Mars

Radius: 3397 km (0.5 R_earth)
Mass: 6.4x10²³ kg (0.1 M_earth)
Distance from Sun: 1.54 AU (but e=0.09)

Observation #1: Mars looks red. (Why? Iron oxide - FeO.)
Observation #2: You can see stuff.

Rotating Mars animation courtesy STScI

Rotation Period: 24h, 37m
Orbital Period: 687 Edays

At its distance from the Sun, Mars has an equilibrium temperature which is ~ 210K - 240K. This is below the freezing point of water (273K). But there are seasonal variations which bring regions of Mars close to the freeze/thaw point...

The martian surface is very uneven. A topographical map from the Mars Orbiting Laser Altimeter (MOLA):

(blue is low, red is high; click image for hires maps )

We see

Northern lowlands
Southern highlands
Tharsis Bulge
Volcanos
Impact Basin ("Hellas Planitia")
Giant Rift Canyon ("Valles Marineras")

What are these things telling us about Mars?

Mars has an atmosphere. Mostly CO₂, with only a trace amount of H₂0. Surface pressure is ~ 5 millibars (0.5% that of the Earth).

The atmosphere shows daily and seasonal variations: dust storms and clouds.

Dust Storm	Clouds

What causes these variations?

Moons: two little ones

Phobos ("Fear")	Deimos ("Panic")
27x20 km	15x12 km