Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
Hello Rob, All, Comets are generally considered to be a thin layer of rocky material over a lot of volatites, the complete opposite. I could well be wrong on this. Virgin comets are unusually bright on their first perihelion passage. One theory is that the surface volatiles ar vapourised away leaving this outer layer of dark material. This would suggest that if EL61 is indeed, becoming a comet, this is it's first journey inward which seems most unlikely. And yet, this would all depend on the amount of hydrovolcanism on the surface of the body itself - if there were enough activity to completely resurface the2003 EL61 with ice since it experienced it's great impact, what's to say it hasn't been resurfaced since its last close perihelion? I know that some comets have geysers of their own...is there any data around that tells us how long it might take for any particular comet (I know many would be different) to completely resurface itself with ice and thus enter the inner solar system brighter than when it had last left? Regards, Jason On 2/3/07, Rob McCafferty [EMAIL PROTECTED] wrote: Apologies for taking selected bits. Hope it's not out of context. --- Sterling K. Webb [EMAIL PROTECTED] wrote: ''2003 EL61 is a very bright body, reflecting 70% of the light that falls on it, and it is indeed, as you would suspect from this brightness, covered with water ice. BUT, it's not old water ice, but new, freshly fallen crystalline ice, otherwise known on our planet as snow'' Curiously, Halley's comet has an abledo of less than 4%, less than that of coal or black velvet. While Halley is not necessarily typical of comets, it is agreed that comets are very dark objects. Nucleus[nuclei] sizes have been estimated by removing modelled coma brightnesses from Hubble images and for nearby comets radar measurements seem to confirm the low albedo. Cometary dust may begin as silicate grained materials mantled with organic matter. To this hundreds of 0.01micron ice particles may form from a protosolar nebula into .5micron grains. These cluster into loose agglomerates which end up being part of the coma of comets. The evidence for this theory is the particles swept up by high altitude research planes [18km up] believed to be cometary in nature. This being the case it explains the brightness of the coma and -might I suggest- the brightness of EL61. It need not be covered in ice, just covered in this cometary 'snow' ''Now, we come to the Giant Comet Notion. Obviously, 2003 EL61's ice is a surface feature, a thin layer of volatiles over what is essentially a rocky body.'' Comets are generally considered to be a thin layer of rocky material over a lot of volatites, the complete opposite. I could well be wrong on this. Virgin comets are unusually bright on their first perihelion passage. One theory is that the surface volatiles ar vapourised away leaving this outer layer of dark material. This would suggest that if EL61 is indeed, becoming a comet, this is it's first journey inward which seems most unlikely. Also, comets sublimating ices have a temperature of 230K. Virgin comets can achieve this much farther out than comets on subsequent passes. This is because the dark silicate layer protects the icy material, insulating it. Only when the comet gets much closer does the heat conduct in to cause the sublimation of the ices. However, I doubt anyone would suggest EL61 has a surface temperature of 200K. There has to be an alternative explanation. Sorry the reply so lengthy. I just don't think EL61 can be cometary in nature. One other think caught my attention in this post '' A mere 10% decrease would lower the planetary temperature by 7 degrees C'' I thought the difference between aphelion and perihelion in earth's orbit made a 7% difference in solar intensity. Does anyone have a guess as to how long a change need apply for to effect earth? I suspect not Rob McC Expecting? Get great news right away with email Auto-Check. Try the Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/newmail_tools.html __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
