by Deborah Bass

Since Phoenix landed in the northern hemisphere of Mars, the spacecraft has discovered:

1. Water ice near the surface of Mars! And it is really close to the surface, as the orbiting Odyssey spacecraft predicted, and Phoenix confirmed. This demonstrates science in action: data, hypothesis, confirmation of hypothesis.

2. The pH of Martian arctic soil is basic (or alkaline), rather than acidic. On Earth, soil pH is important because most food plants prefer an acidic or neutral soil to grow. Bacteria usually thrive in acidic soils as well. So what we found on Mars is not necessarily the best news for the search for life. One thing I think astrobiologists would agree upon, however, is that life is very adaptable and can exist in many extreme environments!

These lumps of ice, in a trench nicknamed
“Dodo-Goldilocks,” sublimated, a process similar to
evaporation, over the course of four days. › Image and caption

3. Unlike the landing sites of the Spirit and Opportunity rovers near the planet’s equator, there are no soils with sulfur compounds, or sulfates, in this part of Mars. Spirit and Opportunity found that the soils at their landing sites were cemented together with sulfur compounds. Sulfates do not act as cementing chemicals where Phoenix landed in the Martian arctic.

4. The soil grains Phoenix found are a mixture of angular and rounded particles, with a myriad of colors from rust to white to black. They show degrees of weathering and different chemical compositions.

5. There are high level clouds and ground fogs every night, and the general weather patterns are repeatable.

6. A chemical called perchlorate appears to be prevalent in the soil. On Earth, perchlorate forms in arid areas where there is very little rainfall. The team is still working to understand how perchlorate affects whether life could have existed in this region on Mars.

What does all of this mean? Well for starters, Mars has a diverse geology and geochemistry, much like Earth. Making generalizations about Mars planetwide is probably not the right approach, because of the planet’s diversity. What does it all mean for the bigger picture? Ah, that’s where the difficult science comes in. This takes time. Many members of the science team expect to have their findings ready by December, to coincide with a big science conference in San Francisco. So stay tuned!

This view combines more than 400 images taken during the first several weeks after
NASA’s Phoenix Mars Lander arrived on an arctic plain at 62.22 degrees north latitude,
234.25 degrees east longitude on Mars.
› Full image and caption

Thanks to all those who posted comments! I’m glad to see that there is
so much interest in the Phoenix mission! I wanted to address a few key
items.

First off, some staff from the Mars Science Laboratory project
will be writing blog entries, so please hold your questions about that mission until
the end of summer, when those blogs begin!

Phoenix’s Thermal and Evolved-Gas Analyzer, or TEGA, has given the team some
head-scratchers, and those challenges continue. In my last blog I talked about lumpy
soil, sprinkling and delivery mechanisms. TEGA has been using a method to agitate its
cells to help move the soil down from the collection area into the oven as well. Well, it
turns out there was a short circuit in a TEGA cell number four when we used the agitator
on that cell in June. We used that same agitator for repeated periods of many minutes
each time while we were getting the first soil sample into TEGA. Project engineers
determined the likely cause was running the screen-agitator longer than we ever had done
in pre-launch testing. Running the circuit for such a long time caused some wire
insulation to get too warm, causing a short. That short in itself did not cause or
threaten any problem with operating TEGA, just on the “grounded” portion of the circuit.
It was on the return part of the circuit, between where the current does its work and the
ground connection. And then that short apparently healed itself when doors for cell
number zero were opened on July 19! However, the occurrence of any short raised concerns
that another short circuit might possibly occur, and if it did, it might be a more
harmful one. That concern still exists, and has prompted at least two precautions — a
decision to change sampling strategy to treat each TEGA sample as if it could be the
last, and an operational rule to avoid running a screen-agitation for more than three
minutes without a cool-down period before resuming.

Trying to get samples into the chemistry experiment was a big topic during development. When Peter Smith proposed to send Phoenix to the Martian arctic, the intention was to use as many already-developed pieces as possible. New methods of delivering material to the chemistry experiments on the lander deck had to be simple, because the original design was to use the scoop to dump soil. However, based on pre-launch testing, the original method of scraping/scooping the soil to generate a sample didn’t appear to work on ground that is frozen so hard that the ice and soil behaves like cement! The Phoenix team has been doing many tests to ensure that the alternative method, using a little Dremel-like tool called the rasp, works. These tests were done on analogs of extra-hard Martian soil, but there is still nothing like testing with the real stuff on Mars. The Phoenix team had established that the rasp will acquire enough icy soil to deliver a proper sample to TEGA. Those on-Mars tests have taken a long time, as expected. Mars continues to amaze the science and engineering team - the Martian soil is behaving unlike any sample the team used in practice back on Earth! The exciting news is that the team was able to get a sample with a bit of ice into TEGA after all!

Another item came up regarding better ways to clear off the ice table. I’ll tell you that the Phoenix development team wrestled with this topic for quite some time. Field studies show that a brush is the best way to remove loose soil from a region a geologist wishes to sample. The problem of course, is that then the brush gets dirty! The ability to clean the brush for further use becomes the problem. The soil on Mars is very, very sticky due to small particle sizes, salts and ice that appear to be acting as cements, and electrostatic properties that cause dust-sized particles to be charged and stick to each other that way too. The team could not come up with a reasonable, relatively inexpensive brush/cleaning mechanism in the short development cycle that the Phoenix mission undertook. (Remember that the mission was only approved in August 2003!) The notion of using the scraping blade on the robotic arm was deemed the most expedient, least costly way to clean surfaces.

Hope this answers some of your questions. Thanks for all of your interest!

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 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. › 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.

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!