Vintage NASA – ‘Dust swirls above the Hellas Basin’. Hellas yes!
Mariner 9 arrived at Mars in 1971 – the first spacecraft to orbit the Red Planet. Scientists were anxious to study the crisp new pictures it was expected to send back. Much of Mars had never been seen in any detail, and Mariner 9 would lift the veil at last.
Their feelings must have been mixed indeed when the first images arrived at mission control and revealed …. a world-wide haze. The surface of the entire planet was hidden by the biggest dust storm anyone had ever seen! Only Olympus Mons, a giant volcano 24 kilometers high, peeked above the clouds.
After a month the dust settled and Mariner 9 mapped the Red Planet with great success. Scientists have since learned that huge dust storms, dwarfing desert dust clouds on Earth, are fairly common on Mars. The Mariner 9 event still holds the record as the thickest and longest-lasting we have observed – but perhaps not for long.
On June 26, 2001, the Hubble Space Telescope spotted a dust storm brewing in Hellas Basin on Mars. A day later the storm “exploded” and became a global event.
Source: NASA 2001, Planet Gobbling Dust Storms.