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P248, 1-20
1. Why does Venus appear so bright to the eye? Upon what factors does the planet’s brightness depend?
Venus is highly reflective. Nearly 70 percent of the sunlight reaching Venus is reflected back into space
(compare this with roughly 10 percent in the case of Mercury and the Moon). Most of the sunlight is reflected
from clouds high in the planet’s atmosphere. Venus’s location in its orbit has a DRAMATIC effect on its
brightness when viewed from Earth.
2. Explain why Venus is always found in the same general part of the sky as the Sun.
For the same reason Mercury is; Venus’s orbit lies inside Earth’s orbit so while Mercury is never seen more
than 28˚ from the sun, Venus is never seen more than 47° from the Sun. (Given Earth’s rotation rate of 15° per
hour, Venus is visible above the horizon for at most three hours before the Sun rises or after it sets; Thus the
nicknames “Morning Star” and “Evening Star”)
3. Why do astronomers think that the “near resonance” described in the text (between Venus’s rotation
and revolution, as seen from Earth) is not a true resonance? (i.e. that it’s coincidental)
Because it’s not EXACTLY an integer (the number of Venusian rotations between inf. Conjunctions – or b/w
Earth oppositions, from Venus’s perspective – is nearly but not exactly five. By comparison, the moon rotates
EXACTLY once each and every time it orbits the sun.)
4. Describe one observational problem associated with this “near-resonance,” real or not.
The same problem we have with the moon’s 1:1 resonance: Venus always presents nearly the same face to
Earth at its closest approach (aka when Venus is at inferior conjunction.)
5. What is our current best explanation of Venus’s slow, retrograde spin?
A large impact early in Venus’s life.
6. If you were standing on Venus, how would Earth look?
Venus’s dense, nearly liquid atmosphere makes viewing any “extra-Venusian” (or extra-Venerean, or extraCytherean) objects – or even standing in any unprotected fashion -- completely impossible. BUT IF THERE
WAS NO ATMOSPHERE, the Earth would look like a brilliant blue star.
7. How did radio observations of Venus made in the 1950s change our conception of the planet?
We had hoped that Venus would be habitable, and that Venus’s clouds were actually predominantly water
vapor. BUT…when radio observations measured its thermal energy emission they found its blackbody spectrum
characteristic of a temperature near 730 K (457C, 854 F). So basically, the radio observations shattered our
fragile dreams. <:’-(
8. What did ultraviolet images returned by Pioneer Venus show about the planet’s high-level clouds?
The upper level clouds move very quickly, circling Venus in four days. Ground level clouds move about
4kph/6mph…the speed of someone jogging slowly.
9. Name three ways in which the atmosphere of Venus differs from that of Earth.
Here are five:
- Over 96% CO2, almost all the rest in N2
- 90 times as massive (nearly liquid) [remember, massive is often used as a synonym for enormous, and most of the
time the intended meaning is still communicated. But scientifically it denotes an amount of mass/matter.]
- sulfuric acid (H2SO4) clouds and rain
- extends much farther into space (≈ 5x)
- much hotter
10. What are the main constituents of Venus’s atmosphere? What are clouds in the upper atmosphere
made of?
- CO2 and N2 – upper level clouds are sulfuric acid (H2SO4)
11. What component of Venus’s atmosphere causes Venus to be so hot? Explain why there is so much of
this gas in the atmosphere of Venus, compared with Earth’s. What happened to all the water that Venus
must have had when formed?
- Carbon dioxide, an effective greenhouse gas (i.e. transparent to visible light but nearly opaque to
infrared/heat) has caused a runaway greenhouse effect.
- Venus’s greenhouse gases never left the atmosphere to become dissolved in the oceans and rocks the way they
did on Earth.
- Any water on Venus probably was super heated (Venus is believed to have been MUCH hotter than it is today,
if you can believe that) and rose in the atmosphere where it was broken into H and O atoms.
12. Earth and Venus are nearly alike in size and density. What primary fact caused one planet to evolve
as an oasis for life, while the other became a dry and inhospitable inferno?
Venus is 30 million miles (50 million km) closer to the sun!
13. If Venus had formed at Earth’s distance from the Sun, what do you imagine its climate would be like
today? Why do you think this?
If you agree the two planets had similar beginnings, you could argue that Venus would be much more similar to
earth today. BUT…it’s doubtful Venus’s atmosphere would have as much O2 unless life somehow developed
there.
14. How do the “continents” of Venus differ from Earth continents?
There are fewer of them (8% of Venus’s surface…on earth continents are 25% of surface area).
15. How are the impact craters of Venus different from those found on other bodies?
Many are curiously oblong, and none are smaller than 3km in diameter.
16. What evidence exists that volcanism of various types has changed the surface of Venus?
Many of Venus’s craters are not impact craters but volcanic craters. And there are lava structures (“lava
domes”) scattered on the surface.
17. What is the evidence for active volcanoes on Venus?
No eruption has ever been detected on Venus, but we have observed:
- The level of sulfur dioxide (SO2) above Venus’s clouds shows large and fairly frequent fluctuations. (These
could be from volcanic eruptions on the surface.)
- Both the Pioneer Venus and the Venera orbiters observed bursts of radio energy from the surface. These bursts
are similar to those produced by lightning discharges that often occur in the plumes of erupting volcanoes on
Earth, again suggesting ongoing activity.
18. Given that Venus, like Earth, probably has a partially molten iron-rich core, why doesn’t it also have
a magnetic field?
Most likely because of Venus’s extremely slow rotation which fails to keep Venus’s magma “churning” and
unable to maintain “geomagnetism.”
19. Do you think there might be life on Venus? Explain your answer.
Are you kidding? (Sorry.) In my humble opinion…considering Venus’s extreme temperatures, pressures, and
poisonous atmosphere? Not a chance. Certainly not life as we know it here on earth. In fact, it would be difficult
to design a planet LESS hospitable!) UNLESS….and this is a very big UNLESS…you consider a life form that
floats in the atmosphere about 50 km up from the surface, where the pressure and temperatures are just like
those on earth! (Still though: sulfuric acid.)
20. Do you think that Earth is in any danger of experiencing a runaway greenhouse effect like Venus?
My own feeling is that it’s within the realm of possibility, but highly unlikely. Oh sure, it might warm up and do
real damage to life as we know it, but that’s not the same as being “like Venus.” Earth has several natural
mechanisms for “regulating” greenhouse gases, and while those mechanisms can be fragile (plants that absorb
CO2, cool temperatures that condense water vapor) they’re not going to diminish to the degree they’d need to
for Earth to become “like Venus.”