[meteorite-list] Planet V (for Five)

[Sterling K. Webb]

Hi, List,

    With several stories being posted about the new
research on lunar return samples showing that there
was indeed a Late Heavy Bombardment with a sharp
peak after a quiet period, instead of the Final Flurry 
of an ongoing bombardment, I realized that the Planet V
hypothesis put forward several years ago to account
for the LHB also ties in with several other new 
developments.

    The Asteroid Belt "should be" a zone of relatively
similar objects in relatively circular, non-inclined orbits;
that's what ALL the Solar System formation theories 
would predict, despite the differing formation 
mechanisms they propose.

    But, of course the "real" Asteroid Belt isn't like
that. There are a wide variety of compositions, like
iron asteroids (that could never have formed that far
out), dry asteroids, wet asteroids, carbonaceous 
asteroids, differentiated asteroids, non-differentiated
asteroids, asteroids with diamonds, asteroids that smell
like bubble gum... You name it.  In short, every
oddball composition we know from meteorites.

    The SRI published a computer simulation earlier
this year (about which Ron Baalke posted to The List) 
that suggests the Asteroid Zone is full of objects
that formed elsewhere in the Solar System (like iron
asteroids) because they were ALL deflected there from
other parts of the Solar System. It is silent on what
did the deflecting, but the simulations seems to show
that's the only way they could get there

    And, there are asteroid "families" with very distinctive
eccentric and inclined orbits, grouped together. The
"delta-V" required to drive asteroids into those orbits
requires repeated close encounters with a body larger 
than Mars (about 1 to 4 Mars masses). This observation
is decades old, but no one has ever suggested, again,
what did the deflecting, or when.

    Below is a news story about Chambers and Lissauer's
Planet V (for Five) hypothesis, which they offer as an 
explanation for the Late Lunar Bombardment, but it
seems to me that the hypothesis may have "legs," as 
they say, and that the other unexplained conditions
described above offer some confirmatory implications.

    And, if you're looking for other unexplained facts
to tuck into the envelope, there's the anomalous slow,
backward rotation of Venus (a "day" longer than its
"year"), for which repeated close encounters with a 
large body has been suggested as a cause. Planet V?

    And last, there's the mantle-stripping Big Splat 
on Mercury. We've always "assumed" that it took 
place as early as our own Moon-forming Big Impact, 
but it could have happened at 3.8 to 3.9 billion years 
ago instead, the final outcome of Planet V's rogue 
career. Guess we have to wait for that Mercury 
Sample Return Mission to find out...

    Here's the only Chambers paper on the hypothesis
that I could get to, for free anyway:
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1093.pdf

    There's an Australian paper that tries to duplicate
the results of  Chambers and Lissauer, but can't.
http://eo.ucar.edu/staff/dward/sao/dward617paper.pdf

    Its flaw is that it makes Planet V a puny little
thing, about 5 to 8 times too small to do the job.
But then, so does Chambers, because he wants 
Planet V to end up crashing into the Sun, a silly 
notion whose attractions I am blind to. I like the 
Big Splat.

    But I understand his problem. If you're going 
to stick another planet in the Solar System to 
account for all these things, why, you have to get rid
of it somehow since it doesn't seem to be around 
any more!

    Mercury makes a perfectly good "hit man."


Sterling K. Webb
----------------------------------------------------------

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

Long-Destroyed Fifth Planet May Have Caused 
Lunar Cataclysm, Researchers Say 
By Leonard David, Senior Space Writer
posted: 03:00 pm ET, 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."

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