So long for the we-are-lucky-to-have-a-Jupiter theories

h2ouniverse · Oct 20, 2008

This article on New Scientist considering Jupiter as tha cause of the Late Heavy Bombardmenthttp://space.newscientist.com/article/mg20026784.800-jupiter-produced-greatest-pounding-in-earths-history.html?DCMP=ILC-hmts&nsref=space2_head_Jupiter%20produced%20greatest%20pounding%20in%20Earth's%20historyAnd this paper from Horner at EPSC:http://www.cosis.net/abstracts/EPSC2008/00160/EPSC2008-A-00160-1.pdfExcerpt: "Therefore, for the asteroids and short-period comets, it seems that our Jupiter does offer some shielding, when compared to the case where the planet has a mass of around 0.2 MJ, but, compared to the scenario where no Jupiter is present at all (or the Jupiter in question has very low mass), Jupiter actually acts to increase the Earth-bound flux." Once again, the illusions of the anti-Copernicians take a blow. It has been fashionable these days to believe that having a Jupiter was a necessary condition for survival of complex life in a planetary system. And that we are exceptionnally lucky, that we had enjoyed a set of conditions that were all beneficial and so on... Having one parameter that is not as beneficial as it could have been is a welcome relativization.

Crossover_Maniac · Oct 20, 2008

Look at it like this, if it wasn't for Jupiter, T-Rex would be still be ruling the earth and mammals would be tiny little rat-like, egg-laying things scurring on the ground.  Maybe humans should be thanking God for Jupiter. <div class="Discussion_UserSignature"> Feel the Hope-nosis </div>

MeteorWayne · Oct 20, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>This article on New Scientist considering Jupiter as tha cause of the Late Heavy Bombardmenthttp://space.newscientist.com/article/mg20026784.800-jupiter-produced-greatest-pounding-in-earths-history.html?DCMP=ILC-hmts&nsref=space2_head_Jupiter%20produced%20greatest%20pounding%20in%20Earth's%20historyAnd this paper from Horner at EPSC:http://www.cosis.net/abstracts/EPSC2008/00160/EPSC2008-A-00160-1.pdfExcerpt: "Therefore, for the asteroids and short-period comets, it seems that our Jupiter does offer some shielding, when compared to the case where the planet has a mass of around 0.2 MJ, but, compared to the scenario where no Jupiter is present at all (or the Jupiter in question has very low mass), Jupiter actually acts to increase the Earth-bound flux." Once again, the illusions of the anti-Copernicians take a blow. It has been fashionable these days to believe that having a Jupiter was a necessary condition for survival of complex life in a planetary system. And that we are exceptionnally lucky, that we had enjoyed a set of conditions that were all beneficial and so on... Having one parameter that is not as beneficial as it could have been is a welcome relativization.  Posted by h2ouniverse</DIV> If you read what it said, while Jupiter may have been responsible for the Late Heavt Bombardment (when life was just beginning on earth) it was also at the same time responsible for removing 95 of the future objects that might have hit is from the inner solar syste.I don't think anyone has ever suggested that Jupiter provided protection throughout the solar system's history. In fact this matches exctly the scenario that I understood took place. <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

h2ouniverse · Oct 21, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>If you read what it said, while Jupiter may have been responsible for the Late Heavt Bombardment (when life was just beginning on erath) it was also at the same time responsible for removing 95 of the future objects that might have hit is from the inner solar syste.I don't think anyone has ever suggested that Jupiter provided protection throughout the solar system's history. In fact this matches exctly the scenario that I understood took place. Posted by MeteorWayne</DIV> NOKThe 2nd article is the main motivation for my statement, that I maintain. Excerpt:"In the cases of the asteroids and the short-period comets, Jupiter was observed to significantly modify the impact flux which would be experienced by the planet Earth. It was immediately obvious, however, that the old idea that Jupiter shields us from impacts no longer holds. For both of these populations, the lowest impact rates were experienced when the Jupiter-like planet in the system had the lowest mass, rose rapidly to a peak flux at around 0.2 Jupiter masses, before falling away more slowly. Therefore, for the asteroids and short-period comets, it seems that our Jupiter does offer some shielding, when compared to the case where the planet has a mass of around 0.2 MJ, but, compared to the scenario where no Jupiter is present at all (or the Jupiter in question has very low mass), Jupiter actually acts to increase the Earth-bound flux"...which tells us that the size of Jupiter is not an optimum in terms of influx towards Earth, whether you consider a big flux was beneficial or not. According to their calculations, you would have got a lower flux with a bigger Jupiter, or with an Earth-massed planet.You would have got a far bigger flux with a 0.2 MJ planet.You would get similar amounts than with a Jupiter-massed planet with a planet between one Earth and 0.2MJ (say a kind of Neptune, that can be quite common too).I would add Wayne that the "we-are-lucky-to-have-a-Jupiter theories" I'm making allusion to were the ones where Jupiter destroyed the small bodies (through Shoemaker-Levy9-like collisions) or deflected them outwards. And yes people had repeatedly claimed that Jupiter was a shield (based on a single article, the conclusions of which had been irrationnally repeated over years without verification).We see that a planet at 5AU does not destroy the would-be Earth impactors. Using the Earth-bound flux is a good criterion imho to assess the impact of Jupiter's presence (or absence). And this stands, to quote you, "throughout the solar system's history". The fact that 95% of the objects are cleared is not relevant, if half of them are sent to the inner system!Best regards.

