Real Science Friday: Comets

[Tyrathca]

Actually, yeah, it is in a scientific context.

I'll be sure to tell the string theorists then, they'll be delighted.

The problem is you're all too eager to discuss matters pertaining to a guy's reputation rather than pertaining to actual facts.

When have I discussed the guys reputation. The guys reputation counts for nought, either he or you can provide a source recording him predicting the olivine before NASA's probe returned or not. But I am not going to take his word on it nor should I, not for him and not for anyone else.

Olivine in space doesn't have to come from this planet. It is merely assumed that the olivine in comets did. As far as I can tell you've nothing in the way of data that denies that possibility.

But by your own admission you have nothing in the data to say your assumption is correct.

 

[Stripe]

we'd have to see significantly less elemental fractionation and differentiation. Basically, everything we see when it comes to earth's compositional variation suggests otherwise.

Is it possible for a single location on or in earth to produce the mineralogy found? I think your objection here could only be gotten around by an explanation for how only a certain range of rock was sent into space. If it's impossible for earth to create any such material then it's not going to help if we have a means of selecting a range, but if it is possible (however uncommon) to produce the mineralogy then a mechanism added to the explanation might have merit.

Does that make sense?

Probably not We'll have to get back to it at some point...

Let me know.

Say what now? This I have not heard...you'll have to provide some sources for this.

Gimme a chance on that front. ..

Mineralogy will never trump the physics; in fact, mineralogy and physics agree quite well...

:chuckle:

glad to hear it.

I'll be sure to tell the string theorists then, they'll be delighted.

Who? No matter who we are talking about, the fact that an idea predicts a result is not affected by people having seen the result.

When have I discussed the guys reputation. The guys reputation counts for nought, either he or you can provide a source recording him predicting the olivine before NASA's probe returned or not. But I am not going to take his word on it nor should I, not for him and not for anyone else.

:idunno: Regardless of the timing and the honesty of the reporting if an idea makes a prediction that matches with reality then the idea gains merit. Feel free to keep doubting the validity of Dr. Brown's clearly laid out predictions if you wish. But I'd prefer you started adding something worthwhile to the discussion. :thumb:

But by your own admission you have nothing in the data to say your assumption is correct.

You're not very good at this science thing, are you?

 

[The Barbarian]

Actually, astronomers aren't at all surprised by the number of short-term comets.

The discovery of the farther scattered disk beyond the Kuiper belt shows a huge number of gravitationally unstable comet-like objects exist, which gradually migrate toward the inner solar system, first becoming Centaur objects, and then eventually becoming short-term comets.

As usual, creationist ideas depend on ignorance.

 

[Stripe]

As usual, creationist ideas depend on ignorance.

No, they don't.

 

[Stripe]

Say what now? This I have not heard...you'll have to provide some sources for this.

Consider the implications of inbound material. Were space debris sourced from outside the solar system their visits here would be very brief and very fast. Not to mention you'd have to have an absolutely gigantic source to account for the mass that arrives this far away.

It is far more reasonable to assume that everything in our solar system started out in our solar system.

And think about escape velocities. You know how hard it is to get an object into orbit from the earth. Imagine what is required to escape a solar system!

 

[The Barbarian]

Barbarian observes:
As usual, creationist ideas depend on ignorance.

No, they don't.

This latest one is a good example. Not knowing the source of short-term comets, creationists assumed that there wasn't any way to replenish the number of them. In fact, new ones are constantly being observed, some of them short-term enough that we would have seen them previously if they existed then.

Kepler's laws and Newton's theory of gravity make it fairly easy to predict when they should have been seen previously. New Jupiter-type comets, with periods of less than 20 years are obviously being produced from somewhere.

There's a huge amount of material in the Kuiper Belt and the outer belt, and the Oort cloud is large enough to produce comets for billions of years as well.

 

[Stripe]

This latest one is a good example. Not knowing the source of short-term comets, creationists assumed that there wasn't any way to replenish the number of them. In fact, new ones are constantly being observed, some of them short-term enough that we would have seen them previously if they existed then.

Kepler's laws and Newton's theory of gravity make it fairly easy to predict when they should have been seen previously. New Jupiter-type comets, with periods of less than 20 years are obviously being produced from somewhere.

There's a huge amount of material in the Kuiper Belt and the outer belt, and the Oort cloud is large enough to produce comets for billions of years as well.

"New" comets in Jupiter's family are not new because they just arrived. They're new because they've just been catalogued. You don't get comets falling into Jupiter's family. It cannot happen save by colossal coincidence. And citing an unreachable source for comets simply ignores the glaringly obvious - that water and rocks in the solar system are most likely to come from the place with the most available rocks and water.

 

[The Barbarian]

"New" comets in Jupiter's family are not new because they just arrived. They're new because they've just been catalogued.

That's a testable argument. You see, they can compute the period from the shape of the orbit. And they can go back and search old photos of the sky to see. And some new ones show up from time to time, that weren't there before.

And citing an unreachable source for comets simply ignores the glaringly obvious - that water and rocks in the solar system are most likely to come from the place with the most available rocks and water.

Yep. The Kuiper belt, outer belt, and Oort cloud has more of both than Earth does.

 

[Stripe]

That's a testable argument. You see, they can compute the period from the shape of the orbit. And they can go back and search old photos of the sky to see. And some new ones show up from time to time, that weren't there before.

Like magic when we look closer we see things we didn't see before. :chuckle:

Yep. The Kuiper belt, outer belt, and Oort cloud has more of both than Earth does.

Yep .. they kinda have to fit the data, don't they. It'd be kinda silly to postulate such things where they did not match our observations. :chuckle:

 

[The Barbarian]

Barbarian observes:
That's a testable argument. You see, they can compute the period from the shape of the orbit. And they can go back and search old photos of the sky to see. And some new ones show up from time to time, that weren't there before.

