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How special is the Solar System? (Forwarded)
The next nearest star 4.3 light years away, Alpha Centuri A is a million
miles across or 1,227 times the size of our sun. It could have a very large solar system. Assuming the galaxy is 100,000 light years across go in to it from here about 25,000 light years (halfway to the center) and the stars are much closer together making solar system planets also close together.There must be billions of planets in this galaxy alone. No matter how they are formed there has to be millions of similar types and many binary star systems and mulit-star systems. I think the count is roughly 100 billion stars in this galaxy. Now think of 125 billion galaxies estimated by Hubble and you see very many stars and planets. "Andrew Yee" wrote in message ... Royal Astronomical Society Press Notice Issued by Dr Jacqueline Mitton, RAS Press Officer jmitton -at- dial.pipex.com tel: +44 (0)1223-564914 CONTACTS Dr Martin Beer University of Leicester, UK Tel: +44 (0)116 2231802 Email: Prof. Andrew King University of Leicester, UK Tel: +44 (0)116 2522072 Email: Dr. Mario Livio Space Telescope Science Institute, USA Tel: +1 410 338 4439 Email: Dr. Jim Pringle University of Cambridge, UK Tel: +44 (0)1223 337513 Email: ************************************************** ************ Date: 3rd August 2004 PN04-30 HOW SPECIAL IS THE SOLAR SYSTEM? On the evidence to date, our solar system could be fundamentally different from the majority of planetary systems around stars because it formed in a different way. If that is the case, Earth-like planets will be very rare. After examining the properties of the 100 or so known extrasolar planetary systems and assessing two ways in which planets could form, Dr Martin Beer and Professor Andrew King of the University of Leicester, Dr Mario Livio of the Space Telescope Science Institute and Dr Jim Pringle of the University of Cambridge flag up the distinct possibility that our solar system is special in a paper to be published in the Monthly Notices of the Royal Astronomical Society. In our solar system, the orbits of all the major planets are quite close to being circular (apart from Pluto's, which is a special case), and the four giant planets are a considerable distance from the Sun. The extrasolar planets detected so far -- all giants similar in nature to Jupiter are by comparison much closer to their parent stars, and their orbits are almost all highly elliptical and so very elongated. "There are two main explanations for these observations," says Martin Beer. "The most intriguing is that planets can be formed by more than one mechanism and the assumption astronomers have made until now -- that all planets formed in basically the same way -- is a mistake." In the picture of planet formation developed to explain the solar system, giant planets like Jupiter form around rocky cores (like the Earth), which use their gravity to pull in large quantities of gas from their surroundings in the cool outer reaches of a vast disc of material. The rocky cores closer to the parent star cannot acquire gas because it is too hot there and so remain Earth-like. The most popular alternative theory is that giant planets can form directly through gravitational collapse. In this scenario, rocky cores -- potential Earth-like planets -- do not form at all. If this theory applies to all the extrasolar planet systems detected so far, then none of them can be expected to contain an Earth-like planet that is habitable by life of the kind we are familiar with. However, the team are cautious about jumping to a definite conclusion too soon and warn about the second possible explanation for the apparent disparity between the solar system and the known extrasolar systems. Techniques currently in use are not yet capable of detecting a solar-system look-alike around a distant star, so a selection effect might be distorting the statistics -- like a fisherman deciding that all fish are larger than 5 inches because that is the size of the holes in his net. It will be another 5 years or so before astronomers have the observing power to resolve the question of which explanation is correct. Meanwhile, the current data leave open the possibility that the solar system is indeed different from other planetary systems. NOTES 1. Currently around 100 extrasolar planets are known which have been detected through the wobble of their host stars caused by the motion of the planets themselves. 2. The paper has recently been accepted by the Monthly Notices of the Royal Astronomical Society but no publication date has yet been set. --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.732 / Virus Database: 486 - Release Date: 7/29/2004 |
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How special is the Solar System? (Forwarded)
Rodney Kelp wrote: [Forwarded press release] HOW SPECIAL IS THE SOLAR SYSTEM? On the evidence to date, our solar system could be fundamentally different from the majority of planetary systems around stars because it formed in a different way. If that is the case, Earth-like planets will be very rare. If I was an astronomer, I'd be very wary of making this kind of statement. They've almost always proved wrong in past. Given that we can't detect Earth size planets yet, nor are very good at finding multi-year orbit big planets, this is just pure speculation. And this type of speculation, that the Earth, Sun, or solar system is in some way special, has a very bad track record. The principle of mediocrity applies here (assume we are average unless there is some strong evidence against it), and there is no evidence against it yet. Lou Scheffer |
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How special is the Solar System? (Forwarded)
"Alain Fournier" wrote in message ... wrote: Rodney Kelp wrote: Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. I suspect we've too few samples to draw any real conclusions. I remember talking to an astronomer about extra-solar planets in the early 90's and he was not then prepared to say they existed at all because the data was too flimsy. Given the size and scope, Earths might be rare but I do find it hard to believe they are unique. Dave |
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How special is the Solar System? (Forwarded)
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How special is the Solar System? (Forwarded)
"Alain Fournier" wrote in message ... Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. Keep in mind that most of the techniques used are more LIKELY to find that sort of system than ours. Mostly they focus on the wobble of a star, a star with a Jupiter class planet close in will have a more easily detectable wobble than one further out, for two reasons: 1) Mass closer causes a larger effect. 2) Shorter orbit causes wobbles more often. Alain Fournier |
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How special is the Solar System?
