The morning star
HOW WE DISCOVERED THAT THE GODDESS OF LOVE IS IN FACT DANTE'S INFERNO: THE MORNING STAR
At dawn we can see to the horizon where the sun rises a very bright star. It is very eye-catching because its brightness resembles that of headlights, with almost no blinking. Looking for several weeks, always at the same time, we can see that it wanders among the other stars. Then comes a day when it disappears, then it appears at the beginning of the night, in the opposite horizon. And several months later, it returns to the eastern horizon, again at dawn. This strange light has seduced civilizations and the desire to discover its secrets have launched some of History's greatest adventures of research.
In the British Museum there is a clay tablet with records of observations of this unique star by the Babylonian civilization, 3500 years ago. The intense brightness and the strange movements convinced the Babylonians that it was a very powerful goddess. Centuries later the Greeks believed they were seeing in that bright light a sparkling woman and theorized she was the goddess of love and beauty. They called her Aphrodite, known by the Romans as Venus.
Only in the year 1610 Galileo Galilei pointed the newly-invented telescope to see what it really is. And he discovered something much more mundane: Venus is a sphere, and has phases like the Moon. But by comparing the different phases that Venus shows to the various phases that the Moon shows he discovered that Venus does not revolve around us, but around the Sun. This discovery, along with his discovery of the satellites orbiting Jupiter, agrees with the theory of Nicolau Copernicus that the Earth is not the center of the Creation. But if we are not in the center of the Creation, then the Universe was not made for us, as it is guaranteed by the Bible. For having relied on what his eyes saw and not on what was written in the holy book, Galileo was persecuted by the Church and sent to prison. Despite this, others began to imitate him, and now his method of thinking is widespread: to know the truth we must observe the world by ourselves, and not content us with what others said or wrote. This story marks the birth of modern Science.
Since then we have studied Venus with ever-more-powerful telescopes, but we were unable to see anything new: we still see a big ball, but no details on the surface. Correctly, it was interpreted that Venus has a thick layer of clouds that completely covers the planet. In the early twentieth century, no one doubted that all these clouds were water, so it was thought that Venus was a very wet planet. Many began to compare it to a swamp from prehistoric Earth, maybe even with amphibian monsters. Interesting speculation, but perhaps too risky, considering that in the first place, we were not seeing anything. Then in the 30's, it was proposed that Venus would actually be dry and arid and the clouds were nothing more than a very prolonged sandstorm. Although expectations declined, many still considered it habitable, and some even inhabited: when flying saucers began to make headlines, in the mid-twentieth century, there were those who claimed that they came from Venus, whose civilization was dominated by women. Nothing was proven and the observations continued. Through a sophisticated analysis of the color of Venus, it was discovered that large amounts of CO2 are present in its atmosphere, so other scenarios were imagined: if the planet was wet, then its oceans would be saturated with this gas, as in soft drinks. Signs of sulfur were also discovered, common in petroleum oil, so many advocates of an arid Venus speculated that the entire planet would be some giant Texas or Middle East.
In the late 50's, using gigantic antennas (radio telescopes) it was found that Venus is a powerful natural source of radio waves. Because any hot object emits radio waves, it was concluded that Venus should be at very high temperatures, hotter than a kitchen oven. In 1962, the first successful interplanetary probe, NASA's Mariner 2, arrived in the vicinity of Venus after 8 months of travel, and confirmed that the radio waves come from the surface and not from some magnetic field around the planet. The ground on Venus is really hot. Since 1967, the Soviet Venera probes attempted to descend, but they ceased to operate as they passed through the unbearable atmosphere. Other space probes continued to study Venus from above, and they showed different layers of clouds, made of water combined with sulfur, i.e., sulfuric acid. The measurements also showed that the temperature does not decrease at night, nor going to the poles. In 1975 a reinforced Venera 9 touched down and managed to transmit for a few minutes. It hardly had time to send a single photograph, showing volcanic rocks corroded by acids, at a temperature of 743 kelvins (470 degrees C) and a pressure 90 times higher than we have here on the surface of the Earth. The air is so thick that visibility is no more than a few hundred meters. Other Veneras sent similar data, and photos of the yellow sky. In the late 70's, with help from another U.S. mission, Pioneer Venus, we got a better understanding of this terrible atmosphere: that thick layer of this air made of 96% CO2 traps heat from the Sun, creating what is known as the "greenhouse effect".
