Thursday, July 1, 1999 Published at 14:18 GMT 15:18 UK
Hubble's close-up on Mars
Two views of Mars from Hubble
By BBC News Online Science Editor Dr David Whitehouse
Taking advantage of Mars's closest approach to the Earth in eight years, the Hubble Space Telescope has taken its sharpest views yet of the Red Planet.
While Hubble cannot see as fine a detail as the Mars Global Surveyor, which its currently in orbit around Mars, it can obtain a better global picture.
The telescope's Wide Field and Planetary Camera 2 snapped these images between 27 April and 6 May, when Mars was 87 million km (54 million miles) from Earth.
From this distance, the telescope could see Martian features as small as 19 km (12 miles) wide.
The telescope obtained several images showing the entire planet. Each view depicts one quarter of its daily rotation.
The images were taken in the middle of the Martian northern summer, when the northern polar cap had shrunk to its smallest size because the Sun shines continuously on the polar cap.
Previous telescopic and spacecraft observations have shown that this summertime "residual" polar cap is composed of water ice, just like Earth's polar caps.
The images show that substantial changes in the bright and dark markings on Mars have taken place in the 20 years since the NASA Viking spacecraft missions first mapped the planet.
Some regions that were dark 20 years ago are now bright red; some areas that were bright red are now dark.
Martian winds blow sand and dust from region to region, often in spectacular dust storms. Small details come and go as they are covered and then uncovered by sand and dust.