CLOUDY ORIGINS: A comet called 2001 RX14 likely originated from a hypothesized region called the Oort cloud, far outside the planetary region of the solar system. A new model of how comets wind up near the inner planets may revise estimates of the Oort cloud's properties.
Image: Mike Solontoi/University of Washington
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A few times a year, a visitor from deep space swings by Earth's neighborhood. Usually coming in peace, these interlopers pass by close enough to be seen, then continue on their way.
The uninvited guests are comets, streaky globules of ice and dust dislodged from one of their usual haunts far from the sun and planets: the Oort cloud. Named for Dutch astronomer Jan Oort, who hypothesized its existence in 1950, the theorized cloud is thought to contain billions or even trillions of comets that range out a few thousand to tens of thousands of times as far from the sun as Earth is. Oort cloud comets are occasionally nudged onto trajectories carrying them into the inner solar system by the passing of nearby stars or other interactions with the rest of the Milky Way Galaxy.
During rare extreme stellar encounters, numerous Oort comets are sent flying, with some winding up in orbits that buzz or even collide with Earth. Some theories hold that these comet showers could explain some of Earth's extinction events, much as an asteroid or comet impact 65 million years ago is widely thought to be behind the demise of the dinosaurs.
The conventional wisdom of comet dynamics has long held that comets that manage to skirt Jupiter and Saturn without being thrown clear by those massive planets' gravitational influence 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.
But a new paper published online today by Science contends that the comets that manage to cross the solar system's so-called Jupiter–Saturn barrier do in fact originate in large numbers in the inner Oort cloud, even in the absence of a massive disruption causing a comet shower. What is more, the authors say, this newly unveiled mechanism implies that comet showers are likely not to blame for major extinctions in the past.
The relatively nearby objects of the inner Oort cloud can be temporarily kicked into the reaches of the outer cloud via interactions with the massive planets, according to a simulation carried out by graduate student Nathan Kaib and his doctoral adviser, Thomas Quinn, both of the University of Washington in Seattle. 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, the gauntlet of the massive planets has been cleared. "They can basically hop over the Jupiter–Saturn barrier," Kaib says.
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15 Comments
Add CommentI question very much the present tendency to report computer simulations as research results. They can of course be interesting, but they are not to be regarded as data. In addition what they say about the past is totally untestable. Please give us real popperian testable science.
Reply | Report Abuse | Link to thisJust how often do stars pass by? I may have missed it but I'd have thought that a star passing by was a major event.
Reply | Report Abuse | Link to thisOK, maybe it was recent in terms of astronomic time, who was the culprit? Which way did he go, who's next and when?
Reply | Report Abuse | Link to thisThe numbers of comets has little bearing on extinction events, just the number that hit earth. The probability of an event doesn't matter if it hits you.
The fact that a number of way comets find themselves coming towards earth should be obvious.
The fact that the 'giant' planet protect the inner solar system is not valid. They do not occupy enough space to exclude most comets as they are just pin pricks compared to the space around them. Yes they do herd objects in near orbits but those are little of the mass of the system with 99% already joining the planets, moons, etc to make them.
"Of course, any extrapolation is dicey," Tremaine says. "I think that's an interesting result but not the most interesting result of the paper because...these sorts of calculations always involve an extrapolation of what we KNOW." [my emphasis]
Reply | Report Abuse | Link to thisHmmm, what do we really "know"?
1. Sun formed by Acretion (gravitaional collapse): Falsified by Boyle's Law & the absence of Population III stars (source metals)
2. Solar System formed as a spinning disk according to the Nebula Theory: Falsified by both the laws classical mechanics (conservation of angular momentum - planets spinning and orbiting the wrong way) and common sense (planets dont lie on stellar-equatrial plane - any of them)
3. Oort cloud has never been observed ans has simply been postulated to explain why there are still short period (a few thousand years max) comets floating around a allegedly 4.5 billion year old solar system. Still doesn't explain it, hence this silly new theory.
Yes, Tre, I agree there has been a lot of extrapolation but what do you actually know? I would suggest very little. Even this new theory is "sort of" old.
CGI will be the death of true science. Poor, poor science.
Diagmatic, your comments about what we know make no sense, let alone common...
