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May 19, 1999:
Astronomers using NASA's Hubble Space Telescope (HST) during
Mars's
recent close approach to Earth have
discovered an enormous cyclonic storm system raging in the
northern polar regions of the Red Planet. Nearly four
times the size of the state of Texas, the storm is composed
of water-ice clouds like storm systems on Earth, rather
than dust typically found in Martian storms.
Apparently, this type of cyclonic circulation, though rare on Mars, must be related to specific climatic conditions unique to the planet's northern polar regions at this season. Similar storms, some comparable in size to the Martian storm, have been seen in Earth's polar regions. On Earth, these polar cyclones appear to be low pressure systems fueled by strong contrasts in oceanic versus atmospheric temperatures. In some cases, winds within Earth's polar cyclones can reach hurricane force. Right: This dramatic three-dimensional visualization of Mars' north pole is based on elevation measurements made by an orbiting laser. During the Spring and Summer of 1998 the Mars Orbiter Laser Altimeter (MOLA) flashed laser pulses toward the Martian surface from the Global Surveyor spacecraft and recorded the time it took to detect the reflection. This timing data has now been translated to a detailed topographic map of Mars' north polar terrain. More information. The general appearance of the Martian storm seems consistent with an intense low pressure vortex with rising air causing cloud formation, possibly with a small core that is cloud-free, like the eye of a hurricane. The storm may have been initiated by an unstable frontal system, and then amplified by the strong temperature contrast between the relatively warm high-latitude Martian dark regions and the much colder and stable polar atmosphere. "It seems that our knowledge of the high-latitude weather on Mars is limited by the fact that even Viking, from orbit 20 years ago, could not observe the polar regions very frequently," says Cornell's Bell. "So our HST finding, and forthcoming results from the Mars Global Surveyor spacecraft, may simply be revealing all this activity up there because it's the first time we've been able to look in a detailed and dedicated way with high-resolution instruments during this season." The team of astronomers, besides Bell, operator of HST, included Michael Wolff and R. Todd Clancy (Space Telescope Science Institute), Steven Lee (University of Colorado), Philip James (University of Toledo), and Michael Ravine (Malin Space Science Systems, Inc.). |
Web Links | |
Hubble Views Collossal Polar Cyclone on Mars - STScI Press Release The Planet Mars - from the SEDS Nine Planets web site Life on Mars - A review of evidence of signs of life in the Allen Hills meteorite Mars Global Surveyor - home page Mars at opposition - 1995 images from the Hubble Space Telescope Mars - by Percival Lowell, 1895 Related Stories:
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