MESSENGER completes its 3,000th orbit of Mercury, sets mark for closest approach

April 21, 2014
Artist depiction of the MESSENGER spacecraft in orbit around Mercury. Credit: NASA / JHU/APL

( —On April 20, MESSENGER completed its 3,000th orbit of Mercury and moved closer to the planet than any spacecraft has been before, dropping to an altitude of 199 kilometers (123.7 miles) above the planet's surface.

"We are cutting through Mercury's magnetic field in a different geometry, and that has shed new light on the energetic electron population," said MESSENGER Project Scientist Ralph McNutt, of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. "In addition, we are now spending more time closer to the planet in general—and that has, in turn, increased the opportunities for all of the remote sensing instruments to make higher-resolution observations of the planet."

MESSENGER has been completing three orbits of Mercury every day since April 2012, when two orbit-correction maneuvers reduced its about Mercury from 12 hours to 8 hours. The shorter orbit has allowed the science team to explore new questions about Mercury's composition, geological evolution, and environment that were raised by discoveries made during the first year of orbital operations.

APL's Carolyn Ernst, the deputy instrument scientist for the Mercury Laser Altimeter (MLA), said the change from a 12- to an 8-hour orbit provided her team with 50% more altimetry tracks. "MLA coverage takes a long time to build up, and because of the small footprint of the laser, a lot of coverage is needed to obtain good spatial resolution. The more data we acquire, the better we resolve the topography of the planet," she said. "The 8-hour orbit has also allowed us to make more MLA reflectivity measurements, which have provided critical clues for characterizing Mercury's radar-bright deposits at high northern latitudes."

The probe has been edging closer and closer to Mercury since March 2013, at about the time that the 's minimum altitude passed closest to Mercury's north pole.

APL's David Lawrence, a MESSENGER Participating Scientist, said he is excited about what the low-altitude orbits will reveal about Mercury's surface composition. "To date our compositional measurements with neutron, X-ray, and gamma-ray data have resolved only very large regions on Mercury's surface. Altitudes of less than 100 kilometers will enable us to pinpoint the compositional signatures of specific geologic features, which in turn will help us to understand how the surface formed and has changed over time."

MESSENGER's periapsis altitude will continue to decrease until the first orbit-correction maneuver of the low-altitude campaign, scheduled for June 17.

"The final year of MESSENGER's orbital operations will be an entirely new mission," added MESSENGER Principal Investigator Sean Solomon, of Columbia University's Lamont-Doherty Earth Observatory. "With each orbit, our images, our surface compositional measurements, and our observations of the planet's magnetic and gravity fields will be higher in resolution than ever before. We will be able to characterize Mercury's near-surface particle environment for the first time. Mercury has stubbornly held on to many of its secrets, but many will at last be revealed."

Explore further: NASA's Messenger Spacecraft Returns To Mercury

Related Stories

MESSENGER Spacecraft Reveals More Hidden Territory on Mercury

October 29, 2008

( -- A NASA spacecraft gliding over the battered surface of Mercury for the second time this year has revealed more previously unseen real estate on the innermost planet. The probe also has produced several science ...

Image: Sunlit side of the planet Mercury

October 29, 2013

Another day, another beautiful view of Mercury's horizon. In this scene, which was acquired looking from the shadows toward the sunlit side of the planet, a 120-km (75 mi.) impact crater stands out near the center. Emanating ...

MESSENGER Surpasses 200,000 Orbital Images of Mercury

February 6, 2014

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. "We ...

Recommended for you

Dead comets and near-earth encounters

October 13, 2015

Near Earth Objects (NEOs) are asteroids or comets whose orbits sometimes bring them close to the Earth, thereby posing a potentially threat. The asteroid that struck Chelyabinsk last year was an NEO about 40 meters in diameter. ...

What happens when your brain can't tell which way is up?

October 13, 2015

In space, there is no "up" or "down." That can mess with the human brain and affect the way people move and think in space. An investigation on the International Space Station seeks to understand how the brain changes in ...

What are white holes?

October 9, 2015

Black holes are created when stars die catastrophically in a supernova. So what in the universe is a white hole?

Hubble sees an aging star wave goodbye

October 12, 2015

This planetary nebula is called PK 329-02.2 and is located in the constellation of Norma in the southern sky. It is also sometimes referred to as Menzel 2, or Mz 2, named after the astronomer Donald Menzel who discovered ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.