The Mars spacecraft Phoenix - summary of findings

The Phoenix spacecraft has left us valuable information about the Arctic Circle region of Mars, the composition of the soil in the area and interesting data about the atmosphere and weather in the arctic meridian autumn

introduction

On May 25.5.2008, 68, the American spacecraft Phoenix landed on Mars. The landing was at latitude N°700 at a distance of 3 km from the North Pole. XNUMX months of work were planned for it. The landing took place in the last summer months before the area is covered with snow. The spacecraft's energy source is solar collectors and as long as there is light its systems can be activated. Upon completion of the program The original work and in light of its success in its tasks, it was decided to extend its work for another month from the time this month of work ended and in light of the fact that it was still light Sun, although weaker, the mission was extended for another month. Only with the setting of the sun and the onset of winter, there was complete darkness in the area for several months, did all the operations of the spacecraft come to an end.

The spacecraft was equipped with a laboratory and an extremely long arm. It was possible to extend the arm up to a distance of 2.5 meters. At the end of the arm were a digger and a camera. The arm would collect soil samples and bring them to the laboratory for testing. The intention was to find water and evidence of signs of life. Due to its length and articulated structure, it was also possible to photograph under the lander. A total of 25,000 photographs from the landing site were broadcast to Israel. Both the ground and the sky were photographed. The tests were both mineralogical and climatic.

After 151 days of activity on 27.10 the connection with the Phoenix was cut off. With the arrival of the summer, several attempts were made to renew the relationship, but they were unsuccessful.

satellite communication

In addition to the means of communication of the lander itself, two American orbiters orbiting Mars, the Odyssey and the MRO (Mars Reconnaissance Orbiter), were also used. The landing site is monitored by the MRO even before landing (1). The use of both spacecraft was of great importance in terms of the sequence of transmission of work instructions to the lander. When there was a malfunction in the high praise antenna of the MRO, the Odyssey (2) was used and also when a communication problem arose with the Odyssey, the MRO (3) was used. In terms of communication, the two spacecraft backed each other up. These dashes were therefore, beyond their original work plan, also used as communication satellites. This communication is limited to a certain range of hours, to those hours in which they pass over the place of invention of the Phoenix (4). Parallel observations were also made from the Phoenix and from space. As the Phoenix examined changes in the lower atmosphere and photographed the ground, the MRO examined the atmosphere in the landing zone (5).

The working method of the Phoenix

The lander did not begin sampling the ground upon landing. The immediate actions taken were to photograph the landing environment. Based on these photographs, a preliminary analysis of the soil and its characteristics was made. Accordingly, it is determined where the arm will be sent and dug. The work plan as a whole was flexible. It was clear that scientific discoveries are expected every day and have an important role in soil sampling. In terms of the work of the team of researchers and engineers, the working day was conducted in the following way (4).

1. A short staff conversation that lasted 30 minutes, before information arrives from Mars.
2. The team discusses for several hours each day and reviews the initial database for that day.
3. A second meeting in the middle of the day and receiving a report on the functioning of the lander's instruments.
4. A third meeting at the end of the day in which all the information that arrives that day and the work planning for the next day are reviewed.
5. Transmission of work instructions for the next day.

In the advanced stages of the lander's activity, when the summer season was coming to an end and the hours of daylight available to the researchers each working day were reduced, it was clear that it would no longer be possible to operate the lander to its full extent, it was decided to gradually reduce its activity until the sun was below the horizon line and the area was completely dark. Every time some of the heating devices and appliances are turned off. From the month of November onwards, initially 4 heating devices of the Phoenix were turned off, one device at a time. The shutdown of one heater resulted in the shutdown of part of the landing gear. The saved energy was directed to the operation of the camera and the meteorological monitoring devices (6).

In addition to the normal work in the robotic arm, it was decided to use it for a purpose it was not designed for. The intention was to move a block of rock whose dimensions are 19 cm long, 10 cm wide and 2-3 cm high. There was no assurance that the attempt would be successful. The plan was to move it so that its effect would be minimal on what was below it. On 20.9 The arm expanded an excavation made near it and the next day on 21.9/7 the arm was instructed to create a situation in which it would slide into The excavation. Since a hard layer of ice was discovered in many places, the impression was given that digging under this rock would provide a lot of information regarding the processes that affect the ice below the ground. From what has been observed so far in the excavations, it turned out that the rocks under the ground are darker and that they store ice on the surface The one under the rock will bend. If this is indeed the case, then the ice is probably in equilibrium with the water vapor Another possibility is that the rock absorbed moisture from the atmosphere along with the moisture that became part of the ice layer (22.9). This task was successfully carried out on 40. A preliminary examination of the exposed soil showed color differences between it and the area (8).

