stax opex Astronomy chp 10
What is the composition of clouds on Mars?
Clouds on Mars are of three types: dust clouds; water-ice, like those on Earth; and clouds of frozen carbon dioxide crystals (dry ice).
Compare the current atmospheres of Earth, Venus, and Mars in terms of composition, thickness (and pressure at the surface), and the greenhouse effect.
Earth's atmosphere is about 4/5 nitrogen and 1/5 oxygen; Venus' atmosphere is mostly carbon dioxide, with a pressure about 90 times higher than Earth; Mars' atmosphere is also mostly carbon dioxide, with a pressure only about one hundredth that of Earth. Venus has had an ongoing runaway greenhouse effect, leading to extraordinarily high surface temperatures. Earth is presently seeing the greenhouse effect increase with higher levels of carbon dioxide in the atmosphere. Mars has had a "runaway refrigerator" effect leading to a thinner atmosphere and colder temperatures over time.
What evidence do we have that there was running (liquid) water on Mars in the past? What evidence is there for water coming out of the ground even today?
Images from orbiting spacecraft of runoff channels and outflow channels all show evidence of formation by running water. Several dry basins contain minerals that only form with water and indicate extensive lakes in the past. In 2015, some dark streaks (recurring slope lineae or "gullies") that got longer over the course of several days showed spectra of hydrated salts, and may be evidence of saltwater on Mars today.
Explain the runaway refrigerator effect and the role it may have played in the evolution of Mars.
Martian gravity is not strong enough to hold a gaseous atmosphere over a long period of time, so the atmosphere would have gotten thinner as gas escaped. This would lead to lower temperatures, and more gas would have frozen and deposited out of the atmosphere, lowering temperatures still further. The thinner atmosphere and colder temperatures would lead to the loss of most water from the planet, except for water ice, permafrost ground deposits, and perhaps underground saltwater.
How was the Mars Odyssey spacecraft able to detect water on Mars without landing on it?
Odyssey used a gamma-ray spectrometer to detect hydrogen below the martian surface. Analysis of the signals indicated that the hydrogen was probably from water molecules in ice frozen below the surface.
What is the composition of the polar caps on Mars?
Seasonal ice caps are made up of dry ice, or crystals of frozen carbon dioxide; the northern residual cap is water ice, whereas the southern permanent ice cap is made predominantly of water ice with a covering of carbon dioxide ice.
Describe the current atmosphere on Mars. What evidence suggests that it must have been different in the past?
The martian atmosphere consists mostly of carbon dioxide, but is very thin, less than 1% of Earth's atmosphere. However, the strong evidence of water on Mars in the past that our missions have found means that the atmosphere must have been thicker and warmer, or water would have evaporated away very quickly.
. How might Venus' atmosphere have evolved to its present state through a runaway greenhouse effect?
There may have been carbon dioxide in the Venus atmosphere to begin with. But however large that initial supply was, heat from the Sun could have evaporated water from the surface of Venus, releasing carbon dioxide absorbed in the water. The carbon dioxide in the atmosphere prevented infrared radiation from escaping the planet, leading to a rise in temperatures and further loss of water and release of carbon dioxide. Sunlight would break up water vapor molecules higher in the atmosphere into hydrogen, which escaped the planet, and oxygen, which combined with surface rocks. The loss of water reduces the planet's ability to absorb carbon dioxide.
Describe two anomalous features of the rotation of Venus and what might account for them
Venus has retrograde rotation about its axis, opposite to the direction of spin of most other planets; also, its rotational period is longer than any other planet's. It is in fact longer than its orbital period, so its day is longer than its year. Astronomers think Venus suffered a collision with another large body during the formation period of the solar system, changing its rotational motion in both these ways.
List several ways that Venus, Earth, and Mars are similar, and several ways they are different.
Venus, Earth, and Mars are similar in that they consist of rock and metal for the most part; they are terrestrial planets, closer in to the Sun than the jovian planets; all have atmospheres (although they are of different constituents and with different pressures); all have volcanic activity on their surfaces; and all have or have had some kind of greenhouse effect change their surface temperatures. The three planets are different in many ways, among them: their size (Mars is significantly smaller); their atmospheres (Mars and Venus is dominated by CO2, while Earth's is dominated by nitrogen (and has a significant amount of oxygen); the presence or absence of liquid water on their surfaces today; the major way that their surfaces undergo large-scale changes (plate tectonics on Earth, blob tectonics on Venus, impacts and wind action on Mars); whether they are now or have been in the past suitable for life.
What evidence is there that Venus was volcanically active about 300-600 million years ago
While small impactors burn up in Venus' thick atmosphere, larger chunks from space make craters on Venus' surface, as they do on other worlds. Do counts of larger craters on Venus can be compared to counts of such craters elsewhere in the solar system. Such crater counts on Venus show that its surface is about 300-600 million years old. Nothing older appears on the venusian surface. The implication is that the surface consists of lava flows from that time that covered older surface features, showing only more recent ones.
Why is Mars red?
Winds on Mars are strong enough to blow surface dust all over the planet. This dust contain iron oxide, which gives it the rusty red color.
