This year marks the 50th anniversary of what had been a major step towards exploring the planet Mars. The heroic spacecraft Mariner IX was the first spacecraft to go into orbit around another planet and provide images of the entire surface and record the full diversity of the landscapes it was seeing.
Mariner IX revealed a Mars that was fascinating in its own right, rather than disappointing in the light of previous earthly expeditions. It also allowed a small team of artists to make the first detailed reliable maps of another world.
For centuries Mars had been viewed as an Earth in miniature. It has all the makings of an “Earth” with its 24 and a half-hour day – it showed it has seasons and appeared to possess water. Its polar caps would shrink in its respective hemispheres when approaching the spring and summer seasons. A wave of darkening would coincide with these changes suggesting possible vegetative life happening on the surface.
Mars the Great Red Hope
Astronomers in the 1870’s reasoned that the Martian vegetation might be red instead of green, an eternal autumn. Sightings of “canals” by some European astronomers, coupled with these observations were those of American businessmen/diplomat turned astronomer, Percival Lowell. His own observations would later inspire the notion, due to the lack of water, a world populated with a dying race on an aging, dry planet.
But by 1965 up through 1970, Mars was now thought to be more Moon-like than Earth-like despite these seasonal changes. Because the Mariner probe flyby missions during that period had been directed mainly over the southern hemisphere where most of the prominent “dark patches” are located. All three spacecraft completely missed some of Mars’s most intriguing features. Particularly the Mariner IV spacecraft, the first successful spacecraft to visit Mars. It took only 21 photographs from about 10,000 miles above a surface riddled with craters. The 25-minute fly-by, in an instant, nearly destroyed the dream of life on Mars. Mariner VI and VII flybys followed 4 years later garnering the same results as the Mariner IV flyby.
Mars the Ultimate Jokester
Gone were the Martians, gone were the canals, gone were the blue-green vegetation that came and went with the pseudo Lowellian seasons.
What we thought would be blue skies on Mars were now thought to be perhaps darker owing to an atmosphere being 5,000 times thinner than the Earth’s. Such a meager atmosphere would allow most of the sun’s deadly radiation in, destroying any likely Earthly life forms. But despite this terrible disappointment there was still hope. The Martian craters appear not to be as old as those on the Moon. If the craters are younger, then that might mean Mars once probably had a denser atmosphere with the possibility of extensive weather and larger bodies of water on its surface.
In 1971, Mariner IX would bring to the light the real Mars. Arriving at the planet six months after its launch on May 30th the hardy spacecraft had to bide its time as the planet was going through the throes of a major global dust storm. It was hardly expected what a brave new world was waiting despite the earlier Mariner flybys.
A Brave New World
Having arrived at the planet on November 13th, Mariner 9 had to wait for the dust storm to subside. The first feature to be observed was a dark spot as it approached the planet on the tenth, then three more dark spots two days later forming a line across in the region known as Tharsis. It would turn out these were not Lowell’s Oases or even impact craters but huge volcanic calderas!
By the middle of December, 1971 of that year a vast bright streak had become visible to the east of the three Tharsis volcanoes. The streak would reveal itself to be a vast canyon thousands of miles long. It would become to be known as Valles Marineris or “Valley of the Mariners” for the spacecraft which discovered it.
The spacecraft photographed Mars from pole to pole for several months after the dust settled, taking 7,239 pictures. In those dark areas, the albedo features were shown not to be necessarily connected to topographical features. They had turned out to be volcanic plains that were seasonally covered by Martian dust. Everywhere there were streaks where dust had revealed or hidden the surface beneath.
The difference between light and dark areas reflects nothing more fundamental than the difference in dust grain sizes. The wind now explained these seasonal changes and that they were not due to primitive vegetation as what was once thought by some. Meteorology not biology was the cause of the wave of darkening and wind played a role on how the planet looked.
This brave New World could never have been imagined during the Mariner 4, 6 and 7 missions. Mariner IX presented an alien world of new possibilities, nothing like what had been expected. After slightly less than a year, the probe became a derelict satellite, still orbiting but doomed to an atmospheric fiery death sometime probably in 2022.
But despite the success of Mariner IX and the Viking lander missions that followed in 1976, the planet was largely ignored for two decades. Fourteen missions were eventually sent to Mars by the United States to date with a few failures along the way. Three occurred in the 1990’s with the Mars Polar Lander being the last to fail at the conclusion of the 2nd millennium. Soviet Russia had its fair share of failures. Mars 2 & 3 Landers in 1971 and the Phobos mission in 1988 most notably.
The Dream Continues…
Mariner 9 showed clear analogies to features of the Earth such as the great Tharis shield volcanoes, just like the great shield volcanoes of Hawaii, while other pictures revealed more Earth-like features: canyons and what appear to be dried-up riverbeds. Mariner 9 was the vanguard of things to come. And now instead of little green men building canals; we currently have a world full of robot explorers and that may always be the case until the day humankind steps on its surface and then we become the Martians.
- Mapping Mars, Oliver Morton, Picador; 1st edition (2002)
- Lowell and Mars, William Hoyt, University of Arizona Press; (1976)
- List of missions to Mars: https://en.wikipedia.org/wiki/List_of_missions_to_Mars