The main research instrument in Phoenix is ​​the TEGA (Thermal and Evolved Gas Analyzer). This device has 8 heating cells and each of them is a heat analyzer. Soil samples should be placed into each such cell for testing. Each sample is heated 4 times and the amount of heat needed to raise the temperature is checked. This is of utmost importance for the following reason: if there is ice in the soil sample, heating it to a temperature exceeding C ° 0 will lead to the melting of the ice. It takes more heat to get from C ° 0 to C ° 1 than to get from C ° 1 to C ° 0 because ice has to be melted. By heating to C ° 1000 it is possible to check if there are several transition stages. If there are carbonates they will decompose at high temperatures and release CO2. The release of CO2 at a temperature of C ° 700 – C ° 600 indicates the presence of carbonates and the release of gas at a temperature of C ° 400 can indicate the presence of organic molecules. In the laboratory, there is a carrier of nitrogen that flows this gas over the samples, so that when various gases are released, whether they are organic molecules or just water vapor from the ice, the nitrogen transfers them to a thin tube that transfers them to the gas analysis device. A mass spectrometer measures the released gases, so for example it is possible to measure ratios between different isotopes 12C or 13C in CO2 and on the other hand 18O and 16O. These ratios can tell about the origin of the CO2. At first, difficulties arose in introducing the samples into the cells. The arm did transfer the soil samples to the openings of the cells, but they were unable to get inside. Only the activation of vibration devices solved the problem (10).

Until September 11.9, only 4 of the 8 cells were activated. It was decided to operate the four cells that were not used so far in a slightly different way. Until now, with the analysis of the results of the experiments, additional samples would be included in the content. With the days getting shorter, it was decided to speed up the course of work. They would put in a soil sample, perform the experiment, not wait for the results to be analyzed and put in other samples. In doing so, they wanted to utilize as much as possible the energy of the Phoenix, which is decreasing every day, in an optimal way (11).

The meteorological instruments of the Phoenix allow parallel and coordinated work with the MRO compass. This makes it possible to examine the same atmospheric column from below and above. The resulting perspective is global (12).

Spirits

A common phenomenon on Mars is dust devils. This is a situation in which warm air rises quickly above the ground through a small pocket of less warm air above which the air pressure is lower and if the conditions allow it, the air begins to rotate in a swirling manner. On the surface of Mars these eddies can reach the greatest height due to its low gravity. This figure and the heating of the air cause the energy to be transferred to a swirling movement and to the high altitude. on 20.4. A month before the landing, the MRO noticed two dust devils in the landing area. One of them rose to a height of 920 meters and the other to a height of 790 meters (13). At the beginning of September, at least 6 dust devils were observed and their diameter ranges from 2-5 meters. They are smaller than those observed by the Spirit rover (14).

In the landing area, winds were measured at a speed of 15-20 km/h in an easterly direction in the middle of summer. As autumn approached, the wind speed increased and changed its direction to the west. Winds that blew at higher altitudes reached 60 km/h with the change of the climatic system, which was accompanied by an increase in their number of the dust devils. It also turned out that some of these storms are associated with high winds (15). In the morning the winds come from the south, blow from the north in the middle of the day, from the west in the afternoon and again blow from the south at the end of the day (16).

At 3.6 for 15 minutes an increase in the amount of dust in the atmosphere was observed (17). Until June 16.6, no large dust clouds were observed in the landing area. The dust in the atmosphere is much more mixed than on Earth. Air eddies mix it and lift it up to a height of several kilometers (18). The size of the dust particles that hit the ground is 1/10 of the diameter of a human hair (19). On 11-12.10, the 135-136 days of the mission, it was necessary to reduce many of the lander's activities due to a dust storm that passed through the area, a storm that covered an area of ​​37,000 square kilometers and moved from west to east (20).