In the context of what I had written I concede this is a fair point. However. I'd like to know which comets have confirmed hydrovulcanism and where the info source. I can appreciate it happens but the energy source for such an event seems lacking once beyond the ice line. I am quite willing to blame my own shortsightedness for this. It's just I don't think this thing is coming or has ever has come into the inner solar system before. It just doesn't match the pattern my half arsed look has seen. Rob McC --- Jason Utas [EMAIL PROTECTED] wrote: Hello Rob, All, Comets are generally considered to be a thin layer of rocky material over a lot of volatites, the complete opposite. I could well be wrong on this. Virgin comets are unusually bright on their first perihelion passage. One theory is that the surface volatiles ar vapourised away leaving this outer layer of dark material. This would suggest that if EL61 is indeed, becoming a comet, this is it's first journey inward which seems most unlikely. And yet, this would all depend on the amount of hydrovolcanism on the surface of the body itself - if there were enough activity to completely resurface the2003 EL61 with ice since it experienced it's great impact, what's to say it hasn't been resurfaced since its last close perihelion? I know that some comets have geysers of their own...is there any data around that tells us how long it might take for any particular comet (I know many would be different) to completely resurface itself with ice and thus enter the inner solar system brighter than when it had last left? Regards, Jason On 2/3/07, Rob McCafferty [EMAIL PROTECTED] wrote: Apologies for taking selected bits. Hope it's not out of context. --- Sterling K. Webb [EMAIL PROTECTED] wrote: ''2003 EL61 is a very bright body, reflecting 70% of the light that falls on it, and it is indeed, as you would suspect from this brightness, covered with water ice. BUT, it's not old water ice, but new, freshly fallen crystalline ice, otherwise known on our planet as snow'' Curiously, Halley's comet has an abledo of less than 4%, less than that of coal or black velvet. While Halley is not necessarily typical of comets, it is agreed that comets are very dark objects. Nucleus[nuclei] sizes have been estimated by removing modelled coma brightnesses from Hubble images and for nearby comets radar measurements seem to confirm the low albedo. Cometary dust may begin as silicate grained materials mantled with organic matter. To this hundreds of 0.01micron ice particles may form from a protosolar nebula into .5micron grains. These cluster into loose agglomerates which end up being part of the coma of comets. The evidence for this theory is the particles swept up by high altitude research planes [18km up] believed to be cometary in nature. This being the case it explains the brightness of the coma and -might I suggest- the brightness of EL61. It need not be covered in ice, just covered in this cometary 'snow' ''Now, we come to the Giant Comet Notion. Obviously, 2003 EL61's ice is a surface feature, a thin layer of volatiles over what is essentially a rocky body.'' Comets are generally considered to be a thin layer of rocky material over a lot of volatites, the complete opposite. I could well be wrong on this. Virgin comets are unusually bright on their first perihelion passage. One theory is that the surface volatiles ar vapourised away leaving this outer layer of dark material. This would suggest that if EL61 is indeed, becoming a comet, this is it's first journey inward which seems most unlikely. Also, comets sublimating ices have a temperature of 230K. Virgin comets can achieve this much farther out than comets on subsequent passes. This is because the dark silicate layer protects the icy material, insulating it. Only when the comet gets much closer does the heat conduct in to cause the sublimation of the ices. However, I doubt anyone would suggest EL61 has a surface temperature of 200K. There has to be an alternative explanation. Sorry the reply so lengthy. I just don't think EL61 can be cometary in nature. One other think caught my attention in this post '' A mere 10% decrease would lower the planetary temperature by 7 degrees C'' I thought the difference between aphelion and perihelion in earth's orbit made a 7% difference in solar intensity. Does anyone have a guess as to how long a change need apply for to effect earth? I suspect not Rob McC Expecting? Get great news right away with email Auto-Check. Try the Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/newmail_tools.html
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
On Wed, 21 Feb 2007 15:28:26 -0800 (PST), you wrote: It's just I don't think this thing is coming or has ever has come into the inner solar system before. It just doesn't match the pattern my half arsed look has seen. Yeah, it was a pretty silly article. It just seemed to be saying, what if. He could have just as easily wondered what would happen if Pluto or any other KBO came into the inner solar system. Or Neptune. __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
