PRE2017 3 Groep1

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Project statement

Concept

Goal

Approach

USE aspects

Problem statement

There is a mission going on to send a group of people to Mars for colonisation. In the first stage, this group consists of about 20-30 people. After this, every couple of years a new group is sent to Mars. When the first group arrives on Mars, it is important that there are enough recources to sustain. Since the plan is to stay on Mars for the rest of their lives, merely canned food will not do (it will run out fast). Thus food has to be tailed. As there is a limited amount of crew members in the first stage of this mission, it is favourable that as much work is done autonomous by rational agents. One of the most importan things in order to survive, is the tailing and harvesting of food. In the beginning, this should be focussed on nutritious food which is easy to process (grain for instance takes a lot of work to make into something eatable, which is not favarobale at this stage). We chose to look into the tailing of potatoes. This process is not yet fully autonomous.

Objectives

The objective is to make a model in matlab and simulink for an autonomous controlled environment for potato harvest. This includes the harvesting and the planting of the potatoes at right times, as well as keeping the environment ideal for growth.

Aspects

■ Harvesting and planting robot

■ Greenhouse

■ Climate control

■ Water and nutrition supply

Users

The users can be divided into three groups: primary, secondary and tertiary users. The primary users are the users that directly come into contact with or benefit from the technology. The secondary users usually do not directly use the technology, but benefit from it anyway, for instance when they work on the development or design of the project. The tertiary users are mosly involved in purchasing the technology.

Primary users

Inhabitants of Mars

The direct users of our technology will ofcourse be the inhabitants of Mars. The technology is designed especially for them, so that their life on Mars gets a bit easier. In the first stage of the Mars mission, all the inhabitants are going to be (mechanical) engineers, doctors, biologists, agriculture experts, physicists etc.. They are all going to be trained in advance to be able to handle all kinds of situations. They will be trained to use the technology that is sent up with them, including our techology. There are no experts for the different kinds of technology though, which means all of the techology needs to be relatively easy to understand.

Secondary users

(Mechanical) engineers (on earth)

(Mechanical) engineers are needed in order to design and build the technology on earth.

Programmers (on earth)

Programmers are needed in order to make the process of potato tilt fully autonomous. They need to implement all of the research done by other scientists in order to create the perfect environment for potatoes to grow in.

Biologists (on earth)

Biologists need to do research on the environment on Mars and in and how growing potatoes is possible in that environment.

Agriculture experts (on earth)

Agriculture experts need to establish the perfect kind of potato to grow under these extreme circumstances, as well as they need to determine the perfect conditions for the potatoes in each stage of their growth.

Chemists (on earth)

Chemists need to determine how to change the soil and air so that the right nutritients are in there.

Physicists (on earth)

Physicists need to calculate how the gravity is going to effect the growth of the plants.


All secondary users descrbed above profit from the technology in the sense that it will be their job to contribute to de development of the technology, so they will get paid to do their jobs.

Tertiary users

Buyers of the technology

The buyers of the technology also play an important role of the process. These are the ones paying for everything after all. If they are not happy with the technology, they will not pay, which makes it very important to look at their requirements and prefrences as well. The buyers of our techology will probably be either NASA or the government.

User requirements

Primary users

  • In the early stages of the Mars mission, people might not have the knowledge to make any complex modifications or repairs to the robot. This has to be taken into account when the robot is designed. It is important to make a design that is as simple as possible and make the programming as clear as possible. In this case, when something does break down, it will hopefully be easy to fix.
  • Another consideration will be the material of the greenhouse. Because the resources are limited, it is important that when the technology disfunctions, it can easily be made without using a lot of materials and specific tools. If certain materials or tools aremight be needed in order to fix the technology, it is important to know in advence so that these can be taken with the crew to Mars.
  • The technology needs to be easy to use. Preferably, the technology is fully autonomous so that the crew does not loose precious time while building up Mars.
  • The technology needs to be efficient. It is important that, in an environment where there are so little resources, no food, water, manure or energy is wasted.

Secondary users

  • Money for research.
  • Enough time for research. A lot of the time researchers are set with very strict deadlines in which it is not always possible to deliver the quality of work needed for such a big project.

Tertiary users

  • The technology needs to be as cheap as possible
  • The technology needs to have a long lifespan, so that it does not have to be re-purchased

Society

Enterprice

RPC's

In this subsection the requirements, prefrences and constraints of the technology will be eleborated.

