June 6, 2020

30.03.11: Welcome to Mercury!

A new resident has taken up orbit around the solar system’s inner most-world. Fresh from orbital insertion earlier this month, NASA’s Messenger spacecraft opened its eyes and began relaying images that have been a web sensation over the past 24 hours. Messenger is currently 6 light minutes from Earth; its looping orbit takes it from a periapsis of about 200 km to apsis at 1,500 km.

This highly elliptical orbit of NASA’s Mercury Messenger spacecraft was designed specifically to take advantage of a variety of studies from a battery of onboard instruments. Today’s speakers at the live NASA teleconference were Sean Solomon, Mercury Messenger principal investigator, and Eric Finnegan Mission systems engineer. Science observations for NASA’s Mercury Messenger are set to begin April 4th. The first image acquired and displayed yesterday marked 37 years after the historic flyby of Mariner 10. Messenger’s primary mission will last for a minimum of 2 mercurial “days” and cover 4 complete orbits of the planet about the Sun.

Like our own Moon, Mercury has regions that enjoy continuous darkness and extremely cold temperatures. Messenger will look for evidence of water ice in permanently shadowed regions on Mercury. Areas around Mercury’s north pole region released today are a 1st; these regions have yet to be imaged by either Pioneer 10 or Mercury Messenger’s 3 previous flybys prior to orbital insertion. “We’re really seeing Mercury now with new eyes… an entire global perspective will be on continuous display for the 1st time.” Stated Sean Solomon during the conference.

It will also be intriguing to see Mercury’s interaction with solar cycle #24 and the near solar environment during the Messenger mission. And yes, ongoing studies will still detail and characterize this inner-most solar realm, as well as continue an interesting secondary mission of keeping an eye out for any tiny Vulcanoids interior to the orbit of Mercury. At first glance, Mercury appears much like the Earth’s cratered and airless moon, but looks can be deceiving. Mercury is fairly dark; the surface albedo is less than the Earth’s Moon, which is about that of worn asphalt. Brightness such as the ejecta of crater Debussy revealed in yesterday’s first orbital picture are all relative. This darkening is caused by space weathering, and may allow for further relative dating of fresh cratering relative to the nearby plains. Is the core fluid? What is the source of the magnetic field and the elusive “tail” of Mercury? A key difference between Mercury and our Moon is the relatively high density and the magnetic field, suggesting an active dynamo in the world’s interior. The core must also be a greater fraction of the planet’s overall diameter than the Earth for its density to work out as nearly the same. For the record, the Earth’s average density works out to 5.5 g/cm^3, Mercury is the second runner-up in the solar system at 5.4 g/cm^3, and the Moon is a welter weight at: 3.3g/cm^3. You get the picture; Mercury is largely a super-dense core sprinkled with a crater-filled crust.

Expect some awesome science as we begin to explore this bizarre world in earnest. It was a cool feeling at this past weekend’s star party to show folks a blurry Mercury just past greatest elongation and tell them we’ve now got a permanent orbiting outpost about the inner most world… let’s go explore!


  1. [...] MESSENGER spacecraft was also on the lookout for Vulcanoids on its six year trek through the inner solar system prior to orbital insertion on [...]

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