pia03101-mariner-10-mercury
The Last Image From Mercury
published during a waxing gibbous moon.
06/17/2016

Last Image

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury likes to hang close to the sun, and that makes our solar system’s littlest planet hard to observe. So when a NASA spacecraft was done with its Mercury mission, it crashed into the rocky surface — but no one saw it happen.

It took over six years for the MESSENGER spacecraft to reach Mercury. And when it did, it was the first to nab an image from the planet’s orbit. Before MESSENGER’s launch in 2004, only one other probe visited Mercury: the graceful Mariner 10.

Last Image

Credit: NASA

In the early 1970s, the Mariner mission racked up a lot of technological trophies: Not only was it the first craft to visit two planets, it used the gravitational pull of the first, Venus, to get to the other, Mercury. Its first flyby close-ups of Mercury revealed it was as cratered as our own moon, which further whet scientists’ desire for an even closer look:

Last Image

Credit: NASA/JLP

Then came MESSENGER (which stems from MErcury Surface, Space ENvironment, GEochemistry, and Ranging) was the first to ease into Mercury’s orbit, allowing it to gather more about its details than ever before. Its first image was a crystal-clear portrait of its freckles:

Last Image

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER’s itinerary was initially planned for just one year. But the $445 million mission kept eclipsing its success and was renewed two more times. In that gloriously extended time, a bevy of sophisticated instrumentsaboard the probe mapped Mercury’s topography and mineralogy, which highlights chemical differences on the surface such as the craters’ age and can be seen above as a mishmash of color. It even confirmed water ice deposits and an offset internal magnetic field that differs at each pole.

To keep the probe alive for so long, the probe’s team had to get creative to extend the life of its liquid propellant, using deft techniques like solar sailing to the point of where it was running on fumes and still had some spunk left in it.

Last Image

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

But after four years, its resilience started to fade, and MESSENGER was extremely low on fuel. During its final extension, the probe was on a careful, ultra-low-altitude hover campaign to snap the highest-resolution pictures of Mercury ever. With the sun’s gravity tugging on the craft and no power to boost its altitude, MESSENGER crashed into its surface, the first ever probe to impact the planet and leave a crater of its own.

Its end was a solitary one: Because it crashed on the far side of the planet, Earth’s ground-based telescopes couldn’t capture the moment, and Mercury’s proximity to the sun means even the delicate optics of space telescopes could be damaged. And so MESSENGER transmitted its final dispatch — a photo that sealed its iconic status in technological history.

Last Image

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington