On Earth, 2011 will be another tumultuous year for the National Aeronautics and Space Administration: its space shuttles will be retired, and it will have to wrangle with Congress and the Obama administration over a rocket and a destination for the United States’ human spaceflight program.

In space, though, NASA will have a less contentious time pursuing its science missions.

Planetary scientists will finally get their first extended look at Mercury. After a trip of six and a half years through the inner solar system, NASA’s Messenger spacecraft will finally pull into orbit around Mercury on March 18.

The spacecraft has zoomed past Mercury three times, its camera photographing about 98 percent of the surface. Its other instruments have collected intriguing data regarding the magnetic field and the tenuous atmosphere of molecules that are blasted off the planet’s surface by the Sun’s radiation.

But each of those fly-bys lasted just hours, while the orbital phase of the mission will go on for at least a year. That will allow Messenger to gather enough data to identify elements and minerals in the rocks on Mercury and to observe changes in the atmosphere and magnetic fields as the Sun’s 11-year sunspot cycle emerges from its quiet period.