PX282 - J7a - atmospheres

earth

image: Robert Carroll

• oxygen is a biomarker, a signature of life

• the pressure is $1$ bar $=101,325$ Pa

• the equilibrium temperature: $T_p\simeq -18\mathrm{°}$C

• the surface temperature: $T_s\simeq 15\mathrm{°}$C (due to greenhouse effect)

• temperature inversions in stratosphere and thermosphere due to ultraviolet heating in the ozone layer and x-ray heating, respectively

mars

• pressure $=0.006$ bar $\sim 1\mathrm{\%}$ earth's
• primarily CO${}_2$ ($95\mathrm{\%}$), with $N_2$ ($3\mathrm{\%}$)
• the equilibrium temperature: $T_p\simeq -84\mathrm{°}$C
• the surface temperature: $T_s\simeq -143\to 35\mathrm{°}$C (depending on day/night)
• poor heat redistribution and weak greenhouse

venus

• pressure $=93$ bar $\sim 100\times$ earth's

• primarily CO${}_2$ ($96\mathrm{\%}$), with $N_2$ ($4\mathrm{\%}$)

• the equilibrium temperature: $T_p\simeq -43\mathrm{°}$C (due to high albedo from reflective clouds)

• the surface temperature: $T_s\simeq 462\mathrm{°}$C (due to very strong greenhouse)

• the atmospheric temperature profiles for earth and venus are quite similar in higher atmosphere

image: taylor, 2018

mercury & moon

• the surface gravities ($g$) are too low to retain a significant atmosphere