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 Space.com
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.
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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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