On Earth we depend upon sunshine, warmth, rainfall, and suitable soil to grow crops such as tomatoes. On Earth, almost all agriculture, except for greenhouses and some extensive irrigation, is dependant upon the weather.
On Earth we depend upon sunshine, warmth, rainfall, and suitable soil to grow crops such as tomatoes. On Earth, almost all agriculture, except for greenhouses and some extensive irrigation, is dependant upon the weather.
The question is, "what's the weather like on Mars?"
Mars, being smaller than the Earth, further from the sun, without oceans, and having little water vapour in its atmosphere, has relatively simple weather.
A typical Martian weather forecast, for the Martian equator, might read:
"Sunny today (as usual); the heat wave continues with highs reaching plus 10 degrees Celsius (+10°C) this afternoon, a chance of dust devils late this afternoon and cool tonight with the low approaching minus eighty degrees Celsius (-80°C)."
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The energy that drives the weather on Mars comes from the Sun, exactly the same as all weather on Earth. The energy which drives the Earth's weather, from summer breezes to gigantic hurricanes, comes from the Sun.
However, the Earth's atmosphere and the Earth's oceans store huge amounts of solar energy. The surface of Mars and its atmosphere do not store very much solar energy.
On Mars solar energy heats the Martian surface during the daytime, and at night almost all of the solar energy is radiated back into space as longwave infrared radiation.
Nevertheless Mars does have a thin atmosphere. As the Sun warms Mars' surface, some of the heat is transferred to the atmosphere during the sunny day. As the thin atmosphere near the surface warms up it expands and rises, generating convection currents that transfer heat throughout the atmosphere.
During mid-day the energy from the solar radiation exceeds the amount of energy radiated into space and the surface of Mars warms up significantly.
At night large amounts of energy are radiated from the Martian surface. Since the Martian atmosphere is too thin to inhibit this loss of energy, the nights on Mars are very cold!
Radiation may be considered an “element” of the weather, just like temperature and precipitation. Mars has much higher levels of ultraviolet (UV) radiation than Earth, due in part to its thin atmosphere. We know that protection against UV radiation is important to humans on Earth, but we should also remember that plants also need UV protection – and this will be even more important to plants growing (in a closed environment) on the surface of Mars.
At a given temperature “air” can hold a certain amount of water vapor. The colder it is, the less water it can hold. The ratio of the amount of water it does hold to the amount of water it CAN hold is called the Relative Humidity. When the “air” is cooled so that the humidity would be greater than 100%, the water vapor in the volume turns into solid or liquid water, depending on whether the temperature is above the freezing point.
At around -75 degrees Celsius, a volume of air can hold 0.03% of 7 millibars = 2 microbars worth of water, which is typical of the atmosphere on Mars. At about this temperature, the relative humidity reaches 100%. So when it gets cold, Mars has precipitation. However, this precipitation most likely takes the form of frost, rather than rain or snow. The ground is likely to be colder than the air, and so air hitting the ground cools and the water freezes to the ground as frost. A part of the polar ice caps of Mars is made of precipitated water ice (the rest is made of carbon dioxide as 'dry ice').
A Canadian-designed light detection and ranging (LIDAR) instrument on the Phoenix Lander (2008) observed water-ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. The water-ice clouds were detected at the top of the Atmospheric Boundary Layer and near the ground each night in late summer when air temperatures decreased.
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Just as on Earth, some places on the Martian surface absorb sunlight better than other places. It is partially due to this uneven heating that Mars develops strong convection currents in its atmosphere.
Both the Earth and Mars have extensive weather features which are driven by local convection as a result of the Sun's rays heating the planet's surface.
The Martian convection currents can be strong. Surface winds of up to 130km/h have been recorded by both Viking Landers. The winds also pick up dust from the Martian surface and can create dust storms which cover a large fraction of the planet.
The Mars Global Surveyor has also photographed large Martian "dust devils" and cyclonic storm systems.
Conclusion: The Martian weather and Martian climate seem too hostile to grow crops without greenhouse protection.
It is easy to build a simulator to demonstrate the process of convection in the Martian atmosphere. Use a sturdy cardboard box and a couple of empty soup cans (both ends removed). Construct a "convection box" as shown in the illustration. The dimensions of the box are not critical, but when it is completed it should be absolutely air-tight except for the two soup can "chimneys". A Marscape can be created to give the scene a more authentic appearance. |
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To initiate the convection process "hide" a hot pad in the bottom of the box under one of the chimneys (through the access hatch in the side of the box). An incense stick can be used to generate a small amount of smoke. Place the glowing end of the incense stick over the chimney opposite the hot pad. Allow a few minutes for convection to become established and the smoke will clearly mark the convection trail. |
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If the front of the box contains a "lip" the hot pad will be hidden from view when the box is raised to eye level, or alternatively, cover the bottom of the box with a thin layer of cotton cloth (dyed rusty red if you wish to give your box a more Mars-like appearance). Demonstrate the convection box and challenge students to explain:
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Caution: Only use a "low grade" heat source, that is, a heat source which generates a great deal of heat at a relatively low temperature. Do not use any heat source which has an open flame!
