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Posted on 11/20/2007 7:40:12 PM PST by NormsRevenge
The moon formed after a nasty planetary collision with young Earth, yet it looks odd next to its watery orbital neighbor. Turns out it really is odd: Only about one in every 10 to 20 solar systems may harbor a similar moon.
New observations made by NASA's Spitzer Space Telescope of stellar dust clouds suggest that moons like Earth's are—at most—in only 5 to 10 percent of planetary systems.
"When a moon forms from a violent collision, dust should be blasted everywhere," said Nadya Gorlova, an astronomer at the University of Florida in Gainesville who analyzed the telescope data in a new study. "If there were lots of moons forming, we would have seen dust around lots of stars. But we didn't."
Gorlova and her team detail their findings in today's issue of the Astrophysical Journal.
Violent birth
Shortly after the sun formed about 4.5 billion years ago, scientists think a vagrant planet as big as Mars smacked into infant Earth and ripped off a chunk of our home's smoldering mantle. The rocky, dusty leftovers fell into orbit around our wounded planet, eventually coalescing into the moon we see today.
The scenario is unique among other moons in the solar system, which formed side-by-side with their planet or were captured by its gravity. Gorlova and her colleagues looked for the dusty signs of similar smash-ups around 400 stars, all about 30 million years old—roughly the age of our sun when Earth's moon formed.
Only one of all the stars they studied, however, displayed the telltale dust. Considering the frequency of planetary solar systems, the amount of time the dust should stick around and the window for moon-forming collisions to occur, the scientists were able to peg the frequency of extrasolar bodies that formed like our moon.
The estimate, however, is possibly a generous one.
"We don't know that the collision we witnessed around the one star is definitely going to produce a moon," said study co-author George Rieke, an astronomer at the University of Arizona in Tucson, "so moon-forming events could be much less frequent than our calculation suggests."
Odd moon out?
Planetary scientists like Gorlova and Rieke think infant solar systems can form moons between 10 and 50 million years after a star forms. That only a single star with collision-generated dust could be found in their latest research, the astronomers said, indicates that the 30 million-year-old stars in the study have finished making their planets.
"Astronomers have observed young stars with dust swirling around them for more than 20 years now," said Gorlova, noting that the dust could be collision-derived or primitive planet-forming material. "The star we have found is older, at the same age our sun was when it had finished making planets and the Earth-moon system had just formed in a collision."
While most the our type of moon may be rare, astronomers think there are billions of rocky planets out there with plenty of moons orbiting around them. The upshot for lunar lovers? There could be millions—or billions—of Earth-like moons drifting through the cosmos.
I agree, the Moon was captured. Very short debate about this with RadioAstronomer:
When the Days Were Shorter
Alaska Science Forum (Article #742) | November 11, 1985 | Larry Gedney
Posted on 10/04/2004 1:31:59 PM EDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1234919/posts
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The period when the Earth was Moonless is probably the most remote recollection of mankind. Democritus and Anaxagoras taught that there was a time when the Earth was without the Moon.(1) Aristotle wrote that Arcadia in Greece, before being inhabited by the Hellenes, had a population of Pelasgians, and that these aborigines occupied the land already before there was a moon in the sky above the Earth; for this reason they were called Proselenes.(2)
Apollonius of Rhodes mentioned the time “when not all the orbs were yet in the heavens, before the Danai and Deukalion races came into existence, and only the Arcadians lived, of whom it is said that they dwelt on mountains and fed on acorns, before there was a moon.” (3)
Plutarch wrote in The Roman Questions: “There were Arcadians of Evander’s following, the so-called pre-Lunar people.”(4) Similarly wrote Ovid: “The Arcadians are said to have possessed their land before the birth of Jove, and the folk is older than the Moon.” (5) Hippolytus refers to a legend that “Arcadia brought forth Pelasgus, of greater antiquity than the moon.”(6) Lucian in his Astrology says that “the Arcadians affirm in their folly that they are older than the moon.”(7)
Censorinus also alludes to the time in the past when there was no moon in the sky.(8) ...
