[meteorite-list] Long-Destroyed Fifth Planet May Have Caused Lunar Cataclysm, Researchers Say

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:30 2004
Message-ID: <200203182117.NAA24607_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/solarsystem/fifth_planet_020318.html

Long-Destroyed Fifth Planet May Have Caused Lunar Cataclysm, Researchers Say
By Leonard David
space.com
18 March 2002
              
HOUSTON, TEXAS -- Our solar system may have had a fifth terrestrial
planet, one that was swallowed up by the Sun. But before it was
destroyed, the now missing-in-action world made a mess of things.

Space scientists John Chambers and Jack Lissauer of NASA's Ames
Research Center hypothesize that along with Mercury, Venus, Earth, and
Mars -- the terrestrial, rocky planets -- there was a fifth terrestrial
world, likely just outside of Mars's orbit and before the inner
asteroid belt.

Moreover, Planet V was a troublemaker.

The computer modeling findings of Chambers and Lissauer were presented
during the 33rd Lunar and Planetary Science Conference, held here
March 11-15, and sponsored by NASA and the Lunar and Planetary
Institute.

It is commonly believed that during the formative years of our solar
system, between 3.8 billion and 4 billion years ago, the Moon and Earth
took a pounding from space debris. However, there is an on-going debate
as to whether or not the bruising impacts tailed off 3.8 billion year
ago or if there was a sudden increase - a "spike" -- in the impact rate
around 3.9 billion years ago, with quiet periods before and afterwards?

This epoch of time is tagged as the "lunar cataclysm" - also a wakeup
call on the cosmological clock when the first evidence of life is
believed to have appeared on Earth.

The great cover-up

Having a swarm of objects clobbering the Moon in a narrow point of time
would have resurfaced most of our celestial next door neighbor,
covering up its early history. Being that the Moon is so small, Earth
would have been on the receiving end of any destructive deluge too.

Moon-walking astronauts brought back a cache of lunar material. Later
analysis showed that virtually all impact rocks in the "Apollo
collection" sported nearly the same age, 3.9 billion years, and none
were older. But some scientists claim that these samples were "biased",
as they came from a small area of the Moon, and are the result of a
localized pummeling, not some lunar big bang.

There is a problem in having a "spike" in the lunar cratering rate.

That scenario is tough to devise. Things should have been settling
down, according to solar system creation experts. Having chunks of
stuff come zipping along some hundreds of millions of years later out
of nowhere and create a lunar late heavy bombardment is a puzzler.

If real, what were these bodies, and where were they before they
scuffed up the Moon big time? The answer, according to Chambers and
Lissauer, might be tied to the the
Planet V hypothesis.

"The extra planet formed on a low-eccentricity orbit that was
long-lived, but unstable," Chambers reported. About 3.9 billion years
ago, Planet V was perturbed by gravitational interactions with the
other inner planets. It was tossed onto a highly eccentric orbit that
crossed the inner asteroid belt, a reservoir of material much larger
than it is today.

Planet V's close encounters with the inner belt of asteroids stirred up
a large fraction of those bodies, scattering them about. The perturbed
asteroids evolved into Mars crossing orbits, and temporarily enhanced
the population of bodies on Earth-crossing orbits, and also increased
the lunar impact rate.

After doing its destabilizing deeds, Planet V was lost too, most likely
spinning into the Sun, the NASA team reported.

The temporary existence of more than 4 planet-sized bodies in the inner
Solar System is consistent with the currently favored model for the
formation of the Moon. Work by Chambers and Lissauer also supports the
view that our Moon is a leftover of a massive collision between Earth
and a Mars-sized body 50 million to 100 million years after the
formation of the Solar System.

Striking view

Wendell Mendell, a planetary scientist here at NASA's Johnson Space
Center, said the new theory is intriguing.

"This idea and others within the last few years show that the Solar
System is filled with all sorts of gravitational resonances...that a
lot of potential orbits in the Solar System are chaotic and unstable,"
Mendell told SPACE.com. "My sense is that this is a new idea. It's
another thing to throw into the pot that's not totally crazy."

The work suggests there's a match up in timing, Mendell said, with
asteroids striking the Moon and causing the effects that are seen in
the dating of Apollo lunar rocks.

"By thinking that the Solar System was really quite different in a
major way with an extra inner planet, we might be able to develop some
sort of self-consistent scenario that explains a lot of things. But all
this is at the very early stages now," Mendell said.

"We're moving into a really new regime," Mendell added, "where the
Solar System is not a static dynamic place from day one to now. It
really might have had some nuances and synchronicities associated with
it that we have not really tried to exploit before."

It takes a drill hole Setting the early Solar System and lunar history
record straight means going back to the Moon.

"The Moon is still the keystone to our understanding of the Solar
System," NASA's Mendell said.

That too is the view of Apollo 17 astronaut, Harrison "Jack" Schmitt.
Getting back to the Moon to sort out the real story is a must, he said.

"You're going to have to be very, very specific on what sites you go to
collect new samples," Schmitt told SPACE.com. "It may be very difficult
to get an answer without using missions to fairly large impact craters
that penetrate through the ejecta. Those impacts are sort of a drill
hole into the lunar crust," he said.

Dating service

Places on the Moon where older, large basins have deposited ejecta are
ideal research zones, Schmitt said. Digging into such sites could yield
impact glass formed by basins perhaps dating older than 3.9 billion
years old, he said.

Just taking spot samples -- say from the Moon's South Pole Aitken basin
-- could be risky, in terms of uncovering the Moon's rocky history,
Schmitt said. Such a huge area would take multiple robotic or human
exploration missions, each with significant roving abilities.

Also known as the "Big Backside Basin," Aitken is the largest impact
crater on the Moon, and one of the biggest in the Solar System.

For the near term, sets of low-cost, mini-robotic landers carrying
specialized gear would be ideal in opening up the Moon to further
exploration, Schmitt said.

"Numbers of targeted missions could get a lot of great information on
some of these fundamental questions that we still haven't been able to
answer," Schmitt said.

Getting back to the Moon with a settlement for resource exploitation is
another step forward. From such a site, human explorers can survey
various lunar locales - even the Moon's side that we Earthlings never
see, Schmitt said. "Then we can do the kind of thing that Apollo did
for the near side of the Moon," he said.
Received on Mon 18 Mar 2002 04:17:17 PM PST