About Venus
Venus has almost the same mass, size and density as the Earth (it is incidentally, some 30 million times more massive than the most massive comet known). As the nearest planet, it has for centuries been thought of as the Earth’s sister. What is our sister planet really like? Might it be a balmy, summer planet, a little warmer than the Earth because it is a little closer to the Sun? Does it have impact craters, or have they all eroded away? Are there volcanoes or mountains? Oceans? Life?
The first person to look at Venus through the telescope was Galileo in 1609. He saw an absolutely featureless disc. Galileo noted that it went through phases, like the Moon, from a thin crescent to a full disc, and for the same reason: we are sometimes looking mostly at the night side of Venus and sometime mostly at the day side, a finding that incidentally reinforced the view that the Earth went around the Sun and not vice versa.
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| Venus. Most people go about their daily lives as if nothing is happening. Unthinking, uncaring… (quotations from Megan Jorgensen). Image: Schaller |
As optical telescopes became larger and their resolution (or ability to discriminate fine detail) improved, they were systematically turned toward Venus. But they did no better than Galileo’s. Venus was evidently covered by a dense layer of obscuring cloud. When we look at the planet in the morning or evening skies, we are seeing sunlight reflected off the clouds of Venus. But for centuries after their discovery, the composition of those clouds remained entirely unknown.
The absence of anything to see on Venus led some scientists to the curious conclusion that the surface was a swamp, like the Earth in the Carboniferous Period. The argument – if we can dignify it by such a word – went something like this :
– I can’t see a thing on Venus.
– Why not?
– Because it’s totally covered with clouds!
– What are clouds made of?
– Water, of course.
– Then why are the clouds of Venus thicker than the clouds on Earth?
– Because there’s more water there.
– But if there is more water in the clouds, there must be more water on the surface. What kind of surfaces are very wet?
– Swamps.
And if there are swamps, why not cyacads and dragonflies and perhaps even dinosaurs ou Venus? Observation: There was absolutely nothing to see on Venus. Conclusion: It must be covered with life. The featureless clouds of Venus reflected our own predispositions. We are alive, and we resonate with the idea of life everywhere. But only careful accumulation and assessment of the evidence can tell us whether a given world in inhabited. Venus turns out not to oblige our predispositions.
Note: The Adda cylinder seal, dating from the middle of the third millennium B.C., prominently displays Inanna, the goddess of Venus, the morning star, and precursors of the Babylonian Ishtar.
Venus is Old
When I greet a friend, I am seeing her in reflected visible light, generated by the Sun, say, or by an incandescent lamp. The rays bounce off my friend and into my eyes. But the ancients, including no less a figure than Euclid, believed that we see by virtue of rays somehow emitted by the eye and tangibly, actively contacting the object observed.
This is a natural notion and can still be encountered, although it does not account for the invisibility of objects in a darkened room. Today we combine a laser and a photocell, or a radar transmitter and a radio telescope, and in this way make active contact by light with distant objects. In radar astronomy, radio waves are transmitted by a telescope on Earth, strike, say, that hemisphere of Venus that happens to be facing the Earth, and bounce back. At many wavelength the clouds and atmosphere of Venus are entirely transparent to radio waves. Some places on the surface will absorb them or, if they are very rough, will scatter them sideways and so will appear dark to radio waves.
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| Anaximander of Miletus argued that we are so helpless at birth that, if the first human infants had been put into the world of their own, they would immediately have died. Image: Gorgeous Anime Girl with Fuschia Hair by © Meg Jorgensen (Elena) |
By following the surface features moving with Venus as it rotates, it was possible for the first time to determine reliably the length of its day – how long it takes Venus to spin once on its axis. It turns out that, with respect to the stars, Venus turns out every 243 Earth days, but backwards, in the opposite direction from all other planets in the inner solar system. As a result, the Sun rises in the west and sets in the east, taking 118 Earth days from sunrise to sunrise. What is more, it presents almost exactly the same face to the Earth each time it is closest to our planet. However, the Earth’s gravity has managed to nudge Venus into the Earth-locked rotation rate, it cannot have happened rapidly. Venus could not be a mere few thousand years old, but rather must be as old as all the other objects in the inner solar system.
Radar pictures of Venus have been obtained, some from ground-based radar telescopes, some from the Pioneer Venus vehicle in orbit around the planet. They show provocative evidence of impact craters. There are just as many craters that are not too big or to small on Venus as there are in the lunar highlands, so many that Venus is again telling us that it is very old. But the craters of Venus are remarkably shallow, almost as if the high surface temperatures have produced a kind of rock that flows over long periods of time, like taffy or putty, gradually softening the relief.
There are great mesas here, twice as high as the Tibetan plateau, an immense refit valley, possibly giant volcanoes and a mountain as high as Everest. We now see before us a world previously hidden entirely by clouds – its features first explored by radar and by space vehicles.
If you see a schematic diagram of the electromagnetic spectrum, you’ll see that the wavelength of light is measured in Angstroms, micrometers, centimeters and meters.
