Solar Mixing and Inti

This forum is for discussing space science topics related to Stardust@home.

Moderator: DustMods

Post Reply
ZackG
Stardust@home Team
Stardust@home Team
Posts: 38
Joined: Thu Aug 17, 2006 4:25 pm

Solar Mixing and Inti

Post by ZackG » Thu Feb 01, 2007 8:52 pm

One of the biggest findings of the Stardust mission is the evidence for “large scale mixingâ€
Zack Gainsforth
Space Sciences Laboratory
UC Berkeley

GelDelve

Post by GelDelve » Thu Feb 01, 2007 10:38 pm

How is it known that Wild2 has never in its history flown near the sun or combined with another comet (or debris from such a comet or comets) that did? I know that the reason Wild2 was targeted for this mission was that it was believed to have always been in deep space and far away from the sun before a chance encounter with a major planet (I forget which one it was) caused the former deep space object to alter its path into a cometary object that the Stardust mission aimed to take advantage of. So, is it possible that Wild2 simply combined with another smaller body that was on a cometary path or that it's possibly former cometary path was influenced away from being cometary in the distant past and has now been influenced back to a cometary path? I don't understand why these scenarios are not considered or possibly others I have not thought of, but only the two you have mentioned here.

Nikita
DustMod
Posts: 994
Joined: Wed May 17, 2006 8:33 pm
Location: Indiana, USA

Post by Nikita » Fri Feb 02, 2007 5:33 am

How likely are the molecules to change when orbiting the sun? Is it possible for them to change composition when exposed to the sun on a close pass? Could impact debris from closer material to the sun in earlier formations have drifted out, thus causing the CAIs to be found further out?
How do you know that Inti was only formed near the sun? Is there any way to tell us in simple terms?
From dust we come

ZackG
Stardust@home Team
Stardust@home Team
Posts: 38
Joined: Thu Aug 17, 2006 4:25 pm

Orbits and CAI's

Post by ZackG » Fri Feb 02, 2007 7:29 pm

Oooh! Good questions! Part of the reason those questions are so good is because we don't really know the answer to them definitively. I can't tell you: We're 100% sure CAI's formed near the sun. I can't prove it. I can just point out that it is the simplest possible solution for the evidence and refer you to Occam's razor. That said, here's what we think, and here's why:

Orbits: One way to tell that Wild-2 has never been in an orbit that takes it close to the sun is the fact that it has a tail. It can be observed with comets (over many years of course) that their tails dwindle over time. We also observe methane, water and such in the tail of the comet, which we take to mean that the comet contained ices of these materials, and now under exposure to the sun, these ices are subliming off to form the tail. If the comet had spent much time around the sun, either in the distant past or recently, all the ices would have burnt off by now, and so it would not have a tail. Combine that with the fact that the comet was first seen in 1978, and we have a good reason to think that it has never been near the sun. The chances of being thrown into a near-sun orbit, and out again, and in again are low. Remember that it can't have spent much time near the Sun or the ices would have sublimed, and yet it has to form minerals at 1700 K. That's a tough combination!

On the other hand, the new orbit could possibly be the result of a collision. Nevertheless, we think it came to have an orbit close to the sun by by flying too close to Jupiter because if you trace it's orbit backwards from the first observations in 1978, you find that in 1974 it was within a million km of Jupiter. So the most likely cause is that Jupiter changed its orbit. This is a rather common phenomena we've found with a number of comets. They will suddenly show up one day, and you can trace back their orbits to find that they had interacted with Jupiter's gravitaional field. Remember, Jupiter is BIG. It is so big, in fact that it causes the center of the solar system to lie OUTSIDE the Sun, i.e. the Sun is not actually in the center of the system, because it is being tossed about slightly by Jupiter. (For those with a technical inclination, we say that the "barycenter" of the system lies just above the surface of the Sun.) Now, by contrast, the probability that the comet has collided with another object at some point in its life is actually quite high. On astronomical timescales things collide all the time in the solar system!

Molecules: The molecules certainly do change near the Sun. That is, two molecules can react with one another to become a third, or a larger molecule can break up into two smaller molecules. This can also happen at a great distance from the Sun, but the types of reactions that occur are different. You might remember from chemistry class that you often have to heat mixtures up before they start to react, and then you'll get to that "magical temperature" where suddenly, things happen. Well, we just extrapolate what chemical reactions would precede the formation of certain minerals based on our knowledge of chemistry. The minerals themselves also form only under very specific conditions. For example, diamond (on Earth) comes from deep under the Earth where the temperatures and pressures are very high. We can now manufacture diamonds in factories, but the equipment to do so is quite extreme -- you can't just make diamonds in a frying pan. So based on the chemistry of some of these minerals (for example, melilite) we figure that they had to form at something like 1700 K. Well, what existed in the solar system during its early formation that was at least 1700 K?

