VISITS TO VENUS

Being Earth's closest planet and its name meaning Beauty, you would think that Venus would be a popular choice for space tourists. However, Venus is a planet where beauty really is only skin deep. Venus' thick clouds are full of poisonous sulphuric acid, the temperature on the planet would melt lead, and if you made it to the surface without suffocating in its carbon dioxide atmosphere, you would be crushed by the planet's sky! This lack of hospitality shown by Venus means that it doesn't get many visitors at all, with most scientists deciding to send their expensive space probes over to the slightly more welcoming planet, Mars. In fact, some of the space probes that have visited Venus were actually spares from other missions!

On 7th February 1961, Russia, which was known as the Soviet Union back then, was the first country to attempt to send a space probe to Venus. The probe sent into space was called Sputnik 7. When it was in orbit around Earth, a space craft called Venera would have been launched from it to travel to Venus and land on the planet. However, something went wrong with the ignition and the space craft never left Earth orbit. Slightly more successful was Venera 1, which was launched from Sputnik 5 while in orbit around Earth on the 12th February 1961. This mission was going to be a flyby mission, meaning that it was going to fly by Venus, and send back information about the planet. It was never intended to land on the planet. Venera 1 began its journey to Venus but after 7 days and at about 2 million kilometres from Earth, contact with the space craft was lost. The spacecraft did eventually come within 100,000 kilometres of Venus. Later Russian attempts were made with Venera 2 which was launched on 12th November 1965 and Venera 3, launched on 16th November 1965. Venera 2 was another flyby mission and it did reach Venus, coming within 24,000 kilometres of the planet, but again the spacecraft systems weren't operating so no information could be sent back. Venera 3 was a lander mission, meaning that it was intended to land on the surface of the planet. The space craft did succeed in landing on Venus, but once again, the communications systems failed so no information could be sent back. But Venera 3 was successful in that it became the first manmade object from Earth to land on Venus. The Russians continued to attempt to send probes to Venus over the next few years and finally succeeded in 1967.

It was the United States that reached Venus first. Although the Russians were first to attempt to get to Venus, the Americans were the first to actually get there successfully and by doing this, they became the first nation to reach another planet in the Solar System. Mariner 1 was NASA's first attempt to reach Venus, although it failed to get off the ground at its launch pad on 22nd July 1962. Mariner 2 (pictured left) was launched on 27th August 1962 and although systems nearly failed during its journey to Venus and only one of its two solar panels was working, Mariner 2 flew by Venus on 12th December 1962 and successfully sent back information about the planet, measuring surface temperatures as being at least 425°C, thick cloud layers between 56 to 80 km above the surface of Venus, a mainly carbon dioxide atmosphere, and not much of a magnetic field. The mission officially ended on the 3rd January 1963 when NASA lost contact with the probe at 87.4 million kilometres from Earth.

In 1967, both Russia and America reached Venus again. Russia landed their Venera 4 space probe (pictured right) on the planet on 18th October, and NASA's Mariner 5 mission completed a fly by on the 19th October. The Venera 4 lander was the first successful mission to send data back from below the clouds of Venus. Information about the amount of oxygen and hydrogen in the planet's atmosphere, how much radiation the planet received from the Sun and the pressure on the planet was sent back to Earth while the Venera 4 lander capsule parachuted through the planet's atmosphere. Before this mission, scientists believed Venus to be similar to Earth, and thinking that the planet's surface may have hills and oceans. Venera 4 was designed to communicate while underwater. However, Venera 4 stopped communicating after 94 minutes of its descent when it was about 24 kilometres above the surface, probably due to the intense heat and pressure on Venus. NASA's Mariner 5 was actually designed to go to Mars, but wasn't needed because Mariner 4 successfully went there instead. So, NASA modified it and sent it to Venus. Mariner 5 was designed to orbit Venus. It reached the planet a day after Venera 4 had landed there, and sent back more information about the planet's atmosphere, confirming that it is 85-99% carbon dioxide. 

After 1967, the USA turned most of its attention to the Moon and didn't actually return to Venus until 1973, and that was actually for a mission to Mercury which passed Venus on the way which will be described later. The Russians continued to persevere, sending Venera 5 and Venera 6 to the planet in January 1969, again landing on the planet but communications failing during the descent to the planet's surface. On 17th August 1970, Venera 7 was launched. It entered Venus' atmosphere on 15th December 1970 and successfully sent back signals for 23 minutes after landing on the planet. These were the first signals ever sent to Earth from the surface of another planet, even though they were very weak. Venera 8 also successfully sent back signals from the planet when it arrived there on 22nd July 1972, using a refrigeration system to keep the lander probe cool during its descent, and measuring the level of light on the planet, discovering that it was similar the the level of light on Earth on an overcast day and therefore suitable for photography. This paved the way for future missions which would take the first images from the surface of the planet (maybe scientists didn't think to install a flash on the camera!). 