The only way we can draw maps of Venus is with radar. The first experiments detected large high-terrain, continent-like areas, and low lands comparable to ocean floors. Finally in the 90's the U.S. spacecraft Magellan used a sophisticated military radar, able to recreate photo-quality images. For the first time, the real Venus was unveiled: volcanoes everywhere, valleys full of lava, lava flows that spread over thousands of kilometers, strange geological formations like bubbles, tortillas, flowers and even spiders, all of volcanic origin. Venus is a world completely shaped by volcanism. Rather than the Goddess of Love it is a place more like Hell. The easiness with which lava outpoured may be because the surface would be softened too much by an air so hot. Surprisingly, below the surface Venus is the known planet most like Earth: their chemical composition, internal structure, density, size, mass, gravity and distance from the Sun are very similar. The fundamental difference is in their atmospheres. We have no idea why they became so different, although we know that the key is the CO2 . At a time when we ourselves are increasing the level of CO2 in Earth's atmosphere through the burning of forests and petroleum products, this mystery reveals how little we understand planetary atmospheres and alerts us about the riskiness of experimenting, perhaps irreversibly, with our own atmosphere.
Today, when I watch the morning star I do not try to see a beautiful woman or a powerful goddess. I imagine those tiny metal-plastic-and-ceramics spacecraft built with much effort by our clumsy hands, and that somehow we make them travel millions of kilometers through interplanetary space, facing all sorts of risks, until they faintly begin to transmit data that help us to discover, after thousands of years of speculation, the true nature of that place that we used to consider just a strange light in the sky. Honestly, this feat seems to me much more fantastic than any mythological story.
CHRONOLOGY OF THE EXPLORATION OF VENUS
About 1500 B.C.E.: The Babylonians recorded their movements on the tablet of Ammisaduqa.
1610: First observation with telescopes, by Galileo Galilei
1932: W. Adams and T. Dunham detect signs of CO2 in the atmosphere of Venus
1962: The Mariner 2 flyby probe confirms a very high temperature on Venus
1967: First object built by humans to hit another planet, Venera 3
1975: First images of the surface of Venus, by Venera 9
1978: The Pioneer Venus mission proves that the temperature is due to the "greenhouse effect"
1994: The Magellan probe reveals extensive volcanism on the surface
2006: The European spacecraft Venus Express continues the observation of Venus
KEY DATA ABOUT VENUS
Diameter: 12 104 km
Mass: 4868 trillion tons
Density: 5243 kg/m3
Acceleration of gravity: 8,87 m/s2
Chemical composition: iron oxide, silicon, magnesium, nickel, sulfur, calcium, aluminum.
Internal structure: metal core, fluid mantle, rocky crust.
Atmospheric pressure: 92 000 hPa
Atmospheric composition: 96,5% CO2, 3,5% N2;
besides SO2, Ar, H2O, CO, He, Ne.
Average surface temperature: 737 kelvins (464 degrees C)
Average distance from Sun: 108 million km
Day: 117 Earth days
Year: 225 Earth days
Natural satellites: zero
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Based on a lecture given at USP, on 17 June 1999. Originally published in ABC Color, on 12 March 2006. Illustration: Mariner 2 was the World's first successful interplanetary spacecraft. Launched on 27 August 1962, by an Atlas-Agena rocket, Mariner 2 passed about 34 000 km from Venus, sending, by radio, valuable new information about interplanetary space and the venusian atmosphere. Mariner 2 first reported the temperature on Venus, revealing the very hot atmosphere of about 750 kelvins (500 degrees C) on the planet. The solar wind experiment on the spacecraft first measured the density, velocity, composition and time variance of the solar wind. Credit: NASA / JPL-Caltech.