40 Years Ago Viking Landed on Mars: Photos

See breathtaking images from America's first landing on the Red Planet.

Forty years ago, NASA made its first soft landing on Mars. The space agency sent down the Viking 1 lander on July 20, 1976 after a little bit of drama -- when the spacecraft arrived it was discovered the original landing site was too rocky to support a safe landing. This pushed back the landing date from July 4, which was supposed to coincide with bicentennial celebrations back on Earth.

But the patience was worth it, as Viking 1's lander lasted six years on the surface and transmitted back valuable data about the Martian surface, including its atmosphere, rocks and a bit of Mars history as well. From above, the Viking 1 orbiter sent back thousands of images of the Red Planet, including evidence of ancient water flows on the surface. Here are some of the most interesting pictures from the mission.

style="text-align: left;"> The most important thing to remember about Viking 1 was it was stationary. The spacecraft did have a robotic arm to perform sample work, cameras to take pictures and a few instruments that sensed the weather and local conditions. But it couldn't move, which meant that scientists mostly had to do their analysis from pictures. But even in the area around the lander, there was much to look at. This is a picture (flipped horizontally) looking directly below the spacecraft's feet. You can see some of the Martian soil has been pushed aside due to the landing thrust from the spacecraft, exposing what was underneath.

style="text-align: right;"> Photos: NASA/JPL

style="text-align: left;"> This is an afternoon mosaic of images taken by the Viking 1 lander showing Chryse Planitia. This area was chosen in part because it's so flat, which makes for a safer landing. It's also one of the lowest regions on Mars, which makes it easier for a lander to get to the surface in the thin atmosphere. Today, 40 years after the mission, scientists believe there was water flowing into this region in the ancient past. This hypothesis comes in part from the orbiting Viking spacecraft, which saw evidence of river valleys from high up.

style="text-align: left;"> This is the first full-color picture taken at the Martian surface, on July 21, 1976 (about a day after landing). It must have been a mind-blowing image for the scientists analyzing it -- or anyone used to a blue sky. At the time, the team said the red surface materials could be hydrated ferric oxide, which is known as a "weathering product" on Earth. This would take place if there was water on the ground and enough oxygen in the atmosphere, but given Mars' conditions today this would have had to take place in the ancient past. The red tint in the sky comes from dust particles suspended in the atmosphere.

style="text-align: left;"> While Viking 1 was working on the surface, we can't forget about the achievements of the Viking 1 orbiter. Along with its companion Viking 2, the two spacecraft mapped most of Mars in higher resolution than what was available before, during the Mariner 9 mission. The volcanoes on Mars was one of the big surprises of Mariner 9. Viking 1 got an excellent image here of all of the layers around the tallest mountain, Olympus Mons, which stretches about three times as high as Everest. At the top of the mountain is a caldera, which indicates the mountain actually was a volcano. Many scientists today believe that volcanoes are dormant on Mars because there is not much evidence of volcanic eruptions in the atmosphere, but it's not a sure bet.

style="text-align: left;"> In April 2006, about 30 years after landing, the Mars Reconnaissance Orbiter spotted the remains of Viking 1 on the surface. This photo shows how far imagery at the Red Planet progressed, as surface features were available in very fine detail. You can see here not only the lander, but also what appears to be evidence of the parachute and the protective backshell that carried Viking 1 much of the way to the surface. MRO's ability to see such small details made it possible to get detailed pictures of landing sites for missions such as the Mars Phoenix lander, which touched down on Mars in 2008.