A possible second planet in the system with a 60 - day or longer orbit only gets a passing mention in the paper, ignored in favor of the solid, concrete evidence. (discovermagazine.com)
In addition to Monday's rendezvous, Messenger is scheduled to pass Mercury again this October and in September 2009, using the pull of the planet's gravity to guide it into position to begin a planned year - long orbit of the planet in March 2011. (newscientist.com)
They have really really long orbits around the sun, but like all orbiting bodies, they travel in predictable patterns. (scientificamerican.com)