Mars Facts

Mars Climate:

Scientists think that the climate on Mars 3.5 billion years ago was similar to that of early Earth: warm and wet. But because of chemical reactions between Mars' carbon dioxide atmosphere and water, most of its carbon dioxide was used up forming carbonate rocks. Earth is big enough and active enough that it has plate tectonics which recycles this carbonate back to carbon dioxide. Mars is too small (10 times less massive than the earth) and does not have any recycling of its carbonate. So now the Mars atmosphere is very thin, the temperature is very cold, and what water remains is either frozen in the Martian poles as permafrost or hidden in deep underground springs. Mars' current climate changes drastically during the year. It has seasons similar to the Earth's due the tilt of its axis. But because its orbit around the Sun is elliptical; the distance from the Sun varies about by 20% depending on where it is in its annual orbit. The seasons in one hemisphere (South) are more extreme while in the other (north) they are less extreme.

Temperature:

The temperature on Mars may reach a high of about 70 degrees Fahrenheit (20 degrees Celsius) at noon, at the equator in the summer, or a low of about -225 degrees Fahrenheit (-153 degrees Celsius) at the poles. Obviously this is very inhospitable for humans, but it is also of some concern for the electronics and mechanical parts of a Mars airplane and its instrumentation. In the mid-latitudes, the average temperature would be about -50 degrees Celsius with a nighttime minimum of -60 degrees Celsius and a summer midday maximum of about 0 degrees Celsius.

Humidity:

 

Humidity is the amount of water vapor in the air. This varies from day to day and depends on the temperature: warm air can hold more water vapor than cold air . Humidity is measured as a percentage of the maximum amount of water that the air can hold at a given temperature. The greater the difference between the two temperatures, the greater the evaporation. When there is a lot of evaporation, the air is drier and the humidity is low. The instrument used to measure humidity is called a psychrometer.

On Mars, the air is saturated (100% humidity) at night, but undersaturated during the day. This is because of the huge temperature difference between day and night.

To demonstrate this:

1. Take a clean, dry jar and place the lid on it.

2. Allow to stand 10 minutes in a shaded area and observe.

3. Put it in a freezer for at least an hour.

4. Remove and observe. (At room temperature, the air inside the jar was not saturated, but in the cold freezer the air could not hold much water-it became saturated-and the water condensed and formed frost.)

Wind:

Occasionally, winds on Mars are strong enough to create dust storms that cover much of the planet. After such storms, it can be months before all of the dust settles. The maximum wind speeds recorded by the Viking Landers in the 1970's were about 30 meters per second (60 miles an hour) with an average of 10 m/s (20 mph). Just as on Earth, at certain latitudes, the winds tend to blow in certain directions.

In Mars' northern mid-latitudes, wind blows from west to east just as it does in the United States. (Local variations of this can be caused by nearby mountains, large bodies of water, the season, etc.) Recent satellite images of Mars show that the dust storms have lessened, indicating that Mars winds have lessened, due to unknown causes. Scientists say that the planet is also getting colder.

Air Pressure:

A barometer is used to measure air pressure. The average air pressure on Earth is 29.92 inches of mercury (or 1,013 millibars). This is more than 100 times Mars' average of 0.224 inches of mercury (7.5 millibars).

Air pressure is not the same everywhere on Earth. One reason is because temperature varies from place to place. When air heats up, air molecules move faster, pushing each other away and causing air to expand. With fewer molecules in the same amount of space, the air in that space weighs less: it exerts less pressure on the Earth. Cold air molecules are packed closer and exert more pressure on the Earth.

At any given location on Earth, the air pressure can vary about 10% whereas on Mars it can vary by as much as 50%. Mars' atmosphere is mostly carbon dioxide and therefore behaves differently than Earth's mostly nitrogen and oxygen atmosphere.

Changing air pressure is experienced as ears pop going up and down mountains or when flying in airplanes. Meteorologists, who try to predict the weather, know that a higher than average pressure reading usually brings fair weather while low pressure usually brings stormy weather. Students often have trouble understanding that air has weight and that the whole atmosphere weighs down on everyone and everything everywhere.

We live on the bottom of an ocean of air. Air has weight and exerts pressure on us as a result of its weight. On each square inch of our bodies, there are 14.7 pounds of pressure. On the entire human body surface, the total air pressure varies from 10 to 20 tons! Just as ocean animals are not crushed by the weight of water above them, we are not crushed by the weight of the air because the inner pressure of our bodies pushing out equalizes the air pressure pushing down on us.

To help grasp the concept that air occupies space and has weight, do the following demonstration:

1. Fill a large glass jar/bowl half full of water and place a cork in the water.

2. Place a clear plastic/glass jar or cup above the cork (open end down) and press it into the water.

3. Explain what happened. (The air in the cup pushes the water out of the way because the air needs to occupy that space.)

Planet Profiles

Characteristic	VENUS	EARTH	MARS	Observations
Views
Diameter (km)	12,104	12,756	6,787	Mars is smaller than Earth.
Escape velocity (m/sec)	10,400	11,200	5,000	It is easier to leave Mars because there is less gravity.
Average distance from Sun (AU)	0.723	1	1.524	Mars is our nearest planetary neighbor. We can use the ratio of orbital radii to predict the ratio of orbit duration.
Rotation period (length of day in Earth hours)	-5,832 (sidereal rotation)	23.93	24.62	Earth and Mars are surprisingly similar!
Revolution period (length of year in Earth years)	0.62	1	1.88	Can you see why the gap between missions to Mars is about 25 months? Launch opportunities occur when the distance that the spacecraft must travel between planets is small.
Atmospheric components	96% carbon dioxide, 3% nitrogen, 0.003% water vapor	78% nitrogen, 21% oxygen, 1% argon	95% carbon dioxide, 3% nitrogen, 1.6% argon	Propulsion system cannot use oxygen from the atmosphere at Mars.
Atmospheric Density (kg/m^3)	65 kg/m3	1.2256	0.0155	There is much less gas available at Mars for the wing to generate lift and for the propeller to produce thrust. The density at Venus is extreme. Structural requirements for a plane would be difficult to achieve. Buoyancy is a possible solution for Venus.
Gravity (m/s^2)	8.87	9.8	3.0	An airplane on Mars only needs to generate 40% of the lift that would be required on Earth
Temperature (degrees C)	462° C	~25	~50-30	Low temperature can affect structure instruments and batteries.
Dust	Trace	Varies from trace to significant	Significant	Instruments may need additional protection.
Wind	Slow	Mild to gale force (predictable)	Strong	Affects controllability
Flight Speed	Very Slow	Low	High	Transonic problems limit flight Speed at Mars
Reynolds Number	10,000,000	10,000,000	50,000	Low Reynolds Number at Mars makes flow very sensitive to wing shape
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