The first images from MESSENGER's second flyby of Venus are in! The Mercury-bound probe flew within 338 kilometers (210 miles) of Venus on June 5, obtaining a gravity assist that shrank the radius of the probe's orbit around the Sun, pulling it closer to Mercury. But the encounter also allowed the MESSENGER team to give its two cameras, known as the Mercury Dual Imaging System (MDIS), a thorough workout.
The MDIS consists of wide-angle and narrow-angle cameras that will map landforms, track variations in surface spectra, and gather topographic information at Mercury. It snapped a series of images as it approached Venus.
"Venus is enshrouded by a global cloud layer that obscures its surface to the MDIS," explains Arizona State University's Mark Robinson, a MESSENGER science team member. "This single frame is part of a color sequence taken inbound to help us calibrate the wide-angle camera in preparation for its first flyby of Mercury next January. Over the next several months the camera team will pore over the 614 images taken during the Venus 2 encounter to adjust color sensitivity parameters and better understand the geometric properties of the instrument."
Robinson says that both tasks address two key goals for the instrument once the spacecraft gets to Mercury: understanding surface color differences and their relation to compositional variations in the crust; and ensuring accurate cartographic placement of features on Mercury's surface. "Preliminary analysis of the Venus flyby images indicates that the cameras are healthy and will be ready for next January's close encounter with Mercury," he says.
After acquiring hundreds of high-resolution images during close approach to Venus, MESSENGER turned its wide-angle camera back to the planet and acquired a departure sequence. The first image was taken June 6 at 12:58 UTC (8:58 p.m. EDT on June 5), and the final image on June 7 at 02:18 UTC (10:18 p.m. EDT on June 6). During this 25 hour, 20 minute period the spacecraft traveled 833,234 kilometers (517,748 miles--more than twice the distance from the Earth to the Moon) with respect to Venus at an average speed of 9.13 kilometers per second (5.67 miles per second).
"These images provide a spectacular good-bye to the cloud-shrouded planet while also providing valuable data to the camera calibration team," says Robinson.
"As a gravity assist and dress rehearsal for Mercury, MESSENGER's Venus flyby was a huge success," said MESSENGER principal investigator Sean Solomon, from the Carnegie Institution of Washington. "The spacecraft hit its aim point to within 1.3 kilometers (0.81 miles), removing the need for another trajectory correction in July. Every instrument returned data from the Venus encounter, and the Science Team is hard at work analyzing the new observations. We plan to release further data as fast as we can."
MESSENGER's Venus 2 flyby images are online at http://www.nasa.gov/mission_pages/messenger/multimedia/venus_flyby.html. Additional mission news and images are available at http://messenger.jhuapl.edu/.
