SPACE.com -- Martian Seasons Unfold Before Mars Global Surveyor


	Martian Seasons Unfold Before Mars Global Surveyor By Andrew Bridges Pasadena Bureau Chief posted: 03:02 pm ET 27 April 2000

By Andrew Bridges Pasadena Bureau Chief

NASAs Mars Global Surveyor spacecraft recently snapped two images of Mars that illustrate the seasonal variations that the planet, like our own, undergoes.

The first image, captured on April 17, shows the south polar cap in its sparkling white majesty on a sunlit, midsummer afternoon.

Mars frozen southern pole.

As summer prepares to wane in the martian southern hemisphere -- June will mark the onset of autumn -- the cap of frozen water and carbon dioxide has shrunken to its minimum size, or about 260 miles (420 kilometers) across.

Come winter this December (martian seasons are six months long), the same scene will appear completely blanketed by carbon-dioxide frost.

Even though it is now summer, the southern polar cap remains chilly enough for some carbon dioxide frost to form, seen in white.

Just three days later, on April 20, the Global Surveyor imaged Lomonosov Crater in the northern hemisphere of Mars. There, the planet is still in the throes of winter.

The Lomonosov crater on Mars.

The crater is rimmed with wintry frost. Ground-hugging fogs appear as fuzzy white arcs within the 93-mile (150-kilometer) across crater itself and in the upper right.

As fall approaches in the south, spring beckons in the north.

Mars tilts approximately 25 degrees on its axis, or about one degree more than Earth. Much like our planet, this tilt helps give rise to its annual climatic variations, or seasons.

But Mars also has a highly eccentric orbit that causes its distance from the sun to vary from 126 million miles (203 million kilometers) to 153 million miles (244 million kilometers) over the course of a martian year, which lasts about two Earth years.

This large variation, coupled with the axial tilt, allows for seasonal changes on Mars that are much greater than those found on Earth.

NASAs Global Surveyor has been orbiting the Mars since September 1997. It will be joined late next year by another NASA satellite scheduled for launch on April 7, 2001.

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