origin of a particle ?

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subspace
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origin of a particle ?

Post by subspace »

Hi

I would like to know : how can we be sure that a particle come from outside of the solar system ?
the moon
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Post by the moon »

I went looking for the answer, couldn't find it right away, but from what I remember they can tell from the impact speed and trajectory and also the composition of the particle.

Now I got another question, when I went looking, I found this page
http://stardust.jpl.nasa.gov/science/dust.html
"A Dust Flux Monitor Instrument (DFMI) on Stardust will be used to monitor interstellar dust particle encounters. In addition, a Cometary and Interstellar Dust Analyzer instrument (CIDA) will intercept and perform real-time compositional analysis on this dust. The findings of both instruments will be sent back to Earth for further analysis."

I never heard of those things, what do they do? Were they able to detect particle impacts on the gel or what exactly did they find from those instruments?
marymouse
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Post by marymouse »

and if they could monitor the particles wouldn't they know where they were? :shock:
Nikita
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Post by Nikita »

Zack had this post about the stardust particles. Although it doesn't exactally answer your question, it does give some idea of how they believe where the comet came from. It may give a little bit of info for you and help you understand how what they find helps decide where it was.

I hope that helps!
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jsmaje
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Post by jsmaje »

Nikita wrote:Zack had this post about the stardust particles. Although it doesn't exactally answer your question, it does give some idea of how they believe where the comet came from. It may give a little bit of info for you and help you understand how what they find helps decide where it was.
Hang on Nikita, I hope I've not misinterpreted what you say above, but what comet is that supposed to be then?
Surely we're looking for interstellar galactic dust particles, nothing to do with solar-system comets such as Wild 2 that the other side of the collector was for, and the sort Zack was referring to, but which are not the immediate concern of this SD@H project.

Bryan talks briefly about the interstellar dust stream we're actually concerned with here, and this NASA release helps explain the relationship between solar-system cometary and free-flowing interstellar dust.

By the way, you can easily see the effect of interstellar dust for yourself from the southern hemisphere, where the centre of our galaxy (in Sagittarius) is obscured - I recommend looking up from the middle of the Australian bush on a clear night. Also as a dust-lane within our neighbouring galaxy, Andromeda, through at least a small telescope.

Finally, to subspace who started this thread: I'm still waiting for an answer to this query over a month ago.
bmendez
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Post by bmendez »

Hi all,

The evidence that will tell us if particles recovered from the collector are truly interstellar dust would be (1) the angle of impact, since a head-on impact is expected for interstellar dust because the collector was pointed into the oncoming stream; and (2) the composition of the particles. So, we won't really know if a candidate is interstellar until it has been extracted and analyzed.

The dust detectors on board Stardust were not the same as the aerogel collector. These were similar to those flown on the Galileo and Ulysses missions that first discovered the stream of interstellar dust passing through the Solar System. They can detect the presence and basic composition of dust particles.

Now, since I was not part of the Stardust mission team I do not know what those detectors registered, though I believe they have been mentioned in some of our team meetings. I can ask for clarification at the next meeting. Also, my lack of first hand knowledge of the deployment of the collector was the reason for my "pretty sure" qualifier in the thread you referenced, jsmaje. I didn't mean to convey any lack of certainty. If you'd like, I can track own someone from mission operations to ask them for confirmation that the collector was correctly deployed both times during the mission.

Thanks,
-Bryan
"I am made from the dust of the stars, and the oceans flow in my veins"
- RUSH
Nikita
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Post by Nikita »

Ah John,

Thanks for catching that! What I meant was to say that Zack provides some info on what was found with the comet particles. This logic can help explain how we can look at the stardust particles and get their compositions and determine where they came from. Plus, as Bryan said, the direction they came from. In otherwords, never mind what I said, Bryan just said it better. I really shouldn't post when I'm really, really tired! :?
Perhaps our southern friends (who are enjoying spring right now) can say what they see in the sky?
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jsmaje
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Post by jsmaje »

bmendez wrote:Now, since I was not part of the Stardust mission team I do not know what those detectors registered, though I believe they have been mentioned in some of our team meetings. I can ask for clarification at the next meeting. Also, my lack of first hand knowledge of the deployment of the collector was the reason for my "pretty sure" qualifier in the thread you referenced, jsmaje. I didn't mean to convey any lack of certainty. If you'd like, I can track own someone from mission operations to ask them for confirmation that the collector was correctly deployed both times during the mission.
Bryan, yes indeed - the more solid information you can give us about the dust detector results and aerogel collector deployment the better.
bmendez
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Post by bmendez »

Hi All,

So, here's the latest info I have for you. Telemetry from the spacecraft indicated a proper deployment of the areogel collector during both periods of the cruise phase that it was pointed toward the direction of the interstellar dust stream detected by previous missions.

There were two on-board dust detectors for Stardust: CIDA (http://stardust.jpl.nasa.gov/mission/cida.html) and DFM (http://stardust.jpl.nasa.gov/mission/dfm.html).

I'm still not clear on what CIDA detected, but for DFM the noise levels of the instrument were too high for interstellar dust to be detected. The dust detectors prime purpose was to collect info on cometary dust. I'll keep pouring through the literature on CIDA. You can do the same. Go to Google Scholar and do a search on Stardust and CIDA.

-Bryan
"I am made from the dust of the stars, and the oceans flow in my veins"
- RUSH
ZackG
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From whence little particle?