Hi, Of course, 2003 EL61 presently has water resurfacing going on, even though it orbits further out than Neptune, so it must have a source of internal heat to drive its hydrovulcanism. With its high density (3.2?), it could well be differentiated. The annoying thing is that the BBC (and only the BBC) reported Brown's remarks at a seminar as a kind of science gossip. If Brown has orbital calculations that show 2003 EL61 can be perturbed into the inner solar system, he does not mention it on his website nor has he published them. I think he got the idea from dynamicists who run computer simulations of resonances and the like, rather than an actual orbital calculation. We have observed far too little of 2003 EL61's orbit to know it precisely to determine that, at this point. It's just I don't think this thing is coming or has ever has come into the inner solar system before. After 4+ billion years in the same orbit, I think it's pretty unlikely too. That's a good thing... Sterling K. Webb - - Original Message - From: Rob McCafferty [EMAIL PROTECTED] To: Jason Utas [EMAIL PROTECTED]; meteorite-list@meteoritecentral.com Sent: Wednesday, February 21, 2007 5:28 PM Subject: Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61) In the context of what I had written I concede this is a fair point. However. I'd like to know which comets have confirmed hydrovulcanism and where the info source. I can appreciate it happens but the energy source for such an event seems lacking once beyond the ice line. I am quite willing to blame my own shortsightedness for this. It's just I don't think this thing is coming or has ever has come into the inner solar system before. It just doesn't match the pattern my half arsed look has seen. Rob McC --- Jason Utas [EMAIL PROTECTED] wrote: Hello Rob, All, Comets are generally considered to be a thin layer of rocky material over a lot of volatites, the complete opposite. I could well be wrong on this. Virgin comets are unusually bright on their first perihelion passage. One theory is that the surface volatiles ar vapourised away leaving this outer layer of dark material. This would suggest that if EL61 is indeed, becoming a comet, this is it's first journey inward which seems most unlikely. And yet, this would all depend on the amount of hydrovolcanism on the surface of the body itself - if there were enough activity to completely resurface the2003 EL61 with ice since it experienced it's great impact, what's to say it hasn't been resurfaced since its last close perihelion? I know that some comets have geysers of their own...is there any data around that tells us how long it might take for any particular comet (I know many would be different) to completely resurface itself with ice and thus enter the inner solar system brighter than when it had last left? Regards, Jason __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
is still a year away from the potential encounter point. Wait another two years (four years total); the slower body is now a year past the encounter point. Only after six years will the encounter repeat. That is the product of the two orbital periods ( 2 times 3 = 6 ) and is the time between encounters, or indeed any specific configuration of the two orbits. 2003 EL61's period of 284.5 years times Neptune's period of 164.88 years is 46,900.36 years. That means that the two had an encounter like what is proposed 46,900 years before, and another such close encounter 46,900 years before that, and... Well, 21+ such encounters every million years. Since the very beginning of the solar system, they've had almost 96,000 such encounters, and in exactly NONE of them has 2003 EL61 gone off to visit the inner solar system, not even once. How likely is it that next close encounter will have that result? Or even the next 100 close encounters? How has EL61 managed to hang onto its moons through all these close encounters? Why, after the solar system has held together for more than four billion years, should it decide to unravel right now? Is the solar system just coming apart? On the other hand, there's this: we explain 2003 EL61's extraordinary shape and fantastic spin to a Major Collision with Something. We also assume it happened in the far distant past, early in the history of the solar system (mostly because it was more crowded then and also because we don't want to think it could happen now). What if the body that collided with 2003 EL61 was a moon of Neptune? What if the collision was recent, meaning only half a billion years ago (or less) and that the collision altered EL61's orbit to make a too-close encounter and a voyage to the inner solar system possible? Now, there's a nasty thought... Which is why, instead of a news snippet with three sentences of potential information, there ought to be an actual publication, however informal, with, you know, real numbers and real calculations and real information. To modify a great movie line: Show me the numbers! Since EL61 has only been observed for 2-3 years of its 285 year orbit (1%) and the earliest prediscovery photo is 1955 (18% of an orbit ago), just how accurate are those orbital determinations and the resultant calculations? Inquiring minds want to know... My considered scientific opinion? 