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NASA's Phoenix Finally Fills Oven
JoeRobe writes "Phoenix has successfully filled oven #4 of the Thermal and Evolved-Gas Analyzer instrument (TEGA). They have spent several days now vibrating the screen above the oven, trying to get a significant amount of soil sample into it. From the article: '[T]he oven might have filled because of the cumulative effects of all the vibrating, or because of changes in the soil's cohesiveness as it sat for days on the top of the screen.' Either way, this is the first step toward getting some interesting data from this instrument."
No. But that's not the issue here. What we're talking about here is getting less data than we'd like (because of what was excluded from the sample). Data is not "flawed" for being a smaller quantity, it's just, less. Some data is better than no data at all.
"Convictions are more dangerous enemies of truth than lies."
For the common man who needs a frame of reference: This is the same length as the distance between the solder balls of many BGA IC packages. Good lord, that didn't help him at all. For the common man: a dime is about 1mm thick.
Changa hates change.
This is just the first test. At this point, Phoenix is supposed to be testing the soil, not the ice. Later, they are going to dig down into the ice. They have a special drill-like object on the digging tool which will drill into the ice and produce fine shavings. These shavings will then be scooped up and dumped into the oven. But that will come later, first they are testing the soil. This is what has been a problem so far, it's good that they have managed to make progress with it.
It is a real concern, but it isn't a mistake.
The JPL engineers who designed it knew from the start that certain compounds, including water ice, would begin to sublimate once the soil was disturbed. For this reason, they wanted to get the samples into the chamber relatively quickly. It is very likely that the 3-4 day delay caused some loss of volatiles. It doesn't completely invalidate this sample because it's unlikely that all the ice sublimated, and water isn't the only thing they're looking for.
Also, there are 7 other chambers in this instrument, and they believe they've figured out how to avoid this trouble in the future.
They did test the aparatus pretty thoroughly on earth, but the soil properties ended up being quite a bit different from what they expected. No mission before has handled soil in quite the way Phoenix does, and the soil at the north pole may well be different from that in locations where previous landers have touched down.
Note the portion where solid and vapor phases are adjacent with no liquid phase in between (sublimation/deposition).
Water doesn't sublime.
It does if the pressure is low enough, I think on mars there would be a liquid phase though it would be much much narrower than on earth such that it would be almost too narrow to notice.
note: i'm known as plugwash most places but i screwd up registering that here somehow in the past and now can't register
Water Ice sublimes even in the earth's atmosphere. Ever wonder why ice cubes shrink after they've been in a freezer for a really long time? It's also the reason that all the ice will "melt" off your car if you expose it to the sun, even if it's below freezing out. Freezer burn on your food is also caused by sublimation. So yes, water ice does sublime, and in low pressures would probably do so even more.
Gee, and all this time I thought of it merely as a tenth of a centimetre :-)
Another easy frame of reference is twice the diameter of the most common mechical pencil lead size: 0.5mm. Wooden pencils usually have 2mm leads. Virtually all of them are metric.
What I'm sure the 'grandparent' article is referring to as a false negative is that if there were water (ice) in the original sample when it was taken, there's a risk that several days vibrating it in under low atmospheric pressure may cause it to evaporate. If it's a small enough sample, or the pressure is low enough, it could sublime, converting directly from ice into steam.
This would result in a false negative if the original sample did, in fact, contain water, because spending that much time between gathering a sample and analyzing it invalidated the test results. This of course, assumes that the first paragraph is true.
The reason for sifting it is probably because anything too large could damage their 'oven.'
I wouldn't consider the mad hatter mad. Just reality impaired. He sure can make a mean cup of tea.
I have a phase diagram of water here that disagrees with you (and anyone who modded you informative. geez, people, hand in your geek licenses please).
See that boundary line in the lower-left corner, where vapor and ice are directly adjacent to each other ? That's where water sublimes.
http://encarta.msn.com/media_461541579/phase_diagram_for_water.html