Mercury—Messenger of the gods and the god of trade Mercury by 17th-century Flemish sculptor Artus Quellinus. Note the winged sandals.

Mercury

Mercury is about 1/3 the Earth's distance from the Sun It's diameter is only 1/3 that of the Earth's. It has only 6 % the mass. If you weigh 180 lbs on the Earth, you would weigh 64 lbs on Mercury. Mercury has a magnetic field about 1% as strong as the Earth's.

3:2 Anomalously high!

Spin—Orbit Coupling Earth’s moon is tidally locked to its revolution in a 1:1 spin-orbit coupling Mercury’s rotation tidally locked to revolution about Sun … but in a 3:2 spin-orbit resonance, i.e, Orbital period 88 days Spin period 59 days

Question In one orbit around the Sun, Mercury rotates _____ about its axis. chaotically 3 times. 1½ times. once, in a synchronous orbit about the Sun like the Moon about Earth 59 times

Mercury’s Scarps Figure 11-10 A Scarp A long cliff, or scarp, called Santa Maria Rupes runs across this Mariner 10 image. This scarp is more than a kilometer high and extends for several hundred kilometers across a region near Mercury’s equator. The area shown is approximately 200 km (120 mi) across. (NASA)

Figure 11-12 The Internal Structures of Mercury and the Earth Compared to the Earth’s core, Mercury’s iron-rich core takes up a much larger fraction of the planet’s volume. Indeed, Mercury is the most iron-rich planet in the solar system. Surrounding Mercury’s core is a 600-km-thick rocky mantle.

Caloris Basin

The Surface of Mercury Very similar to Earth’s moon: Very similar to Earth’s moon: Heavily battered with craters, including some large basins. Largest basin: Caloris Basin Terrain on the opposite side jumbled by seismic waves from the impact.

Mercury’s Formation Figure 11-13 Stripping Mercury’s Mantle by a Collision To account for Mercury’s high iron content, one theory proposes that a collision with a planet-sized object stripped Mercury of most of its rocky mantle. These four images show a supercomputer simulation of a head-on collision between proto-Mercury and a planetesimal one-sixth its mass. (Courtesy of W. Benz, A. G. W. Cameron, and W. Slattery)

Figure 11-13 Stripping Mercury’s Mantle by a Collision To account for Mercury’s high iron content, one theory proposes that a collision with a planet-sized object stripped Mercury of most of its rocky mantle. These four images show a supercomputer simulation of a head-on collision between proto-Mercury and a planetesimal one-sixth its mass. (Courtesy of W. Benz, A. G. W. Cameron, and W. Slattery)

Hypothesis 2: Mercury formed from solar nebula before Sun completely formed. Initially Mercury had twice its present mass, but as protosun contracted, temperatures near Mercury could have reached10,000 K! Much of Mercury's surface rock would have vaporized, which could have been carried away by the solar wind. Hypothesis 3: Solar nebula caused drag on the particles from which Mercury was accreting. Lighter particles were lost; heavies remained. Each hypothesis predicts a different surface composition. Space mission, MESSENGER, found higher-than-expected potassium and sulfur levels on the surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur. Potassium and sulfur would have been driven off by the extreme heat of these events.

Question The weird (jumbled) terrain on Mercury could have been formed _______. when the Mariner 10 astronauts landed there and left their trash behind by aliens who erected a station there to secretly observe Earth by seismic waves generated by the impact of a large meteorite that created the Caloris Basin by plate tectonics that occurred during Mercury’s first billion years when Mercury cooled too rapidly on the side facing away from the Sun

Earth Mercury Magnetic Fields About 1% of Earth’s Figure 9-20 and Figure 11-14 About 1% of Earth’s