Requirements
Prefrences
Constrains

Scenario's

Assumptions

Since this model will be a very first draft, lots of assumtions and approximations need to be made. All of the made assumptions and approximations will be listed below, including an explenation of why these are valid. Throughout the project, we will try to eliminate as many approximations as possible, in order to make a more detailed model. The assumptions will be divided over a couple of subsections, such as the things we assume the robot can do, the composition of the ground and the growth of a potato. This in order to try and give a clear overview of all the simplifications in our model.

Users

It is important for the developers of the technology to keep in mind what tasks the users can perform. This way the developer can make sure that the technology can be maintaied as well as needed and that the technology will have a long lifetime. For this, a couple of assumptions are made about the primary users.

  • The primary users are trained in solving minor problems with all kinds of technology
  • There wil be (mechanical) engineers amongst the primary users with the skill of performing a bit more complicated maintenance
  • The martian crew will be able to contact earth at all times
  • The crew members have minimal knowledge about potato plantation
  • The crew members have minimal knowledge of the specific technology

Robot in greenhouse

Ground on Mars

In order to grow potatoes on Mars we need to know what the soil of Mars contains regarding for instance nutritions. Though there has been a lot of research about the soil on Mars (see literature), the exact composition is hard to find. In order to make the soil right for potato growth, it needs to be fertilized. Before this fertilization can be included in the model, a set of assumptions and basic boundary conditions needs to be made.

  • The composition of the Martian soil is seen as equally distributed around the whole planet
  • The values found in the literature do not include errors
  • Only take into account that the potato is able to take up ions from above it (so 10 cm in depth to take up these substances)
  • Take size 28/35 potatoes (so width between potatoes in same row 28 cm) if size 35/55 was taken than it should be 38 cm. It is better to have more potatos in the field, therefore, size 28/35 has been taken.
  • Each potato is able to get ions half the distance till the next potato.
  • If there is shortage in ions in the ground this can be easily dealt with by putting the shortage in the fertilizer.

Greenhouse


Potato tilt

Model

In this subsection, a description of our model will be made.

Summary literature search

Conditions on Mars

Soil on Mars

Climate change on the planet Mars by detection of ground ice. Th water layer is 10 - 40 cm thick and occurs in between latitudes of 30 degrees and 60 degrees. This means that water is available on Mars. Because of this carbonates can be produced. The exact substances will be discussed below.

Ions

A layer of ice has been found at a depth of 5 – 15 cm deep. In the soils around the Phoenix landing site calciumcarbonate has been discovered (3-5 wt%) by scanning calorimetry. It showed an endothermic transition at around 725 degrees Celsius accompanied by the evolution of calciumcarbonate and the soil had the ability to buffer pH against acid addition. It formation in the past was due to interaction of the atmospheric CO2 and the water on particle surfaces. The Martian soil has been further looked into, where around 10mM of dissolved salts have been found out of which 0.4 – 0.6 % perchlorate (ClO4). The other negatively charged ions included small concentrations of bicarbonate, chloride and possibly sulfate. The cations detected (positively charged ions) included Magnesium, natrium and small concentration of Kalium and calcium. Besides this, an alkaline pH was measures of 7.7 (with a marge of 0.5). These findings included that the soil at Mars has changed of the past years due to the action liquid water. It has also been found out that there is mechanism to place ice at the surface: clouds of ice crystals precipitated back to the surface and formed a daily basis. Even though ions have been found, nitrate is an important ion for the Martian soil to be able to grow crops. In the table below, the concenrtations of a few ions are given.

Nitrate should naturally be formed through the oxidation of atmospheric N and then accumulate on the surface. On Mars odd nitrogen (N and NO) can eventually be turned into NO2, which can form nitric acid. Nitrate, thus, has not yet been detected on Mars: there are only some possible detections. In table 3 multiple acid formations can be seen.

These results are bases on the Phoenix landing site in 2008. In 2014 a meteorite from Mars (EETA79001) has been investigated. When investigating this meteorite, it had been concluded that the soil composition was Mars origin because those substances have been detected within the meteorite that is difficult to reconcile with terrestrial contamination. EETA79001 showed the presence of 0.6 ± 0.1 ppm ClO4-, 1.4 ± 0.1 ppm ClO3- and 16 ± 0.2 ppm NO3-. It has been said that because of ClO3-, ClO2- or ClO- should also be presented. This was then produced by Cl- and γ- and X-ray radiolysis of ClO4-.

