orbits would then be determined
with high accuracy.

ˇ ISHTAR: In addition to measuring the mass, density and surface
properties of an NEO, this spacecraft would probe the interior of an
NEO in order to study its structure and internal strength. This would
be done using radar tomography, a new technology that uses
ground-penetrating radar to make images of the interior of a solid
body.

ˇ SIMONE: A fleet of five low-cost microsatellites that would each
fly by and/or rendezvous with a different type of NEO. Each
spacecraft would carry a suite of scientific instruments that would
provide valuable insights into the nature of large asteroids (400 -
1000 metres in diameter) with different physical and compositional
properties. Low-thrust ion propulsion would be used to rendezvous
with each target. 

ˇ Remote observation of NEOs from Space: A space-based observatory to
carry out remote sensing and detect physical characteristics of NEOs,
such as size, composition and surface properties.

"We now have a number of excellent proposals that are both feasible
and affordable," said Franco Ongaro, head of ESA's Advanced
Concepts & Studies Office.

"These phase A studies by industry and academia, which were completed
in January 2003, provide a valuable framework for developing future
missions. They will now be discussed within the Agency and with ESA's
international partners in order to determine how best to proceed."

LINKS:
ESA NEO studies: http://www.esa.int/gsp/completed/neo/index.htm 
ESA Advanced Concepts Team: http://www.esa.int/gsp/ACT/index.htm


For further information, please contact:
ESA Media Relations Service
Tel: +33(0)1.53.69.7155
Fax: +33(0)1.53.69.7690

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