[meteorite-list] Deep Impact Mission Could Help Earth's Defence Against Space Rocks

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jul 4 20:16:14 2005
Message-ID: <200507050015.j650FQ617616_at_zagami.jpl.nasa.gov>

http://www.terradaily.com/news/deepimpact-05c.html

Deep Impact Mission Could Help Earth's Defence Against Space Rocks
AFP
June 30, 2005

Paris (AFP) - An extraordinary US mission to whack a passing comet may
indirectly provide a windfall for guardians monitoring any space rocks
that could hit Earth.

The NASA probe Deep Impact is to eject a 372-kilo (820-pound) projectile
that on Monday is scheduled to smack into Comet Tempel 1 as the heavenly
wanderer flies past Earth at a great distance.

The collision, occurring at 37,100 kph (23,000 mph, 6.3 miles per
second) could gouge a crater as big as a football stadium and spew out a
mass of cometary gas and dust, eagerly recorded by telescopes, radars
and spectrometers.

The goal behind the 333-million-dollar (275-million-euro) mission is to
uncover the inner secrets of one of the Solar System's strangest phenomena.

Comets are believed to comprise primitive material created in the early
Solar System and, say some experts, may hold organic molecules that may
have been the chemical building blocks for creating life on Earth.

But comets can also be bringers of death, too.

The long reign of the dinosaurs is believed to have been snuffed out
some 65 million years ago when a comet smashed into modern-day Mexico,
kicking up a pall of dust that obscured the Sun and chilled the climate.

Scientists involved in Near Earth Objects (NEOs) -- comets and asteroids
that may pose a threat to our home -- say Deep Impact could yield
precious data.

"The more we know the better, and there might be some surprises in this
mission," David Harris, chairman of a NEO advisory panel set up by the
European Space Agency (ESA), told AFP.

"We might learn some something crucial about the structure of comets
that could help us in the event that we faced something like this."

The risks posed by NEOs must be put into context, for the probability of
any collision is extremely remote.

A stepped-up US-led effort to scour the skies for this threat has not
yielded any prospect of a hit, although several rocks could make
near-misses in coming decades.

But any collision would carry astronomical costs. Smaller objects
measuring two or three hundred metres (yards) across could devastate a
region or trigger a tsunami, while larger ones could be climate-crushers.

In this respect, "Deep Impact", the 1998 sci-fi movie about a doomsday
comet, was not wrong, and the threat from NEOs is gaining credibility
among politicians.

Only a fraction of potentially risky asteroids -- the rocks that circle
the Sun between Mars and Jupiter and which can sometimes be jostled into
a different orbit -- has been identified and their orbits mapped.

And nothing is known about types of comets, mercifully rare, that take
centuries to orbit the Sun. Never spotted before, these could hurtle out
of almost nowhere, giving mankind very little time to react.

As to what that response should be, two main options present themselves:
to send a space tug to gently deflect the rock to a different trajectory
or to blow the brute up, Hollywood-style.

Both are dependent on knowledge about the density and structure of the
comet or asteroid -- and this is where Deep Impact comes in.

"We don't really know whether most asteroids are mostly solid, riddled
with cracks or voids, or made up of lots of loose rubble," the British
magazine New Scientist said last week, a comment that also applies to
comets, which are likened to "dirty snowballs" and are usually bigger
than asteroids.

"Any attempt to push one out of the way, whether with rocket blasts or
bombs, might shatter it instead and just lead to even more impacts."

Former Apollo astronaut Rusty Schweickart last month lobbied the US
Congress to consider funding a scouting mission or even a deflection
mission to 2004 MN4, a 320-metre (1,000-feet) asteroid that raised an
alarm last December.

Initial calculations suggested a risk that 2004 MN4 could strike Earth
on April 13 2029, but this was downgraded to an extremely close shave --
a miss by about 36,000 kms (22,600 miles), which is inside the orbits of
some geostationary satellites.

But the tug effect of Earth's gravity during this fly-by means that 2004
MN4's orbit may be slightly altered, and an impact seven years later in
2036 cannot be ruled out.
Received on Mon 04 Jul 2005 08:15:26 PM PDT