MESSENGER began its 2,000th orbit around Mercury earlier this week, on May 22. The spacecraft completed its primary mission on March 17, 2012, and its first extended mission on March 17, 2013. The team is awaiting word from NASA on a proposal for a second extended mission. In the meantime, instruments aboard the spacecraft continue to gather new data on Mercury and its environment.

From May 6 to May 14, MESSENGER traversed a superior solar conjunction, during which the spacecraft was on the far side of the Sun from Earth. Scientists used the opportunity to measure the characteristics of the solar magnetic field from the Faraday rotation of its radio-frequency carrier.

"We found the orientation of the magnetic field within a coronal mass ejection (CME) that crossed the line of sight on May 10," says Elizabeth Jensen, of the Planetary Science Institute in Tucson, Arizona.

"We saw the rotation of the plane of polarization of MESSENGER's radio-frequency signal as it moved deeper into the corona, giving information on the Sun's magnetic field configuration on May 11; and on May 12, we saw magnetohydrodynamic waves, a very important mode of energy transfer in the corona."

Solar storms cause communications disruptions, expose spacecraft and personnel in airplanes to radiation, and threaten electrical grids. Jensen says that the observations of the CME demonstrate the utility of this technique to predict the threat of solar storms headed toward Earth almost immediately after they erupt.

"Understanding the accuracy of models for the solar magnetic field and solar wind generation requires testing," she says. "Although other methods can be used in active regions, Faraday rotation is the only way to test the magnetic field models in the largest part of the corona where the solar wind is accelerating."

At its closest point to Mercury, MESSENGER will be about 447 kilometers (277.8 miles) above a point near 83.1A N latitude. Since its most recent orbit-correction maneuver on April 20, 2012, the spacecraft has completed three orbits of Mercury every day.

At this rate, says mission trajectory lead James McAdams of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, the spacecraft will reach its 3,000th orbit around Mercury on April 20, 2014.