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Table of contents
It is true that some of the earliest robotic spacecraft were sent to the planet, and the Soviet Union made great strides when it landed its hardy Venera landers there a few years later, but since then the planet has only been visited intermittently. It's not for any lack of scientific interest, it's just that Venus is the backwoods, The Hills Have Eyes trailer park of the solar system.
Once upon a time — say, about the same time that people thought Mars might be crisscrossed with canals built by an advanced civilization — it was thought that Venus might be the primeval planet. With boundless optimism, learned academics speculated that, since Venus is closer to the sun, and therefore warmer than the Earth, it followed that the planet might be one giant marshy swamp, perhaps even inhabited by primitive life forms.
Some less-pedigreed souls even suggested there might be dinosaurs stomping about. This was a steamy, romantic vision of the friendly solar system we would have loved to find. It's a damn shame it didn't work out that way. Venus was instead revealed to be a true hellhole of a planet. With an atmosphere of about 96 percent carbon dioxide, and its proximity to the sun, the planet is the poster child for runaway global warming, with temperatures of at least a balmy degrees Fahrenheit.
The atmospheric pressure is nothing to sniff at either quite literally, since the air is suffused with sulfur dioxide , equivalent to that about two-thirds of a mile under Earth's oceans, or about 90 times that at sea level. You might call the planet dense in more ways than one. No swamps or dinosaurs for our closest neighbor, but a sunbaked, dry, and un-cratered landscape that makes Death Valley look like a day at the beach. Nevertheless, at the dawn of the space race, reaching Venus with unmanned probes was a top priority. The Soviet Union initiated efforts to reach the planet in , trying first for flybys, then impactors, and then later for orbiters and landers.
It would take eleven tries and six years to attain success.
VENUS by Ben Bova | Kirkus Reviews
The US program fared better — in mid, Mariner 2 successfully flew past Venus after Mariner 1 failed during launch. This was an endorsement of NASA's habit of flying robotic spacecraft in pairs when possible, allowing for one to fail but hopefully not both the Soviets had also tried this, but inconsistently. Mariner 2 was a lightly modified Ranger lunar spacecraft that had no cameras and was capable of basic measurements of radiation and magnetic fields and micrometeoroid impacts.
It also measured solar wind and a number of small solar flares during its mission. Due to the small lifting capacity of the rocket used to loft Mariner 2, the portion of the spacecraft relegated to scientific instruments had to be kept under forty pounds. The United States followed this in with Mariner 5, the updated Mariner design that was similar to those being flown to Mars. It was originally built as part of the Mariner 3 and 4 series for a possible Mars launch, but with the success of Mariner 4 was repurposed for Venus through the addition of more thermal insulation and the removal of the TV camera — since the planet was permanently veiled with a dense layer of clouds, rendering the surface invisible, a camera was not thought to be needed.
Had they included one, Venus would have looked like a smog-yellow billiard ball with some streaks across it. Mariner 5 was also a flyby mission, and the spacecraft is still in a long orbit around the sun, dead and slowly baking in the harsh light. Additionally, because it was a single, surplus Mariner, the spacecraft flew alone. But fortune smiled on the mission, which was successful.
About the same time as Mariner 5, the Russians succeeded with their much more ambitious Venera 4. It also consisted of a flyby spacecraft, but with a lander attached that disengaged from the main spacecraft before the encounter with the planet. The lander transmitted data from the planet's atmosphere during its descent, confirming that the atmosphere was overwhelmingly carbon dioxide, with a small amount of nitrogen, traces of oxygen, and a tiny amount of water vapor.
The flyby portion of the spacecraft was eleven feet high, and the solar panels had a deployed span of about thirteen feet. The landing stage was a metal ball three feet in diameter, with a gas-cooled heat shield. It was pressurized, a unique design that was characteristic of Soviet robotic explorers — they were almost like miniaturized crewed spacecraft. In this case, however, it was pumped up to over twenty-five times Earth's atmosphere at sea level, designed to withstand the crushing pressures thought to be endemic to the Venusian atmosphere.
A TRIP TO VENUS
While it was considered unlikely, it was still thought there might be oceans on Venus. The Soviet engineers designed a very clever but simple arrangement to deploy the landers' antennas — sugar was cured into the seam of the hatch covering the antenna, and if the lander had come to rest in a liquid, the sugar would dissolve, releasing the antennae. Its burn-proof parachutes were tested up to a temperature of about degrees.
During its ninety-minute trip through the dense Venusian atmosphere , the heat shield experienced temperatures up to 11, degrees Fahrenheit, and at thirty-two miles in altitude the parachute was deployed. Data on atmospheric pressure, temperature, and gas composition were transmitted back to Earth. At the point at which the parachute was released, the air temperature was only about 91 degrees, about the same as on that sunny day in Pasadena when Curiosity was about to land on Mars.
