Friday, January 18, 2008

Fly-By Data...

I've posted several times about the MESSENGER robotic explorer's fly-by of the planet Mercury earlier this week. The data (including images) are now safely back here on Earth, and the MESSENGER team has started posting them. It's already clear that the fly-by was a complete success – both for the technology and for the science results.

NASA's prowess with highly-reliable robotics has allowed them to make use of slower but much more efficient courses, leveraging fly-bys of planets as “slingshots” to change the spacecraft's speed without the use of rockets. In the case of MESSENGER, the spacecraft has “fallen” from the dizzying heights of Earth (above the sun) down to the lowly altitude of Mercury, and in the process it picked up a lot of speed (its potential energy converted to kinetic energy). The multiple fly-bys of Mercury are reducing its speed with only trivial use of its rockets (for navigation). The end result of this technique is that the spacecraft itself can be much larger and heavier than it could with any sort of direct-flight course. The earlier missions (such as Cassini-Huygens) that used this slingshot technique were real edge-of-the-seat cliff-hangers, as there was some perfectly reasonable doubt that NASA could pull off the missions that lasted a decade or more, and that required fantastical feats of navigation and course control. They've proven it now, though, and made it seem almost routine...

About the photo above (click on it for a larger version):
Shortly following MESSENGER’s closest approach to Mercury on January 14, 2008, the spacecraft’s Narrow Angle Camera (NAC) on the Mercury Dual Imaging System (MDIS) instrument acquired this image as part of a mosaic that covers much of the sunlit portion of the hemisphere not viewed by Mariner 10. Images such as this one can be read in terms of a sequence of geological events and provide insight into the relative timing of processes that have acted on Mercury's surface in the past.

The double-ringed crater pictured in the lower left of this image appears to be filled with smooth plains material, perhaps volcanic in nature. This crater was subsequently disrupted by the formation of a prominent scarp (cliff), the surface expression of a major crustal fault system, that runs alongside part of its northern rim and may have led to the uplift seen across a portion of the crater’s floor. A smaller crater in the lower right of the image has also been cut by the scarp, showing that the fault beneath the scarp was active after both of these craters had formed. The MESSENGER team is working to combine inferences about the timing of events gained from this image with similar information from the hundreds of other images acquired by MESSENGER to extend and refine the geological history of Mercury previously defined on the basis only of Mariner 10 images.

This MESSENGER image was taken from a distance of about 18,000 kilometers (11,000 miles) from the surface of Mercury, at 20:03 UTC, about 58 minutes after the closest approach point of the flyby. The region shown is about 500 kilometers (300 miles) across, and craters as small as 1 kilometer (0.6 mile) can be seen in this image.

Hats off to the entire MESSENGER team – a fantastic accomplishment!

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