Furthermore, an article was found comparing the findings on Mars and Antarctic Dry Valley soils. The article includes tables including the concentrations of certain ions found in each place. It has been concluded that the salts of the Phoenix landing site and the salts of the meteorite are similar and that the ADV are also a good match. This also strengthens the argument that ADV is a good Mars analog environment of Earth. The occurring ions and concentrations of it in ADV and on Mars are the same within one order of magnitude. ClO4¬- is three orders of magnitude bigger on Mars than on Earth. NO3- is may be present on Mars but this is at a level below the detection limit of the nitrate sensor. The soil of the meteorite and on the Phoenix landing site are alike, however, on average the concentrations in the meteorite are 4% of those on the Phoenix site and the concentration Ca+ is 16% bigger on the meteorite

The last article includes information about the nitrogen cycle and the ratio of the loss of nitrogen isotopes. This mainly has to do with the air activity, therefore, not relevant for the piece of text about the ground. There was a good explanation, however, why it is difficult to detect nitrate on Mars. This explanation is given below. A cause could be leaching. This means that the nitrate will be at a bigger depth in comparison to less soluble ions such as sulfates.

Nitrates on Mars?

Some articles say the opposite of one another. Some state that nitrate has been detected on Mars and others do not. As nitrate is crucial for growing crops, it is essential to know whether there is actually nitrate on Mars. Because of the fact that all articles are reliable and some are even produced in the same sort of magazine, it has been decided to trust the articles which are more recently made. It could namely be the case that nitrate has not been discovered in 2001 but in between 2001 and 2013 for example. When trusting the most recent article, nitrate has been discovered on Mars.

What is in Martian soil

Several investigations have been taken place in order to find out what substances are located in the soil on Mars. First of all, the Phoenix Mars Lander WCL soil has been analysed and the Mars meteorite EETA79001 sawdust. These type of soils have been compared to soil on the Antarctic Dry Valley and to a Mars simulant. This research is about being able to grow crops (potato’s) on Mars. In order to succeed into this, the easiest way would be to do experiments with the ground which is available on Earth. This is the reason why the Martian soil has been compared to soil on Earth. To be able to grow crops, the soil should be fertile and the amount of fertilizer must be known. What is in the fertilizer and the amount of is needed, is based on the composition of the soil and the needs of a certain crop (in this case the potato). In the table below, the concentration of ions is given for the meteorite and Phoenix Landing soil. 1 gram of soil was added to 25 mL of DI water.

Ionic species Phoenix WCL mars (μM) EETA79001 Meteorite (μM)
Ca2+ 600 ± 300 1180 ± 1
Cl- 470 ± 90 13.2 ± 0.8
K+ 390 ± 80 1.8 ± 0.5
Mg2+ 3300 ± 1700 136 ± 1
Na+ 1400 ± 300 110 ± 1
NH4+ ND 62 ± 2
NO3- <1000 48.5 ± 2.5
SO42- 5400 ± 800 117 ± 5
ClO4- 2400 ± 500 1.02 ± 0.11

It has already been concluded that both of these soils are comparative for the Martian soil. It has not yet been decided which soil to take as a representative. Because of the fact that the numbers for what a potato needs are in grams, the amount of μM has to be converted into grams. In the table below, the amount of grams for each ion is given within 1 gram of soil.

Ionic species gram per gram soil (Phoenix) gram per gram soil (Meteorite)
Ca2+ 6,01E-04 1,18E-03
Cl- 4,17E-04 1,17E-05
K+ 3,81E-04 1,76E-06
Mg2+ 2,01E-03 8,26E-05
Na+ 8,05E-04 6,32E-05
NH4+ 0,00E+00 2,79E-05
NO3- 0,00E+00 7,52E-05
SO42- 1,30E-02 2,81E-04
ClO4- 5,97E-03 2,54E-06

In reality, each potato has access to a certain amount soil. The potato is placed in the ground at a depth of 10 cm. The space between the potatoes in the same row is 28 cm and the distance between potatoes in different rows is 75 cm. These numbers have been taken into account in order to calculate the volume of the soil that each potato is able to use. By taken the density of the Martian soil into account, the amount of grams for each ion can be calculated. The results are shown in the table below.