'Tain't happenin', dude! Sterling K. Webb --- - Original Message - From: Ron Baalke [EMAIL PROTECTED] To: Meteorite Mailing List meteorite-list@meteoritecentral.com Sent: Wednesday, January 17, 2007 11:32 AM Subject: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61) http://news.bbc.co.uk/2/hi/science/nature/6268799.stm Dwarf planet 'becoming a comet' By Paul Rincon BBC News January 17, 2007 An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known. 2003 EL61 is a large, dense, rugby-ball-shaped hunk of rock with a fast rotation rate. Professor Mike Brown has calculated that the object could be due a close encounter with the planet Neptune. If so, Neptune's gravity could catapult it into the inner Solar System as a short-period comet. If you came back in two million years, EL61 could well be a comet, said Professor Brown, from the California Institute of Technology (Caltech) in Pasadena. When it becomes a comet, it will be the brightest we will ever see. Cosmic oddball 2003 EL61 is a large object; it is as big as Pluto along its longest dimension. It is one of the largest of a swarm of icy objects that inhabit a region of the outer Solar System known as the Kuiper Belt. But it is extremely unusual: spinning on its axis every four hours, it has developed an elongated shape. 2003 EL61 is apparently composed of rock with just a thin veneer of water-ice covering its surface. Other Kuiper Belt Objects (KBOs) contain much more water-ice. Professor Brown's computer simulations show that the object is on a very unstable orbit and set for a close encounter with Neptune. The eighth planet's gravitational force could either sling the icy rock ball into the inner Solar System as a comet, out into the distant Oort Cloud region, or even into interstellar space. Orbits of Kuiper Belt Objects tend to be very stable, but the region is thought to be a reservoir for short-period comets. Occasionally, some of these objects must get tossed inward to become the fizzing lumps of ice and dust that criss-cross our cosmic neighbourhood. Shedding surface Mike Brown and his colleagues have come up with a scenario to explain 2003 EL61's physical characteristics and behaviour. About 4.5 billion years ago
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
System as a short-period comet. The likelihood of any close encounter repeating itself is easy to calculate. Suppose two bodies with orbital periods of 2 and 3 years respectively have a close encounter. Two years later, when the first body has returned, the slower body is still a year away from the potential encounter point. Wait another two years (four years total); the slower body is now a year past the encounter point. Only after six years will the encounter repeat. That is the product of the two orbital periods ( 2 times 3 = 6 ) and is the time between encounters, or indeed any specific configuration of the two orbits. 2003 EL61's period of 284.5 years times Neptune's period of 164.88 years is 46,900.36 years. That means that the two had an encounter like what is proposed 46,900 years before, and another such close encounter 46,900 years before that, and... Well, 21+ such encounters every million years. Since the very beginning of the solar system, they've had almost 96,000 such encounters, and in exactly NONE of them has 2003 EL61 gone off to visit the inner solar system, not even once. How likely is it that next close encounter will have that result? Or even the next 100 close encounters? How has EL61 managed to hang onto its moons through all these close encounters? Why, after the solar system has held together for more than four billion years, should it decide to unravel right now? Is the solar system just coming apart? On the other hand, there's this: we explain 2003 EL61's extraordinary shape and fantastic spin to a Major Collision with Something. We also assume it happened in the far distant past, early in the history of the solar system (mostly because it was more crowded then and also because we don't want to think it could happen now). What if the body that collided with 2003 EL61 was a moon of Neptune? What if it was only half a billion years ago (or less) and that the collision altered EL61's orbit to make a too-close encounter and a voyage to the inner solar system possible? Now, there's a nasty thought... Which is why, instead of a news snippet with three sentences of potential information, you ought to actually publish something yourself, with, you know, real numbers and real calculations and real information, Mike. To modify a great movie line: Show me the numbers! Since EL61 has only been observed for 2-3 years of its 285 year orbit (1%) and the earliest prediscovery photo is 1955 (18% of an orbit ago), just how accurate are those orbital determinations and the resultant calculations? Inquiring minds want to know... My considered scientific opinion? 