On March 28, the MESSENGER spacecraft completed 40% of its 6.6 year cruise phase as measured by time traveled—and one-third of its flight distance to Mercury. DTM director Sean Solomon serves as Principal Investigator of the mission. The cruise phase has been used to commission the spacecraft systems and instruments, and to fine-tune the mission operations procedures of the team at the Johns Hopkins University Applied Physics Laboratory, ensuring that the spacecraft and its instruments will perform flawlessly at Mercury. The average speed of the spacecraft has continued to increase during the cruise phase and will reach a spacecraft record of close to 63 km per second (141,000 miles per hour) in mid-October 2008.

The highly accurate astrometric method involves observing the movement of a host star’s position in the sky as it orbits around the center of mass of the star-planet system. Knowing the mass of the star then allows the true mass of the planet, as well as its orbital parameters--including the semi-major axis, eccentricity, and inclination--to be determined. CAPSCam should yield astrometric accuracies of 0.25 millarcsec per epoch. This accuracy is sufficient to detect planets with masses as low as 1/10 the mass of Jupiter on 12-year orbits around nearby late M dwarf stars, with a signal-to-noise ratio of four.