Mercury MESSENGER Mission Concludes with a Smashing Finale!

The planet Mercury has a brand new 52-foot-wide crater. At 3:26 p.m.  EDT this afternoon, NASA’s MESSENGER spacecraft bit the Mercurial dust, crashing into the planet’s surface at over 8,700 mph just north of the Shakespeare Basin. Because the impact happened out of sight and communication with the Earth, the MESSENGER team had to wait about 30 minutes after the predicted impact to announce the mission’s end. 

NASA predicted that the MESSENGER spacecraft would crash into Mercury this afternoon at 3:26 p.m. EDT near the 30-mile-wide crater Janacek  and the large Shakespeare Basin on the opposite side of the planet from Earth. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Even as MESSENGER faced its demise, it continued to take pictures and gather data right up until impact. The first-ever space probe to orbit the Solar System’s innermost planet, MESSENGER has completed 4,103 orbits as of this morning. Not only has it imaged the planet in great detail, but using it seven science instruments, scientists have gathered data on the composition and structure of Mercury’s crust, its geologic history, the nature of its magnetic field and rarefied sodium-calcium atmosphere, and the makeup of its iron core and icy materials near its poles.

Color-coded view of Carnegie Rupes at left with low elevations in blue and high in red. The ridge formed as Mercury’s interior cooled, resulting in the overall shrinking of the planet. Parts of the landscape lapped over other parts as the planet shrunk. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Images show those ubiquitous craters but also features that set its moonlike landscape apart from the Moon including volcanic plains, tectonic landforms that indicate the planet shrank as its interior cooled and mysterious mouse-like nibbles called “hollows”, where surface material may be vaporizing in sunlight leaving behind a network of holes. To learn more about the mission’s “greatest hits”, check out its Top Ten discoveries or pay a visit to the Gallery.

The rounded depressions, called “hollows”, are a fascinating discovery of MESSENGER’s orbital mission and may have been formed by vaporization of materials in the surface when exposed by the Raditladi impact. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER mission controllers conducted the last of six planned maneuvers on April 24 to raise the spacecraft’s minimum altitude sufficiently to extend orbital operations and further delay the probe’s inevitable impact onto Mercury’s surface, but it’s now out of propellant. Without the ability to counteract the Sun’s gravity, which is slowly pulling the craft closer to Mercury’s surface, the team prepared for the inevitable.

False color images of Mercury taken with MESSENGER’s Mercury Atmosphere and Surface Composition Spectrometer (MASCS) in everything from infrared to ultraviolet light reveal colorful differences in terrain and surface mineralogy. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The spacecraft actually ran out of propellant a while back, but controllers realized they could re-purpose a stock of helium, originally carried to pressurize the fuel, for a few final blasts to keep it alive and doing science right up to the last minute. During its final hours today, MESSENGER will be shooting and sending back as many new pictures as possible the same way you’d squeeze in one last shot of the Grand Canyon before departing for home. It’s also holding hundreds of older photos in its memory chip and will send as many of those as it can before the final deadline.

Farewell MESSENGER! Artist view of the spacecraft in orbit about Mercury. Credit: NASA

“Operating a spacecraft in orbit about Mercury, where the probe is exposed to punishing heat from the Sun and the planet’s dayside surface as well as the harsh radiation environment of the inner heliosphere (Sun’s sphere of influence), would be challenge enough,” said Principal Investigator Sean Solomon, MESSENGER principal investigator. “But MESSENGER’s mission design, navigation, engineering, and spacecraft operations teams have fought off the relentless action of solar gravity, made the most of every usable gram of propellant, and devised novel ways to modify the spacecraft trajectory never before accomplished in deep space.”

Face northwest starting about 45 minutes after sunset to find Mercury tonight. It’s located about two fists to the lower right of Venus and just 1.5° below the Pleiades star cluster. Use binoculars to see the star cluster more easily. Source: Stellarium

Ground-based telescopes won’t be able to spy MESSENGER’s impact crater because of its small size, but the BepiColombo Mercury probe, due to launch in 2017 and arrive in orbit at Mercury in 2024, should be able to get a glimpse. Speaking of spying, you can see the planet Mercury tonight (and for the next week or two), when it will be easily visible low in the northwestern sky starting about 45 minutes after sundown. The planet coincidentally makes its closest approach to the Pleiades star cluster tonight and tomorrow.

Use the occasion to wish MESSENGER a fond farewell.

Bob King

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. I also write a daily astronomy blog called Astro Bob. My new book, "Wonders of the Night Sky You Must See Before You Die", a bucket list of essential sky sights, will publish in April. It's currently available for pre-order at Amazon and BN.

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