Weather

The temperature difference between day and night is very large. On average it ranges from C ° 80 - at night to C ° 30 - during the day. There were days when the temperature rose slightly and stood at -23°C. The atmospheric pressure gradually decreased from 8.5 millibars on the first day of landing to 7.43 millibars on the 115th day. Continuous monitoring from the first day of activity until the 115th day shows a decrease in atmospheric pressure with the approach of winter and the shortening of the number of daylight hours per day (21).

water

In the excavation made on 15.6 a bright block was revealed and it was seen in its entirety on 16.6. It was clear that this was a block of ice and exposure to air resulted in its evaporation. What supported the assessment that it is indeed water is the fact that CO2 in the state of ice cannot be stable in this state of accumulation even for one day (22). In a bright block observed on the 8th day under the lander nothing remained on 1.9, the 97th day also due to evaporation (23). It turned out that there is water under the regolith. How the water got there is unclear. They may be remnants of a layer of a large polar ice cap that shrank, or a frozen ocean, or frozen snow on the ground. The most likely possibility is that water vapor that came from the atmosphere was slowly absorbed by the soil and froze at the temperature at which it turns into frost (24).

More on water finds during Operation Phoenix

To the researchers' surprise, perchlorates were found in the places where the soil was tested; (perchlorates)-compounds in which one atom of chlorine and 4 atoms of oxygen. They make up 1% of the amount of land tested. This means that they can lower the freezing point of water below C ° 0. The perchlorates can contain magnesium and sodium and in this case the freezing point of water drops to C ° 72 - in the case of magnesium and to C ° 37 - in the case of sodium and these were indeed found in the soil samples. On Earth they are rare and found mainly in arid areas such as the Atacama Desert in Chile. During the summer, the water in these regions on Mars can be in the liquid phase for several hours a day (25,26).

On days 8,31,44, 1, 27 of the Phoenix operation, liquid drops were observed on one of the lander's legs. It was estimated that the water could be liquid. Because of a high concentration of the perchlorates that act as we mentioned as freezing inhibitors. One of the drops began to slide along the landing leg and reached a size of XNUMX cm. Before it began to slide, it became dark, which is consistent with melting ice (XNUMX).

The meteorological instruments performed atmospheric measurements on a daily basis and observed the drop in atmospheric pressure which is a sign of seasonal change (28). In a report from August 29.8, it was stated that the movement of clouds of water ice was observed in the lander's photographs. On this day, a series of cloud photographs was taken for 10 minutes. Running the images one after the other created an animation of cloud movement for several seconds (29). In the month of September, clouds and frost were observed night after night as the air got colder. They also noticed snow falling from clouds at an altitude of 4 km above the landing site. The snow melts before reaching the ground (30).

During the day, the water vapor pressure is 10-1000 times weaker than its equivalent on Earth. At night starting at 8 pm (according to local time) the water vapor starts to disappear and reaches its minimum at 2 am at 1% of its daily value. It may be that molecules originating from the air condense into the form of thin membranes that cover the ground. On Earth such membranes are formed when the air contains water vapor. Sometimes these membranes turn into dew drops or ice crystals (frost). On Mars these thin membranes do not turn into a solid or a liquid. They don't flow like water, but they are more mobile than ice. A kind of intermediate state (31). On the 106th day, frost spots were seen on the ground (32). On the 113th day, in a photo of one of the excavations made by the arm, you see morning frost (33).

the nature of the soil

On 3.6, a number of particles were photographed that were collected on the ground exposed during the landing and remained there for 5 days afterwards. It was part of tests that allowed for first work with the microscope before the excavator delivered particles to a lab inside Phoenix. The color of the particles is reddish brown (19).

The soil is of a membranous nature and tends to crystallize into small balls when it falls on a metal slope like in the TEGA device. In addition to this, it is also sticky and adheres to the surface of the furnace floor, which is inclined at an angle of 45 °. The soil seems to have chemical or electromagnetic properties, unlike what is found elsewhere on Mars (35). Fine particles found in the sample are similar to dust particles that were carried by the wind and that were examined several days before in a microscope (18). To the researchers' surprise, the analysis found that part of the soil is alkaline. Such soil is by its nature typical of an acidic environment probably associated with a nearby crater (36). One of the estimates that turned out to be correct was that the activity of the braking engines near the ground during the landing would reveal part of what is under the surface. In the simulation it turned out that this pulse of the engines digs into the ground in less than a second. As a result, the soil layer under the engines is liquid and behaves like water (37).