Ionic species gram total (Phoenix) gram total (Meteorite)
Ca2+ 1,26E+01 2,48E+01
Cl- 8,75E+00 2,46E-01
K+ 8,01E+00 3,69E-02
Mg2+ 4,21E+01 1,74E+00
Na+ 1,69E+01 1,33E+00
NH4+ 0,00E+00 5,87E-01
NO3- 0,00E+00 1,58E+00
SO42- 2,72E+02 5,90E+00
ClO4- 1,25E+02 5,33E-02

Air on Mars

Several articles were found on the best condition in which potatoes can grow. Most of these only addressed the relations between for example CO2 and the leaf area, but one article gave values with those relations.

CO2

The CO2 level in normal air is about 401 ppm (0.00401 %) in which potatoes can grow well. But to get to know if potatoes can grow better in atmospheres with more or less CO2 tests using FACE rings are done. A FACE ring is a ring of pipes around a field of crops which emits CO2 so that the CO2 values around the crops rise and measurements with different levels of CO2 can be done. With the outcomes of these experiments it can be concluded that when the CO2 levels are raised (in this case to 660 ppm or 0.00660 %) the Leaf Area will decrease, but the activity of the photosynthesis is raised and therefore the number of tubers will increase. The size and weight of the tubers were more or less the same in all the experiments. With these values in mind it would be a good idea to make an atmosphere in the greenhouse on Mars that has more CO2 in it than the normal air on earth, to make the tuber yield higher and thus create more food from the same amount of crops.

What nutrients does a potato need

Potatos need the following substances in order to develop themselves and grow. Macronutrients

  • Nitrogen
  • Phosphate
  • Potassium
  • Calcium
  • Magnesium
  • Sulfur

Micronutrients:

  • Boron
  • Copper

For the concentration of the nutrients needed, a look can be taken in a certain graph. It is still unsure how to read this graph, therefore, it will be asked during the meeting how to do this.

Farming robots

Several articles were found on farming robotics. However most of these articles focus on robots that are (partially) manually controlled. It has only been a couple of years since designing and experimenting with fully autonomous farming robots has begun. The hardest part in programming the robots is to make them able to see whether a fruit or vegetable is ripe, or even to tell apart a fruit or vegetable from the plant. Furthermore the robot needs to be very delicate in order for the plant not to be damaged.

In one of the found articles a robot is described that is used to farm tomatoes. In this case colour is used as a measure of how ripe the tomato is. When the colour is above a certain teint, the robot takes it. Otherwise it waits till the tomato gets a darker shade. The robot described, is a very small robot which climbs up the plant and cuts the stem of the tomato if it is ready. This technique is however very hard to apply in our case, since we want to focus on potatoes which grow under the ground. Though there might be a way to use colour underground if we introduce a light in our robot. Another downside to this technique is that it requires a lot of these small robots, which can turn out to be expensive. On the positive side, these obots are very precise and do not waste a lot of vegetables (once the programming is perfected). An adjustment can be made from looking at the colour by looking for example at the size when it comes to potatoes.

Another article describes how a prototype is built of a fully autonomous harvesting tractor. This is used for vegetables which grow underground, but it is a very blunt device. It basically pulls out everything, including the potatoes that might not be ripe yet. In a very restricted area like Mars this is not desirable, since there are limited supplies and every potato counts.

Also a very useful article was found on how the ideal farming robot could be designed.

Potato research

The book “Introduction to potato production” gives an overview of the entire potato production process.

From the sources, it is clear that there are many factors that decide the size of the tuber yield. These factors include the breed of the potato and also the day length as well as the light intensity. The tuber growth is more delayed as the light intensity decreases (while the haulm growth is stimulated).

It is known that as the light intensity decreases, the tuber growth also decreases, but the growth of the haulm is stimulated.

There are two kinds of potato breeds, these are “long cycle” and “short cycle” potatoes, The short cycle potatoes start growing tubers earlier than the long cycle potatoes, but the long cycle potatoes will outgrow the short cycle ones in the long run. These tubers will become larger.

Some potato breeds do not grow tubers when the day is long, every breed has its own “critical day length” it is thus important that potatoes get a day cycle. The sugar content in the tuber is also dependent of the day length.

From the potato related sources it is also clear what the nutritional requirements are for potatoes per hectare, all these quantities are stated in “nutritional requirements for potatoes”.