Post by ZackG »

It looks like you all figured most of this out on your own, but I'll take a shot at answering the questions, and maybe I can give you a little more detail. Like Bryan said, the primary methods of knowing it is interstellar are:

1) The direction of impact should be normal to the aerogel (it went straight in and not at a slant).

2) Looking at the elements of the particle itself may render a clue as to whether it is from our system or not. For example, the relative amounts of certain elements differs in crystals from different parts of the galaxy, and our own star has a signature we can recognize.

That said, there are some pretty big caveats. Regarding 1, the spacecraft was in an elliptical orbit, and the collector was exposed for about 100 days on each shot. This means that the direction the collector was pointing actually changed by as much as 10 degrees. In addition, the accuracy to which we can measure the angle of a track in aerogel is limited by a few degrees. However, the lion in the den is the fact that we don't know the exact direction of the interstellar dust stream. We pointed our collector in the direction we expect it to be in, but we could be wrong by as much as 20 degrees. Well, that's settled! ;-)

So what about 2? It all hinges on what the particle is. It is a good possibility that the particle could vaporize on impact. In this case, there isn't a whole lot of material to study. More likely (and hopefully) there will be a fair bit of residue in the track. We can then apply various measurements to try to find out what elements are there, as well as if those elements came from our solar system. The first step is almost certainly to get an x-ray image of the track, and get a general idea of what elements are in there. We'll also make a quick check for organics using infrared spectroscopy. These are relatively harmless methods but should give us enough information to know where to go next. After that it's anybody's guess what happens, because it entirely depends on what we found.

Zack
Zack Gainsforth
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ZackG
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CIDA and DFM

Post by ZackG »

Y'all wanted to know about CIDA and DFM. So here goes.

CIDA is what is called a mass spectrometer. Dust enters it down a little tube, and strikes a plate in the back of the tube. Because it only strikes the plate if it goes down the tube, we know what direction it came from. That is to say, it came from the part of the sky that you can see standing at one end of the tube and looking out the other.

When it hits the plate, it vaporizes. The atoms are then run through a magnetic field that bends them around and collides them with a detector. Where they hit the detector depends on what element they were -- i.e. heavy elements are pushed differently by the magnetic field than light elements. So what CIDA tells us is: "A particle just hit. It has such and so much oxygen, iron, etc."

DFM is not sensitive to what is in particles. It is just sensitive to the fact that a particle hit and how much oomph it hit with. It is also a lot bigger than CIDA, so it sees more particles. DFM is basically a sensitive plate that generates a small electric signal when something strikes it. The purpose of DFM was more to tell us how many particles hit the aerogel collector when we were passing the comet. Of course, it was also operating the rest of the time, because it was there. They might as well leave it on eh? So it recorded dust that just happened to be floating around in our system in the path of the spacecraft.

Zack
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Post by the moon »

Of course, it was also operating the rest of the time, because it was there. They might as well leave it on eh? So it recorded dust that just happened to be floating around in our system in the path of the spacecraft.
I think you forgot to type the last sentence, here let me start it for you. And it discovered that the amount of dust in the path of the spacecraft was...

As you can see in the other thread, this is the question on everyone's mind. How many dust particles are expected to be found in the gel? If this data is avalible it must be a much easier way to get an estimate then all the trouble Ryan went through.
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Post by DTF »

the moon wrote:I think you forgot to type the last sentence, here let me start it for you. And it discovered that the amount of dust in the path of the spacecraft was...

As you can see in the other thread, this is the question on everyone's mind. How many dust particles are expected to be found in the gel? If this data is avalible it must be a much easier way to get an estimate then all the trouble Ryan went through.
It's my understanding that the DFM was mounted on the whipple shield with it's opening toward dust particles in the direction the space craft was heading, which would allow it to collect dust coming in from the front of the craft's path. The interstellar dust came from the opposite direction, i.e., from the aft of the craft's direction while the aerogel collector was deployed to collect the interstellar dust (which, of course, was on the opposite side of the aerogel collector for cometary dust collection). If that's true, then this instrument wouldn't have been useful in calculating interstellar dust particles during the phases of interstellar collection. And I think it was Bryan who said it wasn't sensitive enough to be useful in collecting information on interstellar dust anyway.

I can't tell if the CIDA was mounted in a fixed direction from the information I've seen. It's acronym does infer, however, that it collected data from both the comet and the interstellar dust. It looks like it might have been mounted so that it's direction could be changed from fore to aft, but I don't know that for a fact.

I'm sure we'll get more info on what your asking and my comments above when someone in the know is able to find time to make a reply to us.
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DFM orientation

Post by ZackG »

Yes, that's correct. The DFM was forward pointing, mounted on the whipple shield. That means that it reads mostly on any dust that the spacecraft runs into. This is mostly interplanetary dust when we're not near the comet. The quantity of interplanetary dust dwarfs the flux of interstellar particles so that even when the spacecraft was flying towards the interstellar dust, you wouldn't see the bonsai tree from the forest.

However, interplanetary particles don't generally hit the back of the spacecraft much like you don't get bugs on your back window, only on the windscreen. However, because the interstellar particles are traveling so fast, they do hit the back window -- which in our case is the interstellar collector. The DFM is sitting right where the radiator is. [Ptew! Spitting astrobug out of my mouth!]

Hope that helps!

Zack
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Post by DTF »

Thanks, Zack! But what about the CIDA: was it rotatable and, if so, could (and did) it make a count of the interstellar dust particles that entered it during interstellar dust collection? Also, if it was indeed pointed aft and making counts during the interstellar collection phases, couldn't that be used to extrapulate an estimate of interstellar dust that the aerogel would have encountered?
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