It also turned out that the soil is more lumpy and cohesive than its components, dust and sand which were deposited by winds, should be. There is some unknown factor that sticks them together. Another possibility that is being considered is that water molecules stick them to the ground. Another possibility is that the water carries and deposits salts that Phoenix identified in the soil such as magnesium perchlorate or calcium carbonate (CaCO3). The changes in the electrical properties of the soil correspond to the accumulation of water molecules on the surface of the soil grains during the daily cycles of the water vapor moving through the soil. There is an exchange between the atmosphere and the ice below the ground. It was found that a film of water molecules accumulated on the surface of mineral particles. The tests showed that these molecular membranes were formed according to the prediction (37). It turned out that the soil was different from that examined in the equatorial region by the Spirit and Opportunity rovers. The soil is alkaline similar to sea water and contains calcium carbonate which is usually formed in the presence of water (38).

The perchlorates found by the Phoenix were observed in a small amount taken from the surface. A larger amount was found in a second sample taken a few centimeters below the first sample, at the boundary line between the ground and the ice. On its surface, liquid water should have been found here, but this was not found (39). On Earth there are several microorganisms that feed on processes involving perchlorates and in a number Plants have a concentration of them (40). Another mineral found in the samples is a silicate similar in structure to mica (a transparent mineral found In trace amounts in granite and many rocky materials, but it is probably found in phyllosilicate (9). The pH of the soil is about 41.

Photo findings

The photographs show that they are similar to the upper layers of the dry valleys in Antarctica (42). One of the surprises observed on Mars are the polygons. A similar phenomenon is known on Earth in the frozen ground in the high latitudes, places where there is a phenomenon of soil circulation and contraction (43). Another body in the solar system where similar formations have been found is Enceladus, a moon of Saturn photographed by the Cassini spacecraft (44). When the ice is very cold it shrinks and cracks in geometric formations like mud cracks in the desert. The width of the cracks is several millimeters. If they are filled with material such as the dry dust of Mars, the ice on the ground will not have room to expand with the increase in temperature and will rise upwards and create mounds in the centers of the polygons and shallow excavations at the borders of the polygons. The size of the polygons is affected by the thickness of the soil layer above the ground and by the climate itself. In general, the closer the ice is to the ground, the more it is affected by extreme temperatures. It cracks more and more and smaller polygons are formed. Ice found deeper in the ground forms large polygons on Mars. If the ice is 30 cm deep, the polygons will disappear (45). During the excavator's work, samples were taken from a place between two polygons. The researchers' intention was to see if the material in this place would be different from previous samples taken from excavations near the center of a polygon. It turned out that there were indeed differences. The soil in the deeper place than the previous excavations is lumpier (46).

Carbon measurement

The CO2 measurements in the atmosphere showed that Mars is more active than they thought. The findings show that Mars has replenished its atmospheric CO2 recently and that this gas has created a new interaction with liquid water on the ground. The small gravity and the absence of a magnetic field should mean that the accumulation of gas in the atmosphere will lead to its escape. This process encourages the escape of light isotopes of 12 C relative to the isotope 13 C. If Mars only experienced this process, the 12 C would disappear if there was no resupply of it. The ratio of 13 C to 12 C was higher than that measured by Phoenix. This means that the atmosphere has recently received an addition of CO2 from volcanic eruptions. But no recent evidence was found for such activity that should have left its mark on other isotopes such as 18O and 16O. According to the estimate, the CO2 interacted with liquid water and thus the amount of oxygen in CO2 was enriched with 18O. According to a proposed model, this isotope of oxygen indicates that liquid water was recently (in geological terms) on the ground in a quantity large enough to influence the composition of the atmosphere today (47).

agriculture

One of the encouraging results of the Phoenix findings is that the soil is similar to what is found in several dry places on Earth. The substances found in particular magnesium, potassium and sodium are important nutrients for sustaining life. It turned out that asparagus could be grown on this soil (48).

