By Paul Doherty
Dry Ice Explorations
The Martian atmosphere is 95% carbon dioxide gas, Earth's atmosphere is 0.03 % carbon dioxide gas.
Put dry ice into a plastic aquarium. The dry ice will sublime and fill the aquarium with carbon dioxide. You can sweep your hand through the tank of carbon dioxide and sweep out handfuls of gas. Smell the gas to experience the smell of Mars.
Float soap bubbles full of air in the aquarium of dry ice. This is the Bubble Suspension exhibit at the Exploratorium.
Put dry ice in water to create mist, pour the mist into the aquarium to make a layer of clouds as it floats atop the CO2.
Flick a lighter inside the aquarium, it will not burn, yet lower the burning lighter into the gas slowly and its flame will rise out of the top of the aquarium as the gas burns when it reaches oxygen.
Some fires can burn on Mars. Burn magnesium inside a block of CO2, the metal burns with the the oxygen from the carbon dioxide leaving carbon behind.
Carbon dioxide solidifies on Mars when the temperature drops to 148 K, which is -125°C or -193°F. The Martian polar caps contain dry ice.
Dry ice will slide around on a warm surface as it sublimes to create a nearly frictionless gas layer between the surface and the ice. So a warm flat object should be able to slide across flat surfaces on the martian polar caps.
Dry ice on earth, make George Washington scream, hold a quarter against dry ice. This experiment turns the escape of invisible carbon dioxide gas into an audible signal.
You can make dry ice into liquid carbon dioxide simply by putting some of it into a plastic, tygon, tube. As the carbon dioxide sublimes it raises the pressure above the 5 atmosphere triple point and the dry ice becomes a liquid. This can also be done inside a soda straw. Release the pressure and the liquid immediately solidifies.
Martian Ice Crystal Halos
Exploratorium Scientist Paul Doherty once grew Martian snowflakes in his laboratory. He discovered that martian snowflakes are made from dry ice, and are cubeoctahedrons, cubes with the corners cut off.
Once you know the shape of an ice crystal and what it is made of you can predict where colorful ice crystal Halos will appear in the sky. In the Martian sky several Halos will appear one at about 28 degrees is slightly larger than the most common water ice halo on earth which is 22 degrees in radius. A second Mars Halo is predicted at 40 degrees nearly the size of a rainbow on earth and another martian halo is larger than 60 degrees in radius. There are no halos on earth as large as 60 degrees.
We used to have an exhibit Rainbow Collisions which showed this.
Ice crystals on earth also make sundogs.
A cube of plastic will make two sundogs if it is rotated in front of a slide projector. Plastic has an index of refraction similar to that of martian carbon dioxide. So it will create approximately the position of martian sun dogs and halos. (To make the halo the prism has to be rotated on two axes in a gimbal.) We'll need a bit of help in the shop to build this.
Martian atmospheric Pressure and the triple point of water.
A solid steel rod, 5.5 feet long and one square inch in cross section, exerts the same force as the multi-mile thick atmosphere of earth. A rod 1/100 as long, 0.5 inches, exerts the force of the Martian atmosphere. A rod 100 times as long exerts the same force as the Venus atmosphere. The Teacher Institute has these rods for earth and mars but not the 550 foot long one for Venus.
Water Freezer Exhibit = Go To Mars
Try the Martian water exploration, use a vacuum pump to make water boil until it freezes.
Water can be made to boil inside a syringe just by lowering its pressure. See the Boyle-ing water exploration.
The average pressure at the surface of Mars is near 6 millibars (the atmospheric pressure on earth is 1 Bar.)
6 Millibars is the pressure of the triple point of water. Water boils at lower and lower temperatures as mountaineers go to higher altitudes on earth. When the atmospheric pressure reaches 6 millibars liquid water can boil at 0°C, where it is also freezing at the same time. On Mars water can be in a glass that is freezing and boiling at the same time.
In a cloudfree sky where the air is clean, the sky on earth is blue due to scattering of sunlight by molecules and atoms in the air. This makes the sun appear red at sunrise and sunset. There is an activity "Glue Stick Sunset" that creates blue scattering and red sunsets.