Reply | Report Abuse | Link to thisConservation of angular momentum holds up just fine - take 2 drifting clouds of material, that approach each other and become gravitationally bound. Their joint angular momentum will depend almost solely upon their angle and closeness of intersection. Since 99.9+ percent of the mass of the solar system is in the Sun, which rotates in only one way, the solar system as a whole has clearly retained a significant amount of angular momentum - it is not just all over the place. All the planets continue to orbit very close to this direction as well (Exactly what planet ORBITs the wrong way?) The amount of change in angular momentum required to change a planets rotation is miniscule compared to the rest of the angular moment of the system - events similar to the theory of the creation of the moon can result in an individual planet having a totally arbitrary resulting spin, so that, or individual moons rotating in arbitrary directions are like comparing specs of dust to elephants (Dust can float in air, so elephants must as well etc. ).
Regarding Boyle's law and acretion, again, no conflict. Boyle's law will keep a hot gas spread out (such as a hot gas caused by colliding clouds), but a hot gas will radiate it's heat away over time - both by radiation, and by ejecting the fastest moving particles. What is left will gradually cool (eventually to <4 Kelvin, given an infinitely long time), and thus clearly will collapse (again heating it, and ejecting and radiating more energy). One can debate over how much energy the system initially contained, and how fast it can be removed, but Boyle's law only prevents an ideal gas from collapsing in a closed system, with Nebula's and such clearly are not.
Regarding the Oort cloud, well, some stuff has been observed, some directly, some due to pertubations, so while the total mass may be in question, that is a far cry from claiming it is a silly theory...
Diogmatic,
Reply | Report Abuse | Link to thisMy 7th grade science teacher gave these same arguments many years ago. As I did not have enough experience in science I was unsure if his claims were correct or not. However, I became strongly skeptical of what he was telling us when he said there was far more evidence in the Bible that the earth was created 6500 years ago then there was evidence in the fossil record supporting the idea that the earth was far, far older than 6500 years old.
Now I know better than to apply laws of closed systems to open systems and expect the same results.
I know it's a bit pendantic but you should look up the word "Falsified", as in: http://paleo.cc/paluxy/wilker6.htm
It remains a strange fact that about 98 % of the angular momentum of the solar system resides in the planets while 99+ % of the mass is in the sun. The center of the sun, that is the poles, also rotate slower than the periphery at the equator. This is the opposite of what one might expect as the mass became concentrated at the center of the solar system. There is an explanation in a discontinuous universe but I don't see one in terms of classical mechanics. See the website article on Cosmology at www.cosmic-mindreach.com.
Reply | Report Abuse | Link to thisThere are also strange anomolies in the revolution and rotation periods of the inner terrestrial planets. Gravitational torque was believed to hold Mercury in autorotation around the sun like the moon around the earth. Then it was discovered that Mercury's rotation period is 58.65 days which is 2/3 (0.6667) of its revolution period of 87.97 days. A year is precisely half a day on Mercury since it exposes opposite faces to the sun on each revolution. It has no tilt to its axis and no seasons. One Venus day (117 Earth days) is 2/3 (0.665) of a Mercury day (175.94 Earth days). Now the rotation period of Venus is (243.17 Earth days) which is 2/3 (0.666) of an Earth Year (365.24 days). Moreover Venus is in retrograde rotation and every time it comes directly between the Earth and the sun it exposes the same face toward the Earth, even though exactly five Venus days have elapsed between such conjunctions. Mars is outside of Earth without direct resonances with other planets, however there are 666.8 Mars solar days of 24.6587 hours in a Mars year. It is an extraordinary coincidence that resonances such as these should arise with the terrestrial planets. There is no explanation for them in classical dynamical theory or in theories of planetary formation.
If comet showers are now disproven as causes of mass distinction, how to explain the periodicity of iridium deposition, crater formation, and magnetic pole reversal demonstrated by Richard Muller, Walter and Luis Alvarez, et. al, and described in Muller's excellent book "Nemesis: the Death Star"?
Reply | Report Abuse | Link to thisdgc75044 says:
Reply | Report Abuse | Link to this"Conservation of angular momentum holds up just fine - take 2 drifting clouds of material, that approach each other and become gravitationally bound."
I can see why you would be confused. I would ask: From whence, my dear friend, do these postulated "clouds of material" arise? The singularity must have simultaneously created and ejected matter outward (at faster-then-light velocities) in order to ensure that the substantial mass did not instaneously collapse upon itself. Each primordial particle was accelerating away from every other particle and continued to do so, as legend has it, for some time. So at what point and for what reason did some of these turn back? Don't say 'dark matter'.
I goofed on the "planets orbiting backwards", I meant the moons (some of them - on the same planet - google it). The solar system is in general totally resistent to naturalistic mechanistic explanations as Weir outlines above. I believe the philosopher's friend (God of the gaps) in Stellar evolution is the "asteroid impact".
