LRO Finds GRAIL's Lunar Impact Sites

In this image, both of the impact sites of the mirror-image GRAIL spacecraft can be seen. The final resting spots of these two spacecraft were imaged by the Lunar Reconnaissance Orbiter. Image Credit: NASA/GSFC/Arizona State University

In this image, both of the impact sites of the mirror-image GRAIL spacecraft can be seen. The final resting spots of these two spacecraft were imaged by the Lunar Reconnaissance Orbiter. Image Credit: NASA/GSFC/Arizona State University

NASA’s Lunar Reconnaissance Orbiter (LRO) has found the impacts made by its cousin(s), the Gravity Recovery and Interior Laboratory, or “GRAIL” spacecraft. Both of the mirror-image GRAIL spacecraft impacted the lunar surface Dec. 17, 2012, after it had completed its primary science mission.

The duo plummeted into the Moon’s north pole in hopes of squeezing one last tidbit of science out of them. LRO would review the plume ejected by the two spacecraft’s impacts in order to sniff out what the ejected material was comprised of. With less than a month prior to impact, this was no easy task for the LRO team.

“We were informed by the GRAIL team about three weeks prior to the impact exactly where the impact site would be,” said LRO Project Scientist John Keller. “The GRAIL team’s focus was on obtaining the highest-resolution gravity measurements possible from the last few orbits of the GRAIL spacecraft, which led to uncertainty in the ultimate impact site until relatively late.”

During GRAIL’s impact, LRO was approximately 100 miles (about 160 kilometers) above the lunar surface. By all accounts it was a bumpy ride with gravitational anomalies giving the spacecraft a bit of a hard time.

GRAIL was launched in 2011 atop a United Launch Alliance Delta II rocket from Cape Canaveral Air Force Station's Space Launch Complex 17 in Florida. Photo Credit: Mike Killian / Zero G News

GRAIL was launched in 2011 atop a United Launch Alliance Delta II rocket from Cape Canaveral Air Force Station’s Space Launch Complex 17 in Florida. Photo Credit: Mike Killian / Zero G News

LRO’s history seems to be made up of watching other spacecraft smack into the Moon’s surface. First, it was the Lunar CRater Observation and Sensing Satellite (LCROSS) which accompanied LRO to the Moon after they were launched in 2009. Now, GRAIL joins the list of the lost.

During the time of the impact, the site itself was cast in shadow, forcing LRO team members to wait until the plume ejected by GRAIL’s demise to rise high enough before they could begin making observations. LRO has a number of scientific equipment onboard the spacecraft; for this particular experiment the team used the Lyman Alpha Mapping Project, or “LAMP.” LAMP is an ultraviolet imaging spectrograph. It saw an increased amount of mercury and atomic hydrogen in the material ejected by GRAIL.

“The mercury observation is consistent with what the LRO team saw from the LCROSS impact in October 2009,” said Keller. “LCROSS saw significant amounts of mercury, but the LCROSS site was at the bottom of the Moon’s Cabeus crater, which hasn’t seen sunlight for more than a billion years and is therefore extremely cold.”

When searching for the impact craters left by GRAIL, once again LRO was brought into action. It was a harder task than it might seem due to the relatively small size of the craters left behind by the two craft. Each of the GRAIL spacecraft were about the size of a washing machine. Each weighed around 440 lbs (200 kilograms). When they impacted, the spacecraft were traveling at around 3,800 miles (6,100 kilometers) per hour.

“Both craters are relatively small, perhaps 4 to 6 meters (about 13 to 20 feet) in diameter, and both have faint, dark, ejecta patterns, which is unusual,” said Mark Robinson, LROC principal investigator. “Fresh impact craters on the Moon are typically bright, but these may be dark due to spacecraft material being mixed with the ejecta.”

LRO also measured how much residual heat was left over after the impact, using its Diviner lunar radiometer. The spacecraft used its Lunar Orbiter Laser Altimeter, or “LOLA,” to develop a precise map of the lunar surface, which now includes the features placed on the surface by the GRAIL impacts.

“Both impact sites lie on the southern slope of an unnamed massif [mountain] that lies south of the crater Mouchez and northeast of the crater Philolaus,” Robinson said. “The massif stands as much as 2,500 meters [about 8,202 feet] above the surrounding plains. The impact sites are at an elevation of about 700 meters [around 2,296 feet] and 1,000 meters [3,281 feet], respectively, about 500 to 800 meters [approximately 1,640 to 2,625 feet] below the summit. The two impact craters are about 2,200 meters [roughly 7,218 feet] apart. GRAIL B [renamed Flow] impacted about 30 seconds after GRAIL A [Ebb] at a site to the west and north of GRAIL A.”

The mirror-image GRAIL spacecraft were launched to provide the most accurate gravitational map of the Moon's surface. Upon completing their primary mission they were directed to impact the lunar surface on Dec. 17, 2012. Photo Credit: Alan Walters / awaltersphoto.com

The mirror-image GRAIL spacecraft were launched to provide the most accurate gravitational map of the Moon’s surface. Upon completing their primary mission, they were directed to impact the lunar surface Dec. 17, 2012. Photo Credit: Alan Walters / awaltersphoto.com

 

 

4 comments to LRO Finds GRAIL’s Lunar Impact Sites

  • Sometime in the distant future, the Moon will be host to many historical areas for future generations to see and appreciate: Apollo landing sites, Luna/Lunakhod, Ranger, Surveyor sites and Grail impact regions. They will serve as a testament not only to mankind’s early technological capabilities but also to our first tentative steps to expand our presence in space. Imagine being a “tourist” on the Moon and seeing these artifacts. A kind of “Air and Space Museum” 240,000 miles away – wow!

    • Matt McClanahan

      Provided the sites can be adequately protected. NASA’s published guidelines for exclusion zones around most of the stuff left behind on the moon. Apollo 17, for example, was given a 225m exclusion zone. But these are just recommendations, obviously NASA can’t prevent some organization that achieves a lunar landing from walking right up to a descent stage and stealing its plaque.

  • Karol

    If the individuals were foreign nationals and returned to their own country, we probably could not extradite them, however, if an American entrepreneur greedily looted U.S. Government property which is of great importance to all Americans, the Department of Justice and FBI might be waiting for him when he returned to the United States. These irreplaceable sites and artifacts MUST be protected as monuments to space exploration. These items are not “abandoned property” or “space debris”. We only hold them as trustees for future generations, this is not the place for selfish, unbridled greed.

    • Leonidas

      Karol, this touches on many urgent and pressing legal concerns regarding outer space that everyone should start to contemplate on: property rights for space hardware and infastructure in outer space, real estate rights, ownership rights and so forth. Today, we only have an Outer Space Treaty, which for me personally, is a relic of the Cold War. A treaty which stops anyone for doing anything in space, and strips away any incentives to build infrustructure and colonies in space.

      The Outer Space Treaty reflects a mindset that sees space as something out of reach for everyone. If we don’t start seeing space as something we can go build and live into, and start making the right set of laws amd regulations about it, then all planetary bodies will remain just ‘bright specks in the sky’.