"How special is the Solar System?" by M. E. Beer1.,
A.R. King1, M. Livio2 and J. E. Pringle2 is posted at: http://arxiv.org/pdf/astro-ph/0407476 MY COMMENT The high eccentricity of the extraterrestrial gas giants implies that all or nearly all extraterrestrial planets have eccentric orbits and that solar system is uncommon. In addition to the nearly circular orbits (except for Pluto), the solar planets are almost evenly distributed as predicted by the Titius-Bode Law. The Titius-Bode Law also works for moons orbiting solar planets, but does not work well for Neptune and Pluto: http://astrosun2.astro.cornell.edu/a.../bodes_law.htm Apparently the solar system accretion disk was not disturbed by interlopers when planets and moons formed 4.5 billion years ago, except for the most distant planets: Neptune and Pluto. We still do not know if planetary orbits are inherently unstable. It seems that planetary systems having many planets should be less stable than planetary systems having few planets. The absence of massive bodies in the middle of the solar system (known as the main asteroid belt) may have stabilized the solar system. If planetary orbits are inherently unstable than solar system is uncommon and SETI is a waste of time. Simple forms of life may survive on a somewhat unstable planet, but they cannot create a technological civilization. We need better computer simulations of orbital stability -- these simulations are more important than all the microwave SETI research. PS. I wonder if the Moon (Luna) acts like a vacuum cleaner in a sense that it hurls deadly asteroids away from the Earth. __________________________________________________ ______________ RELATED ARTICLES Computer simulations of orbital stability are difficult. For example, the following paper is based on simulations made on a supercomputer having 128 processors, and yet it neglects possible inclinations as well as planetary systems having more than 3 planets: Stability of Terrestrial Planets in the Habitable Zone of Gl 777 A, HD 72659, Gl 614, 47 Uma and HD 4208 http://arXiv:astro-ph/0403152 Excerpt from "The Stability Of The Orbits Of Earth-Mass Planets In And Near The Habitable Zones Of Known Exoplanetary Systems" by Barrie W Jones, David R Underwood, P Nick Sleep, http://www.astrophys-assist.com/educate/cgino617.pdf: "We have shown that Earth-mass planets could survive in variously restricted regions of the habitable zones (HZs) of most of a sample of nine of the 93 main-sequence exoplanetary systems confirmed by May 2003. In a preliminary extrapolation of our results to the other systems, we estimate that roughly a third of the 93 systems might be able to have Earth-mass planets in stable, confined orbits somewhere in their HZs." This is a poor quality article. It does not explain how they calculated the orbital stability. Excerpt from "Dynamical Stability and Habitability of a Terrestrial Planet in HD74156" by M. Colleen Gino, http://www.astrophys-assist.com/educate/cgino617.pdf: "The dynamical stability of the system must be taken into account as well, particularly in light of the impact that large planets can have on the orbit of the terrestrial planet. For a terrestrial planet to remain habitable, there is a dynamical requirement that other planets in the system don’t gravitationally perturb the planet outside of its habitability zone. In a recent study involving 85 of the known extrasolar planetary systems, Menou and Tabachnik (2003) found that more than half of these systems, primarily those with distant eccentric giant planets, are not likely to support terrestrial planets and are therefore dynamically inhabitable. Marcy and Butler (2000) give similar evidence for the likelihood of terrestrial planets to be scattered gravitationally from the high eccentricity of Jupiter-like planets that exist between 2 – 3 AU. Under such circumstances the circular orbits and the long term survival of terrestrial planets is not guaranteed." |
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How special is the Solar System? (Forwarded)
Dave O'Neill dave @ nospam atomicrazor . com wrote:
"Alain Fournier" wrote in message ... wrote: Rodney Kelp wrote: Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. I suspect we've too few samples to draw any real conclusions. I remember talking to an astronomer about extra-solar planets in the early 90's and he was not then prepared to say they existed at all because the data was too flimsy. Umm... Earth style planets are coupe of orders o magnitude what we can detect. Presently it would probably have to massively collide with something for us to detect. This is about to change in not too distant fture so peple saying such things now is particularily odd. Given the size and scope, Earths might be rare but I do find it hard to believe they are unique. It depdends on what you mean by "Earths" - given that this system has 2 2/3-s, I don't really see why they should be rare. Dave -- Sander +++ Out of cheese error +++ |
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How special is the Solar System?
