Space Collisions

NASA Completes MESSENGER Mission with Expected Impact on Mercury’s Surface

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 Artist concept of the MESSENGER spacecraft in orbit around planet Mercury. Image Credit: NASA
Artist concept of the MESSENGER spacecraft in orbit around planet Mercury. Image Credit: NASA

A NASA planetary exploration mission came to a planned, but nonetheless dramatic, end Thursday when it slammed into Mercury’s surface at about 8,750 mph and created a new crater on the planet’s surface.

Mission controllers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, have confirmed NASA’s MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft impacted the surface of Mercury, as anticipated, at 3:26 p.m. EDT.

Mission control confirmed end of operations just a few minutes later, at 3:40 p.m., when no signal was detected by NASA’s Deep Space Network (DSN) station in Goldstone, California, at the time the spacecraft would have emerged from behind the planet. This conclusion was independently confirmed by the DSN’s Radio Science team, which also was monitoring for a signal from MESSENGER.

“Going out with a bang as it impacts the surface of Mercury, we are celebrating MESSENGER as more than a successful mission,” said John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington. “The MESSENGER mission will continue to provide scientists with a bonanza of new results as we begin the next phase of this mission–analyzing the exciting data already in the archives, and unravelling the mysteries of Mercury.”

Prior to impact, MESSENGER’s mission design team predicted the spacecraft would pass a few miles over a lava-filled basin on the planet before striking the surface and creating a crater estimated to be as wide as 50 feet.

Mercury’s lonely demise on the small, scorched planet closest to the sun went unobserved because the probe hit the side of the planet facing away from Earth, so ground-based telescopes were not able to capture the moment of impact. Space-based telescopes also were unable to view the impact, as Mercury’s proximity to the sun would damage optics.

MESSENGER’s last day of real-time flight operations began at 11:15 a.m., with initiation of the final delivery of data and images from Mercury via a 230-foot (70-meter) DSN antenna located in Madrid, Spain. After a planned transition to a 111-foot (34-meter) DSN antenna in California, at 2:40 p.m., mission operators later confirmed the switch to a beacon-only communication signal at 3:04 p.m.

The mood in the Mission Operations Center at APL was both somber and celebratory as team members watched MESSENGER’s telemetry drop out for the last time, after more than four years and 4,105 orbits around Mercury.

“We monitored MESSENGER’s beacon signal for about 20 additional minutes,” said mission operations manager Andy Calloway of APL. “It was strange to think during that time MESSENGER had already impacted, but we could not confirm it immediately due to the vast distance across space between Mercury and Earth.”

MESSENGER was launched on Aug. 3, 2004, and began orbiting Mercury on March 17, 2011. Although it completed its primary science objectives by March 2012, the spacecraft’s mission was extended two times, allowing it to capture images and information about the planet in unprecedented detail.

During a final extension of the mission in March, referred to as XM2, the team began a hover campaign that allowed the spacecraft to operate within a narrow band of altitudes from five to 35 kilometers from the planet’s surface.

On Tuesday, the team successfully executed the last of seven daring orbit correction maneuvers that kept MESSENGER aloft long enough for the spacecraft’s instruments to collect critical information on Mercury’s crustal magnetic anomalies and ice-filled polar craters, among other features. After running out of fuel, and with no way to increase its altitude, MESSENGER was finally unable to resist the sun’s gravitational pull on its orbit.  

“Today we bid a fond farewell to one of the most resilient and accomplished spacecraft to ever explore our neighboring planets,” said Sean Solomon, MESSENGER’s principal investigator and director of Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York. “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.”

Among its many accomplishments, the MESSENGER mission determined Mercury’s surface composition, revealed its geological history, discovered its internal magnetic field is offset from the planet’s center, and verified its polar deposits are dominantly water ice.

APL built and operated the MESSENGER spacecraft and managed the mission for NASA’s Science Mission Directorate in Washington.

