Evidence For 200-Year-Old Comet Impact On Neptune 83
astroengine writes "Astronomers using ESA's Herschel space observatory have spotted evidence of a cometary impact in Neptune's upper atmosphere (publication, PDF). Whereas impact craters on rocky planetary bodies can remain for billions of years, an impact in the dynamic atmospheres of gas giants aren't obvious, especially if long periods of time have elapsed. This ultimate 'cold case' tracked the unusual distribution of carbon monoxide in Neptune's stratosphere, a sure sign it was deposited there by an external source. Once they realized they were looking at a comet impact, researchers were able to deduce when the impact occurred: 200 years ago."
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Barack Obama has shown the same type of birth certificate that I showed to get my drivers license and passport.
How come all the white Presidents didn't have their American birth citizenship questioned by racist idiots?
As soon as a black guy shows up, you immediately assume he was born in Kenya despite overwhelming proof and documentation including a valid birth certificate??
Racism.
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those who questioned bush were "against us" after 911. What's good for the goose...
Impact probability (Score:5, Interesting)
Note that this hypothesis is more plausible than it might seem at first glance since we've seen comets impact gas giants before. Most famously, in 1994 Shoemaker-Levy 9 was observed directly impacting on Jupiter http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9 [wikipedia.org]. This also isn't the first time this sort of technique has been used to detect historic comet impacts. As TFA notes, this technique was previously used to show that a similar event likely occurred around 230 years ago on Saturn.
Although comets hit the outer planets frequently, this is due to a variety of issues including the large size of the planets and the exact orbit of Jupiter (which makes Jupiter very effective at clearing interplanetary debris). Thus, this sort of situation doesn't pose much of a risk for Earth. However, even a single such comet colliding with Earth would be an extinction level event. The asteroid that caused the Chicxulub crater in the Yucatan is generally estimated to be around 10 km diameter and most comets are generally larger than that (Halley's Comet has a mean diameter of 11 km, and many have larger mean diameters). Comets are also much easier to spot generally than asteroids and so we have a better idea about their orbits and are more likely to have a lot of warning before a potential impact event on Earth. Asteroids are much harder to see and pose much more of a threat even though they are smaller objects (with the exception of a handful such as Ceres).
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You and I have different definitions of impact, but I suppose you're correct about SL9. I tend to think exploding in the atmosphere isn't an impact, but on a gaseous planet you aren't going to get much other than an airburst.
What I want to know is how we know what a comet that impacted a gas giant 200 years ago would look like in the atmosphere 200 years after the fact.
Maybe its just me, but it seems like an aweful lot of 'science' recently has been based on pure speculation. I mean, I know there are some
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On earth we measure the intensity of UV light in Antarctica and conclude that the wrong sort of gas is being used in air conditioners in the tropics. Of course you have to follow a few steps from the observation to the conclusion, and uncertainty accumulates along the way. But thats science for you.
While we are at it, how can Toyota assemble an engine in a factory, sell it, and have it operate flawlessly for 20 years without even testing it once? I don't know either. Thats engineering for you.
Re:Impact probability (Score:4, Informative)
RTFA.
We're talking about the distribution of gases between layers of the atmosphere. This same technique could be used on earth to extrapolate when the industrial revolution started to have an impact on the upper atmosphere, and is based on a similar principle as analyzing ice cores to determine the composition of the atmosphere of the earth a thousand years ago, and as a result, make inferences regarding the general climate at the time. This isn't that far-fetched.
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If you read the abstract or the article linked in the summary, you'd know.
The balance of your reply makes it clear why you didn't however.
Yes, I believe you're full of bullshit. Willfully and knowingly so. And you revel in it.
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All science should be therefore taken with a grain of salt, it's kind of the point. There is now a theory for a spot on Neptune, you aren't obligated to take it as some sort of absolute truth.
And then to apply the 'logic' of "well we suck at this aspect of science so how could we be right about this other compl
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I wrote a long response to this. Then I deleted it, because it can be easily summarized...
It is just you. Just because you are a fucking "aweful" idiot doesn't mean that everybody is.
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Maybe its just me, but it seems like an aweful lot of 'science' recently has been based on pure speculation.
It is, indeed, just you.
"Pure" speculation would be speculation without reference to facts or well established abstract principles.
