[meteorite-list] Trojan And Other Asteroids, Part Two
From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Sun Jun 26 02:54:56 2005 Message-ID: <42BE50FC.3A93FA41_at_bhil.com> Hi, All, Having trouble posting. If this a duplicate, delete. Sorry In an earlier post, I pointed out that Venus Trojans would be brighter and easier to spot. Since then, I have been pondering that. We're detecting minor minors at a fantastic (to me) rate these days. There's always the problem of collecting more data than you evaluate, stories of yet-unexamined Viking Mars data tapes crumbling to crackles in vaults somewhere because there's no money to pay somebody to look at them for the first time (don't know if it's true). Every detection has to be re-acquired to calculate orbital elements. Is it done often enough that some one would notice that an orbit was a Trojan? Except for when someone occasionally gets a wild hair about searching for Vulcanoids or intra-Mercurial bodies, astronomers do not willingly work the sky near the Sun for obvious reasons: it' difficult, very hard to do, constricted in observing times, no really dark skies, messy, frustrating and probably worthless. And solar telescopes never look away from the bright god they study. Many volunteers search the SOHO images for comets (all of them?) plunging toward the Sun and are finding them by the hundreds while sitting on their butts in front a computer just like I'm doing now. There are LOTS of objects in the inner system coming and going all the time! Yet, when you turn to minor planet lists you see crowds and crowds of stuff outside the Earth's orbit and very little inside it. You could call the inner system "depleted." To me, that doesn't make sense. In countless computer simulations of encounters in the outer system over the decades, most (80%) perturbed objects are ejected from the solar system completely, and some (20%) are sent into the inner system. If 20% of all encounter generated orbit changes send bodies inward and if this persists for the lifetime of the solar system, the inner system should not be "depleted" of objects. Inner system terrestrial bodies have the the millions of craters to prove it just ain't so. That was then. This is now. The inner system bodies we know of rarely have long-term stable orbital dynamics. You can expect most NEA's to last up from a million to ten million years, a fraction of a percent of the age of the solar system. Therefore, the inner system must be continually resupplied to maintain the reservoir. I think that reservoir is larger than we think. We have been deceived by a "selective observer effect." It's hard to search, so we don't search as much, so we don't find, so if we don't find, it ain't there, so we search less, and so on. in a feedback cycle. It was hard to get people to search for NEA's. Then, there's what I call the "LeVerrier-Lescarbault Effect." The great discoverer of Neptune, LeVerrier, was convinced by an amateur astronomer, Lescarbault, that he, Lescarbault, had observed the transit of a small planet with an orbit inside of Mercury's, the planet Vulcan. In retrospect, it's clear that Lescarbault's observation, although possibly real, was vague and imprecise, untimed and not of much use, and his equipment was junk, but LeVerrier jumped on the discovery, in which he believed to his dying day, recalculating the "orbit" and trying to re-acquire it. Don't suppose the lure of being the only man in history with TWO planets to his name had anything to do with that, do you? Since that incident, professional astronomers have a wise and natural reluctance to even think about investigating the inner system for small bodies, understandably, "I'll pass on that." The XIXth century is over-run with numerous discoveries of small inner system bodies never recovered, and with that grade of equipment, transits were about your only chance to detect an inner system minor planet. Is EVERY old observation of this kind just a whacko aberration? Probably not. During the 29 June 1878 solar eclipse, two experienced astronomers, Professor James Craig Watson, director of the Ann Arbor Observatory in Michigan, and Lewis Swift, an amateur from Rochester, New York, both claimed independently to have seen a "planetary" object close to the Sun at totality, about magnitude five or six. These guys were not jerks nor incompetent. Watson was the discoverer of 20 confirmed minor planets (a lot in those days) and Swift was the discoverer of a number of comets some of which you've probably heard of as they bear his name. They knew what they we doing. Both saw a detectable disk, not a bright point. Because their positions for the object differ from each other more than can be accounted for by the Earth distance between Wyoming and Colorado (where they respectively were), that half-degree parallax says to me that they observed a honking big asteroid in the inner system that was actually passing very close to the Earth and only incidentally in line with the Sun at the time of eclipse. Its relative motion could account for some of the parallax, but eclipse totality observing time is