Energy Needed to Divert a Life-Extinction Event Asteroid

     Long-Destroyed Fifth Planet May Have Caused Lunar Cataclysm,  Researchers Say

     Muller's Nemesis theory -- that our Sun has a companion star responsible for recurring
     episodes of wholesale death and destruction here on Earth

             Recent Crash Created Youngest Known Asteroid Family

                               By Robert Roy Britt   Senior Science Writer for
                                                   posted: 02:00 pm ET, 12 June 2002

     A few million years ago, two asteroids collided in interplanetary space. The smaller, aggressor rock was
pulverized to dust as it shattered the larger target rock into millions of small and large fragments which
were violently dispersed in all sorts of new directions.  Today astronomers said they have traced the paths
of a handful of these fragments back to their origin, piecing together what is now the most well documented
and recent example of asteroid destruction and creation. The work will provide a wealth of new information
about rocks from space and the overall development of the solar system, including Earth.
   It could also help scientists model what would happen if they ever try to blow  up an asteroid that is heading
toward our planet.   Fresh faces Asteroids were originally formed more than 4 billion years ago, during a chaotic
time when the planets developed around a new Sun.
   Since then most of them -- including the handful that have been visited by spacecraft -- have undergone
multiple impacts and are mere vestiges of their  parent bodies. Some are piles of rubble, the result of many
impacts. Most are scarred and pitted, their courses altered many times over, their origins difficult to trace.
   About 20 asteroid families, however, were created recently enough to be identified as having common origins.
Now David Nesvorny and his colleagues at the Southwest Research Institute  (SwRI) have identified 39 known
asteroids as debris from a collision that took place practically yesterday in the history of the solar system. These
new creations are expected to be largely unaltered since their violent generation  just 5.8 million years ago.
The largest remnant is an asteroid named Karin, roughly 12.5 miles wide (20 kilometers). The cluster of boulders,
which all exhibit similar composition, has  now been given the same name.  The Karin cluster was born when an
asteroid estimated to be 1.9 miles wide  (3 kilometers) slammed into a 16-mile-wide (25 kilometers) rock at about
11,180 mph (5 km/s), Nesvorny explained. The target rock was 600 times more massive than the smaller one.
   At least hundreds and perhaps thousands of fragments larger than 0.62 miles (1 kilometer) were produced,
Nesvorny said. An asteroid this large could cause a global catastrophe if it met up with Earth. The collision also
generated up to 100 million fragments as big as a football field, he said. Such rocks could  destroy a city.
Preliminary observations also found space dust that appears to  be associated with the crash.  The results will be
published in the June 13 issue of the journal Nature.
                                                                 Glimpsing our past and future
  University of Maryland researcher Derek Richardson, who was not involved in the study, said it offers
"unprecedented insight into the dynamics of asteroid collisions-- and hence into how the planets of the solar
system formed."
                                                                               Here's why:
         Earth and the other rocky planets had humble beginnings as rocks, essentially  asteroids that grew by gentle
collisions to become planets shortly after the  Sun was born.   Back in those days, before Jupiter was fully formed,
asteroid collisions were  more frequent. They also
tended to be gentler, however, because most of the material was orbiting the nascent Sun in the same direction.
Rocks could join forces and grow into larger objects, eventually able to absorb almost any punch and continue on as
a planet.
        When Jupiter evolved into the massive object it is now, it began to fling asteroids on wilder courses, thereby
generating more catastrophic collisions.  What had been a freeway with well-designed onramps that led to mild fender
benders gained intersections with no stop lights that forced some serious  crackups.  The more violent collisions put a
lid on further planet formation among all  but the most stout objects -- the four that became Mercury, Venus, Earth
and  Mars. [Most astronomers believe a Mars-sized object once hit Earth. The result? Our  Moon was forged during
24 hours of chaos. And yet Earth had enough bulk to hang in there.]
           Richardson, who wrote a review that is also published in Nature, said the  Karin cluster "will no doubt be the
focus of attention for the asteroid  community for some time" and is a compelling target for a space mission.
Asteroids as small as Karin cannot be photographed or studied in detail any other way.  Because the family-building
crash occurred relatively recently, Richardson  said, "many erosional and weathering processes thought to occur on
asteroid surfaces may not have had time to erase the tell-tale signatures of the  break-up event."
                                                                       The Bruce Willis factor
  The cluster could also serve as a laboratory for scientists bent on blowing up space rocks that might threaten Earth.
Most asteroids orbit the Sun in a belt between Mars and Jupiter. Astronomers already knew the objects sometimes
collide and send fragments on new trajectories around the Sun. A few fragments, large and small, can be gravitationally
booted (by Jupiter) or lured (by the Sun) into the inner solar  system where they cross the path of Earth's orbit.
That's when they become dangerous, of course.    Some researchers have suggested that if an asteroid is ever found
to be on a collision course with our planet, a bomb or missile might be used to destroy or  deflect it. But since the idea
hasn't been tested, no one knows how an  asteroid might come apart. It's possible that the fragments would end up
doing more harm than a single object, experts say.    "This event may teach us about how asteroid material breaks up
when an energetic impact and explosion occurs," Nesvorny said. The study team also included William F. Bottke Jr,
Luke Dones & Harold F. Levison, all of the SwRI, which is in Boulder, Colorado.

                 Researchers Say Asteroid Impact Could Alter Climate
                                    By Associated Press   posted: 11:44 am ET   26 June 2002

  ALBUQUERQUE (AP) _ Here's the scenario: An asteroid slams into Earth, kicking up a huge plume of debris that
settles into a disk around the planet, like the rings of Saturn.    The ring's massive shadow chills the tropics and sends
Earth into a  100,000-year freeze.   University of New Mexico climate researcher Peter Fawcett has found  evidence
that something like that might have happened 35 million years ago during the Eocene epoch. Rocks from that time show
a layer of asteroid debris, followed by evidence of a 100,000-year cold spell.
   So Fawcett and Sandia National Laboratories physicist Mark Boslough believe scientists trying to understand the
Earth's hot and cold spells need to consider rings.  Occasional asteroids hitting Earth just right could kick up a disk
which could stick around long enough to cause major climate changes, the scientists  suggest in a research paper to
be published in the Journal of Geophysical Research.  The pair used a computer simulation of Earth's climate to show
what might  happen if Earth had a Saturn-like ring.
   Fawcett said similarities between the computer simulation and the Eocene cold spell are not proof of anything, but
the similarities suggest a ringworld is worth considering.  That one particular event may or may not have been a ring,
he said. But everything in it is consistent.  The idea came from Boslough, a physicist who has spent much of his career
studying what happens when asteroids hit.  The giant gas planets in the outer solar system _ Jupiter, Saturn, Neptune
and Uranus _ have rings.  You've got nine planets, and four of them have rings of some kind,  Boslough said.  He had
worked with Fawcett to modify climate simulation computer  programs to run on Sandia's supercomputers, so using
those programs to test the ring hypothesis seemed logical.
  Boslough ran the simulation, plugging in data about a hypothetical ring blocking the sun. He turned the results over
to Fawcett, who uses computer simulations and field studies to try to understand changes in the climate of ancient
Earth.  Fawcett's maps show cold spells in the tropics.  If you've got less heat in the tropics, there's less to export
to the poles,  Fawcett said.  Beneath the shadow cast by the ring, average temperatures in the Sahara desert drop
below freezing. Cold spells spread quickly across the planet, lowering the global average temperature by nearly 20
degrees Fahrenheit.  Ice spreads across the Bering Strait and reaches up from Antarctica to  Australia.
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