- 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.
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- 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.
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- Moreover, Planet V was a troublemaker.
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- 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.
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- 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?
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- 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.
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- The great cover-up
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- 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.
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- 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.
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- There is a problem in having a "spike" in the
lunar cratering rate.
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- 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.
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- 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.
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- "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.
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- 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.
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- After doing its destabilizing deeds, Planet V was lost
too, most likely spinning into the Sun, the NASA team reported.
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- 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.
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- Striking view
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- Wendell Mendell, a planetary scientist here at NASA's
Johnson Space Center, said the new theory is intriguing.
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- "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."
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- 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.
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- "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.
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- "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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- It takes a drill hole Setting the early Solar System
and lunar history record straight means going back to the Moon.
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- "The Moon is still the keystone to our understanding
of the Solar System," NASA's Mendell said.
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- 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.
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- "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.
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- Dating service
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- 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.
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- 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.
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- 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.
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- 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.
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- "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.
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- 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.
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