Cometary commotion: A new mechanism for how icy bodies get past Jupiter and Saturn suggests that comet showers did not play a big role in Earth’s extinctions.
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The chunks of ice and dust that make their home in the Oort cloud, far beyond the orbit of Pluto, sometimes become dislodged and head into the solar system as streaky comets. Some disruptions, caused by passing stars and other interactions with the Milky Way galaxy, are severe enough to send Oort comets into orbits that buzz or even collide with Earth. New simulations have revealed a novel mechanism for their entry into our part of the solar system, a method that also suggests that comet showers may not have been strongly involved in major extinctions on Earth.
Comet dynamics depend heavily on Jupiter and Saturn: their huge gravitational fields tend to keep objects away from Earth. Comets that manage to skirt Jupiter and Saturn, the conventional thinking goes, had to have originated in the outer reaches of the Oort cloud, where perturbations from outside the solar system can be felt most strongly and are writ large across vast cometary orbits that take hundreds of years to complete. Only during comet showers caused by close stellar passages, the theory holds, have extreme gravitational disruptions brought inner Oort cloud comets into the mix.
A computer simulation by Nathan Kaib and Thomas Quinn, both at the University of Washington, have upended this thinking. They have found that the comets that manage to cross the Jupiter-Saturn barrier do in fact originate in large numbers in the inner Oort cloud, even in the absence of a large disruption causing a comet shower. Specifically, they found that the relatively nearby objects of the inner Oort cloud can be kicked into the reaches of the outer cloud via interactions with the massive planets. Those newly far-flung comets, suddenly enjoying a longer orbit and greater gravitational perturbations from interstellar space, can find their orbits so changed that, by the time they pass through the planetary region again, they slip past the gas giants. “They can basically hop over the Jupiter-Saturn barrier,” Kaib says.
Kaib and Quinn estimate that more than half of the comets we observe streaking in from the Oort cloud reach our neighborhood via this route, and other researchers agree the simulation appears valid. “This mechanism, this dynamical path, as we call it, could work and could be a significant contributor,” says Paul Weissman, a senior research scientist at the NASA Jet Propulsion Laboratory.
The new research presents a route for comet production “that goes some way” toward resolving discrepancies between the standard model and the observations, says Scott Tremaine, an astrophysicist at the Institute for Advanced Study in Princeton, N.J. “One of the issues is that [the conventional view of] the cometary formation process is so inefficient; in order to produce the number of comets that we see, you’d need a really massive protoplanetary disk, one that appears to be incompatible with our best estimates from other sources,” Tremaine says.
Kaib and Quinn used their newfound mechanism, as well as the number of observed comets, to estimate an upper limit on how much material could be in the inner Oort cloud. They then produced a statistical model of how many comets would have hit Earth in comet showers in the past several hundred million years. Their conclusion: large cometary showers were few and hence probably did not cause more than one extinction event.
Using cometary dynamics to unwind the extinction history on Earth will likely meet with some controversy. Weissman notes that the extinction implications of Kaib and Quinn’s analysis would involve comet showers, not comets in general, and that even a diminished profile of showers does not rule out the role of comets in extinctions. One big strike, rather than a shower of small ones, is all that’s needed to trigger extinctions, he points out.
Note: This article was originally printed with the title, "Not Set in Stone (or Ice)."
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15 Comments
Add CommentOnce again, this is a helluva lotta speculation. Yes, I am a creationist, but even putting that aside, they are speculating based upon computer models (which are based on degrees of speculation). And even when new "evidence" contradicts older conclusions, there are still "But it still works in this way . . ."
Reply | Report Abuse | Link to thisIn the end, whether we worship the Bible or Science, it is hard to get past our own preconceived notions. Even when "evidence" presents itself. I guess the only evidence we want to believe is the evidence that supports our present belief system. Does that make us arrogant, or just too lazy to deal with our changing environment?
The belief in the Oort cloud stems from observations not computer models. The models are trying to figure out how comets in the cloud get pulled into our solar system, and how they interact in passing through all the gravitational pulls of the larger planets and the sun. It is not creating evidence, simply trying to help us understand how the universe works.
