Astronomers capturing images from the Hubble Space telescope have detected a monstrous cyclone raging over a vast area of Mars, and they predicted that more storms are likely to develop now that Martian summertime is warming the planet's northern hemisphere.
The storm system near the North Pole of Mars covered an area four times larger than the state of Texas, the astronomers said -- but because the upper atmosphere of Mars is so thin, it apparently kicked up little, if any, dust from the surface.The fierce storm was first detected April 27 and continued to blow for at least three days, said Jim Bell, the Cornell University astronomer who led the team that tracked it. Bell observed it again six hours after the telescope transmitted the first sign of the storm, and it seemed to be already dissipating, he said in an interview Wednesday.
The Hubble telescope flies in Earth orbit at an altitude of 300 miles, but despite its superb ability to observe planets, stars and galaxies at high resolution, it cannot determine the speed of a windstorm. Bell estimated that at its height, the cyclone's winds must have been swirling at 200 miles per hour or more.
Analysis of the storm cloud's spectrum indicated that the winds were composed of clouds of water ice like similar storm systems on Earth. The water originated in the ice cap of the North Pole, and apparently rose after the frozen carbon dioxide that makes up most of the cap had dissipated as the planet warmed under the summer sun.
Warming is only relative, however, because the surface temperature of the polar cap is now roughly a frigid 9 degrees Fahrenheit, although the temperature of the upper atmosphere where the storm winds blow is a far colder 100 degrees below zero, Bell said.
The large difference in temperature between the polar cap and the planet's summertime upper atmosphere is what probably created a low-pressure vortex, with rising air causing clouds to form -- a phenomenon similar to hurricanes on Earth, the Hubble scientists said.
The huge cyclone, they noted, was very different from the dust storms that frequently rage over the surface of Mars. Dust storms were first observed by the Mariner 9 spacecraft in 1971 when one violent cloud of sandy dust obscured the view from the orbiting spacecraft's cameras and took more than three weeks to settle.
The newest cyclone's "eye" was nearly 200 miles in diameter. The entire storm covered an area nearly 1,100 miles across and 900 miles long -- larger than the entire north polar ice cap itself, Bell said. The planet should see similar storms over the next few months during the Martian summer, he said.