Here is the most far-fetched speculation I have ever made:
HOW WE BECAME THE FIRST INTELLIGENT SPECIES IN THE UNIVERSE 4.5 billion years ago an accretion disk formed around the young Sun. The accretion disk had uniform density except low density in its center. When planets formed, the center became the main asteroid belt. The absence of large mass in the main asteroid belt divided the solar planets into two nearly isolated planetary systems. The separation stabilized planetary orbits. Stable, nearly circular planetary orbits are rare outside the solar system. They are very important because they ensure stable climate which is necessary for advanced forms of life. ...quick fast forward... About 4 billion years ago two planets collided and were transformed into the Earth and its Moon. The young Earth was pelted with debris produced by the collision. When the debris entered the atmosphere, it broke into dust which fell into primordial oceans and was transformed into clay minerals. The primordial oceans were hot and covered with a thick layer of hydrocarbons. Clay crystals floated on the surface of the oceans due to surface tension. These crystals were alive and they were our ancestors. They bred when they broke into smaller crystals and they died when they sank. Their lifestyle was "survival of the weakest." The weakest crystals broke easily, so they bred faster than strong crystals, and they did not sink because their small size kept them afloat due to the surface tension. The weakest clay crystals were microscopic tubes with helical defects. The surface tension attracted nucleotides into the tubes. The helical defects polymerized the nucleotides into RNA chains. These long, strong RNA chains pulled the tubes apart, thereby breaking them and breeding them. ...quick fast forward... Natural bush fires are common in periodically dry habitats. From 2.9 million to 2.4 million years ago Africa was relatively dry, but not as dry as it is today. South and east Africa and Sahara were covered with savanna. The dry period coincides perfectly with the existence of Australopithecus africanus. This hominid lived in dry african woodlands surrounded by grasslands. At present time July is the driest month on the Mediterranean coast of Africa. 2000 kilometers south, in southern parts of Mali, Niger, Chad, and Sudan, July is the wettest month. South Africa has the same wet/dry weather pattern: June is the wettest month in Kaapstad but it is the driest month in Johannesburg. If the same weather pattern existed in the past, Sahara and south Africa were ravaged by natural bush fires. Large fires suppress rain, so they can burn for a very long time. In some years favorable winds must have spread bush fires in these zones for several weeks -- it was only natural for the apiths to walk in front of the fire, scavenging fried carcasses, and shoo the competing birds. With a little artificial help the fires followed the dry season and burned for thousands of years. Australopithecus africanus fossils abound with carbon-13. This means that either they ate large quantities of carbon-13 enriched foods such as grasses and sedges, or they ate animals that ate these plants, or both. Grasses have large quantities of silica crystals which scratch tooth enamel. Fossil teeth of the Australopithecus africanus do not have scratches compatible with eating grasses and they do not have sharp edges that can cut raw meat. Australopithecus africanus could not eat sedges because sedges grow in wet places only. This means that Australopithecus africanus ate cooked meat, probably snakes and lizards killed by wildfires. Australopithecus afarensis was a bipedal hominid and immediate ancestor of the Australopithecus africanus. It inhabited dry bushland, riparian woodland, probably with seasonal floodplains, and riverine forest habitats. Australopithecus afarensis could not sleep on trees because its hands were too weak, and its feet did not grasp well. It was vulnerable to predators at night unless it slept inside a shelter. Chimps make tree nests, so the idea of more intelligent australopithecines making shelters is not far fetched. The shelter was probably just a pile of sticks on the ground with large cavity in its center. The shelter was a safe hiding place, so a lone apith could forage in the vicinity of the shelter and exploit its low density food sources, such as the gallery forest. When a lion prowled the gallery forest, the apiths screamed "danger" and retreated into the shelters. A gallery forest surrounded by a desert was a perfect habitat because there were no competitors and no predators. Some of the shelters were destroyed by natural bush fires. As