MESSENGER at Rest

In this perspective view, we look northwest over the Caloris Basin, a depression about 1500 km in diameter formed several billion years ago by the impact of a large projectile into the surface of Mercury. The mountain range at the edge of the basin can be seen as an arc in the background. In the foreground, we see a set of tectonic troughs, known as Pantheon Fossae, radiating from the center of the basin outward toward the edge of the basin interior. A 41-km-diameter impact crater, Apollodorus, is superposed just slightly off from the center of Pantheon Fossae. White and red are high topography, and greens and blues are low topography, with a total height differences of roughly 4 km. The MESSENGER spacecraft was launched in 2004 and ended it's orbital operations yesterday, April 30, 2015, by impacting Mercury's surface. Background image texture is provided by the Mercury Dual Imaging System (MDIS) instrument while color corresponds to surface elevation data obtained from the Mercury Laser Altimeter (MLA) experiment, with both draped over a digital elevation model derived from MLA altimetric data. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Goddard Space Flight Center

Speaking of signing off with a bang, because, you know, nobody really was, we might take a moment for MESSENGER:

Mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., confirmed today [30 April 2015] that NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft impacted the surface of Mercury, as predicted, at 3:26 p.m. EDT this afternoon (3:34 p.m. ground time).

MESSENGER Mission Complete: Final statistics for MESSENGER probe, which crashed into Mercury 30 April 2015 SCET.  Image from screenshot from mission page at Johns Hopkins University.Mission controllers were able to confirm the end of operations just a few minutes later at 3:40 p.m., when no signal was detected by the Deep Space Network (DSN) station in Goldstone, California, at the time the spacecraft would have emerged from behind the planet had MESSENGER not impacted the surface. This conclusion was independently confirmed by the DSN’s Radio Science team, who were simultaneously looking for the signal from MESSENGER from their posts in California.

MESSENGER was launched on August 3, 2004, and it began orbiting Mercury on March 18, 2011. The spacecraft completed its primary science objectives by March 2012. Because MESSENGER’s initial discoveries raised important new questions and the payload remained healthy, the mission was extended twice, allowing the spacecraft to make observations from extraordinarily low altitudes and capture images and information about the planet in unprecedented detail.

Last month — during a final short extension of the mission referred to as XM2′– the team embarked on a hover campaign that allowed the spacecraft at its closest approach to operate within a narrow band of altitudes, 5 to 35 kilometers above the planet’s surface. On April 28, the team successfully executed the last of seven orbit-correction maneuvers (the last four of which were conducted entirely with helium pressurant after the remaining liquid hydrazine had been depleted), which kept MESSENGER aloft for the additional month, sufficiently long for the spacecraft’s instruments to collect critical information that could shed light on Mercury’s crustal magnetic anomalies and ice-filled polar craters, among other features.

With no way to increase its altitude, MESSENGER was finally unable to resist the perturbations to its orbit by the Sun’s gravitational pull, and it slammed into Mercury’s surface at around 8,750 miles per hour, creating a new crater up to 52 feet wide.

“Today we bid a fond farewell to one of the most resilient and accomplished spacecraft ever to have explored our neighboring planets,” said Sean Solomon, MESSENGER’s Principal Investigator and Director of Columbia University’s Lamont-Doherty Earth Observatory. “Our craft set a record for planetary flybys, spent more than four years in orbit about the planet closest to the Sun, and survived both punishing heat and extreme doses of radiation. Among its other achievements, MESSENGER determined Mercury’s surface composition, revealed its geological history, discovered that its internal magnetic field is offset from the planet’s center, taught us about Mercury’s unusual internal structure, followed the chemical inventory of its exosphere with season and time of day, discovered novel aspects of its extraordinarily active magnetosphere, and verified that its polar deposits are dominantly water ice. A resourceful and committed team of engineers, mission operators, scientists, and managers can be extremely proud that the MESSENGER mission has surpassed all expectations and delivered a stunningly long list of discoveries that have changed our views not only of one of Earth’s sibling planets but of the entire inner solar system.”

(Johns Hopkins University)

It is of course worth noting that this is yet another example of what NASA can do. MESSENGER mapped the surface of Mercury in such detail that you can even get a Google Earth module to examine the planet in closer detail.

And also make sure to say hello to Carolan, Enheduanna, Karsh, Kulthum, and Rivera, the names given to five previously nameless craters surveyed during MESSENGER’S orbit.

MESSENGER certainly did the job, and it is always with a hint of sadness that we say goodbye to another faithful pioneer. But the science team will push on at least until this time next year; the accumulated mission data will keep engineers and astrophysicists busy long beyond that. This was a good mission. MESSENGER had a good run.

____________________

Image note: Top―Detail of Appollodorus crater on Mercury via Johns Hopkins University. Right―Final mission statistics for MESSENGER, which crashed into Mercury on 30 April 2015 SCET; image via MESSENGER mission page at Johns Hopkins University.

Johns Hopkins University. “NASA Completes MESSENGER Mission with Expected Impact on Mercury’s Surface”. 30 April 2015.

—————. “Global Mosaics of Mercury”. (n.d.)

—————. “Three Easy Steps to Explore Mercury in Google Earth”. (n.d.)

—————. “Five New Crater Names for Mercury”. 29 April 2015.

—————. “In Tribute”. 1 May 2015.

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