¡SkyCaramba! Weekly astronomy blog for the week ending January 31, 2015
Thousands of years ago, one of the planets wandering the sky earned a distinct reputation for the way it behaved. It was a lot faster than the others, it never got far from the sun, and it quickly moved from the evening sky to the morning sky and back again. To some observers, this planet was quick and sneaky like a thief. To others, it was dutifully quick like a messenger. Mercury became known as the messenger to the gods.
Mercury is less than 5,000 km wide, making it the smallest planet in the solar system. It’s smaller than some of Jupiter’s moons. It’s the closest planet to the sun and needs just 88 days to complete one orbit. It rotates once every 176 days. And Mercury’s gravity is 38% of Earth’s.
The planet is heavily cratered and of various shades of gray like Earth’s moon. There’s evidence of ancient lava flows on the planet. Much of the planet remains unmapped because only a few spacecraft have visited and they couldn’t make an image of the entire surface. Mercury’s most distinct feature is called the Caloris Basin. It’s where ...