Jupiter's (and Saturn's) "surface" temperature is defined as that at 1 bar. It is inconsistent to say the other planet's surface is their hard surface. Applying the same measure what is the equivalent standard temperature of all the IAU defined planets?
At 1 bar (0.9869 atm / 14.5 psi) pressure level the planets have the following average temperatures:
- Venus: 30 degrees Celsius (1 bar level is about 33 mi or 53 km high)
- The Earth: 15 deg C
- Jupiter: minus 145 deg C
- Saturn: minus 178 deg C
- Uranus: minus 197 deg C
- Neptune: minus 200 deg C
- Titan's temperature ranges from minus 180 deg Celsius on the surface to minus 93 deg Celsius in the upper stratosphere. Titan's surface air pressure is 1.45 atm (1.47 bar).
Mercury has no atmosphere while Mars' atmosphere doesn't reach 1 bar anywhere on the planet.