On the evening of March 17 2011, nearly seven years after it blasted into space, NASA’s MESSENGER spacecraft (Mercury Surface, Space ENvironment, Geochemistry, and Ranging) made history when it became the first satellite ever to orbit Mercury.
Four years later, having paved the way to the most ambitious study of the planet yet, MESSENGER is set to crash land on the planet’s rocky surface; bringing to an end a bountiful mission that has allowed us closer access to Mercury than ever before.
Since 2011, MESSENGER’s instruments have mapped, in astonishing detail, the surface of our solar system’s innermost planet. Peter Bedini, former MESSENGER project leader, called the mission,“extraordinary”. Noting that, “During its pre-orbital Mercury flybys alone, MESSENGER collected as much data as Mariner 10 – the only other spacecraft ever to visit the innermost planet.”
With the probe now ‘running on fumes’, mission engineers from John Hopkins University are preparing to conduct a series of five burns over the course of a month to extend the life of the mission, before leaving it prey to the ever-present gravitational pull that drags it down to the planet’s surface.
Even in its final days, MESSENGER has the potential to provide valuable data on Mercury’s geological composition, with the auxiliary burns putting the probe between 5 and 39 km above the planet; giving it the ability, “ to see at a close range portions of the planet we haven’t seen in such detail before”.
This may give a new perspective to some of the mission’s greatest discoveries, particularly the presence of ice found in the permanently shadowed craters near the planet’s poles. MESSENGER has photographed over a dozen of these craters in the last few months, revealing patterned areas of light and dark resulting from carbon rich materials overlying the ice underneath.
One theory for their presence is that water in the form of ice, and the darker materials atop it were deposited following a collision with a body from further out in the solar system. This aligns with speculations that the planet is subject to periodic meteor showers, with high levels of Calcium in the exosphere serving as an initial indicator confirming this hypothesis.
This is not the only ‘big find’ of the mission. MESSENGER may have discovered tectonic activity on the planet’s surface. Mercury’s ‘scarps’, are long ridges that can extend for hundreds of kilometers, and are thought to be caused by fluctuations in the crust’s temperature as the planet rotates. Now, thanks to MESSENGER’s low orbit photography, smaller scarps have been discovered clustered in similar patterns to those found near tectonic hotspots on Earth. Planetary Scientist Thomas Watters noted that, “These faults are so young that they are probably forming today.”
The spacecraft’s destructive decommission is projected to occur sometime in late spring, but not before it provides even more information in its ever closer approach to Mercury. As this mission draws to a close, the European and Japanese Space Agencies are counting down to the launch of their probe the BepiColombo. Launching next year, it aims to pick up where MESSENGER left off and explore some of the unsolved mysteries that Mercury has left to offer.