'Tain't happenin', dude! Sterling K. Webb --- - Original Message - From: Ron Baalke [EMAIL PROTECTED] To: Meteorite Mailing List meteorite-list@meteoritecentral.com Sent: Wednesday, January 17, 2007 11:32 AM Subject: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61) http://news.bbc.co.uk/2/hi/science/nature/6268799.stm Dwarf planet 'becoming a comet' By Paul Rincon BBC News January 17, 2007 An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known. 2003 EL61 is a large, dense, rugby-ball-shaped hunk of rock with a fast rotation rate. Professor Mike Brown has calculated that the object could be due a close encounter with the planet Neptune. If so, Neptune's gravity could catapult it into the inner Solar System as a short-period comet. If you came back in two million years, EL61 could well be a comet, said Professor Brown, from the California Institute of Technology (Caltech) in Pasadena. When it becomes a comet, it will be the brightest we will ever see. Cosmic oddball 2003 EL61 is a large object; it is as big as Pluto along its longest dimension. It is one of the largest of a swarm of icy objects that inhabit a region of the outer Solar System known as the Kuiper Belt. But it is extremely unusual: spinning on its axis every four hours, it has developed an elongated shape. 2003 EL61 is apparently composed of rock with just a thin veneer of water-ice covering its surface. Other Kuiper Belt Objects (KBOs) contain much more water-ice. Professor Brown's computer simulations show that the object is on a very unstable orbit and set for a close encounter with Neptune. The eighth planet's gravitational force could either sling the icy rock ball into the inner Solar System as a comet, out into the distant Oort Cloud region, or even into interstellar space. Orbits of Kuiper Belt Objects tend to be very stable, but the region is thought to be a reservoir for short-period comets. Occasionally, some of these objects must get tossed inward to become the fizzing lumps of ice and dust that criss-cross our cosmic neighbourhood. Shedding surface Mike Brown and his colleagues have come up with a scenario to explain 2003 EL61's
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
EL61 gone off to visit the inner solar system, not even once. How likely is it that next close encounter will have that result? Or even the next 100 close encounters? How has EL61 managed to hang onto its moons through all these close encounters? Why, after the solar system has held together for more than four billion years, should it decide to unravel right now? Is the solar system just coming apart? On the other hand, there's this: we explain 2003 EL61's extraordinary shape and fantastic spin to a Major Collision with Something. We also assume it happened in the far distant past, early in the history of the solar system (mostly because it was more crowded then and also because we don't want to think it could happen now). What if the body that collided with 2003 EL61 was a moon of Neptune? What if the collision was recent, meaning only half a billion years ago (or less) and that the collision altered EL61's orbit to make a too-close encounter and a voyage to the inner solar system possible? Now, there's a nasty thought... Which is why, instead of a news snippet with three sentences of potential information, there ought to be an actual publication, however informal, with, you know, real numbers and real calculations and real information. To modify a great movie line: Show me the numbers! Since EL61 has only been observed for 2-3 years of its 285 year orbit (1%) and the earliest prediscovery photo is 1955 (18% of an orbit ago), just how accurate are those orbital determinations and the resultant calculations? Inquiring minds want to know... My considered scientific opinion? 'Tain't happenin', dude! Sterling K. Webb --- - Original Message - From: Ron Baalke [EMAIL PROTECTED] To: Meteorite Mailing List meteorite-list@meteoritecentral.com Sent: Wednesday, January 17, 2007 11:32 AM Subject: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61) http://news.bbc.co.uk/2/hi/science/nature/6268799.stm Dwarf planet 'becoming a comet' By Paul Rincon BBC News January 17, 2007 An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known. 