Mercury
* Very thin exosphere: Mercury's atmosphere is incredibly thin, almost a vacuum. It's more accurately called an exosphere, a layer of gases held loosely by gravity.
* Composition:
* Sodium (Na)
* Potassium (K)
* Helium (He)
* Hydrogen (H)
* Oxygen (O)
* Trace amounts of other elements
Venus
* Dense and toxic atmosphere: Venus has an extremely dense and thick atmosphere, about 90 times thicker than Earth's.
* Composition:
* Carbon Dioxide (CO2) - 96.5%
* Nitrogen (N2) - 3.5%
* Trace amounts of:
* Sulfur dioxide (SO2)
* Argon (Ar)
* Water vapor (H2O)
Earth
* The "Goldilocks" atmosphere: Earth has an atmosphere that's just right for life.
* Composition:
* Nitrogen (N2) - 78%
* Oxygen (O2) - 21%
* Argon (Ar) - 0.93%
* Carbon dioxide (CO2) - 0.04%
* Other trace gases: Water vapor, neon, helium, methane, ozone, etc.
Mars
* Thin and cold atmosphere: Mars has a much thinner atmosphere than Earth, about 100 times thinner.
* Composition:
* Carbon Dioxide (CO2) - 95.3%
* Nitrogen (N2) - 2.7%
* Argon (Ar) - 1.6%
* Trace amounts of:
* Oxygen (O2)
* Carbon monoxide (CO)
* Water vapor (H2O)
* Others
Key Points
* The Greenhouse Effect: Venus's thick carbon dioxide atmosphere traps heat, causing a runaway greenhouse effect that results in scorching temperatures.
* Oxygen: Earth's atmosphere is the only one in our solar system with a significant amount of free oxygen, a vital component for life as we know it.
* Atmospheric Pressure: The pressure of an atmosphere is significantly different on each planet, ranging from almost nonexistent on Mercury to crushing on Venus.