Like magic when we look closer we see things we didn't see before.

It only looks like magic when you don't understand it.

Barbarian regarding rock and water:
Yep. The Kuiper belt, outer belt, and Oort cloud has more of both than Earth does.

Yep .. they kinda have to fit the data, don't they.

Must seem like cheating to creationists. "No fair!" You change your theories to fit the data!"

 

[Jukia]

And think about escape velocities. You know how hard it is to get an object into orbit from the earth. Imagine what is required to escape a solar system!

What is the escape velocity from the earth? What is the escape velocity from the solar system?

Hint: the escape velocity from the earth is about 25,000 miles per hour.

 

[Stripe]

Must seem like cheating to creationists. "No fair!" You change your theories to fit the data!"

Not at all. It's much harder to defend the idea that comets started life on Earth. Nothing fair about that .. especially if it's true.

 

[The Barbarian]

Wouldn't matter if comets started life on Earth. Fact is, short-term comets are being replenished from all those bodies out beyond Neptune.

And the long-term ones are coming from the Oort cloud. Would you like to learn how we know that?

 

[Stripe]

Wouldn't matter if comets started life on Earth. Fact is, short-term comets are being replenished from all those bodies out beyond Neptune.

No, they're not. in a few thousand years they will almost all be gone.

And the long-term ones are coming from the Oort cloud. Would you like to learn how we know that?

They don't come from the Oort cloud .. that's just a thing someone invented to try and explain the data. A far more reasonable, and falsifiable, explanation is that they all (long and short) came from Earth.

 

[Flipper]

No, they're not. in a few thousand years they will almost all be gone.

You seem pretty sure of that. Bearing in mind that there's no way to detect comets that aren't involved in sunfall beyond their periodicity, I don't know how you can be so sure that they aren't refreshed on a semi-regular basis.

They don't come from the Oort cloud .. that's just a thing someone invented to try and explain the data. A far more reasonable, and falsifiable, explanation is that they all (long and short) came from Earth.

Well, the good news is that there are a number of observations in the pipeline that should provide indirect or even direct evidence to support or destroy the Oort Cloud hypothesis. But based on our current observations, it is a reasonable inference.

Walt Brown's hypothesis, on the other hand, is founded on bad science that doesn't fit with current observations, so it's hardly a compelling contender.

 

[Stripe]

You seem pretty sure of that. Bearing in mind that there's no way to detect comets that aren't involved in sunfall beyond their periodicity, I don't know how you can be so sure that they aren't refreshed on a semi-regular basis.

Because the means to capture a comet will almost certainly destroy it and because even if it did survive the chances of capture happening are so remote as to be safely disregarded as a source of new comets.

Perhaps there is a mechanism lined up that regularly chutes comets in from a factory line somewhere in space (that's what it's going to take), but it is far more reasonable to assume that what we see started out with what we know of the inner solar system.

Well, the good news is that there are a number of observations in the pipeline that should provide indirect or even direct evidence to support or destroy the Oort Cloud hypothesis. But based on our current observations, it is a reasonable inference.

Observations are good and assumptions are fine, but the assumption of Earth as the source for comets is a far more reasonable one than any other source, known or postulated.

Walt Brown's hypothesis, on the other hand, is founded on bad science that doesn't fit with current observations, so it's hardly a compelling contender.

I doubt you've read more than a few paragraphs of his. How about you add some substance to an otherwise useless disparagement. :up:

 

[The Barbarian]

Perhaps there is a mechanism lined up that regularly chutes comets in from a factory line somewhere in space (that's what it's going to take)

No factory. The discovery of countless bodies in unstable orbits beyond Neptune is sufficient. The evidence shows that these eventually decay first into Centaur objects and then short-period comets. No magic.

Observations are good and assumptions are fine, but the assumption of Earth as the source for comets is a far more reasonable one than any other source, known or postulated.

Not in science. Your thinking is O.K. as a religion, but science needs evidence. And the evidence shows the existence of an Oort cloud. We know where it is, because one can compute the aphelion of each of the long-term comets, and they show the location of the cloud from which they came.

 

[Stripe]

Not in science. Your thinking is O.K. as a religion, but science needs evidence. And the evidence shows the existence of an Oort cloud. We know where it is, because one can compute the aphelion of each of the long-term comets, and they show the location of the cloud from which they came.

There must be an Oort cloud otherwise there is no alternative but to assume comets originated on Earth .. .and that can't have happened!

 

[The Barbarian]

There must be an Oort cloud otherwise...

Otherwise, we'd have to conclude everything Kepler and Newton showed us is wrong. You see, by looking at the paths of long-term comets, we can see where they go, and if you add up all the perhelia of such comets, we end up with a cloud of dots far out beyond Neptune. So the cloud exists, merely by observing long-term comets.

there is no alternative but to assume comets originated on Earth .. .and that can't have happened!

Why not simply take the evidence as it is? The mass of all comets is much greater than the mass of all the water on the Earth. How, exactly did all that water and dust get lifted off the earth and moved out up to a light year from the sun?

Show us your numbers, Stipe.

 

[Flipper]

In 2003, I wrote up and posted detailed annotations on the appallingly bad section he wrote on Out of Place fossils, calling out the shamefully poor scholarship that he hid in the technical footnotes (Pravda as a source to prove dino/human coexistence in a "scientific" book? - no, that's quality stuff).

I was wrong - he didn't change his book until 2008 or 2009, when an Amazon reviewer raised some of the same points I had made about the section (plus a whole slew of other problems). He summarizes a lot of the serious issues with Walt Brown's big idea.

This wasn't supposed to be an edit of the original post, but rather a new post, so I have accidentally deleted the original content. Oops.