Reply | Report Abuse | Link to thisWhen are scientists going to learn that computer models are grossly inaccurate at predicting reality. Look at the climate change models they came up with. Even the worst-case scenarios they PREDICTED, pale in comparison to what is actually taking place on Earth. And regarding the K-T extinction, we have the crater at chixulub, we have the layer of iridium worldwide, we have 70% of all life suddenly die, WHY oh WHY is everyone and their uncle coming up with half-baked cockamamie "theories" to try to cast doubt on the FACT that even though Dinosaurs may have already been in decline, which is not to say they would have died out totally, there were other times when they were in decline and they re-innovated themselves and came back with renewed vigor, they and 70% of all life died, suddenly, at the K-T boundary. So that was the cause of the extinction, regardless of the pressures mounting from such things as the Deccan Traps, climate change, continental drift, etc, etc. An asteroid wiped the Dinosaurs out (except for birds which we all know by now are living dinosaurs). END. OF. STORY.
Reply | Report Abuse | Link to thisTher's been a fair amount of evidence already, that suggests that the infamous Yucatan meteorite ws really more the icing on the cake for the KT kill off...
Reply | Report Abuse | Link to thisThis model changes the probability that a comet hits Earth, but not the fact that a comet indeed hit Earth in the K-T boundary. We have a crater, there is no need to discuss how probable it was for comets hiting Earth by the time the crater was formed. About a month ago, the lottery in Hungary had the same 6 numbers for two weeks in row. Does it matter for the winners wondering how improbable was it?
Reply | Report Abuse | Link to thisRE jaqcp at 09:22 AM on 10/01/09
Reply | Report Abuse | Link to thisSince no one worships science (Worship being deference and reverence out of fear or love of a creature you consider worthy of public or private praise) , and science builds on past discoveries with new ones based on evidence, I would think you would view this as any scientist would, not as something that supports or denies our present "belief" system but rather as more information that may or may not be useful in the overall theory or model. I find it quite amusing when I am called a worshiper of science or Darwin when in reality all I am doing is basing my understanding of the world based on the principles of science which coincide with the principles of logic and reason. Faith is believing something despite what the evidence says, Science is a very hard methodical collection of evidence from which a hypothesis is derived and from which complex well supported theory's can be derived. It constantly remains open to new information (in fact most scientists would welcome having their grand theories smashed to bits as they would learn something totally new, those who wouldn't are not really scientists but politicians in the field of science. True science is about learning of and about the world in which we live. If that knowledge is at times disturbing or goes against your core belief or faith, then bury your head in the sand and move on, your not a scientist. If on the other hand you are open to new information and willing to use each piece of knowledge as a building block for the next, welcome to it. Science builds lots of ladders, many of them are shaky and fall, but eventually some pretty solid theories get established and we are all the wiser and better for it.
First we don't know if the object that hit us 65 million years ago was a comet or a big rock.Second the amout of water on the surface of the earth,is evidence enough that millions if not billions of comets have hit the planet in the last 4.5 billion years,what ever the cause.
Reply | Report Abuse | Link to thisModels are a means of comparing our understanding with reality. The model is a composition of our understanding. If the model behaves like the real world we can have a certain measure of confidence about our understanding of the real phenomenon. If the model does not match reality we can use those clues to guide further scientific investigation. No one claims the model IS reality. Newtonian physics describes a model of the universe in which time and space are separate entities. But despite the fact that time and space are not separate, it is very accurate. We put satellites into orbit around planets based on it. Yet, it has its limitations. We cant use it to predict the orbit of Mercury for example. Still, if Newtonian physics predicted that a boulder was going to roll down a hill and crush my house, it would be really stupid not to move just because of the Mercury limitation.
Reply | Report Abuse | Link to thisNot so true about the amount of water on the earth...one cannot really call the origins of the earth the arrival of comets to it. Rather the entire solar system was forming out of gas and dust and some of that gas was in fact water amongst other components and due to the high temperature level at the distance from the sun to the area or ring that eventually coalesced into the rocky planets, some of that material was water. When the sun ignited the intensity of the heat and the location of the early earth might very well have been closer than it is today and also possibly, the water on the earth would have been vapour rather than liquid..very, very sure in fact that it was soon enough especially since the earth was being smacked every second with more and more energetic chunks of rock, gas lumps and pieces of ice or if you will comets. As the earth became larger,its gravitational field became stronger and thus,things arrives with a loud whizz and bang and the kinetic energy of their million of arrivals melted the surface of the earth and later even, the radio nucleotides resulted in internal melting of the earth also and the driving out of the forming core yet more water..It is a constantly changing system and the arrival of comets still keep the pot boiling though at a rather more leisurely pace. The formation of life, its destruction and its reforming more than once according to the sediments found on the planet point out that our existence is unsure but pretty likely to last a while. One great thing is that when we humans go the silly notions of the Creationists will go with them! How can people be so damn bloody minded and ignorant is bey0nd me but luckily it is contained in this one part of the world..mostly in Kentucky, Nebraska and such like. Must be in the water that came from a strange comet. The rest of the world see science as what it is..not a thing to worship ( nothing is ) but a growing body of evidence as to what makes the universe tick. It is forever being refined and rejuvenated by new minds seeking better solutions to the age old questions. Creationism is utter balderdash invented on the fly by know nothings who are fighting for their lunacy while their heads are stuck like the bird dinosaur in the parched mud of their ignorance. Let's move on and in my opinion the Scientific American ought to have an editor to keep non science out of here. amen.