Sources

1. Mckee M.-"Dust devils spotted at Mars probes' landing site" 7.5. 2008
http://space.newscientist.com/article/dn13852- dust -devils- spotted -at- Mars- probes’-landing- site.html?DCMP =LLC-hmts1mts&nserf-new2_head_dn13852

2. http://www.spaceflightnow.com/mars/phoenix/status.html 28.5.2008

3. "Phoenix captures highest resolution images ever from surface of Mars" 6.6.2008
http://marsdaily.com/reports/ Phoenix _Captures_ Highest_ Resolution_ Images_ Ever_ From_ Surface_ Of_ Mars_999.html

4. "Working on Mars is more than 9-to-5.40" 21.7.2008
http://marsdaily.com/reports/ Working _On _Mars_ Is_ More_ Than 9_to_5.40_999.html

5. "NASA Phoenix Mars lander works through the night" 22.7.2008
http://marsdaily.com/reports/ NASA_ Phoenix_ Mars_ Lander_ Works_ Through_ The_ Night_999.html

6. "NASA Phoenix mission faces survival challenges" 29.10.2008
http://marsdaily.com/reports/ NASA_ Phoenix_ Mission_ Faces_ Survivel _Challenges_999.html

7. "NASA Phoenix Mars lander might peek under a rock" 23.9.2008
http://marsdaily.com/reports/ NASA_ Phoenix_ Mars_ lander_ Might_ Peek _Under _A_ Rock_999.html

8. "Rock moved by Phoenix lander arm" 25.9.2008
http://marsdaily.com/reports/ Rock_ Moved_ By_ Phoenix_ Lander _Arm_999.html

9. Thompson A.- "Snow seen on Mars" 29.9.2008
http://space.com/misionlaunches/080929-phoenix-update.html

10. "Phoenix shake and bake" 24.6.2008
http://marsdaily.com/reports/ Phoenix _Shake_ And_ Bake_999.html

11. "Next Mars soil scoop slated for last lab cell" 11.9.2008
http://marsdaily.com/reports/ Next_ Mars_ Soil _ Scoop_ Slated_ For _ Last_ lab _Cell_999.html

12. "NASA lander will sprinkle Martian soil for microscope to view" 11.1.2008
http://marsdaily.com/reports/ NASA_ Lander_ Will_ Sprinkle_ Martian _Soil_ For_ Microscope_ To _View_999.html

13.. Mckee M.-"Dust devils spotted at Mars probes' landing site" 7.5. 2008
http://space.newscientist.com/article/dn13852- dust -devils- spotted -at- Mars- probes’-landing- site.html?DCMP=LLC-hmts1&nserf-new2_head_dn13852

14. Baldwin A. - "dust devils pay a visit to Phoenix" 12.9. 2008
http://www.astronomynow.com/080912 Dustdevilspayvisito Phoenix.html

15. "Telltale tells story of winds at Mars Phoenix landing site" 17.9.2009
http://marsdaily.com/reports/ Telltale_ Tells_ Story _Of_ Winds _At _Mars _Phoenix_ Landing _Site_999.html

16. "third scoop is a keeper for Phoenix Mars lander" 6.6.2008
http://marsdaily.com/reports/ Third_ Scoop_ Is_ A_ Keeper_ For_ Phoenix_ Mars_ Lander_999.html

17. "Phoenix lander robotic camera sees possible ice" 3.6.2008
http://marsdaily.com/reports/ Phoenix_ Lander _Robotic_ Camera_ Sees_ Possible _Ice_999.html

18. "NASA's Phoenix Mars lander inspects delivered soil samples" 16.6.2008
http://marsdaily.com/reports/ NASA_ Phoenix_ Mars_ Lander_Inspects _Delivered _Soil_ Samples_999.html

19. "Phoenix captures highest resolution images from surface of Mars" 6.6.2008
http://marsdaily.com/reports/ Phoenix_ Captures_ Highest _Resolution _Images _From_ Surface _Of_ Mars_999.html

20. "Phoenix weathers dust storm" 15.10.2008
http://marsdaily.com/reports/ Phoenix_ Weathers _Dust _Storm_999.html

21. Martian weather report
http://www.space.gc.ca/asc/eng/exploration/phoenix_weather/asp

22.” Phoenix craft confirms frozen water found at landing site" 21.6.2008
http://www/spaceflightnow.com/marsphoenix/080621.html

23. PIA11074: Underneath Phoenix lander 97 sols after touchdown
http://photojournal.jpl.nasa,gov/catalog/ PIA11074

24. Thompson A. - "Scientist explain Martian soil surprises" 6.8.2009
http://www.msnbc.msn.com/id/31712980/technology-and-science-space/