the apiths learned how to protect their shelters from the fires, they understood how fire works. Perhaps the firestick farming was invented by a subspecies of Australopithecus afarensis which evolved into the Australopithecus africanus. The migrating Australopithecus africanus did not have time to make the shelters, so it had to sleep in the trees. This explains its ape-like features: curved hand and foot bones, short legs, divergent big toes, and upward oriented shoulder joints. So far the Australopithecus africanus fossils were found only in east and south Africa, but east Sahara was also good habitat for the migrating fire apes. In Egypt the lowest level of Nile is in April and May, while the highest level is in September (Asuan) and October (Cairo). Low water level is attractive to hunting hominids because it concentrates prey animals in a small area and it dries up reeds and grasses. The fire apes migrated north in the spring along the Nile River. They had to return to south Sahara in the fall. Microwave images of Sahara taken by satellites show dry, ancient bed of a river that flowed through the center of Sahara in the south-west direction. The lowest level of water in this river was in late summer or fall. This is exactly what the fire apes needed to migrate to south Sahara in the fall. The fire apes followed the dry season as they migrated counterclockwise around the present day Chad. What tools did the fire apes use? Their most difficult task was spreading the fire. They were not smart enough to start a fire, so they must have invented some ways of transporting it. A single stick taken from the fire does not burn longer than a minute. A bundle of parallel, long sticks or reeds (like fasces) burns much longer. Hollow bones could also be used to transport fire. There are biological arguments in favor of the fire ape theory: - We cannot eat red meat unless it is cooked or ground. - We have sweat glands. Sweat mixed with soot protected the fire apes from the fires. - The smell of fire is probably offensive to the sensitive olfactory organs of the wild animals, but we tolerate it so well that some people inhale smoke for fun. - People, including hunters, have weak sense of smell. - Cooked meat is devoid of parasites, so it is safe to eat. - Playing with fire is dangerous -- this explains why we are the only species having Homo level of intelligence. - Humans have eyelashes, but they are not well adapted to life in a desert, so their eyelashes have different purpose than camel's eyelashes. - Broad nasal aperture of Australopithecus africanus and external nose of genus Homo may indicate environment polluted with dust or smoke. |
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How special is the Solar System? (Forwarded)
Alain Fournier wrote:
Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. No - its just that that type of objects and star systems are what we can detect best so of course they are most numerous. Oh, and even with a hot super-Jupiter you could get terrestrial planets in habitable zone given favourable presence of smaller gas giants. Alain Fournier -- Sander +++ Out of cheese error +++ |
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How special is the Solar System? (Forwarded)
Sander Vesik wrote: Alain Fournier wrote: Yes there is evidence against it. The evidence isn't very strong but we are now getting some serious data on the matter. Well the evidence is somewhat strong that our solar system is fundamentally different from the majority of planetary systems around stars. It is much weaker about Earth-like planets being very rare. Most planets found to date are Jupiter sized or bigger in an elliptical orbit with periapsis less than 1 AU. If Jupiter had an elliptical orbit with periapsis less than 1 AU, then Earths orbit wouldn't be stable and Earth wouldn't be. No - its just that that type of objects and star systems are what we can detect best so of course they are most numerous. Oh, and even with a hot super-Jupiter you could get terrestrial planets in habitable zone given favourable presence of smaller gas giants. We can detect large planets close to the star. But why are they in elliptical orbits. We can detect circular orbits as well as elliptical orbits. I agree that there could still be lots of Earth like planets. But it does seem likely that our solar system is atypical, if only because our planets close to the sun are in circular orbits. It still is early to declare what is a typical solar system but we are now getting some data. And that data is not pointing towards our solar system being typical. Alain Fournier |
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