Mars and Pluto: Exploring old and new horizons

Next month the New Horizons mission will make its closest pass to Pluto and its moons and send back images and data that will revolutionise our understanding of some of the most distant members of our solar system. This is a hugely exciting time to be a fan of space exploration and I thought for this month’s blog it would be interesting to revisit the era when space flight was in its relative infancy and the first missions travelled to Mars.

Pluto and its moon Charon imaged on June 29th as New Horizons moves ever closer.

Pluto and its moon Charon imaged on June 29th as New Horizons moves ever closer to the distant world. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Pluto is intriguing because of its remoteness whereas Mars has always been tantalisingly close. Mars is near enough for telescopes to track seasonal changes in the colour of its surface and image Earth like polar ice caps. It’s not surprising that Mars was long considered a world that might host life comparable to that of Earth’s and that it became a regular feature in many works of science fiction. Despite its relative proximity it was not possible to study the surface for further Earth like features like volcanoes, rivers and lakes without travelling to the planet and studying it up close.

The first missions to Mars were flyby probes that photographed and studied whatever part of the planet was facing them before carrying on into space. Unfortunately the results were not particularly inspiring as the surfaces photographed looked like the lifeless heavily cratered lunar crust. It was not until the much more complex endeavour of putting a probe in orbit was successfully achieved in 1971 that truly exciting results were generated. New Horizons is a flyby mission but its modern cameras are so powerful that they can begin to acquire high resolution images of Pluto from a considerable distance and therefore capture the majority of the surface.

The name of the first mission to successfully orbit Mars was Mariner 9 and it produced a global map of images that revealed huge volcanoes, a massive equatorial chasm, carved river like channels and windblown dust. Though the mission found that vegetation and liquid water were absent from the surface it discovered that dynamic processes including volcanism plus water and wind erosion had been active for much of Mars’ history. Dynamic processes create diverse environments and mix the chemical precursors for life, possibly creating habitable environments on Mars in the past. Mariner 9 also discovered that Mars is characterised by smooth northern lowlands and heavily cratered southern highlands. It was the unfortunate luck of the early flyby missions to only capture relatively featureless areas of the southern highlands. Mariner 9’s results paved the way for every subsequent mission to the red planet. No one can know for sure what New Horizons will reveal in a few weeks’ time but it is safe to bet that its findings will be as important and paradigm shifting as the first significantly successful mission to Mars.

The giant martian volcano Olympus Mons as photographed by Mariner 9. What features on Pluto will New Horizons reveal? (McCauley et al., 1972).

The giant martian volcano Olympus Mons as photographed by Mariner 9. What features on Pluto will New Horizons reveal? (McCauley et al., 1972).

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