In the present case, there is a distinct feature in the upper atmosphere of Neptune. That is a fact. We also have a whole bunch of facts about the details of the feature. Furthermore, we have a bunch of facts about the properties of comets and the odds of a comet of a given size hitting Neptune in the past few hundred years. And finally, we have a bunch of facts about how th
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You know, what's actually kind of scary about what you've written is ju
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My guess is that a comet orbits the sun dozens or hundreds of times before it hits anything, and many of them never come as close to the sun as the Earth anyway. When it does hit something the probability of an impact with a comet may scale with the mass of the planet. Jupiter has 317.8 time the mass of earth and 10 times the radius. Another guess is that the probability scales with cross sectional area (for the actual impact) and mass (for the effective range of the gravitational field). Multiply the two (
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Well for a start the gravitational field of Jupiter (for example) can change the path of a comet to collide with the planet. Additionally if the comet goes within the roche limit of a planet it can fall to bits. This causes momentum to be split between parts of the comet, resulting in much of the object entering the atmosphere. This was why we say shoemaker levy 9 on its last orbit. Looking further out the gravitational field of a planet can alter the orbits of comets so they have a resonant relationship wi
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I don't see how these arguments warrant a *linear* relationship between the relative masses and the probability of impact
Oh okay. My argument was really intended to be back of the envelope but I looked up Gravitational acceleration [wikipedia.org] (its been a while since I had to use it). Acceleration due to gravity is proportional to mass so if you pass Earth at 100000km and Jupiter at the same distance you will get 317 times the acceleration from Jupiter at that distance. So if you think about a target 100000 km in radius the gravity alone should make it 317 times more likely you will hit the planet, if the planet is Jupiter.
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I am not an astronomer, but I did watch Cosmos the other night...
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Which is more than I knew.
Thanks for the info.
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Metallic Hydrogen? Man, from the article you linked, I see the words "alkali metal" and "superconductor, up to room temperature".
Man, is science ever cool. :-P
Cheers
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Note that this hypothesis is more plausible than it might seem at first glance since we've seen comets impact gas giants before. Most famously, in 1994 Shoemaker-Levy 9 was observed directly impacting on Jupiter http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9 [wikipedia.org]. This also isn't the first time this sort of technique has been used to detect historic comet impacts. As TFA notes, this technique was previously used to show that a similar event likely occurred around 230 years ago on Saturn.
So why do you think this technique shows evidence of a comet impact at a particular date? At best, it shows evidence of comet impact. Going from that to make a particular claim about the number of large impacts that could generate the observed atmospheric details, seems hasty. We may be seeing the results of many impacts over thousands of years rather than single large impacts a couple centuries ago.
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If your hypothesis was true - they wouldn't be a sharp gradient of CO concentrations between atmospheric layers. However, such a gradient was observed, showing the impacts occurred in a relatively short time frame a relatively short time ago.
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If your hypothesis was true - they wouldn't be a sharp gradient of CO concentrations between atmospheric layers. However, such a gradient was observed, showing the impacts occurred in a relatively short time frame a relatively short time ago.
Why is that assertion true (that a sharp gradient implies what they claim it implies)? From what I understand, there appears to be observations of perhaps two or three impacts that they're basing this assertion on, Shoemaker-Levy and single addition impacts on Jupiter and Saturn since. That seems very sparse evidence on which to base such claims.
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Why shouldn't it be true? (With the caveat that science doesn't claim to produce truth - only to produce explanations that match observations.) The theory matches all available evidence, so it'll do until someone comes up with a better explanation.
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Why shouldn't it be true? (With the caveat that science doesn't claim to produce truth - only to produce explanations that match observations.) The theory matches all available evidence, so it'll do until someone comes up with a better explanation.
I didn't come up with a "better" explanation, but I did come up with a different one that apparently is just as compatible with the evidence.
That's the way science works - they examine the available facts and produce a theory that explains it. Then other people seek to find if the theory holds up over time, as more facts are discovered.
Save the lecture. My point was that there was other hypotheses that could explain the existing evidence. Why should we get into a discussion of the scientific method when it isn't an issue? Isn't that a bit unscientific to introduce extraneous information?
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If it's the one I replied to, it's not compatible with the evidence.
You asked a question, and I answered it
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If it's the one I replied to, it's not compatible with the evidence.
This is what I'm talking about. There isn't enough evidence for the claim you make. Recall that you claimed a sharp gradient in carbon monoxide implies a single impact sequence some point about two centuries ago. That may well be true and I do not disagree that the hypothesis is compatible with the evidence. But again, that differential can also be explained through a combination of a steady rain of comets combined with some enhanced mechanism for destroying/sequestering carbon monoxide in the lower layer o
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Ceres isn't an asteroid.
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And Pluto isn't a planet. Not any more. Sniff!
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Ceres isn't an asteroid.
Depends on who you ask. It arguably is. And before someone leaps forward with links about Ceres being classified as a "dwarf planet", let me note that saying what Ceres is doesn't prove what it isn't, as things can answer to more than one description (you don't contradict someone claiming that a man is a father by noting that he's a brother -- he can be both). "Planet" has now received a much less ambiguous definition than it once had, and "dwarf planet" has be coined, but, as far as I know, "asteroid" h
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Interesting, I didn't know that.