Reply | Report Abuse | Link to thisDoes the comments section not have an arbitrator who can edit out the non science and obvious nutters who just want to push their wierd faith in an invisible friend? Please appoint one Sci Am. I enjoy the informed comments and debateable points, but really such god guff must have another forum rather than on a science site.
Reply | Report Abuse | Link to thisPerhaps we need an arbitrator who can edit out those who misspell words like weird.None of us are perfect.Censorship is a bad idea.I myself am a non believer,but it is just as wrong to say there isn't a God as it is to say there is,because we don't know.Science is the seeking of the unknown,and there by through experiment,and repeating it,and getting the same answer we move forward,and gain knowledge.Where in faith is a matter of seeking what can't be proven,such as,God.What happens after death?,What's going on inside a black hole.What is dark matter?Just because you can't see,test or prove something through experiment doesn't mean it can't exist.Just as I am certain that any mistakes I have made in spelling,and grammar will be pointed out to me.Like I said nobody is perfect.
Reply | Report Abuse | Link to this" I guess the only evidence we want to believe is the evidence that supports our present belief system. Does that make us arrogant, or just too lazy to deal with our changing environment?". Isn't this what you are asking us to do as a creationist? We are to accept what was written in a book by a list of men that wanted to control the minds and wills of the masses because they said so? You are using the same arguments that have been levied against religious faith in a not-so-clever turn about. No evidence or truth, but silly word games. You are nothing but an annoyance.
Reply | Report Abuse | Link to thisWould not an orbit by an Oort Cloud object take hundreds of thousands of years to complete as opposed to hundreds of years as stated by the author?
Reply | Report Abuse | Link to thisStarmas, I tend to agree with you about what science is. I am a mystic, a scientist of the spirit. As such I am attacked by both "scientist" and "religionist". I am a seeker of "the kingdom of heaven" and the "indwelling presence of God". What man has done, man can do or it is not scientific. If the experiment cannot be replicated then there is reason to question the authenticity of the experiment.
Reply | Report Abuse | Link to thisJesus was the greatest scientist the world has ever known and he said that the things that he did we would also do and greater things. He came to liberate us from false doctrine and dogma, superstition, idol worship, and the sense of sin and death which causes us to feel unworthy. Those who cannot understand his methodology or his teaching have put him on a pedestal and worship him. They have turned him into an idol. They cast dispersion on those who take Jesus at his word and seek to prove that the kingdom of God is indeed inside of us and that we really are intended to "put on that mind that was also in Christ Jesus" and become the Christs that we were destined to be.
Science has long contemplated the existence of the L field and the M field which co-exist with and interpenetrate with the physical. Quantum physics is beginning to explain how this is possible. At the subatomic level there are no particles but wave lengths, frequencies, vibrations, energy which oscillates in a sine wave between a physical and non-physical matrix. The "physical" planes actually contain 4 levels which are: etheric (fire, memory), mental (M field, air, mind), emotional (L field, water, feeling), and physical (earth). The mind is separate from the brain.
The etheric body of man has organs called chakras (wheels, whirling vortices of energy), which act as step-down transformers for the Energy of God to be received in the body of man. In the Heart of hearts, the Secret Chamber of the Heart chakra, there is a "cosmic interval" and an Unfed Threefold Flame of Power (blue, Father), Wisdom (yellow, Son) and Love (pink, Holy Spirit) which arise from a cube of white fire (Mother). This flame connects us to the Crystal Cord or River of Life and is our portal to the kingdom of heaven. We go within to this flame and make the connection to our Higher Mind, the Christ Mind which is our Real Identity. From thence we contact the Presence of God individualized for each of us, our Mighty I Am Presence (the name of God given to Moses was I AM THAT I AM).
Lucifer created a godless, soulless race devoid of the spirit and not a part of the above.
this whole thing does make some amount of sensebut still you cannot base everything on computer moduls mind my spelling
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