MeteorWayne · Oct 21, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>NOKThe 2nd article is the main motivation for my statement, that I maintain. Excerpt:"In the cases of the asteroids and the short-period comets, Jupiter was observed to significantly modify the impact flux which would be experienced by the planet Earth. It was immediately obvious, however, that the old idea that Jupiter shields us from impacts no longer holds. For both of these populations, the lowest impact rates were experienced when the Jupiter-like planet in the system had the lowest mass, rose rapidly to a peak flux at around 0.2 Jupiter masses, before falling away more slowly. Therefore, for the asteroids and short-period comets, it seems that our Jupiter does offer some shielding, when compared to the case where the planet has a mass of around 0.2 MJ, but, compared to the scenario where no Jupiter is present at all (or the Jupiter in question has very low mass), Jupiter actually acts to increase the Earth-bound flux"...which tells us that the size of Jupiter is not an optimum in terms of influx towards Earth, whether you consider a big flux was beneficial or not. According to their calculations, you would have got a lower flux with a bigger Jupiter, or with an Earth-massed planet.You would have got a far bigger flux with a 0.2 MJ planet.You would get similar amounts than with a Jupiter-massed planet with a planet between one Earth and 0.2MJ (say a kind of Neptune, that can be quite common too).I would add Wayne that the "we-are-lucky-to-have-a-Jupiter theories" I'm making allusion to were the ones where Jupiter destroyed the small bodies (through Shoemaker-Levy9-like collisions) or deflected them outwards. And yes people had repeatedly claimed that Jupiter was a shield (based on a single article, the conclusions of which had been irrationnally repeated over years without verification).We see that a planet at 5AU does not destroy the would-be Earth impactors. Using the Earth-bound flux is a good criterion imho to assess the impact of Jupiter's presence (or absence). And this stands, to quote you, "throughout the solar system's history". The fact that 95% of the objects are cleared is not relevant, if half of them are sent to the inner system!Best regards. Posted by h2ouniverse</DIV> I guess I've never looked at the data the way you are suggesting. From my view, I have always looked at it that Jupiter cleaned out the chunky bits in the solar system early enough for the impact rate to decrease later. So that once multicellular life on earth was established, it had a chance to survive long enough to develop intelligent (?) creatures like us. <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-laughing.gif" border="0" alt="Laughing" title="Laughing" /> <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

h2ouniverse · Oct 21, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I guess I've never looked at the data the way you are suggesting. From my view, I have always looked at it that Jupiter cleaned out the chunky bits in the solar system early enough for the impact rate to decrease later. So that once multicellular life on earth was established, it had a chance to survive long enough to develop intelligent (?) creatures like us. Posted by MeteorWayne</DIV> Ok, this means we have to compare the rate after the LHB. But if I understood well the talk (from the second link), the issue with a Jupiter is that it destabilizes asteroids (from Asteroid Belt) and short period comets. So there is still an issue post LHB. The first link has simulated "40,000 small objects in circular orbits between the outermost planets" but the study of the second link has simulated asteroids and short period comets: "The asteroidal and short-period comet populations each contained 100,000 test particles, moving on orbits typical of their class. The asteroids were initially distributed between 2 and 4 AU, with orbits of varying eccentricity and inclination, with number density varying as a function of semi-major axis. The short-period cometary flux was obtained through simulation of a population based on the subset of known Centaurs and Scattered Disk Objects which are Neptune-crossing, and have perihelia beyond the orbit of Uranus".Also they have followed the "100,000 particle populations for 10 million years, under the influence of the giant planets. Each particle was followed until it either hit something, or was ejected from the system. In this manner, we were able to follow the flux of objects onto the Earth as a function of time."So we see that the two types of simulations that are not incompatible. The second one would stand for establishing post-LHB statistics. So according to their calculations you get less Chixculub-like impactors with no Jupiter at all, and more with a 0.2MJ planet at 5AU.Best regards.

MeteorWayne · Oct 21, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Ok, this means we have to compare the rate after the LHB. But if I understood well the talk (from the second link), the issue with a Jupiter is that it destabilizes asteroids (from Asteroid Belt) and short period comets. So there is still an issue post LHB. The first link has simulated "40,000 small objects in circular orbits between the outermost planets" but the study of the second link has simulated asteroids and short period comets: "The asteroidal and short-period comet populations each contained 100,000 test particles, moving on orbits typical of their class. The asteroids were initially distributed between 2 and 4 AU, with orbits of varying eccentricity and inclination, with number density varying as a function of semi-major axis. The short-period cometary flux was obtained through simulation of a population based on the subset of known Centaurs and Scattered Disk Objects which are Neptune-crossing, and have perihelia beyond the orbit of Uranus".Also they have followed the "100,000 particle populations for 10 million years, under the influence of the giant planets. Each particle was followed until it either hit something, or was ejected from the system. In this manner, we were able to follow the flux of objects onto the Earth as a function of time."So we see that the two types of simulations that are not incompatible. The second one would stand for establishing post-LHB statistics. So according to their calculations you get less Chixculub-like impactors with no Jupiter at all, and more with a 0.2MJ planet at 5AU.Best regards.  Posted by h2ouniverse</DIV>Still the geological record indicates that the last extinction even was ~ 65 million years ago, so the analysis in the paper isn't really supported or not by the data. Although, since they only followed it fo 10 million years, I'm not sure what that tells us. That's a very short period in solar system history.I guess we shall see! <img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-laughing.gif" border="0" alt="Laughing" title="Laughing" />Wayne <div class="Discussion_UserSignature"> But the Krell forgot one thing John. Monsters. Monsters from the Id. I really, really, really, really miss the "first unread post" function </div>

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So long for the we-are-lucky-to-have-a-Jupiter theories

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