Mercury

Vital statistics l R = x 10 6 m l M = 3.30 x kg l R orbit = 5.79 x m l T = l Eccentricity =.206 l 0.38 R  l M  l 0.39 A.U.

Claims to fame l Smallest planet l Highest eccentricity l Orbit displays GR effects l Only planet with orbital/rotational resonance other than 1:1 l 2 nd densest planet in the Solar System

A bit of background l Known at least since the time of the Sumerians (3000 BCE) l Greeks had 2 names for it (Apollo when it appeared in the morning, and Hermes when in the evening), but they knew it was the same object Heraclitus believed that it and Venus orbited the Sun, not Earth

Viewing Mercury l Since Mercury is an inner planet, it will always look close to the sun

Phases of Mercury l Some views of Mercury at different points along its orbit (with a ground-based telescope)

Mercury’s orbit l 3:2 spin-orbit resonance l 88 days to go around, 59 to rotate

Structure l Iron-rich core has a radius of about 1800 km, while the radius of the planet is only 2440 km l Mercury is probably solid at least most of the way to the center (if not the whole way) l Magnetic field is 1/100 that of Earth, while Venus and Mars have no magnetic field

Structure l The fact that there is relatively little mantle suggests that Mercury underwent a very large impact that knocked off most of the mantle

Space visits l 3 flybys in 1974 and 1975 l Can’t be observed by HST - too close to Sun l MESSENGER was launched in 2004, and will orbit Mercury in 2011 after several flybys

Mariner 10 l a) mosaic of images taken during approach at about 200,000 km above surface l b) mosaic of images taken while moving away, again 200,000 km from Mercury

Terrain l As Mercury’s iron core cooled, the planet began to shrink, compressing the crust. This compression produced scarps. l This scarp is several hundred km long and up to 3 km high in places

Terrain l From about 20,000 km up. The double-ringed crater at the upper left, named C. Bach, is about 100km across; it exemplifies many of the large craters on Mercury, which tend to have double, rather than single, rings. The reason is not yet understood.

The Caloris Basin

l Result of a HUGE impact l 1400 km across l ringed by concentric mountain ranges that reach more than 3km high in places l spans more than half of Mercury’s radius l caused “weird terrain” at antipodal point

Formation of the Caloris Basin

Weird terrain on opposite side of Mercury

2 prominent craeters with bright halos. The craters are about 40 km (25 mi) in diameter. The halos and rays cover other features on the surface indicating that they are some of the youngest on Mercury.

Discovery quadrangle