Mars has changed. After almost 50 years of spacecraft imaging, landers and rovers examining the planet that we know as a cold, arid and desolate world suggest that Mars has not always been such a forbidding place.
Pictures taken from orbit around Mars show that the exterior of the Red World has features that appear to have been formed by liquid water. On its surface, chemical testing — in particular by the rover Opportunity — implies that there was once standing water there.
If liquid water had been present, then the Red Planet was once a warm environment. The next mission to Mars, scheduled for launch on Nov. 18, will help scientists understand why the planet has changed and how it is currently changing.
Exploring Mars up-close with spacecraft began on Nov. 5, 1964, with the launch of the Mariner 3 mission. Although the spacecraft had a successful lift-off, once in Earth orbit the rocket’s nose cone failed to open and release the spacecraft. Its twin, however, Mariner 4, had a successful launch and became the first spacecraft to fly by another planet on July 14-15, 1965.
Mariner 4 returned 21 pictures of Mars that covered 1 percent of the planet. Its images showed a cratered, moon-like terrain that later missions, by contrast, would find is not typical for Mars. Data from the Mariner 4 probe showed that Mars had a daytime temperature of 150 degrees below zero and no magnetic field, information that would be confirmed by later missions.
The first successful dual mission to fly by Mars was Mariner 6 and 7. These spacecraft left Earth in early 1969 and reached the Red Planet in late July of that year. Both spacecraft flew over the equator and south polar region of Mars at less than half the distance that Mariner 4 was from the planet.
The two probes photographed roughly 20 percent of the planet’s surface, showing dark features that had been seen from Earth, and illustrated that these so-called “canals” were only an illusion.
Mariner 8 and 9 were the next set of missions to Mars and were launched in May 1971. The rocket that launched Mariner 8 failed but Mariner 9 successfully made the trip to Mars. On Nov. 14, 1971, it became the first spacecraft to orbit another world.
Mariner 9 imaged the entire Martian world with the sharpest images of any mission to that point. The pictures showed dried riverbeds, extinct volcanoes and the largest canyon known in the solar system. The canyon was named after the spacecraft and is known as the Mariner Valley.
Mariner 9 also found evidence of fog, wind and water erosion on the Martian surface and photographed the two small moons of the planet, Phobos and Deimos.
Atmosphere the key
These early missions had the engineering goals of demonstrating and developing technologies required for future Mars missions and the science goal of establishing a foundation for potential investigations of the Red Planet, particularly those relevant to the search for life there. A planet’s atmosphere is the key to life and, as studies of Mars have shown, the key to an atmosphere is the planet’s magnetic field.
Earth generates its magnetic field deep in its core where hot, molten metal flows. This field surrounds our planet and plays the important role of deflecting high-speed charged particles flung off the surface of the sun known as the solar wind.
Just as a pea will cool off faster than a potato, Mars — about half the size of Earth — lost most of its internal heat during the first 2 billion years of the solar system; since Earth is larger, it still retains much of its internal heat.
Once the core of Mars cooled, the molten metal there stop flowing and its magnetic field diminished.
Now the Red Planet is no longer protected from the solar wind. Collisions between these high-speed particles and the Martian atmosphere slowly knock the molecules of its air into space. This process has been gradually eroding the atmosphere for billions of years. The next mission to Mars will investigate the details of this process.
MAVEN to Mars
The Mars Atmosphere and Volatile Evolution Mission (MAVEN) will examine the uppermost regions of the Martian atmosphere from low orbit and by flying through the highest portions of the Mars atmosphere. Scientists will use the data sent back by this probe to learn what effect the loss of molecules such as carbon dioxide, nitrogen and water from the air of Mars to space has had over time.
If MAVEN launches as scheduled on Nov. 18, it will arrive at Mars on Sept. 22. After five weeks to stabilize its orbit for data collection and to perform instrument calibration, MAVEN will be tracking only 90 miles above Mars, where it will make most of its observations. Throughout the mission, it will also execute five “deep dip” maneuvers down to 77 miles altitude that will each last five days. At that height, it will directly sample the upper atmosphere of Mars.
MAVEN is designed to work in coordination with Curiosity, the rover of the current Mars Science Laboratory mission that landed on Mars on Aug. 6, 2012. By synchronizing these two active Mars missions, scientists hope to gain insight into the history of the planet’s atmosphere and ultimately an understanding of the past existence of liquid water on Mars as well as the planet’s past habitability.
Venus will continue to brighten throughout November. It can be seen in the southwestern evening sky and it will set about the same time throughout the month. During the late evening, Jupiter rises from the northeast and appears against the stars of Gemini; its whitish-blue orb outshines the bright twin stars Castor and Pollux.
As the sun comes up over the east-southeastern horizon on the morning of Nov. 3, it will be undergoing a partial solar eclipse. Special safe solar filters will be needed to view this event, which will last about 45 minutes.
Richard Monda is an astronomer living in the Capital Region.