An Interplanetary Weather Forecast for Mars

Astronomers are used to seeing strange things when they turn their telescopes toward the Red Planet—some of them tantalizingly, and often deceptively, Earthlike. The image above, a stereographic projection centered on Mars's north pole, was returned by the Hubble Space Telescope Wide‐Field Planetary Camera 2 on 27 April. It depicts a “spiral storm” 1600 km in diameter (the storm is a diffuse white spiral to the left of the bright ice cap) just south of the planet's northern polar ice cap. Although such Storms were first observed over 20 years ago, April's tempest was three to four times the size of previously observed storms. So far detected only in Mars's northern hemisphere during its summer, the storms bear some resemblance to terrestrial polar cyclones.