In 1973, the USA returned to Venus, but only in passing! Mariner 10's main goal was to reach Mercury, the closest planet to the Sun in the Solar System. Mariner 10 is the only space craft to have visited Mercury so far. Another (Messenger) is on its way now, due to reach Mercury in 2011 and a mission currently under development (called BepiColombo) is planned to launch in 2011, due to end its mission in 2015. To get to Mercury though, they need the help of Venus. Mariner 10 pioneered a new method of getting around the Solar System. In order to get to Mercury, the space probe used the gravity of Venus to propel it to the next planet. It did this by being sent from Earth to Venus, and when it reached Venus, was pulled in by the planet's gravity. The space craft builds up speed as it orbits Venus which is travelling at 35 kilometres a second around the Sun, and is then propelled to its next target. The means that the space craft actually uses velocity rather than fuel to travel around space, which is handy seeing as there are no fuel stations in space! This method is called Gravity Assist, or the Slingshot Effect. Since then, gravity assist has become standard in space travel. Voyager 2 managed to visit all four of the Gas Giants in the 1970s and 1980s using gravity assist! Mariner 10 was a technical nightmare with systems constantly failing as it made its journey to Mercury via Venus. However, it successfully took the first close up images of Venus and returned more information about the planet before leaving for Mercury. The picture to the left was taken by Mariner 10 and is now over 30 years old.

Although Mariner 10 successfully returned pictures of Venus as it passed, images from the planet's surface had still not been received. This was to change when, on 8th and 14th June 1975, Russia launched Venera 9 and Venera 10. These space crafts had probes which descended into the planet's atmosphere and, when they landed on the planet's surface on the 22nd and 25th October 1975, took the first images and sent them back to Earth, shown below.

These images are distorted, giving a "fish-eye" view of the planet. They showed shadows on the planet, rocks that were about 30 to 40 cm in size and signs of lava or weathered rocks. Missions to Venus continued by the Russians throughout the rest of the 1970s and in the 1980s. Venera 13 and took more images of Venus when they arrived on the planet in 1982, including the first colour pictures. Below is an image taken by Venera 13, showing the planet's fine soil and flattened (or pancake) rocks.

The final Russian Venera missions were Venera 15 and Venera 16 which were both launched in 1983. The Venera missions were not the only missions attempted by Russia to visit Venus. The Zond missions ran from 1964 to 1970. Although most of these were designed for exploration of the Moon, Zond 1 was launched towards Venus on 2nd April 1964 while in orbit around Earth. Although systems failed on 14th May, the space craft flew by Venus on 14th July. The Vega mission was launched in 1984, designed to visit Halley's comet, which was due to come close to Earth in 1986. Two Vega craft were launched on 15th and 21st December 1984. They reached Venus in June 1985, using the gravity of the planet to propel them to Halley's Comet in a similar way to Mariner 10's mission to Mercury. However, when they arrived at Venus, two lander probes were launched from the Vega spacecraft and landed on the planet, sending back more information about Venus' atmosphere and surface conditions. The Vega probes themselves continued on to Halley's Comet, reaching it in 1986. 

In the 1970s, the United States focussed mainly on Mars and the Outer Planets, successfully sending two Viking probes to Mars, and two Voyager probes to Jupiter, Saturn, Uranus and Neptune. Towards the end of the decade though, Venus was finally  revisited. The Pioneer mission consisted of two spacecraft, Pioneer 12 and Pioneer 13. Pioneer 12 was an orbiter which was launched from Earth on 20th May 1978. Pioneer 13 was a multiprobe, launched on 8th August 1978. The Pioneer Venus Orbiter (Pioneer 12's other name) arrived at Venus on 4th December 1978 and was able to conduct 17 experiments, including experiments which attempted to discover what the surface was like by radar. It also measured the atmospheric make-up of the planet, its magnetic field, gravity field, and gamma ray bursts, and took the picture you can see to the left. Most of Pioneer 12's experiments took place up to July 1980, although it did  make observations of comets between 1984 to 1987. However, in 1991, when the orbiter was orbiting the southern parts of Venus, it was reactivated to obtain information from these parts of the planet. The orbiter ran out of fuel in May 1992 and fell into the planet's atmosphere, burning up as it did so like a meteor. Pioneer 13 released 4 separate probes to examine the planet in different places. The first probe (known as the large probe) was released from the space craft on 16th November 1978 to enter Venus near its equator on the side facing the Sun (the day side). Three smaller probes were released on 20th November 1978, two of them entered the side not facing the Sun (the night side) and one entered the day side. The spacecraft itself (the bus) entered the planet on 9th December 1978, aimed at the planet's day side. When the probes left the Pioneer 13 bus, they were actually powered down. Because they didn't have much on-board power or solar cells to charge their batteries, the probes had timers which switched them back on when they were about 17 minutes from entering the planet's atmosphere. During their descent through the planet's atmosphere, the probes sent radio signals back to Earth, but none of the probes were designed to survive after impacting the planet's surface. However, one of the small probes (the one which landed on the day side of the planet) continued to send data back for 67 minutes after hitting the planet's surface, showing that the temperature inside the probe rose to 126°C before the battery power ran out. 

