Messenger is finishing its fourth orbit within the next few hours. Antoniseb, you are right. I had forgotten how fast things move in this region of the solar system. I was thinking it would take longer for Messenger to reach Mercury's orbit. As it is, it is almost there (~16,000,000 km away). It will reach perihelion on the 28th.

This is how things stand. On 16 August: Mercury, the Sun, Messenger, Venus and the Earth will be in a rough line in that order. Messenger is presently on a very elliptical orbit that will take it just BEYOND Venusion orbit (the aphelion of its previous orbit). Mercury will stay 180 degrees ahead of Messenger while the probe is in the vicinity and will have completed a full orbit at about the time Messenger drops (this for the final time) inside of Venus. This will place the probe about 90 degrees ahead of Mercury on 25 October this fall.

Mercury will catch up to Messenger as it falls in to finish its fifth orbit on 28 December. The two will encounter on 15 Jan 2008. The probe will then make one orbit in the time that Mercury makes two orbits and will make its second encounter on 9 Oct 2008. Three more orbits and Messenger will encounter its target for the third time on 1 Oct 2009. By this time, Messenger's orbit will take it only slightly outside Mercury orbit and will take five orbits for Mercury to be in place for orbital capture on 18 March 2011.

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Keeper of the Jabberwock