2003 EL61 is a large, dense, rugby-ball-shaped hunk of rock with a fast rotation rate. Professor Mike Brown has calculated that the object could be due a close encounter with the planet Neptune. If so, Neptune's gravity could catapult it into the inner Solar System as a short-period comet. If you came back in two million years, EL61 could well be a comet, said Professor Brown, from the California Institute of Technology (Caltech) in Pasadena. When it becomes a comet, it will be the brightest we will ever see. Cosmic oddball 2003 EL61 is a large object; it is as big as Pluto along its longest dimension. It is one of the largest of a swarm of icy objects that inhabit a region of the outer Solar System known as the Kuiper Belt. But it is extremely unusual: spinning on its axis every four hours, it has developed an elongated shape. 2003 EL61 is apparently composed of rock with just a thin veneer of water-ice covering its surface. Other Kuiper Belt Objects (KBOs) contain much more water-ice. Professor Brown's computer simulations show that the object is on a very unstable orbit and set for a close encounter with Neptune. The eighth planet's gravitational force could either sling the icy rock ball into the inner Solar System as a comet, out into the distant Oort Cloud region, or even into interstellar space. Orbits of Kuiper Belt Objects tend to be very stable, but the region is thought to be a reservoir for short-period comets. Occasionally, some of these objects must get tossed inward to become the fizzing lumps of ice and dust that criss-cross our cosmic neighbourhood. Shedding surface Mike Brown and his colleagues have come up with a scenario to explain 2003 EL61's physical characteristics and behaviour. About 4.5 billion years ago, the object that became 2003 EL61 was a ball, half composed of ice and half of rock - like Pluto - and about the same size as Pluto. Some time early in its history, it was smacked, edge on, by another large KBO. This broke off much of 2003 EL61's icy mantle, which coalesced to form several satellites. As expected, the satellites seem to be composed of very pure water-ice. Professor Brown suggested that some of 2003 EL61's mantle may already have made it into the inner Solar System as cometary material. The oblique impact also caused 2003 EL61 to spin rapidly. This rapid rotation elongated 2003 EL61 into the rugby ball shape we see today. It's a bit like the story of Mercury, Professor Brown explained. Mercury got hit by a large object early in the Solar System. It left mostly a big iron core, with a little bit of rock on the outside. This is mostly a rock core with a little bit of ice on the outside. Mike Brown outlined details of his
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
The Sun's light would be scattered, diffused and dispersed. The skies would be brighter at night and dimmer in the daytime. AH HA!! Finally a solution to global warming. Jerry Flaherty - Original Message - From: Sterling K. Webb [EMAIL PROTECTED] To: Meteorite List meteorite-list@meteoritecentral.com Cc: Ron Baalke [EMAIL PROTECTED] Sent: Saturday, February 03, 2007 3:26 PM Subject: Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61) __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
I believe it's called The End of The World. OOPS I stand [sit or lie] corrected Jerry Flaherty - Original Message - From: Sterling K. Webb [EMAIL PROTECTED] To: Meteorite List meteorite-list@meteoritecentral.com Cc: Ron Baalke [EMAIL PROTECTED] Sent: Saturday, February 03, 2007 3:26 PM Subject: Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61) __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
Apologies for taking selected bits. Hope it's not out of context. --- Sterling K. Webb [EMAIL PROTECTED] wrote: ''2003 EL61 is a very bright body, reflecting 70% of the light that falls on it, and it is indeed, as you would suspect from this brightness, covered with water ice. BUT, it's not old water ice, but new, freshly fallen crystalline ice, otherwise known on our planet as snow'' Curiously, Halley's comet has an abledo of less than 4%, less than that of coal or black velvet. While Halley is not necessarily typical of comets, it is agreed that comets are very dark objects. Nucleus[nuclei] sizes have been estimated by removing modelled coma brightnesses from Hubble images and for nearby comets radar measurements seem to confirm the low albedo. Cometary dust may begin as silicate grained materials mantled with organic matter. To this hundreds of 0.01micron ice particles may form from a protosolar nebula into .5micron grains. These cluster into loose agglomerates which end up being part of the coma of comets. The evidence for this theory is the particles swept up by high altitude research planes [18km up] believed to be cometary in nature. This being the case it explains the brightness of the coma and -might I suggest- the brightness of EL61. It need not be covered in ice, just covered in this cometary 'snow' ''Now, we come to the Giant Comet Notion. Obviously, 