On 5th May 1989, the first space probe ever to be launched from a Space Shuttle was Magellan. Named after a 16th Century Portuguese explorer who became the first man to sail all the way around the world, Magellan was launched from the Space Shuttle Atlantis and sent to Venus to map the entire planet's surface using radar. The picture to the right shows Magellan in the payload bay of Atlantis. Radar images allowed scientists to be able to see through Venus' thick cloud cover and to finally discover what the planet's surface was like.  Mapping of the planet's surface began when Magellan arrived at Venus on 10th August 1990. After 8 months, 84% of Venus' surfaces was mapped. Magellan mapped Venus twice more in 1991 and 1992. On 11th October 1994, Magellan's mission ended when the spacecraft was sent into Venus' atmosphere to burn up. By then, 98% of the planet's surface had been mapped, revealing that the planet had a volcanic history, its surface was covered in lava flows and large craters and that in some places Venus may still be geologically active. There is however no evidence of tectonic plates, such as those on Earth which cause Earthquakes. Venus, like Earth, is a geologically young planet. Its surface features are about half a billion years old, whereas places like the Moon, Mars and Mercury have remained the same for over 4 billion years. The picture to the left shows a computer image of Venus without its cloud cover with information from the Magellan mission.

Other missions which visited Venus were NASA's Galileo mission, launched in 1989, and the NASA/European Space Agency/Italian Space Agency Cassini-Huygens mission, launched in 1997. Both of these missions were actually going to Jupiter, but visited Venus to build up momentum, using the gravity assist method mentioned earlier. Galileo sent more information back about Venus' clouds, and Cassini-Huygens tried to detect lightning on Venus. The first suggestion of the possibility of lightning on Venus was reported during a Russian Venera mission in the 1970s, but Cassini-Huygens found no evidence of lightning during its visit.

On 9th November 2005, the European Space Agency launched its first probe to Earth's nearest neighbour. Named Venus Express, the space craft is very similar to ESA's Mars Express which visited Mars in 2003 and is currently in orbit around the planet. It actually contains spare parts from Mars Express and the European Space Agency's Rosetta space craft. Venus Express is expected to arrive at Venus in April 2006 where it will examine the planet's atmosphere in a mission that will last about 500 Earth days. It will go as close as 250 kilometres from the planet. 

Other future missions to Venus include the Venus In-Situ Explorer and (VISE) and the Venus Surface Explorer (VSE). VISE is expected to launch in 2013 and VSE should be going to Venus in 2020. So, once again, despite being close to Earth, and similar in size, after April 2006, Venus has quite a while to wait until it gets visited again. 

Before 1961, Venus, like the other planets in the Solar System, was a mystery to people on Earth. But it was probably the one planet that people believed to be most similar to Earth. It is the nearest planet to Earth, is a very similar size, its name means Beauty and, from Earth, it shines brightly in the night sky. The swirling clouds probably covered a surface of hills and mountains, trees and flowers, grass and water; a planet suitable for life. However, when the first space craft arrived at Venus, it soon became obvious that Venus was not quite the Earth-like planet it seemed. The atmosphere was discovered to be poisonous, and space crafts designed to land on Venus were simply destroyed by the intense heat and immense pressure as they got closer to the surface. The Russians persevered with their Venera missions and did eventually land a probe on Venus and successfully managed to take pictures from the planet's surface, whereas the Americans concentrated on exploration of the Moon and Mars. Even so, today we have a good idea about the atmospheric make-up of Venus, we know that life simply can't exist there, and we finally know some of the secrets of what lies below the cloud cover. People will never visit Venus, but will always be able to see its deceptive beauty in the night sky.

All images on this page are courtesy of NASA/JPL.

Sources for this page: Chronology of Space Exploration, NASA's Solar System Exploration, Journey through the Galaxy, BBC Science and Nature: Venus

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