Solar System Exploration: Planet Selector: Mercury

PLANET SELECTOR

ABOUT MERCURY

Sun-scorched Mercury is only slightly larger than Earth's Moon. Like the Moon, Mercury has very little atmosphere to stop impacts and it is covered with craters. Mercury's dayside is super heated by the Sun, but at night temperatures drop hundreds of degrees below freezing. Ice may even survive in a few craters.
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Featured Mission: MESSENGER
NASA's MESSENGER will make three flyby surveys of Mercury before settling into orbit around the planet in April 2011. It will be the second spacecraft to visit Mercury.
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VITAL STATISTICS

Average Distance from Sun:	57,909,175 km (35,983,093 miles)
Diameter:	4,878 km (3,031.9 miles)
Volume:	0.054 x Earth's
Mass:	330,200,000,000,000,000,000,000 kg (0.055 x Earth's)
Length of Day:	175.94 Earth days
Length of Year:	87.97 Earth days
Known Moons:	0

SIZE & DISTANCE

If the Sun was as tall as a typical front door, Earth would be the size of a nickel - and Mercury would be about as big as a sweet pea.

Average Distance from the Sun: 57,909,175 km (0.39 A.U.)

EXTREME SPACE

Catastrophic Crash
The impact that created Mercury's Texas-sized Caloris Basin equaled roughly 1,000,000,000,000 1-megaton hydrogen bombs. The shockwave from the collision was so powerful it created a hilly region the size of Germany and France on the opposite side of the planet.

Double Sunrise
Because of Mercury's elliptical - egg-shaped - orbit and sluggish rotation, the morning Sun appears to rise briefly, set and rise again from some parts of the planet's surface. The same thing happens in reverse at sunset. The Sun looks nearly three times as large as what you see on Earth.

Made in the Shade
Even though it will be working in temperatures up to 450 degrees Celsius (about 840 degrees Fahrenheit), sensitive parts of the MESSENGER spacecraft will remain at a pleasant room temperature thanks to a heat-resistant ceramic cloth sunshade.

Running Hot and Cold
Mercury is not only one of the hottest places in our solar system - it's also among the coldest. As darkness falls on Mercury, temperatures can drop more than 600°C (1,080°F).

Speed Racer
True to its namesake (the speedy messenger of ancient Roman gods), Mercury is the fastest planet in our solar system. It zips around our Sun at an average of 172,000 kph (107,000 mph) - about 65,000 kph (40,000 mph) faster than Earth. A year on Mercury is equal to 88 Earth days.

The Long and the Short of It
Mercury completes three rotations for every two orbits around the Sun. That means if you wanted to stay up from sunrise to sunrise on Mercury, you'd be up for 176 Earth days.

TIMELINE

265 B.C. - Greek scientists study Mercury in the morning and evening skies.

1631 - French astronomer Pierre Gassendi uses a telescope to watch from Earth as Mercury crosses the face of the Sun - a transit.

1965 - After believing for centuries that the same side of Mercury always faced the Sun, astronomers discover the planet rotates three times for every two orbits.

1974-1975 - NASA's Mariner 10 spacecraft photographs about half of Mercury's surface. The spacecraft makes three flybys.

1991 - Scientists using Earth-based radar to study Mercury find signs of ice tucked in permanently shadowed areas of craters in the planet's polar regions.

2003 - Mercury makes a rare pass - a transit - across the face of the Sun as seen from Earth. On average, there are 13 transits of Mercury each century.

SLIDE SHOW

Mercury Crosses the Sun (2003)
Mariner 10: First Mercury Image (1974)
Mercury Seen From Earth (1995)
Mercury's South Pole
Young Craters
Impact Marks on Mercury
Terraced Craters
Caloris Basin
Mercury's Minerals Revealed
Possible Ice in a Crater (Bright Spots)

MOONS

Mercury has no known moons.