Atmospheres of Venus, Earth, and Mars

At one time mars had large amount of surface water. Where is the remaining H2O located and what happened to the rest of it?

Subsurface ice at the poles. H2O vapor was broken into hydrogen and oxygen. H being lighter escaped. Oxygen migrated downward to the surface and bonded to surface minerals as red rust.

Explain the atmospheric greenhouse effect.

The atmosphere is transparent to visible light. Light is absorbed by the ground warming it and is reradiated as infrared radiation. CO2 and H2O vapor are greenhouse gasses in our atmosphere that absorb infrared and reradiate it back to the ground.

Explain the phenomenon of auroras. Are they unique to earth?

The earth has a magnetic field caused by the spinning liquid conductive core. Charged particles from the solar wind interact with the magnetic field. The magnetic field is pinch together at the poles funneling charged particles down into the ionosphere. Electrons collide with atoms of O2, N, and H2 causing them to glow like gas in a neon sign.

Oxygen is an extremely reactive gas. Will chemically combined with nearly any substance it touches. In order for a planet to have significant amounts of O2 in its atmosphere requires a means of replacing what is lost through oxidation. Explain why earth developed to have so much free O2

Billions of years ago cyanobacteria evolved and began producing O2 through photosynthesis. At first O2 combined with minerals and was removed from the atmosphere as quickly as it formed. As plant life evolved atmospheric O2 approached present levels.

Venus, Earth, and Mars shared similar geological histories early on. This suggests their early secondary atmosphere might have been quite similar. Describe the secondary atmospheres of Mars and Venus. Why are they similar and why are they different?

Both are mostly CO2 with smaller amounts of nitrogen. Venus has far more atmosphere than Earth, Mars far less. Mars being less massive is unable to hold much atmosphere.

What happened to Mercury and the Moon's secondary atmosphere.

Both were lost. Mercury small mass, close to the Sun. Moon very small mass.

Describe the makeup and formation of Earth's secondary atmosphere.

During accretion minerals containing H2O and CO2 collected in Earth's interior. As the interior heated, the gasses were released through volcanism. Comets and asteroids perturbed by the outer planets impacted Earth bringing H2O, CO3, methane and ammonia. Most H2O vapor condenses as rain to form oceans UV light from Sun broke ammonia and methane into hydrogen and nitrogen.

Describe the formation of primary atmospheres for both the inner planets and outer planets. Also, explain what happened to those atmospheres.

Gases in protoplanetary disk, mostly hydrogen and helium. Captured by gravity of planets. N and He are light gasses. When supply ran out into space. Heat from evolving Sun increased molecular motion to escape velocity. Impacts heated gasses to escape velocity. Outer planets were more massive and farther from Sun so they were able to retain primary atmosphere.

Explain how the greenhouse effect operates to cause such drastic temperature differences on Mars, Venus, and Earth.

Venus: hot early, so no water on surface. Mars: very cold due to thin atmosphere. Not enough of the gas to raise the temperature. Earth: water removes CO2 from atmosphere forming limestone. The greenhouse effect keeps it habitable.