Whats in it for us? (Score:2)
We are rapidly learning more about the cometary impact rate on Jupiter, and now Neptune. It should be possible to extrapolate from this to calculate the impact rate on Earth.
Clearly, a dangerous object spends some time orbiting across the orbits of the planets before it hits something, and the probability of an impact on Jupiter is much greater than an impact on Earth.
We seem to be getting a handle on the risk from asteroids, but a comet can come our way without warning.
Re:Whats in it for us? (Score:5, Informative)
We are rapidly learning more about the cometary impact rate on Jupiter, and now Neptune. It should be possible to extrapolate from this to calculate the impact rate on Earth.
Better extrapolation method: look at historic impacts on Earth. See Chapman's 1994 paper in Nature "Impacts on the Earth by asteroids and comets: assessing the hazard" v. 367, Issue 6458, pg. 33-40. This paper gives a good summary of the literature at the time (my impression is that this hasn't changed much since then but this is far from my area of expertise).
We seem to be getting a handle on the risk from asteroids, but a comet can come our way without warning.
Not exactly. Comets that are anywhere near the inner system become visible very quickly due to their outgassing. In contrast asteroids are much harder to spot. On the other hand, asteroids stay where they are supposed to and don't have wildly elliptic orbits so they are much easier to track in the long run and tag. So there's a mix here, but overall asteroids are more likely to strike without warning. Comets will likely give us at least a few days to have a giant orgy.
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Comets will likely give us at least a few days to have a giant orgy.
Big deal, I won't be invited that time either :(
Oh well, atleast that time I won't have to wish for everyone else to die... They will anyway! >:]
Re:Whats in it for us? (Score:4, Informative)
So there's a mix here, but overall asteroids are more likely to strike without warning.
...until we catalog them. We can do that from low earth orbit with infrared telescopes. The wise mission [berkeley.edu] has massively increased the rate of discovery, which is why I think the uncertainty about impacts will come from comets in the future.
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Another issue with the highly eccentric orbits is that a comet can do a close pass past the sun, and hit us almost directly from the direction of the sun. A large object on that trajectory could easily be missed entirely.
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But... (Score:1)
No... (Score:2)
... and it also wiped out any dinosaurs that were there...
Cometary Impact on Neptune about 230 years ago (Score:2)
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We have. Elzar [wikipedia.org] is Neptunian.
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Perhaps this is why we have never seen any Neptunians?
Neptune is outside the goldilocks zone [slashdot.org] [fiction]
If that is 200 earth years (Score:5, Interesting)
Voyager 2? (Score:4, Informative)
That's funny, because my back-of-the-napkin estimate is that at the time, Voyager 2 was 3 billion miles further away from Jupiter than the Earth is. Wonder what they thought they were gonna see with 15-year-old technology that they weren't going to see with, say, the Hubble telescope, new ground-based instruments, or hell, even the naked eye that was 3 billion miles closer to the event.
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Maybe they had lights attached to the probe, like you had with old movie cameras.
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The Shoemaker-Levy impacts were happening on the side of Jupiter not visible from Earth. Voyager, Galileo and Ulysses all had a different view of the planet, so the view from 3 billion miles away is better than "none at all".
Re:Voyager 2? (Score:5, Informative)
PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
VOYAGER MISSION STATUS
August 1, 1994
Both the Voyager 1 and 2 spacecraft are healthy and they are
continuing to take data on fields and particles in interplanetary
space.
The Voyager 2 spacecraft used two of its scientific
instruments to look at the impacts of Comet Shoemaker-Levy 9
fragments as they impacted Jupiter July 16-22. Both the
ultraviolet spectrometer and the planetary radio astronomy
experiments were used in the observations. Neither instrument
detected any UV emission or radio signals during the impacts.
The spacecraft began its observations of Jupiter on July 8 and
will continue to observe the planet until August 17. At the
time of the comet impacts, Voyager 2 was 6.1 billion kilometers
(3.7 billion miles) from Jupiter.
Voyager 1 is currently 8.4 billion kilometers (5.2 billion
miles) from Earth. Voyager 2 is 6.4 billion kilometers (4
billion miles) from Earth.
My question would be, why not try? It's not like it took time away from mission-critical operations.
200 year (Score:1)
Evidence For 200-Year-Old Comet Impact On Neptune
I thought most comets were much older than 200 years. How does a comet form, and crash, in a mere 200 years?
Damn you Negaverse! You too Serenity! (Score:2)
If the moon kingdom had a damned militia this wouldn't have happened....
Instead they put all their funding for palaces built in the inhospitable airless vacuum that is the surface of the moon. Instead of building some sorta real defense force...