But by the time the Venera drop probe stopped functioning, temperatures had reached degrees and pressure was twenty-two times Earth normal — they had clearly not yet gotten to the even hotter ground level when Venera 4 packed it in. Nonetheless, it was the first set of direct measurements of another planet's atmosphere and its chemical composition, temperature, and pressure. But the Soviet Union wasn't done with Venus yet, not by a long shot.
Four attempts later, they succeed in reaching the surface with a functioning spacecraft. The intervening flights had been a mixed bag of launch and landing failures, each a lesson for the next attempt.
Pioneer venus missions
In August , Venera 7 plummeted to the planet's surface, making a successful, though lopsided, landing. It transmitted data for twenty-three minutes before dying, and was the first radio transmission to originate from another planetary surface. In July , Venera 8 entered the planet's atmosphere at about 25, miles per hour, using a heat shield to slow in the dense air to a speed of about miles per hour before opening its parachute at an altitude of thirty-seven miles and landing upright. Its data generally matched that of Venera 7.
The temperature was over degrees, with greatly diminished light due to heavy cloud cover, and an onboard spectrometer indicated that the nearby surface was granitic in composition. Venera 8 operated for just over an hour. But this was a flyby of convenience; the primary target for the spacecraft was sunny Mercury, which it reached in September While experiencing nearly five times the solar radiation of that near Earth, the probe managed to image both Venus and Mercury with its TV camera and returned copious amounts of data.
In , the Soviets finally scored big. Never mind that they had been beaten to a manned lunar landing by the Americans — they finally managed to land a sophisticated, advanced machine on the surface of Venus, the truest of no-man's lands. Venera 9 consisted of an orbiter and a lander, and held the additional distinction of being the first spacecraft to go into orbit around the planet.
The spacecraft was a behemoth, weighing almost 11, pounds — truly appropriate for a mission to Dante's seventh circle of hell. The ability to launch this heavier machine was due to the successful development of the newest Russian booster, the Proton, which is still in use. While the orbital component was primarily a relay station for the lander, it performed a range of experiments as it circled the planet, transmitting for months.
But the lander was the real prize. After its high-speed entry, a series of parachutes delivered it to low altitudes, where it was bravely released about thirty miles above the surface, using an innovative aerodynamic shield to continue its descent through the scorching air — the atmosphere was now known to be so dense at this level that no parachutes were required.
It plopped onto the rocky surface on its donut-shaped metal landing cushion at about fifteen miles per hour. Time was of the essence, as the Soviets had learned that machines on Venus did not last long. Within two minutes, instrumentation had been activated and was returning data. Cooling was achieved via circulating fluids, and soon the first image ever transmitted from the surface of another planet was sent back to Earth — a desolate, flat, rocky plain that, while fascinating, was truly uninviting.
First, let me introduce you to the atomic constituents of that substance chemists call H2O, which most of us more commonly know as water.
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The H represents the atom hydrogen. The O represents the atom oxygen. The number two after the letter H tells us that a single molecule of water is composed of two hydrogen atoms and one oxygen atom. In order to enter the world of CSI: Solar System, we need to understand the structure of atoms in a bit more detail. Hydrogen is hydrogen because its nucleus has one positively charged proton, which is orbited by one negatively charged electron. The nucleus, however, can also include one neutron, which lacks a charge. Chemists call this kind of heavy hydrogen deuterium.
Remember that H2O molecule? It would taste the same, and it would provide the same sustenance to your flowers and gerbils, but it would weigh more. Jupiter is such a massive planet that neither hydrogen nor deuterium can escape.
Future missions
We take it as a given that all the water originally deposited on Venus, on Earth, and on Mars also had that same ratio of hydrogen to deuterium. If I wanted to make 20, water molecules, I would need a total of 40, hydrogen H and deuterium D atoms of which 39, would be H and 1 would be D , plus, of course, 20, oxygen O atoms. In my mixture of 20, water molecules, I would be able to make 19, H2O molecules and one HDO molecule, given my initial ratio of hydrogen to deuterium atoms.
Why so low? As the hydrogen atoms escaped to space, the H-to-D ratio would have dropped from 40,to-1 to only 6,to The clear implication of this discovery is that Venus was once wet but is now bone-dry. Venus, as we now know, has a surface temperature of Fahrenheit Celsius. Venus once had oceans, but Venus warmed up and the oceans boiled off the surface.
Then ultraviolet light from the sun split the water molecules apart into their constituent atoms. This measurement tells us that Mars, like Venus, has lost lots of hydrogen, which means Mars, like Venus, has lost lots of its water.