Two evenings ago, Venus and the Moon hung close together in the deep blue twilight. Their alignment, along with the location of the fading sunset glow, gave a suggestion of the sweep of the ecliptic plane.
Zooming in on the pixels of the above photograph, it’s just possible to see that Venus is not a point source. The hint of a half-illuminated world indicates that the planet is now fairly near maximum elongation. In our lifetimes, I think we’ll likely see images of habitable extrasolar terrestrial planets that harbor something like this level of detail.
Venus gets a bad rap because the surface is so unpleasant. The Venera landers were built like submarines, and yet they still managed only an hour or two on the ground before expiring. The coke-bottle lens panoramas of basaltic slabs that they radioed back do little to fire the imagination.
My attitude toward Venus was transformed by David Grinspoon’s Venus Revealed, which I think is probably the best trade book ever written on planetary science. The text is filled with gems of insight. One passage that sticks is:
There is a level in the clouds (about 33 miles up), where the atmospheric pressure is about 70% of the pressure at sea level on Earth, and the temperature is a balmy 107 degrees Fahrenheit. For ballooning at this altitude on Venus, you would need only a thin, acid resistant suit, and oxygen tank and a large supply of cold lemonade. It’s cool enough for liquid water, and small amounts of it exist there (in a strong sulfuric acid solution).
By contrast there’s no place on Mars that could be explored using gear from an Army Surplus store.
Are there other similarly “visitable” environments in the Solar System? Surprisingly, the answer is yes. On Jupiter, at a level where the atmospheric pressure is ~6 times that at sea level, the temperature is chilly, and yet still comfortably above freezing. This level (at which hot tea might be preferable to lemonade) lies in the midst of the Jovian water cloud deck, and is subject to torrential downpours accompanied by lightning and thunder. If one were ballooning at this level, you would see an misty gray expanse, stabbed by lightning discharges, with the rotten-egg smell of hydrogen sulfide seeping in through your uncomfortably heavy scuba-store face mask.