The ideal soil temperature for potatoes is around 15-18 degrees Celsius.

The potato plant grows in certain stages, these are: dormancy (here the plant is not yet growing), sprout growth, emergence (haulm growth), tuber growth. These last three stages do overlap and it is strongly dependent of the breed and the circumstances when these stages are initiated and when these end.

Literature search

To start of our project we are doing a literature research. We divided the literature search into the following areas:


1) The conditions on mars (including the effects on aggro culture due to these conditions)

2) Robots and machinery that are already used in outher space

3) Farming robots that are already being used on earth


For all of these areas papers will be searched and a summary of the overall findings will be given with refrences to the found papers.


Mars conditions

- C. Leovy. “Weather and climate on Mars” (2001)

- F. Gifford Jr. “The Surface-Temperature Climate of Mars.” (1955)

- S. R. Lewis, et al. “A climate database for Mars” (1999)

- G.W. Wieger Wamelink, et al. “Can plants grow on mars and the Moon: A growth experiment on Mars and Moon soil simulants” (2014)

- Mars – Sterren en Planeten (2005-2009). Retrieved from: http://www.worldwidebase.com/science/mars.shtml

- M. Nelson, et al. “Integration of lessons from recent research for “Earth to Mars” life support systems (2006)

- S. Silverstone, et al. “Development and research program for a soil-based bioregenerative agriculture system to feed a four person crew at a mars base” (2003)

- Journal of Climate. Jun2001, Vol. 14 Issue 11, p2430. 13p. 23 Graphs..... no access

- Agriculture, Ecosystems & Environment. Feb2018, Vol. 254, p99-110. 12p....... no access

- Climate Research. 2009, Vol. 39 Issue 1, p47-59. 13p. 7 Charts, 5 Graphs, 1 Map..... no access

- Canadian Journal of Forest Research. Oct2010, Vol. 40 Issue 10, p2036-2048. 12p. 1 Chart, 1 Graph..... no accesss

- Global Change Biology. Jan2007, Vol. 13 Issue 1, p169-183. 15p. 1 Diagram, 7 Graphs, 2 Maps..... (no access)

- James I. L. Morison,Michael D. "plant growth and climate change" (2006)..... (no access)

- R. RötterS.C. van de Geijn. "Climate Change Effects on Plant Growth, Crop Yield and Livestock". pp 651–681 (1999).... (no access)

- Angela T. Moles. "Global patterns in plant height"- Journal of ecology. (2009).... access


Potato - Aardappel – YARA. Retrieved from: http://www.yara.nl/gewasvoeding/gewassen/aardappel/

- Adam H. Sparks. "Climate change may have limited effect on global risk of potato late blight" - Global change biology (2014).... (no access)

- Bakhtiyor Pulatov. "Modeling climate change impact on potato crop phenology, and risk of frost damage and heat stress in northern Europe"- Agricultural and Forest Meteorology. Pages 281-292. (2015).... (no access)

- D.T. Westermann “Nutritional requirements of potatoes” (2005)

- Van Ittersum, M.K. & Scholte, K. Potato Res (1992) 35: 365. https://doi-org.dianus.libr.tue.nl/10.1007/BF02357593

- H.P. Beukema, D.E. van der Zaag "Introduction to potato production" (1990)

- Pootaardappels – Carel Bouma biologisch poot- en plantgoed (2018). Retrieved from: https://www.biologischpootgoed.nl/teeltadvies-pootaardappelen/

- P.L. Kooman et al. "Effects of climate on different potato genotypes 2. Dry matter allocation and duration of the growth cycle" (1996)


Existing farming technology

- Tillet, N. (2003). Robots on the farm. The industrial robot, 30(5), 396. Retrieved February 23, 2018, from [1]

- Giles, F. (2017). Agricultural robots no longer science fiction. Florida grower, 110(2), 12-13. Retrieved February 23, 2018, from [2]

- Hill, P. (2016). 9 robots designed to enhance the farm workforce. Farmers Weekly, 165(3), 66-70,72,75. Retrieved from [3]

- Robert Bogue, (2013) "Can robots help to feed the world?", Industrial Robot: An International Journal, Vol. 40 Issue: 1, pp.4-9, [4]

- Victor Bloch, Avital Bechar, Amir Degani, (2017) "Development of an environment characterization methodology for optimal design of an agricultural robot", Industrial Robot: An International Journal, Vol. 44 Issue: 1, pp.94-103, [5]

