6. Martian Climate and Weather
Discovery: Years of observations are providing a picture of martian weather and atmosphere dynamics.
Significance: The climate impacts whether life could evolve and survive there.
Daytime martian sky, red with suspended atmospheric dust. Approximately true color. Opportunity rover image: NASA/JPL/Cornell |
Sunset at Gusev crater, approximately true color. At the horizon, light scattering through the longer column of dust appears blue, as in a smoke-filled room. Spirit rover image: NASA/JPL/Texas A&M/Cornell |
On Earth, Rayleigh scattering of sunlight from extremely small particles
produces blue skies and red sunsets. On Mars, light scattering from much
coarser dust has the opposite effect: red skies, blue sunset. Dust is key to
martian weather. Mars lacks abundant liquid water and rock recycling
mechanisms, so eroded rock accumulates and the grains become fine. Large daily
and seasonal temperature fluctuations create wind. Dust-lifting winds are
common on all scales, from dust devils to regional and occasionally planetwide
storms. Once airborne, dust may remain suspended for months.
The “dark streak” is the devil track. At the Spirit and Opportunity sites, dust devils have prolonged the rovers’ lives by repeatedly whisking dust off their solar panels. MGS MOC Image: NASA/JPL/MSSS |
Regional dust storms merge and become planetwide. Image: Hubble Space Telescope. |
The view from underneath, 2007: Opportunity photographed the sky as a dust storm intensified. Her incident sunlight dropped to 1% of normal for six weeks. Image: NASA/JPL/Cornell. |
Click for animated gif of Gusev crater dust devil near Spirit: http://tinyurl.com/nag3gv
James, P.B. and B.A. Cantor. (2002). Atmospheric monitoring of
Mars by the Mars Orbiter Camera on Mars Global Surveyor. Adv. Space Res. 29 (2),
121-129.
Bridges, N.T. et al. (2007). Windy Mars: a dynamic planet as seen by
the HiRISE camera. Geophys. Res. Lett. 34, L23205.
The north polar cap over a spring, showing its seasonal carbon dioxide layer sublimating to reveal the residual water cap by summer. Images: Hubble Space Telescope. |
Surface atmospheric pressure over a martian year, recorded by the Viking landers and showing seasonal fluctuation. The two landers recorded different absolute pressures because they were sited at different altitudes. |
The martian atmosphere is less than 1% the density of Earth’s (see Planetary Magnetism) and is about 95% CO2. Carbon dioxide cycles between the atmosphere and the polar caps, where it freezes out in winter, so that surface atmospheric pressure fluctuates by nearly 30% in a normal year.
James, P.B. (2005). The carbon dioxide cycle. Adv. Space Res. 35, 14–20.
Continuous observations by Mars Odyssey, Mars Global Surveyor and Mars Reconnaissance Orbiter over multiple years have led to a preliminary general climate model, in which Mars’s highly elliptical orbit (9%, compared to Earth’s 3%) is a driving factor. The Viking Orbiters estimated that the surface temperature reached as high as +27ºC (sic) and as low as -143ºC.
Smith, M.D. (2008). Spacecraft observations of the martian
atmosphere. Annu. Rev. Earth Planet. Sci. 36:191–219
and references cited therein.
MGS TES infrared mapping of atmospheric dust, water ice (clouds), water vapor and temperature over three martian years: all four are both latitude- and time-sensitive. Ls indicates Mars’s orbital position, where 0 = the position at northern spring equinox. Atmospheric dust levels peak in the perihelion half of Mars’s orbit (Ls 180-360), and drop in the cooler aphelion half, when water clouds can also be seen at low latitudes. The southern hemisphere faces the Sun during perihelion and away during aphelion, and southern seasons are significantly more intense than northern.
