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MESSENGER knocks on Mercury’s door, again

By Jacqueline Hewett

Taken on October 4 as MESSENGER approached Mercury. The time of closest distance is October 6, 2008, 04:40:22 EDT. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Back in August 2004, I wrote a feature about NASA’s MESSENGER mission to Mercury and the laser altimeter that would provide a topographic map of the planet. I subscribed to the mission’s emailing alerting service at that time, but knew that there would be a while to wait for news as MESSENGER had a 7.9 billion km journey to go on.

In my Inbox this morning though is the fantastic news that MESSENGER is (at this very moment) making its second fly-by of Mercury, passing just 200 km above the planet’s surface. The main reason for the fly-by is a “gravity-assist” that will set MESSENGER on the right track to enter orbit around Mercury in 2011. It is also a fantastic opportunity to observe the planet.

We reported on MESSENGER’s first fly-by back in January 2008 when the Mercury Dual Imaging System (MDIS) cameras imaged almost half of the planet including terrain that had never previously been viewed by a spacecraft. The encounter added another 21% of Mercury’s surface to the total imaged close-up by spacecraft. The camera data include high-resolution (less than 200 m per pixel) images and colour images using the instrument’s 11 colour filters. This provided the most comprehensive colour data of Mercury to date. The Mercury Laser Altimeter (MLA) provided the first measurements of the topography of Mercury as determined from a spacecraft.

This time, NASA says that the MDIS will acquire around 1200 images of a completely new area of Mercury’s surface, the opposite side of the planet compared with the first flyby. The MLA will also be in action as the second fly-by will allow the first comparison between previous topographic observations and the high-resolution images. I’ll add some images to this post in the next few days - they haven’t made it back to the NASA website as I write this.

The excitement will soon be over however, and we will have to wait until late September 2009 for the third and final fly-by before MESSENGER enters Mercury’s orbit in March 2011. Keep your eyes out for those updates! It’s fascinating science, and certainly worth waiting for.

Posted by Jacqueline Hewett on October 6, 2008 10:44 AM | Permalink