Now, there is another twist to this: As you know atoms differ in the numbers of protons their nuclei have AND in the number of neutrons they have. Changing the number of protons makes the atoms a comletely different kind of atom. But, for the most part, changing the number of neutrons doesn't make much of a difference. For example, there are three common types of oxygen. They all have 8 protons, but one has 8 neutrons, one has 9 and one has 10. We call them O-16, O-17, and O-18 (16 = 8 protons + 8 neutrons, etc.) These are called isotopes of oxygen. Isotope comes from iso = equal, and topos = place (Greek). They all three take up the same spot on the periodic table! :-)

In CAI's we can tell from an isotope of aluminum, that they are the oldest things in the solar system. This is a form of radioisotope dating similar in some respects to carbon dating which you probably have heard of. We can also tell from other isotopes in the CAI's that they are different than the rest of the solar system. Since we know they formed early (from the aluminum), and we know that they are different (from other isotopes) we think that they formed before the isotopes in the solar system had a chance to "mix" and that they haven't changed since they formed. This means they didn't do time on some planet where geological processes would have mixed them in, etc. So, the occam's razor solution is that they formed near the sun and haven't really changed since. There are other possibilities, but the *simplest* solution is just that they formed near the Sun. Who knows, maybe someday we'll discover something about them that points to a completely different source! It would be just another day in science! :lol:
Zack Gainsforth
Space Sciences Laboratory
UC Berkeley

GelDelve

Post by GelDelve » Fri Feb 02, 2007 9:12 pm

Thanks, Zack!

I think I already knew that the answer was likely to be that the two hypotheses under consideration have a far greater probability than any other explanations the experts could envision. I didn't know if other possibilities were considered or, in particular, whether any thought was given to the ones that immediately came to my mind (and Nikita's).

I only hope that more samples from actual asteroids in the deep parts of our solar system and "new" comets can be obtained in order to refine and build more confidence in whatever theory is eventually generally accepted about the migration of atoms, isotopes, and molecules from near the sun to those deeper regions.

Nikita
DustMod
Posts: 994
Joined: Wed May 17, 2006 8:33 pm
Location: Indiana, USA

Post by Nikita » Sat Feb 03, 2007 7:52 am

OK, so based on what you are saying, I can say with a fair degree of certainty that Comet McNaught is
1. A newbie to our neck of the woods
2. A guest compliments of Jupiter

Since it is a recent discovery, it hasn't been in our area before, or at least not for a long time. But, it had an amazing tail, so it probably hasn't been this close before. Therefore, long tail, new find, even without tracing its orbit, I can guess Jupiter's gravitational field played a role.
Am I right?

Also, if the comet's tail gets smaller each time it passes, does it lose less material each time? Is it an exponential decline? Will it get to a point that, unless it impacts with something, it will no longer have a tail and be just another unimpressive chunk rolling around our solar system?

Thanks for the info, it does make this more of a real science and not just a project! It's exciting to think about what the star dust will show!
From dust we come

GelDelve

Re: Orbits and CAI's

Post by GelDelve » Sat Feb 03, 2007 3:09 pm

ZackG wrote:Since we know they formed early (from the aluminum), and we know that they are different (from other isotopes) we think that they formed before the isotopes in the solar system had a chance to "mix" and that they haven't changed since they formed. This means they didn't do time on some planet where geological processes would have mixed them in, etc. So, the occam's razor solution is that they formed near the sun and haven't really changed since. There are other possibilities, but the *simplest* solution is just that they formed near the Sun. Who knows, maybe someday we'll discover something about them that points to a completely different source! It would be just another day in science! :lol:
Does this aluminum/isotope "mix" also rule out that these CAI's could have been part of the primordial soup from which the solar system evolved? In other words we (well the scientists anyway) can tell that the aluminum and/or the other isotopes of the molecules are old enough that they could not have formed on a planet, but too young to have already been formed and joined as molecules prior to becoming part of that primordial soup? I guess another possibility would be that the scientists would expect to find these particular isotopes and molecules occurring more frequently than they do, if they were here from the very beginning (of the solar system)? Just curious :!:

jsmaje
Posts: 603
Joined: Tue Aug 15, 2006 8:39 am
Location: Manchester UK

Post by jsmaje » Sat Feb 03, 2007 3:57 pm

Zack -

Following on from GelDelve, is it known for sure that CAIs are not in fact older than the solar system, and not simply "the oldest things in the solar system"?

Presumably our system formed not only from pristine gas clouds but also from earlier interstellar/galactic material created during prior epochs of supernovae explosions etc. In fact, aren't we supposed to be either in or on the edge of a 'local bubble' in the galaxy, thought to have arisen from just such an ancient event?

So, if CAIs were in fact older than the solar system, wouldn't that readily account for their presence in remote Kuiper belt objects, without need for non-mixing or other fancy mechanisms to explain how they might have been made close to (& then ejected far from) the sun at a later date?

In other words, is it not possible they came from an earlier 'sun'?
And - if any interstellar particles found by the present project eventually turn out to be like CAIs, could that settle the matter?
Last edited by jsmaje on Sat Feb 03, 2007 4:41 pm, edited 2 times in total.

