421-GeologyReport

Geologist's Report

Date: April 21, 2015

Crew Geologist's Name: Auriane Canesse

Hello Earth,

Here is a summary of everything that has been done for our geology

experiment. I will begin by reminding briefly the goal of our study

and I will then describe the results we obtained.

\\introduction

The initial goal of our experiment was to map the magnetic

susceptibility of the ground in order to study its variation. The

susceptibility varies with the composition of the soil: it is quite

low for sand but very high for iron for example. But since our

instrument also measures electric conductivity, we decided to measure

this second property too.

\\ field sessions

We began by mapping the magnetic susceptibility of the ground around

the station then went to further places to take more measurements.

On April the 15th we mapped the surrounding of the hab but since

Gaspard's GPS didn't work we had to take positions by hand with a

meter. Since it was much slower than planed we took only two small

sets of measurements. For the first one we mapped an area of 25x3m

behind the hab. The buried tank behind the hab appeared very well on

the data. For the second set of measurements we took measurements

every 3m on 140m to see if there was a global change. But we only had

only insignificant variations around a constant mean. The magnetic

susceptibility of the ground seems quite uniform. We will try to take

new measurements at a totally new location to see if we measure

different values.

On April the 16th as we went to a dry river bed to take hydraulic

measurements we also took magnetic susceptibility measurements in the

river bed and on the banks but the results appeared to be similar to

the previous ones.

On the April 17th we took measurements on several hills close to the

station. Again, there was no significant changes of the magnetic

susceptibility.

On the April 18th we went to another river bed, the instrument was

showing biased results for the magnetic susceptibility because of the

heat. So we measured the electric conductivity of several river's

sections instead. We found interesting variations: it had rained on

the previous day and the conductivity appeared to be much higher in

the bottom of the river than on the banks (so its humidity was

higher). The two banks also had different mean conductivity values

which could explain the presence of plants on the right bank only (the

wetter one).

On the April 19th we went on the cliff West of the station to measure

susceptibility and conductivity. They both appeared to be

approximatively constant and not very different from the values

obtained in the plain.

On April the 21st, since the weather had been dry for 4 days we went

back to the second river to take more conductivity measurements in

order to compare them with the previous ones. We had expected the soil

to be dry but surprisingly it was still wet only 2cm below the clay

crust. The measurements we obtained were quite similar to the previous

ones: we measured the same river profile, which did seem coherent.

\\ Results

I will now sum up the results mentioned above

The magnetic susceptibility turned out to be uniform: the measurements

can be taken at different locations, on different geological stratum

(plain, hills, cliffs), with different humidity rates (stream-beds,

dry or rainy weather), the results are always similar: small

variations around a nearly null mean. The measured values don't seem

to be differentiable from the noise of the instrument.

The talkie-walkies interferes with the instrument (which is very

sensitive), therefore they should not be used while measuring. This

can be a problem for automatic measuring (instrument connected to a

computer) since the talkie-walkie's interference would not be

differentiable from soil abnormalities.

Magnetic susceptibility can be used to detect buried metallic objects,

like tanks (but I don't think we will loose any of these on Mars.)

The electric conductivity varies around river beds in a significant

way, it shows an important difference of humidity between the banks

and the bottom, even long after the last rain. The soil stays wet for

quite a long time (which isn't obvious for a desert).