Before the advent of Mars-orbiting spacecraft, astronomers had a sketchy view of the Red Planet's ever-changing weather. Though Mars is one of the nearest planets to Earth, the distance between it and Earth varies greatly. The two planets circle the Sun like race cars circling a track at different speeds — and Earth "laps" Mars approximately every two years.
Martian dust storms are most likely to erupt during the spring and early summer in the planet's southern hemisphere — a time when Mars is closest to the Sun. Since Mars has a more elliptical orbit than Earth, its distance from the Sun varies widely. This variance causes a significant variability in the Martian climate.
Local dust storms, regional obscurations, and discrete "yellow" clouds on Mars have been reported throughout the last century; however, it is the planet-encircling dust storms that have captured our attention in the age of spacecraft exploration of Mars.
1796 — Astronomer H. Flaugergues noted "yellow clouds" (now known to be clouds of dust) on Mars, as opposed to fleecy, whitish water-ice clouds.
1920 — Patchy, yellow dust clouds observed and photographed at Lowell Observatory in Arizona.
1956 — First extensive observations of a planet-encircling dust storm on Mars.
1965 — Mariner 4 conducts first fly-by of Mars; sends back dust-free photographs of a narrow swath of the planet.
1969 — Mariners 6 and 7 fly by Mars to photograph clear and cool atmospheric conditions.
1971 — The first Mars-orbiting spacecraft (Mariner 9) arrives to find the planet already shrouded in dust — the first definitive planet-wide dust storm ever seen. The dust covered everything except the poles; tall volcanic peaks poked above the dust, revealing themselves as high mountains rather than as circular basins.
1973 — Ground-based telescopes detect another planet-encircling dust storm just one Martian year after the global storm viewed by Mariner 9.
1977 — Viking spacecraft watch two planet-encircling Martian dust storms in succession from a Mars orbit and, for the first time, from the surface of Mars.
1982 — Viking Lander 1 detects what appears to be another planet-encircling dust storm just weeks before the loss of communications ends its nearly seven-year observational record on the surface of another planet.
1994 — Ground-based microwave monitoring of Mars atmospheric temperatures indicates a planet-encircling dust storm in progress, the first such planet-wide storm detected since Viking.
1997 — Mars Global Surveyor begins aerobraking at Mars and finds that planet-wide warming events can be produced by as little as a regional dust storm.
2001 — In late June the Hubble Space Telescope captures a Mars opposition photograph. (Opposition occurs when Earth lies in a straight line between the Sun and an outer planet.) The image shows seasonal dust activity in Hellas and at the North Pole. In a few weeks, these regional dust storms developed into a near-global, planet-encircling dust storm. Unprecedented details of this unusually early, blossoming storm were followed by the Mars Global Surveyor, which takes daily all-planet images and measures atmospheric temperatures.
"Tales of ... Dust storms seen on Mars" details the weather on Mars from the earliest account in 1796 to 2001. This information can be used to introduce the idea that other planets experience seasons like Earth. This selection originally appeared as background information for a press release on Mars.
Teachers can use this resource as:
A content reading selection. Teachers should discuss the meaning of unfamiliar vocabulary prior to having students read this selection.
An engagement activity. Have students read the selection. Ask them how technology helped us understand the observations. Have students speculate what might have happened (both technologically and politically) between 1956, when the first extensive observations of a planet-encircling dust storm were made, and 1965, when Mariner 4 flew by the planet.
An inquiry tool. Propose a question, such as, "Do other planets experience seasons like the Earth does?" Have students read the selection and write down as many questions as they can about the information in the text.
A source of information. Students can use this as a tool to begin sequencing the history of our exploration of Mars. Several Mars missions are listed by name. Students can research the others and fill in the gaps. For instance, Mariner 4 was the first fly-by of Mars. What happened to Mariner 3?
HubbleSite press release: "Hubble Captures Best View of Mars Ever Obtained from Earth"
HubbleSite press release: "Hubble Charts Changes on the Red Planet"
HubbleSite press release: "Colossal Cyclone Swirls Near Martian North Pole"
HubbleSite press release: "Scientists Track 'Perfect Storm' on Mars"