Furthermore the origin (and existence) of the first star is a significant hurdle. You again postulated "colliding clouds", but from where? Cooling gases do not just change direction and the first "cloud" radiated from a single source. According to the experts the universe is still expanding so we haven't yet reached your postulated "infinitely long time" which would allow some particles to form clouds and "collide". Yet we have the sun the earth and all that is in them. Actually they say the expansion is still accelerating...
Your reference to open systems is meaningless - rather a red herring. A hot cup of tea, over time cools to room temperature by dissapating its most energetic water molecules. The more heat you apply to the tea-cup the faster the evaporation (dispersal). If you apply heat to the room, the tea will still cool to room temperature (slowly and to a different temperature). What YOU require is for all the heat to be sucked out of the tea-cup instantly while excluding the air in the room. Where are you proposing this external mechanism comes from and why is it so intelligently applied only to your tea cup?
Oort cloud observed? Let me guess, the observation is the presence of short period comets? That of course would be circular. I would suggest that, as the imagined Oort cloud is not the only know source of gravitational "pertubations" and given its speculative nature, more direct evidence is required.
Perhaps you can refer me to som
"The solar system is in general totally resistent to naturalistic mechanistic explanations as Weir outlines above." Really? Are theories really disproven because of chance (or perhaps not by chance but by processes yet unknown.) coincidences? There are many theories about why most of the angular momentum lie in the planets and not in the sun. The most current involves magnetic braking as the cause of the sun losing most of it's angular momentum.
Reply | Report Abuse | Link to thisAs well recent obverstions of discs of material around stars such as Beta Pictoris tend to support the protoplanet hypothesis.
Ungolythe says:
Reply | Report Abuse | Link to this"Really? Are theories really disproven because of chance (or perhaps not by chance but by processes yet unknown.) coincidences?"
No, theories are disroven by running counter to observable, testable and known facts such as the conservation/transfer of angular momentum, with no other facts in support of them (theories that is). Seems like (bad) Scientists are always appealling to Khronos and Tykhe (the Gods of Time and Chance) to help them escape the implications of the supernatural.
Magnetic breaking would be good if you chaps could determine unambigously the source and properties of planetery magnetic fields. Dynamo effect is defunct. I think you're just compounding the problem.
Finally "discs around stars" do not prove the nebular hypothesis any more than a car parked outside my drive proves it formed by spinning my house. Science, thankfully is made of weightier stuff.
I simply do not believe the conventional model of the Oort Cloud. Supposedly comets were propelled into distant elongate orbits, then the orbits were circularized by stellar perturbations. But I don't believe there can have been enough encounters to do that, and a stellar passage one light year away on one side of the solar system will have the opposite effect from an encounter on the other side. In short, stellar perturbations should have random effects and should make orbits more eccentric as often as they make them less eccentric.
Reply | Report Abuse | Link to thisI believe the Oort Cloud objects are still in extremely elliptical orbits and spend the vast majority of their time near aphelion (Kepler's Second Law). An orbit with an aphelion of one light year will have a period of about six million years. A star passing through the Oort Cloud is not going to cause comets to fall inward any more than ordinary orbital mechanics do anyway.
If a passing rogue star perturbed our ort cloud, shouldn't that star still be nearby and a discernable trjectory calc'd for it using today's mega software? If it isn't still nearby, having traveled at such a high velocity wouldn't it have dissipated itself and left a glowing ion tral for us to see? I think no such event took place. Look to gravity waves from collided Black holes to have perturbed the oort and kieper belt
Reply | Report Abuse | Link to thisUngolythe,
Reply | Report Abuse | Link to thisYour response is slightly puzzling; in answer to my statement that the solar system resists naturalistic explanations, you start asking me about chance and probability.
I didn't make any appeal to chance or probability, that's part of the evolutionists tool-kit, in fact I think it IS the damn tool-kit!
What may have escaped your attention, is that these plethora of theories you tout are actually mutually-exclusive. That is, they may satisfy one isolated phonomenon observed in the soloar system, but they are diametrically opposed to any other theories (or premises) that are necessary to explain the numerous other obseveravtions in the self-same solar system. What you need is one theory that covers all the facts/observations.
What this leaves you with is many gods but no saviour for your self-inflicted ideology.
RE: Beta Pictoris, I suggest you tend to your own garden (explain the solar system) which you have access to, before you go theorising about things in a galaxy far far away...
I kinda expected from the article title a little bit more about cometary formation process rather that the how, what, when of how the may or may not get knocked into a solar-skimming orbit. I guess it's just me?
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