Water Ice and Soil Samples on Mars - by Deborah Bass

Phoenix landed on May 25, 2008 in the icy northern plains of Mars.
Phoenix landed on May 25, 2008 in the icy northern plains of Mars.› Full caption

We’ve been steadily learning about what it takes to run this thing called the Phoenix lander. As expected, not everything has gone exactly as planned. But that in its own way was planned — we work to maintain flexibility in our schedule and our design, so that we can absorb new things that happen without throwing the whole team into a tizzy!
So what have we been doing?

The Robotic Arm Camera on Phoenix  captured this image underneath the lander on the fifth Martian day of the  mission.
The Robotic Arm Camera on Phoenix captured this
image underneath the lander on the fifth Martian day
of the mission. The abundance of excavated smooth
and level surfaces adds evidence to a hypothesis
that the underlying material is an ice table covered
by a thin blanket of soil.
› Full caption

The really big thing so far is that the Phoenix team discovered what is believed to be water ice beneath the surface under the lander. Computer models suggested that the ice would be several inches beneath the surface and, in fact, that is where we found it! We watched some soil lumps fall apart over several days (in a set of images taken to “monitor change”) and concluded that what was holding the lumps together was ice. After a few days exposed to the Martian atmosphere the cementing agent sublimed — in other words, it changed from a solid to a gas without ever being a liquid. If it had been, say, salts that were holding the lumps together, exposure to the atmosphere over several days wouldn’t have made a difference.

This conclusion about the ice has been arrived at rather carefully. First we saw some bright patches under the lander that had been exposed by the thruster engines during landing. We couldn’t do much with those patches, so we just noted them as “light-toned, forward-reflecting material.” We tried to come up with different hypotheses to explain the bright patches that might be consistent with something other than water ice — like frozen hydrazine fuel that we brought with us, or salt patches, or just lighter-toned rock! We took pictures in different wavelengths and decided that the light-toned material had the right reflective properties of water. We also scraped down a few inches and found the same light-toned material as we were seeing just beneath the lander. Then the team looked at the cloddy soil.

Small clumps of Martian soil were delivered to the MECA wet chemistry experiment.
Small clumps of Martian soil were delivered to the MECA wet chemistry experiment. › Full caption

The wet chemistry experiment in one of the lander’s instruments called the Microscopy, Electrochemistry and Conductivity Analyzer, or MECA, also found salts in the soil samples. Salts are only formed when water has been present! So that is another indicator that there was abundant water in this region of Mars. What are these salts? They appear to be chemicals containing sodium, magnesium, potassium and chlorine. The soils were found to be alkaline, with a pH greater than 7 — similar to soils in the upper dry valleys of Antarctica.

Small clumps of Martian soil were delivered to the MECA wet chemistry  experiment.
This animation shows a sprinkle test,
where the scoop on the Robotic Arm
is vibrated so material gently falls to the target below.
› Full caption

But, like I said, everything hasn’t been totally smooth. The team discovered that the Martian soil is lumpy and sticks together. That made the first sample difficult to deliver! So the team thought about how to make the process easier, and we figured out various ways to break up the lumps. We tried three methods: de-lumping, sprinkling and agitation.

De-lumping refers to shaking the acquired material in the scoop by running a Dremel-like tool that vibrates the entire scoop, breaking up clumps. Then there is sprinkling: By running the rasp while slightly tipping the scoop, the team can command Phoenix to send a small shower and sift particles down into the TEGA (Thermal and Evolved-Gas Analyzer ) and MECA instruments rather than dumping a whole load of clumped-up dirt onto each instrument. As for agitation, the TEGA instrument has a method to shake itself — it has an agitator which shakes the sample loose if anything has stuck to its entry port. The sprinkle and agitation methods have been routinely adopted for sample delivery.

The neat consequence of this is that it solves what had always been our worry about how to deliver the same sample to each instrument for comparison of science results. The sprinkle delivery method enables us to put a large sample into the scoop and deliver part of it to MECA microscopy, part to MECA wet chemistry and part to the TEGA instrument. Same sample problem: solved!!

When life gives you lemons, make lemonade! Or in this case, Marsade!

    9 Responses to “Water Ice and Soil Samples on Mars - by Deborah Bass”

  1. Gustavo Rivera Says:
    July 17th, 2008 at 5:27 pm

    Hi would you see if there is clay wrer you are at and if there is would you put some to the side . so we could come back to look . Thank you much.

  2. David Harris Says:
    July 18th, 2008 at 3:30 am

    Deborah Bass seems not to mention another problem to be overcome: that the shaking seems to have created a short circuit that requires a considerable change in plans to test the soil with the TEGA.

  3. Paleoprof Says:
    July 18th, 2008 at 8:03 am

    Thanks for the blog and all your good work. I was wondering about the lumping. Is it possible there are clays in the regolith and that’s what’s making it clump? I don’t suppose you have a set of sieves up there and a shaker huh? :)
    thanks again

  4. Farhan Riaz Says:
    July 18th, 2008 at 10:45 am

    good to see JPL BLOG.Can u plzz give us a mission status about Mars Science Laboratory.

  5. Tom Wright Says:
    July 18th, 2008 at 5:53 pm

    Congratulations on successes to date. Astonishing how much we already have learned about Mars.

  6. Sergio Gomar Says:
    July 19th, 2008 at 12:41 am

    First of all, I would like to thank you Deborah for sharing you time with us.

    Related to current issue in getting enought ice to put it inside the TEGA… Iit´s a pitty that Phoenix team didn´t considered the possibility to include a small “vacuum cleaner” :-) (or even a broom) to draw in the “ice dust” that Phoeix is getting up with all those rasps and scraps over that “rocky-like” frozzen soil.. Seems that this part of Phoenix mission planning should be delivered to a “cleaning company” instead to an engeriering one :) .

    Thanks once again.

  7. John Jobe Says:
    July 20th, 2008 at 8:39 am

    Hi
    Regarding the short circuit, doesn’t it affect only one of the several TEGA ovens?

    Thanks

    John

  8. John Jobe Says:
    July 20th, 2008 at 9:03 am

    Hi Again

    I forgot to thank you, Deborah, for the excellent summary with photos. Let me also mention that the photo album with all the 3-D photos are outstanding.

    Now here is my question background. It was recently stated in one of the press releases that TEGA/Wet Chemistry results indicate that the Mars soil was not unlike that in one’s own back yard. As such, the release implies, the soil should be life-sustaining. But many interpret this as meaning there could at least be microbial life in the soil on Mars.

    The question is that doesn’t it also take a reasonable atmospheric pressure for microbial life? Has anyone done experiments on earth where arctic-like habitats containing microbial life were put into a vacuum chamber, at Martian temperatures, where about 1 millibar of CO2 was introduced? Would the life survive under these conditions?

    Thanks

    John J

  9. James Moore Says:
    July 25th, 2008 at 9:08 am

    Deborah,

    Thanks for the update, especially the information on determining whether or not what the Phoenix team was seeing was water ice. I’m looking forward to the water ice sample being delivered to the TEGA!

    Clear skies! — James