very short, not long enough to observe relative motion. Did we have a coincident "near miss"? A number of distinguished XIXth century astronomers saw mysterious solar transits of short duration, which they always interpreted as a body close to the Sun because of it. They had planets on the brain. Finding a planet would make you "immortal." But a short transit is just what you'd expect if a NEA made a daytime close approach to the Earth. By the next night, it would be long gone beyond the magnitude limit of XIXth century equipment. The fact that no Vulcan or Vulcanoid observations were ever repeated or recovered only strengthens the case for a potential NEA close-approach observation. In the famous Lescarbault transit of so-called Vulcan, "an eminent French astronomer, Emmanuel Liais, who was working for the Brazilian government in Rio de Janeiro in 1859, claimed to have been studying the surface of the Sun with a telescope twice as powerful as Lescarbault?s at the very moment that Lescarbault said he witnessed his mysterious transit. Liais, therefore, was 'in a condition to deny, in the most positive manner, the passage of any planet over the sun at the time indicated' (Popular Science, Volume 13, pages 732-735, 1878)." I say, parallax again. The object was real; it just wasn't near the Sun but the Earth! Close enough to be in line with the Sun from France; off to the side from Brazil, 8,000 miles away. In 1970, Henry C. Courten found what he believed to be an intra-Mercurial object or objects in eclipse photos, and hypothesized an intra-Mercurial asteroid belt, the Vulcanoids. The idea was logical enough. Rubble trapped close to the Sun's gravity ain't going nowhere! It was a good enough idea to inspire several searches, but nothing was found, of course. Checking back, I discover they couldn't have found anything smaller than 100 kilometers, anyway. Still looking for a planet, Vulcan size, not asteroids, if you ask me. If there are Vulcanoids, they are not a threat like NEA's. SOHO images contain a number of small anomalous objects that are routinely and thoughtlessly ignored. They aren't comets, so who cares? They show no coma, are often irregular in outline, and much fainter. Gee, wonder what they could be? To better understand my parallax argument, look at it this way. The Sun covers one half degree of the sky; it's almost a million miles across, but it's almost 100,000,000 miles away. An object half the size of Mercury 10,000,000 miles from the Sun, like the imaginary Vulcan, was said to have shown a disk about 1/500 to 1/800th of the size of the Sun's disk. If that object were only ten million miles away from the Earth, instead of 10,000,000 miles from the Sun, it would have only been a 150 kilometer body. Working our way down that scale of things, If that object were only one million miles away from the Earth, it would have only been a 15 kilometer body (Chicxulub). If that object were only 100,000 miles away from the Earth, it would have only been a one mile body (too many of those to even try a name). That's bigger than any bodies we have OBSERVED to have passed within the Moon's distance, but since literally dozens of smaller bodies have done so in the last decade, it's not an impossibility by any means. And in the most fascinating case (to me), if a one mile body were to just barely miss us, not quite grazing the Earth's atmosphere at 150 miles of altitude (boy, you can't get a nearer miss than that!), it would eclipse the Sun COMPLETELY, covering the entire solar disk exactly as the Moon does in a "normal" solar eclipse, but only visible in a very narrow precise path. The duration of totality would be 0.1 to 1.0 second, and the width of the umbral path would be... one mile, same as the asteroid. So, if you're ever out in the open flat land and see a mile-wide shadow like a highway of darkness racing straight toward you, the Sun blink out for a second when it reaches you, and turn to watch a vanishing ribbon of blackness speeding away from you in a straight line, you run and tell somebody, OK? Since the largest sunspots, those over about 120 arc-seconds, or about 6% of the Sun's diameter, are clearly visible to the naked human eye (careful!), an Earth close-approach object transiting the Sun, one about 3 arc-minutes or more in diameter, would be very noticeable, particularly on an overcast day, and since the transit would last some minutes, last long enough to be noticed. There are a small handful of XIXth century anomalous daytime transiting object reports, reported by "ordinary" people, not astronomers, all seen in a single narrow locality but nowhere else, lasting for a few minutes up to twenty minutes, and most describing the dark object not as a round spot, but irregular, "like a fist," a "mountain," or a "potato." (The famous potato strikes again.) Ten close approaches per century by a good sized object is not out of the question if there are more of them than we think there are. Sterling K. Webb ---------------------------------------- Received on Sun 26 Jun 2005 02:53:48 AM PDT |
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