Answers

ConceptChecks

ConceptCheck 11-1: No. Venus is perpetually shrouded in a thick layer of clouds and because visible light does not penetrate the clouds, no light escapes for us to observe from Earth.

ConceptCheck 11-2: When Caloris Basin formed, all existing craters in that area would have been wiped out, and the craters we see today occurred afterward. The density of craters inside Caloris Basin is low compared to typical regions that still show high densities from the Late Heavy Bombardment. Therefore, it appears that Caloris Basin would have formed later.

ConceptCheck 11-3: The high temperatures of such an impact would “boil off” the volatile elements, and would be consistent with a low abundance on Mercury. However, we observe a high abundance of volatile elements, and this is a great mystery.

ConceptCheck 11-4: 1.35-cm microwaves are absorbed by water molecules. If the surface of Venus contained a significant amount of water, it would absorb these wavelengths. The same is true for the Venusian atmosphere. Since microwaves at 1.35 cm were readily detected, there can be little water on or around Venus.

ConceptCheck 11-5: The northern hemisphere has a younger surface. Compared to the southern hemisphere, the northern hemisphere is almost free of impact craters. This indicates that craters must have been erased on the northern hemisphere by a more recent process.

ConceptCheck 11-6: The age of a planetary surface is indicated by how many craters it has. Venus has more craters than Earth, yet fewer than Mercury. Detailed analysis estimates the age of Venus’s surface at 500 million years old.

ConceptCheck 11-7: If CO₂ could be added to the atmosphere, the temperature on Mars might be increased through the greenhouse effect.

ConceptCheck 11-8: Methane-producing microbes, volcanic activity, and the interaction of UV sunlight with small meteorites could all produce variable amounts of methane on Mars.

ConceptCheck 11-9: The “runaway” term refers to the fact that an increase in temperature causes changes in the atmosphere, which causes the temperature to rise even higher and higher.

ConceptCheck 11-10: A global magnetic field can deflect the solar wind, protecting the Martian atmosphere from high-energy collisions. These collisions can break apart the greenhouse gases CO₂ and H₂O, allowing the constituent atoms to escape into space.

ConceptCheck 11-11: It appears that hydrogen, presumed to reside in frozen water, is absorbing neutrons on the surface of Mars (Figure 11-38). Also, impact craters have directly revealed water-ice (Figure 11-39).

ConceptCheck 11-12: Phobos raises a tidal bulge on Mars that lags behind Phobos due to Phobos orbiting faster than Mars rotates. Through gravity, this bulge pulls back on Phobos, slowing it down. As Phobos slowly loses orbital energy, it spirals in toward Mars.