The capture of the Moon, like moths flying to a new light, is the dramatic event that killed the dinosaurs.
I don't think we are capable of resolving images, visible or radio frequencies, of stars in other galaxies sufficient to discern the tell-tale wobble of even a binary star much less the wobble of a planet.That is indeed one of the methods used, and it does work.
Such collisions would require large numbers of planetary bodies having formed by accretion with wildly differing orbital shapes... Something that the stellar accretion ring to planet theory does not support... The odds that numerous planet/moon combinations like ours were caused by collisions with cosmic interlopers, planets from outside the stellar system, are also beyond astronomic. First we would have to postulate a free roaming planet that had somehow escaped its own birth star. Then we would have to have sufficient time for this hypothetical impacting planetoid to cross interstellar distances while only moving at non-relatavistic speeds. *Free-roaming planets have in fact been found. Also, the composition of our own gas giants suggests wandering; for that matter, the orbits of some of the moons of the gas giants are suggestive of one or more impacts, or other interactions with an interloper. While it is true that non-relativistic speeds might be involved, the times needed are nowhere near the age of the universe. Rotation of our galaxy takes something like 25 million years. :')
alternatively and more likely, earth’s rings were attracted by the largest pieces in orbit and by the earth. They competed in attracting, sweeping if you will, all the earth orbital matter.
Now, only the moon is left, the ring is gone
I agree it works, Sunken... just not in other galaxies. We are capable of seeing the induced wobble of large Jovian sized planets, and perhaps some smaller ones, in our Galaxy but the resolution to discern even huge stars in other galaxies is extremely limited.
Free-roaming planets have in fact been found.
Found? Or theorized to explain an unexplained observation? Can you provide evidence of these free-roaming planets. I have not seen any such evidence. I know about the micro-lensing phenomena that some have postulated to be "free-roaming planets" but we cannot even demonstrate enough lensing on solar planets to even be sure that we could tell its sign on an object thousands of lightyears away. Some astronomers have not even accepted gravitic lensing as proof of superdense dark stars.
Any free-roaming planets would tend to be moving with their surrounding objects... certainly not counter to the orbital velocity of the galaxy.
In addition, unless we postulate that our free-roaming planet comes only from the nearest stellar systems, we are talking about even further distances and longer times.
Rotation of our galaxy takes something like 25 million years. :')
You're off by an order of magnitude, Sunken... it takes 225-250 million years for one rotation of the Milky Way Galaxy (Galactic Year). That would be the time required for Sol to travel approximately 180 Light Years.
The average distance of any star to Sol is approximately 30,000 light years... at that rate, it would take a free-roaming planet from a star the average distance from us, moving at the orbital velocity of the galaxy (220 km/s at our distance from the center) relative to us toward us, approximately 38 BILLION years to arrive. The Universe is only 18 to 22 Billion years old... of course there are closer stars (a free-roaming planet from Alph-Centauri would take about 6,000 years at that rate... but what force would get it to move at that rate toward us? Gravity?) so it is possible, but the odds are extremely small.
Think about our solar system this way... imagine the sun is the size of a bowling ball... about 8"... in comparison, the earth is about 1/16th of an inch (half the size of a BB) and Jupiter is about 9/10"... Earth would be somewhere on an orbit about 78 feet away from the bowlingball and somewhere on a circle 245 feet around. Jupiter would be 405 feet away from the Bowlingball sun and poor demoted Pluto would be 3/5ths of a mile away. Now, throw several thousand of sand, one at a time, at this model solar system... what are the odds that you would hit the 1/16th inch sized Earth?
I would bet the odds of rolling snake-eyes 10,000 times in a row with honest dice are far larger than the odds of being hit by a extra-solar planet of sufficient mass to create the moon in the scenario given.
I think there is something else at work.
The theory holds that both bodies were in a molten state after the collision.