Learn more about the accomplishments of NASA’s MESSENGER mission at: and

NASA’s Hubble, Chandra Find Clues that May Help Identify Dark Matter

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Here are images of six different galaxy clusters taken with NASA’s Hubble Space Telescope (blue) and Chandra X-ray Observatory (pink) in a study of how dark matter in clusters of galaxies behaves when the clusters collide. A total of 72 large cluster collisions were studied. Image Credit: NASA and ESA


Using observations from NASA’s Hubble Space Telescope and Chandra X-ray Observatory, astronomers have found that dark matter does not slow down when colliding with itself, meaning it interacts with itself less than previously thought. Researchers say this finding narrows down the options for what this mysterious substance might be.

Dark matter is an invisible matter that makes up most of the mass of the universe. Because dark matter does not reflect, absorb or emit light, it can only be traced indirectly by, such as by measuring how it warps space through gravitational lensing, during which the light from a distant source is magnified and distorted by the gravity of dark matter.

To learn more about dark matter and test such theories, researchers study it in a way similar to experiments on visible matter — by watching what happens when it bumps into other objects. In this case, the colliding objects under observation are galaxy clusters.

Researchers used Hubble and Chandra to observe these space collisions. Specifically, Hubble was used to map the distribution of stars and dark matter after a collision, which was traced through its gravitational lensing effect on background light. Chandra was used to detect the X-ray emission from colliding gas clouds. The results are published in the March 27edition of the journal Science.

“Dark matter is an enigma we have long sought to unravel,” said John Grunsfeld, assistant administrator of NASA’s Science Mission Directorate in Washington. “With the combined capabilities of these great observatories, both in extended mission, we are ever closer to understanding this cosmic phenomenon.”

Galaxy clusters are made of three main ingredients: galaxies, gas clouds, and dark matter. During collisions, the gas clouds surrounding galaxies crash into each other and slow down or stop. The galaxies are much less affected by the drag from the gas and, because of the huge gaps between the stars within them, do not slow each other down.

“We know how gas and stars react to these cosmic crashes and where they emerge from the wreckage. Comparing how dark matter behaves can help us to narrow down what it actually is,” said the study’s lead author David Harvey of the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland.

Harvey and his team studied 72 large cluster collisions. The collisions happened at different times and were viewed from different angles — some from the side, and others head-on.

The team found that, like the galaxies, the dark matter continued straight through the violent collisions without slowing down much. This means dark matter does not interact with visible particles and flies by other dark matter with much less interaction than previously thought. Had the dark matter dragged against other dark matter, the distribution of galaxies would have shifted.

“A previous study had seen similar behavior in the Bullet Cluster,” said team member Richard Massey of Durham University in the United Kingdom. “But it’s difficult to interpret what you’re seeing if you have just one example. Each collision takes hundreds of millions of years, so in a human lifetime we only get to see one freeze-frame from a single camera angle. Now that we have studied so many more collisions, we can start to piece together the full movie and better understand what is going on.”

With this discovery, the team has successfully narrowed down the properties of dark matter. Particle physics theorists now have a smaller set of unknowns to work around when building their models.

“It is unclear how much we expect dark matter to interact with itself because dark matter already is going against everything we know,” said Harvey. “We know from previous observations that it must interact with itself reasonably weakly.”

Dark matter may have rich and complex properties, and there are still several other types of interactions to study. These latest results rule out interactions that create a strong frictional force, causing dark matter to slow down during collisions.

The team also will study other possible interactions, such as dark matter particles bouncing off each other like billiard balls and causing dark matter particles to be ejected from the clouds by collisions or for dark matter blobs to change shape. The team also is looking to study collisions involving individual galaxies, which are much more common.

“There are still several viable candidates for dark matter, so the game is not over. But we are getting nearer to an answer,” said Harvey. “These astronomically large particle colliders are finally letting us glimpse the dark world all around us, but just out of reach.”

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington.

NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

For images and more information about the Hubble Space Telescope, visit:

For more Chandra images, multimedia and related materials, visit: