Science article: Elemental Compositions of Comet 81P/Wild 2

Discuss your experiences with and ideas about Stardust@home here.

Moderators: Stardust@home Team, DustMods

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

Science article: Elemental Compositions of Comet 81P/Wild 2

Post by ZackG » Thu Dec 21, 2006 2:58 pm

Hi Everyone,

Good news! We just released the findings from our preliminary analysis on the cometary side. The results were so spectacular that we’ve hijacked a special edition of Science magazine! I figured that you’ll be interested even though this is the other side of the collector because, frankly, comets are cool too. :D

There’s a lot of material – almost two hundred scientists contributed to the preliminary analysis, so the papers published in Science are a synopsis of the last year’s work (and in many cases more than a year) for a large number of scientists. I’d like to give you a synopsis of what we found in a form that is accessible to those of you who don’t speak “scientist.” So, I figured I’d just cover one paper every couple days. That’ll give me time to get some other work done too... These are going to be very much an overview. If you want the hard numbers, and nitty gritty details, you’ll have to go get your own copy of Science. My hope is to write this in such a way that you get the broad brushstrokes in an enjoyable read.

The first article I’ll cover is the one I participated in: Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust

By elements we mean iron, carbon, magnesium – the standard elements you find on a periodic table. By elemental composition we mean “how much of each element is present in the comet?” and “how does this compare to meteorites and other extraterrestrial objects?”

We want to know the elemental composition of comet Wild 2 because these measurements can be used by theorists to determine how the comets formed and changed over time. As an example, you find gold veins on Earth due to geologic processes. As water journeys down toward the magma (molten rock) under the Earth, it begins to dissolve gold atoms from the nearby rocks. On it’s way back up, it then carries the gold atoms along with it and when the high pressures and temperatures decrease, the gold condenses into veins of pure metal. This is a natural process, but the simple fact that gold is separated tells us something about how the land formed. The same is true for the formation of the solar system: the concentration of elements in any solar system object, comets included, tells a story.

We compared what we found in Wild 2 to that found in a specific class of meteorites called “CI chondrites.” The CI chondrites are thought to have similar proportions of elements to those of the entire solar system. This is because many elements in CI meteorites are present in the same proportions as the solar photosphere – or the outer layer of the sun that you see through a telescope. It’s not clear why this is, and in fact it is somewhat remarkable, since CI meteorites are the most changed by water of any class of meteorites. As you saw from the gold example, water tends to move elements about and create artificial concentrations of them that don’t represent the average. It is a long-standing mystery, therefore, why CI chondrites have such similar proportions to the sun. Regardless, in our investigation of Wild 2 particles, we found a few things that were surprising:

1) The concentrations of elements in the comet varies tremendously between particles. We expected them to be more similar to one another. This means that the comet really is an aggregate of very different stuff, and hasn’t undergone any real geologic change to shake a stick at. It also means that the comet is not made of small, pristine interstellar materials either. If it were, the particles would have been much more similar to each other than they are.

2) The average composition for our sample is different in some ways from the CI chondrite meteorites: namely we found more zinc, gallium, and copper, and less sulfur. It turns out that zinc, gallium, and copper are very difficult to measure precisely in the solar photosphere so our measurements of the sun may not be quite right. They are also so-called semivolatile elements – that is, they evaporate at relatively modest temperatures. So there might be more of them in the Kuiper Belt (where comets come from) as compared with the inner solar system near the sun. If so, the consequences for solar system formation could be interesting. Or it may mean that there are more of these elements in the solar system than we thought. The sulfur mystery is so far unresolved – we’re busy scratching our heads about that one.

3) Some people have reported seeing more semivolatile elements in a class of interplanetary dust particles (IDPs) called “chondritic porous” IDPs. If you look over the element ratios we measured, you might conclude that our comet particles look more like chondritic porous IDPs than CI chondrite meteorites. And in some ways this looks consistent with the mineralogy/petrology studies that have been done on the cometary Stardust samples – I’ll cover that paper too. On the other hand we also found minerals that seem to be less consistent with CI chondrites and IDPs, and more consistent with yet other classes of meteorites. The answer may be that we have a completely new kind of sample that we’ve never seen before. Wouldn’t that be neat!

So… stay tuned! We like a good puzzle!
Zack Gainsforth
Space Sciences Laboratory
UC Berkeley

Howie
Posts: 331
Joined: Wed Jun 21, 2006 2:47 pm
Location: Florida

Very Interesting, I have a question...

Post by Howie » Sun Dec 24, 2006 4:20 am

in the article below...
http://www.berkeley.edu/news/media/rele ... dust.shtml
The way I read it, there are 2 sets of collectors?
Nasa has one and been searching and we are searching the second?
Nasa's has almost 40 good tracks and thousands of smaller ones"
That means ours could have thousands, not just 40?

Howie

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

Post by Nikita » Sun Dec 24, 2006 8:07 am

They were collected at different times and locations. The previous one was getting comet debris from the tail. They were larger and easier to find. We are doing the difficult search!
From dust we come

Howie
Posts: 331
Joined: Wed Jun 21, 2006 2:47 pm
Location: Florida

Thanks..........and............

Post by Howie » Sun Dec 24, 2006 8:26 am

Are there any of their tracks posted somewhere that we can take a look at? Would like to see some!

Howie

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

Post by Nikita » Sun Dec 24, 2006 8:38 am

Hi Howie,

On a quick search, this is what I found, see here. Perhaps we can look for more, but n a few days, things are a little busy right now....
From dust we come

fjgiie
DustMod
Posts: 1253
Joined: Sat May 20, 2006 8:47 am
Location: Hampton, SC, US

See comet particle tracks

Post by fjgiie » Mon Dec 25, 2006 7:36 am

Hi Howie,

Try a search at Google Images like this: Comet particle tracks

http://images.google.com/images?q=Comet ... N&filter=0

Thanks,

fjgiie

Post Reply