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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."
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).