On Mars the sky is always tinted by the presence of salmon colored dust. This makes the sun at sunrise and sunset on Mars appear greenish blue. Maybe I can create a material that will scatter red light and thus make a cyan Martian sunset.
Every once in a while a volcano will inject sulfuric acid into the stratosphere. The sulfuric acid will form particles that scatter red light. When the full moon is viewed through these particles it appears blue. Thi is one type of blue moon. (The other blue moon occurs when there are two full moons in the same month.)
"Red sky at night, earth is in sight. Blue sun at morning, Martian day dawning."
Mars sand and dust
The exhibit Aeolian Landscape shows the behavior of blowing sand in a dry environment. Many of the same features are shown by the blowing sand on Mars. The Exploring Magazine, Dirt, has an article about extraterrestrial dirt including a bit about Mars dirt.
Mars Surface dirt contains iron superoxide. When you add water to iron superoxide it releases oxygen gas. I can probably concoct a pseudomartian soil from manganese dioxide which will erupt oxygen when wetted with the appropriate chemicals.
A common martian rock is basalt. This is also a common rock on earth. We can get basalt at the Exploratorium, maybe even some vesicular basalt (vesicles are small gas holes in the basalt.). Spread the rocks around the studio for people to touch. The MER landers will probably encounter vesicular basalt boulders. We can get the basalt blocks at a rock store. Some basalt is old and weathered with a reddish crust like the rock on Mars. We could scrape away the red crust in the studio to reveal the gray to black interior of the boulders just as the RAT, rock abrasion tool, on the MER lander will do. Besides basalt boulders look neat. We could also get layered sandstone or mudstone. These are rocks that scientists looking for water deposited rocks are hoping to find on mars.
Ventifacts. Mars rocks are shaped by the wind. Rocks shaped by the wind on earth are rare and are called ventifacts. I have some fist sized ventifacts which we could put on display. Other exploratorium staff also have ventifacts.
Martian meteorite samples are for sale, for a mere few hundred dollars we can probably get a piece of Mars that people can touch. Martian meteorites are priced by the carat so a sample will me small! Martian meteorites are called shergotites, nahklites, and chasignites. FYI The Nahkla meteor killed a dog when it landed in Egypt. (I can find you a supplier if you need help.)
Martian Dust Devils
We have photographed Martian Dust Devils from space, and have recorded the winds from dust devils hitting previous Mars lander spacecraft. Dust devils look like the Exploratorium Tornado exhibit.
The MER spacecraft have a Mars sundial mounted on them.
You can make your own earth sundial.
I have an activity, Martian Calendar and Clock which asks students to design a Mars clock and calendar.
Magnetic particles on Mars
You can collect magnetic particles on earth just as they did with the landers and rovers on Mars. Put a refrigerator magnet a white paper envelope. Drag the envelope through the gutter on the street near your house. Or in the dirt near the downspout of your house. Or just through sand. Look at the paper for evidence of black particles. Many of these particles came from meteorites.
This is an Exploratorium exhibit. One Martian meteorite contains magnetite grains similar to those produced on earth by magnetic bacteria.
Streamlined Islands on Mars
The Exploring Magazine issue on Islands has an article on Streamlined Islands. Images from space show streamlined islands on Mars. Streamlined islands are also found on earth. One place to look for them on earth is in the channeled scablands of eastern Washington State. Here, giant floods ripped apart the landscape during the ice age. There are photos in the article.
The gravitational acceleration on Mars is 38% of that on earth, i.e. 0.38g. Using a swing and an inclined plane people can feel what it is like to stand on Mars. The angle from horizontal for the inclined plane should be 68 degrees.
Selected Activities for Teachers
Martian Calendar and Clock
Using a swing and an inclined plane people can feel what it is like to stand on Mars.
Snack Glue Stick Sunset
Dry Ice explorations
Return to Activities
Scientific Explorations with Paul Doherty
10 October 2003