25. Shiga D.-"Neutral antifreeze may keep Mars running with water" 18.2.2009
http://www.newscientist.com/article/mg20126965.000- neutral -antifreeze- may- keep- mars- running –with- water.html

26. "Research demonstrates potential for liquid water on present day Mars" 25.5.2009
http://marsdaily.com/reports/ Research _Demonstrates_ Potential_ For _Lliquid _Water_ On_ Present _Day_ Mars_999.html

27. Jagard V. - "Liquid water recently seen on Mars" 18.2.2009
http://news.nationalgeographic.com/news/bigphotos/17161866.html

28. "Phoenix mission conducting extended activities on Mars 1.9.2008
http://marsdaily.com/reports/ Phoenix_ Mission _Conducting _Extended _Activities _On_ Mars_999.html

29. Thompson A - "Very short movie" The clouds of Mars" 2.9.2008
http://www.space.com/missionlaunches/080902-phoenix-update.html

30. Thompson A - "Snowfall seen on Mars" 29.2.2008
http://www.space.com/missionlaunches/080929-phoenix-update.html

31. "Schiber M.-"A sliver of a chance for life on Mars" 27.2.2009
http://marsdaily.com/reports/ A _Sliver _Of_ A _Chance _ For_ Life_ On _Mars_999.html

32. http:/phoenix.lpl.arizona.edu/images/gallery/lg_31041.jpg/

33. "Morning frost in trench dug by phoenix" 23.9.2008
http://marsdaily.com/reports/ Morning_ Frost_ In _trench_ Dug_ By_ Phoenix_999.html

34. "After whole lotta shakin', Mars probe ready to bake" 11.6.2008
http://marsdaily.com/reports/After_ Whole_Lotta _Shakin _ Mars_ Probe_ Ready_To_ Bake_999.html

35. "NASA extended successful Phoenix lander mission" 31.7.2008
http://marsdaily.com/reports/NASA _Extended_ Successful _Phoenix _Lander_ Mission_999.html

36. "Simulation predicted Mars lander would hit surface" 6.6.2008
http://marsdaily.com/reports/Simulation_ Predicted_ Mars_Lander _Would_lit_ Surface_999.html

37. "Phoenix site on Mars may be in dry climate cycle phase" 16.12.2008
http://marsdaily.com/reports/Phoenix_ Site _On_ Mars_ May_ Be_ In _Dry _Climate_ Cycle_ Phase_999.html

38. Sample I.- Its snowing on Mars” 27.1.2009
http://www/guardian.co.uk/science/2009/jan/27/mars-snow-space-technlogy-nasa/print

39. Bortman H. – “liquid water in the Martian North” 25.8.2008
http://marsdaily.com/reports/Liquid_ Water_ In_ The_Martian _North_999.html

40. "Phoenix Mars team opens window in scientific process" 6.8.2008
http://marsdaily.com/reports/Phoenix_ Mars _Team _Opens_ Window _In_ Scientific_ Process_999.html

41. PIA11206: Mars particle and terrestrial soil, comparative microscopy
http://photojournal.jpl.nasa.gov/catalog/ PIA11206

42. "Phoenix returns treasure trove science" 27.6.2008
http://marsdaily.com/reports/Phoenix_ Returns_Treasure_ Trove_ Science_999.html

43. "Phoenix Mars lander explores site by trenching" 22.8.2008
http://marsdaily.com/reports/Phoenix_ Mars_ Lander_ Explores_ Site _By_ Trenching_999.html

44. PIA 06252: Boulder-strewn-surface-narrow-angle camera view
http://photojournal.jpl.nasa.gov/catalog/ PIA 06252

45. Semeniuk I.-"Mars scientists ponder polygon mystery" 27.5.2008
http://www.newscientists.com/article/dn3986- Mars- scientists- ponder- polygon- mystery.html

46. ​​Thompson A. – “Very short movie: The clouds of Mars” 2.9.2008
http://www.space.com/missionlaunches/080902-phoenix-update.html

47. "NASA data shed new light about water and volcanoes on Mars" 10.9.2010
http://marsdaily.com/reports/ NASA _Data _Shed_ New_ Light _About_ Water_ And_ Volcanoes_ On _Mars_999.html

48. Santini JL - "Martian soil good enough for Asparagus" 27.6.2008
http://marsdaily.com/reports/Marian _Soil _Good_ Enough_ For _Asparagus_999.html