Nikita
DustMod
Posts: 994
Joined: Wed May 17, 2006 8:33 pm
Location: Indiana, USA

Post by Nikita » Sat Feb 03, 2007 10:18 pm

Zack,

You have opened Pandora's Box here! :lol:
From dust we come

ZackG
Stardust@home Team
Stardust@home Team
Posts: 38
Joined: Thu Aug 17, 2006 4:25 pm

Pandora's box!

Post by ZackG » Tue Feb 06, 2007 2:20 pm

Wow! What a great Pandora's box! Wait! Didn't Pandora's box unleash the evils unto the world? Questions and curiosity are good! This isn't a Pandora's box! :twisted:

Give me a little bit to answer though. I'm currently evaluating possible tracks -- which is something I think you are also interested in... :wink:
Zack Gainsforth
Space Sciences Laboratory
UC Berkeley

Nikita
DustMod
Posts: 994
Joined: Wed May 17, 2006 8:33 pm
Location: Indiana, USA

Post by Nikita » Tue Feb 06, 2007 4:19 pm

Sorry about the error! Guess I have no analogy for you!
From dust we come

ZackG
Stardust@home Team
Stardust@home Team
Posts: 38
Joined: Thu Aug 17, 2006 4:25 pm

Comet McNaught

Post by ZackG » Mon Feb 12, 2007 1:57 pm

OK, Comet McNaught! (I'll answer the questions regarding CAI's shortly.)

We only have one sighting of Comet McNaught, and so we don't have great orbital data on it. However, based on the last orbital data I saw, McNaught isn't bound to the sun anymore (it has a hyperbolic orbit). Therefore, it shouldn't be coming back. I don't know if Jupiter was what caused the hyperbolic orbit, but that is a good guess. It probably formed with the solar system WAY out in the Oort cloud (that's further than the Kuiper belt where Wild 2 came from), and probably this was it's first trip into the inner system. And yes, that is exactly why the tail is so bright -- it probably was "just visiting." There is also some very, very, very, remotely, itsy-bitsy, slight possibility that it is a comet tossed out of another system, which we caught. It's never been shown that this happens, but it has been considered theoretically. It's such a cool idea that I mention it here despite the fact that it is also a really far-out idea (pun).

Comet tails tend to decay until eventually the nucleus is just a black icky chunk of crud. (That's official terminology.) Once the tail burns out, we may not be able to tell the difference between an ex-comet and an asteroid unless we were to get some pretty good experimental data on it. Some of the near Earth asteroids are supposed to be extinct comets. I haven't seen any equations relating the brightness of the tail over succeeding orbits, but my first guess would also be an exponential decay. Remember, though, that an orbit is a discrete event. So you'd have to be measuring the maximum brightness or some similar statistic against which to plot your theoretical decay equation. Also, you'd have a hard time demonstrating the equation's veracity -- comets have very long orbits and you'd be trying to infer tail brightnesses from historical eyewitness accounts. A fun project to be sure, but it would yield pretty big error bars.
Zack Gainsforth
Space Sciences Laboratory
UC Berkeley

Dreamer
Posts: 20
Joined: Wed Aug 02, 2006 3:29 pm
Location: Karlstad, Sweden

Post by Dreamer » Sat Feb 17, 2007 4:47 pm

So, if I understood this correctly, we have a comet that
A) formed close to the sun, explaining the mineral properties, or
B) formed far away from the sun, and that's why it has so much ice left

A puzzle, but I have an idea. The comet formed close to the sun, migrated outward, for whatever reason, and then somehow acquired the ice. What do you think?
"And then, one day..."
Kim Stanley Robinson, "Red Mars"

ZackG
Stardust@home Team
Stardust@home Team
Posts: 38
Joined: Thu Aug 17, 2006 4:25 pm

Comet formation

Post by ZackG » Mon Feb 19, 2007 2:51 pm

All right! You're thinking with the data! However, I don't agree with your assesment (though I agree with your attitude!) and here's why I think so:

If the comet had formed near the sun and then moved outward and acquired ice, it most likely would have a rock core and an ice rim. However, what we see are tiny grains of material of all types which are mixed in many different ways.

Some of the dust grains in the comet probably formed near the sun. However, I think the comet itself would have formed into a cohesive object with a well defined shape out at the edge of the system because it really is not easy to send something which is on an inner system orbit out into an outer system orbit. There are also some proposed methods by which tiny grains can drift out into the outer system -- and we do see tiny grains of stuff that fits the bill.

See, the tricky part is, when I say that 10% of the cometary material might have formed in the inner system, I don't mean that an object 1/10th the size of the comet formed in the inner system. I mean that the 10% is distributed throughout the body of the comet in tiny specks. It's like if you picked up a handful of sand in Hawaii, and 1 out of 10 grains were from Africa. You wouldn't conclude that the beach formed in Africa, but instead some of the grains found their way across from Africa. (For those of you with way too high an IQ -- who are thinking "What about Pangea?": It's just an example!)
Zack Gainsforth
Space Sciences Laboratory
UC Berkeley

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests