MERCURY
Mariner 10 in 1973 mapped 60% of Surface.
D = 1.4 D(moon) = .35 D(earth)
No axial tilt
Day = 176 earth days = twice orbital period
1.Rocky mantle Same density as earth implying large metallic core,
solid because it is a small planet. Cut down by a large impact or early solar bombardment.
2. Extremely thin atmosphere of helium, sodium, and potassium continually
       escaping into space.  Temps: 425K to 100K (-170C).
3.Rotates 3 times for every 2 revolutions--same side
        faces sun at alternate perehelia (semiperiodic tidal locking).
4.Features: craters and basins filled with lava (like moon) and scarps
        formed as planet cooled.  Core was once liquid.
5. A stronger magnetic field than expected, considering slow rotation and cool core.
           A distorted magnetosphere.
6. Same sequence and timing of formation of moon and mercury.  No plate techtonics.
7. Large impact crater--Caloris Basin (like Orientale Basin on moon)
         --jumbled hills on opposite side of planet.