2003 EL61's ice is a surface feature, a thin layer of volatiles over what is essentially a rocky body.'' Comets are generally considered to be a thin layer of rocky material over a lot of volatites, the complete opposite. I could well be wrong on this. Virgin comets are unusually bright on their first perihelion passage. One theory is that the surface volatiles ar vapourised away leaving this outer layer of dark material. This would suggest that if EL61 is indeed, becoming a comet, this is it's first journey inward which seems most unlikely. Also, comets sublimating ices have a temperature of 230K. Virgin comets can achieve this much farther out than comets on subsequent passes. This is because the dark silicate layer protects the icy material, insulating it. Only when the comet gets much closer does the heat conduct in to cause the sublimation of the ices. However, I doubt anyone would suggest EL61 has a surface temperature of 200K. There has to be an alternative explanation. Sorry the reply so lengthy. I just don't think EL61 can be cometary in nature. One other think caught my attention in this post '' A mere 10% decrease would lower the planetary temperature by 7 degrees C'' I thought the difference between aphelion and perihelion in earth's orbit made a 7% difference in solar intensity. Does anyone have a guess as to how long a change need apply for to effect earth? I suspect not Rob McC Expecting? Get great news right away with email Auto-Check. Try the Yahoo! Mail Beta. http://advision.webevents.yahoo.com/mailbeta/newmail_tools.html __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
[meteorite-list] Dwarf Planet 'Becoming A Comet' (2003 EL61)
http://news.bbc.co.uk/2/hi/science/nature/6268799.stm Dwarf planet 'becoming a comet' By Paul Rincon BBC News January 17, 2007 An unusual dwarf planet discovered in the outer Solar System could be en route to becoming the brightest comet ever known. 2003 EL61 is a large, dense, rugby-ball-shaped hunk of rock with a fast rotation rate. Professor Mike Brown has calculated that the object could be due a close encounter with the planet Neptune. If so, Neptune's gravity could catapult it into the inner Solar System as a short-period comet. If you came back in two million years, EL61 could well be a comet, said Professor Brown, from the California Institute of Technology (Caltech) in Pasadena. When it becomes a comet, it will be the brightest we will ever see. Cosmic oddball 2003 EL61 is a large object; it is as big as Pluto along its longest dimension. It is one of the largest of a swarm of icy objects that inhabit a region of the outer Solar System known as the Kuiper Belt. But it is extremely unusual: spinning on its axis every four hours, it has developed an elongated shape. 2003 EL61 is apparently composed of rock with just a thin veneer of water-ice covering its surface. Other Kuiper Belt Objects (KBOs) contain much more water-ice. Professor Brown's computer simulations show that the object is on a very unstable orbit and set for a close encounter with Neptune. The eighth planet's gravitational force could either sling the icy rock ball into the inner Solar System as a comet, out into the distant Oort Cloud region, or even into interstellar space. Orbits of Kuiper Belt Objects tend to be very stable, but the region is thought to be a reservoir for short-period comets. Occasionally, some of these objects must get tossed inward to become the fizzing lumps of ice and dust that criss-cross our cosmic neighbourhood. Shedding surface Mike Brown and his colleagues have come up with a scenario to explain 2003 EL61's physical characteristics and behaviour. About 4.5 billion years ago, the object that became 2003 EL61 was a ball, half composed of ice and half of rock - like Pluto - and about the same size as Pluto. Some time early in its history, it was smacked, edge on, by another large KBO. This broke off much of 2003 EL61's icy mantle, which coalesced to form several satellites. As expected, the satellites seem to be composed of very pure water-ice. Professor Brown suggested that some of 2003 EL61's mantle may already have made it into the inner Solar System as cometary material. The oblique impact also caused 2003 EL61 to spin rapidly. This rapid rotation elongated 2003 EL61 into the rugby ball shape we see today. It's a bit like the story of Mercury, Professor Brown explained. Mercury got hit by a large object early in the Solar System. It left mostly a big iron core, with a little bit of rock on the outside. This is mostly a rock core with a little bit of ice on the outside. Mike Brown outlined details of his work during a plenary lecture at the recent American Astronomical Society meeting in Seattle. __ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