Molten might not mean hot. The bodies tend to slosh around as if they were liquid because of their size. Even during earthquakes the solid land waves as if liquid and the ground might even liquify altogether allowing buildings to sink. The liquidity of the apparently solid surface is shown clearly by land tides that occur just like ocean tides and the movement up and down is about three feet every day and this without vibration as would be associated with earthquakes of similar motion.
With the Moon's green cheese, we need to find some planetary bread to make a solar sandwich...
You're right, the galactic rotation does take that long, my apologies. My 25 million year figure refers to the Solar System's crossing the galactic plane, and is actually about 33 million years. Shoemaker suggested that the extinction-causing impacts on Earth came about as a direct or (more probably) indirect result of that oscillation.Rogue Planet Find Makes Astronomers Ponder TheoryEighteen rogue planets that seem to have broken all the rules about being born from a central, controlling sun may force a rethink about how planets form, astronomers said on Thursday... "The formation of young, free-floating, planetary-mass objects like these is difficult to explain by our current models of how planets form," Zapatero-Osorio said... They are not linked to one another in an orbit, but do move together as a cluster, she said... Many stars in our own galaxy, the Milky Way, may have formed in a similar manner to the Orion stars, she said. So there could be similar, hard-to-see planets floating around free near the Solar System.
by Maggie Fox
October 5, 2000
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000Sci...290..103Z&db_key=AST
abstract: We present the discovery by optical and near-infrared imaging of an extremely red, low-luminosity population of isolated objects in the young, nearby stellar cluster around the multiple, massive star sigma Orionis. The proximity (352 parsecs), youth (1 million to 5 million years), and low internal extinction make this cluster an ideal site to explore the substellar domain from the hydrogen mass limit down to a few Jupiter masses. Optical and near-infrared low-resolution spectroscopy of three of these objects confirms the very cool spectral energy distribution (atmospheric effective temperatures of 1700 to 2200 kelvin) expected for cluster members with masses in the range 5 to 15 times that of Jupiter. Like the planets of the solar system, these objects are unable to sustain stable nuclear burning in their interiors, but in contrast they are not bound to stars. This new kind of isolated giant planet, which apparently forms on time scales of less than a few million years, offers a challenge to our understanding of the formation processes of planetary mass objects.
I do... but I do not believe the capture came from a free-roaming rogue, I think it is a planet from our own system (not necessarily a "Sol" based system) that we acquired during the break up of the Saturnian System which we were once part.
For a rogue to simply fall into an Earth orbit, it would have to be traveling at a much lower speed than the stellar speeds we were talking about. The current lunar velocity is about 15,500 MPH... far slower than the 490,000 MPH Galactic orbital speed...
Think about our solar system this way... imagine the sun is the size of a bowling ball... about 8"... in comparison, the earth is about 1/16th of an inch (half the size of a BB) and Jupiter is about 9/10"... Earth would be somewhere on an orbit about 78 feet away from the bowlingball and somewhere on a circle 245 feet around. Jupiter would be 405 feet away from the Bowlingball sun and poor demoted Pluto would be 3/5ths of a mile away. Now, throw several thousand of sand, one at a time, at this model solar system... what are the odds that you would hit the 1/16th inch sized Earth?Over how much time / how many passes / how many other interactions (with Jupiter, for example)? Objects in orbit around the Sun can be in a variety of different planes; however, in the ecliptic, odds greatly improved. And I think we have some common ground as to using supposed odds of things happening as evidence of anything.
By the way, our current understanding of the age of the Moon places it about 4 billion years old... makes for even less time for that wanderer to wander about the Galaxy.
I should point out that the current accept cosmology cannot fully account for why there is a plane of the ecliptic... or why the ringed planets have their rings exactly over their equators... gravity alone cannot account for it.
The Cycle of Cosmic Catastrophes:
Flood, Fire, and Famine
in the History of Civilization
by Richard Firestone,
Allen West, and
Simon Warwick-Smith
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