NASA MESSENGER Surpasses 200,000 Orbital Images of Mercury

This image was acquired as part of the MDIS low-altitude imaging campaign. 

During MESSENGER's second extended mission, the spacecraft makes a progressively closer approach to Mercury's surface than at any previous point in the mission, enabling the acquisition of high-spatial-resolution data. 

For spacecraft altitudes below 350 kilometers, NAC images are acquired with pixel scales ranging from 20 meters to as little as 2 meters. 

Credit: NASA

MESSENGER has now returned more than 200,000 images acquired from orbit about Mercury.

The 1996 proposal for the mission promised a return of at least 1,000 images says Robert Gold, MESSENGER's Science Payload Manager.

Robert Gold

"We expected then that we would have some data compression that would probably raise the image total to somewhere near 2,000 images," says Gold, of the Johns Hopkins University Applied Physics Laboratory (APL), but scientists did not imagine then the degree to which MESSENGER would surpass that goal.

"Returning over 200,000 images from orbit about Mercury is an impressive accomplishment for the mission, and one I've been personally counting down for the last few months," says APL's Nancy Chabot, the Instrument Scientist for the Mercury Dual Imaging System (MDIS).

"However, I'm really more excited about the many thousands of images that are still in MESSENGER's future, especially those that we plan to acquire at low altitudes and will provide the highest resolution views yet of Mercury's surface."

During MESSENGER's second extended mission, the spacecraft is making a progressively closer approach to Mercury's surface with each successive orbit.

In about two months, each closest approach will be at a lower altitude than at any previous point in the mission, enabling the acquisition of unprecedentedly high-spatial-resolution data.

For spacecraft altitudes below 350 kilometers, Narrow Angle Camera (NAC) images will be acquired with pixel scales ranging from 20 meters to as little as 2 meters.

Nancy Chabot

To commemorate the milestone, image scientists released this four-image mosaic—one of the first from the MDIS low-altitude imaging campaign—that reveals, among other features, hollows that appear to have formed in one layer in the wall of this 15-kilometer-diameter crater.

The mission marks three additional milestones today: the spacecraft concludes its 12th Mercury year in orbit, its 18th Mercury sidereal day in orbit, and its 6th Mercury solar day in orbit.

"We have come an incredible way since the first mission proposal was submitted to NASA just over 17 years ago," notes MESSENGER Project Scientist Ralph McNutt of APL.

"Getting to launch and then to Mercury, flyby by flyby, and into orbital operations were incredible accomplishments—against all sorts of odds—and yet we are now, almost routinely, noting these statistics about the mission that has literally revealed an entirely new world to humanity."

When MESSENGER was launched in August 2004, he continues, "none of the team in their wildest imagination could have foreseen the successes that we now celebrate with new data coming back week by week from the innermost planet. And we are not done.

With a little more than a year left to go, before gravity brings the end to operations, we will view the planet and its environment from altitudes lower than were ever envisioned only a few short years ago—and, as with any planetary mission providing closer and closer looks at a planetary neighbour, all we can guess is that we have not wrung all of Mercury's surprises and discoveries just yet."

NASA Messenger: Mercury's Volcanic Past Made Planet Look Younger

Even the oldest areas of Mercury's surface (outlined in white) are still younger than the planet itself. Image released on July 3, 2013.

CREDIT: John Hopkins APL

Mercury is looking good for its age.

Even the oldest parts of the surface of the planet closest to the sun are only 4 billion to 4.1 billion years old, not 4.5 billion years old — the age at which the planet formed, a new study finds.

"If the oldest surface visible on Mercury is 4 billion or 4.1 billion years old, then that would imply that the first perhaps 500 million or 400 million years of the planet have been erased," said Simone Marchi, a Southwest Research Institute planetary scientist and lead author of the study.

 "They are gone. There is no record of the oldest surface of Mercury, and we expect that Mercury pretty much formed like the Earth or the moon around 4.5 billion years ago."

Marchi's research suggests that widespread volcanic activity on Mercury during its early years as a planet is to blame for the artificially young surface.

One reason for this could be that when the solar system was pelted with asteroids early in its history, Mercury's thin crust was punctured by space rocks, Marchi said.

The impacts may have caused increased volcanism on the planet, effectively resurfacing the entire planet a short time after Mercury formed.

The team used a detailed map of Mercury by NASA's Messenger spacecraft in orbit around the planet to characterize the oldest regions on the planet's surface.

"Unfortunately we do not have samples from Mercury so we cannot really have precise age estimates of the terrains, but therefore the only thing we can possibly do is just look at the craters," Marchi told reporters.

"If there are more craters, this implies that the surface is older."

Older bits of the planet's face have had the most time to be impacted by errant space rocks, therefore making them the most cratered parts of a planetary body, Marchi said.

Scientists used this to their advantage. By characterizing the most pockmarked parts of the planet, Marchi and his team could compare the number of craters on any given part of Mercury to the number of craters on certain parts of the moon — a celestial object whose surface age is well documented.

"One of the major outcomes of the Apollo program was that those data allow us to make a connection between the number of craters that were observed on some lunar terrain and the true age of those terrains," Marchi said.

"In that way, we calibrated the model and we know how many craters you have as a function of age of the terrain."

"That information we extrapolated out to Mercury using current astronomical models that predict what the impact flux from asteroids is on the moon and what the impact rate [is] on Mercury, so this model will tell us how we have to scale or extrapolate this lunar crater chronology to Mercury," Marchi added.

The model shows that for every one crater formed on a given surface on the moon per year, a similar surface on Mercury is dotted with three new craters in the same amount of time, Marchi said.

NASA's $446 million Messenger probe (which stands for MErcury Surface, Space ENvironment, GEochemistry, and Ranging) was launched in 2004 and has been in orbit around Mercury since 2011.

The new research is detailed in this week's issue of the journal Nature.