NASA’s Mercury-bound Messenger spacecraft dropped into orbit around the tiny, orbitally eccentric planet just a few months ago, and it’s already sent back enough data to notably alter our take on the first rock from the sun.
For starters, indiscernible features that previously resembled “bright, patchy deposits” turn out to be “clusters of rimless, irregular pits varying in size from hundreds of meters to several kilometers.” The reason they look bright is because they’re surrounded by “halos” of reflective material.
(PHOTOS: Images of Mercury’s Surface)
“The etched appearance of these landforms is unlike anything we’ve seen before on Mercury or the Moon,” said Messenger imaging team member Brett Denevi in a statement. “We are still debating their origin, but they appear to have a relatively young age and may suggest a more abundant than expected volatile component in Mercury’s crust.”
We’re also learning that Mercury is less Moon-like than previously thought. Elements like magnesium, aluminum and calcium occur in different ratios to silicon, suggesting that Mercury’s isn’t dominated by feldspar, a rock-forming mineral common to both the Moon’s surface and Earth’s crust.
So what does Mercury look like? The planet already had its close-up back in late March, when NASA released its initial round of high-definition images. I described it as “a bit like a color-leeched bowling ball, and if you didn’t know better, you might call it ‘the Moon’.”
Flat or hilly? After taking upwards of two million “laser-ranging observations,” Messenger has revealed that Mercury’s range of topographical heights so far exceeds 9 kilometers (5.6 miles). Also: its North Pole is “broad” and “low,” with “permanently shadowed…impact craters.” It’s thought these may contain frozen water or other types of ice (though probably not creepy alien monoliths, like the one’s found near Tycho Crater on the Moon in Arthur C. Clarke’s 2001).
What’s next? Three more years of fastidious observation, and, as Messenger principal investigator Sean Solomon puts it, “more surprises as our solar system’s innermost planet reveals its long-held secrets.”