Tiny Mercury is a notoriously difficult planet to see from Earth. Because of its closeness to the sun, Mercury unveils itself to skywatchers only just before sunrise and just after sunset. And even when it can be seen, the Earth's atmosphere blurs the view.
But a new technique of astronomical observation has yielded the best-ever images of Mercury as seen from Earth. The pictures, which show Mercury's crater-pocked surface, reveal an area of the planet missed by the Mariner 10 satellite, which took images of Mercury while it orbited the planet in the mid-1970s.
"It is an amazing feat just to photograph Mercury at all," said Dr. Stephen Maran, press officer for the American Astronomical Society. "Whether it's in sufficient detail to be useful for purposes of landing a spacecraft or planning closeup views or not remains to be seen."
Mercury has intrigued astronomers for ages. The ancient Greeks named the evening-borne Mercury after its messenger God, Hermes, who shuttled back and forth across land like Mercury does in the sky. In modern times, the difficulty of viewing Mercury kept astronomers guessing for more than 200 years about the length of the planet's day. It wasn't until the Mariner 10 spacecraft made its first of three flybys of Mercury that the time was determined: 58.64 Earth days.
But Mariner left a gaping hole in the study of the planet; due to the nature of its solar orbit, the spacecraft could only view half of Mercury's surface in each of its three flybys. With nine years until the next spacecraft visits Mercury, astronomers have only their ground-based telescopes to study the planet. Even the powerful Hubble Space Telescope cannot be used to view Mercury -- NASA fears that a slip in handling could result in the multibillion-dollar telescope being pointed directly at the sun, which would destroy its sensitive instruments.
The new technique used high-speed imaging, and may later be supplemented with a specially developed spectrograph, an object that can take images of spectrums of light. The spectrograph would use a modified grating to filter Mercury's light better than previously possible. In an
published in the May issue of the Astronomical Journal, the researchers, from Boston University, show composite pictures of Mercury, blended from dozens of images of the planet taken in 1998. Those pictures show the side of Mercury unseen on Mariner 10's mission."We captured multiple images of Mercury during these rare instances of 'perfect seeing,'" said Jody Wilson, a research associate at Boston University, in a statement. "And by combining these images, a unique photograph with details and clarity resulted."
Also published in May's Astronomical Journal is a paper by Ronald F. Dantowitz and a team of researchers at the Boston Museum of Science. The team also released Mercury
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These images show how blending images can increase sharpness. This image blends 15 snapshots of Mercury.
This image blends 50 images of Mercury.
This image blends 90 snapshots of Mercury.