- Bac, C. W., van Henten, E. J., Hemming, J. and Edan, Y. (2014), Harvesting Robots for High-value Crops: State-of-the-art Review and Challenges Ahead. J. Field Robotics, 31: 888–911. doi:10.1002/rob.21525


Robots and machinery used in outer space

- Rećko, M., Tołstoj-Sienkiewicz, J., & Turycz, P. (2017). Versatile soil sampling system capable of collecting, transporting, storing and preliminary onboard analysis for mars rover analogue10.4028/www.scientific.net/SSP.260.59 [Robotic arm for Mars Rover] Link to article

- Czaplicki, P., Recko, M., & Tolstoj-Sienkiewicz, J. (2016). Robotic arm control system for mars rover analogue. Paper presented at the 2016 21st International Conference on Methods and Models in Automation and Robotics, MMAR 2016, 1122-1126. 10.1109/MMAR.2016.7575295 [Soil sampling] Link to article

- Sakib, N., Ahmed, Z., Farayez, A., & Kabir, M. H. (2017). An approach to build simplified semi-autonomous mars rover. Paper presented at the IEEE Region 10 Annual International Conference, Proceedings/TENCON, 3502-3505. 10.1109/TENCON.2016.7848707 [Making a Mars Rover semi-automatic] Link to article

- Wong, C., Yang, E., Yan, X. -., & Gu, D. (2017). Adaptive and intelligent navigation of autonomous planetary rovers-A survey. Paper presented at the 2017 NASA/ESA Conference on Adaptive Hardware and Systems, AHS 2017, 237-244. 10.1109/AHS.2017.8046384 [Intelligent navigation] Link to article

- Parness, A., Abcouwer, N., Fuller, C., Wiltsie, N., Nash, J., & Kennedy, B. (2017). LEMUR 3: A limbed climbing robot for extreme terrain mobility in space. Paper presented at the Proceedings - IEEE International Conference on Robotics and Automation, 5467-5473. 10.1109/ICRA.2017.7989643 [Robot with climbing arms (maybe possible to use for planting and harvesting] Link to article

- Garrido, S., Moreno, L., Martín, F., & Álvarez, D. (2017). Fast marching subjected to a vector field–path planning method for mars rovers. Expert Systems with Applications, 78, 334-346. 10.1016/j.eswa.2017.02.019 [Vector field-path planning] Link to article

- Scopus search link


Soil on Mars

- Boynton, W.V. , D. W. Ming, S. P. Kounaves, S. M. M. Young,† R. E. Arvidson, M. H. Hecht, J. Hoffman, P. B. Niles, D. K. Hamara, R. C. Quinn, P. H. Smith, B. Sutter, D. C. Catling, R. V. Morris. (2009). Evidence for Calcium Carbonate at the Mars Phoenix Landing Site – Science

- Hecht M. H. , S. P. Kounaves, R. C. Quinn, S. J. West, S. M. M. Young,† D. W. Ming, D. C. Catling, B. C. Clark, W. V. Boynton, J. Hoffman, L. P. DeFlores, K. Gospodinova, J. Kapit, P. H. Smith. (2009). Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site – Science.

- Kounaves S. P., Brandi L. Carrier, Glen D. O’Neil, Shannon T. Stroble, Mark W. Claire. (2014). Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: Implications for oxidants and organics – Icarus.

- Manning C. V. , Christopher P. McKay, Kevin J. Zahnle. (2008) The nitrogen cycle on Mars: Impact decomposition of near-surface nitrates as a source for a nitrogen steady state – Icarus.

- Mustard J.F. , Christopher D. Cooper & Moses K. Rifkin. (2001). Evidence for recent climate change on Mars from the identication of youthful near-surface ground ice – letters to nature.

- Smith M. L., Mark W. Claire, David C. Catling, Kevin J. Zahnle. (2014). The formation of sulfate, nitrate and perchlorate salts in the martian atmosphere – Icarus.

- Stroble S. P., Kyle M. McElhoney, Samuel P. Kounaves. (2013). Comparison of the Phoenix Mars Lander WCL soil analyses with Antarctic Dry Valley soils, Mars meteorite EETA79001 sawdust, and a Mars simulant – Icarus.

Coaching Questions

Coaching Questions Group 1