Mariner 2 — first successful planetary probe
Launched towards Venus on 27 August 1962, Mariner 2 became the first spacecraft to successfully study another planet as it flew past.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
On 27 August 1962 the American spacecraft Mariner 2 left for Venus on an Atlas-Agena rocket. It was in fact the second attempt. A little over a month earlier, on 22 July, its twin, Mariner 1, strayed from its planned path about five minutes after launch and was destroyed for safety. The cause is usually traced to a single missing symbol in the equations that guided the rocket, and the accident has been nicknamed ‘the most expensive hyphen in history’.
Mariner 2’s own journey was not smooth either. Just after launch the rocket briefly lost control and rolled before righting itself, and during the cruise one solar panel failed and temperatures inside the craft rose above design limits. Even so, most of its instruments kept working. After a cruise of about three and a half months, Mariner 2 passed Venus at a distance of about 34,773 km on 14 December 1962.
For about 42 minutes as it went by, Mariner 2 scanned Venus with microwaves, the same kind of radio waves used in microwave ovens, and with infrared light, which the eye cannot see. The scans showed that the surface of Venus is hotter than 400 °C. The old idea that oceans or jungles might lie beneath its thick clouds lost its footing. No clear magnetic field was found at Venus either.
After passing Venus, Mariner 2 kept circling the Sun and sending data until contact was lost on 3 January 1963. It is probably still going around the Sun somewhere today. The orbit view reproduces its three-and-a-half-month route as it left Earth, slid inward towards the orbit of Venus and met the planet.
Mission goals
Mariner 2 was the first proof that a spacecraft could be sent to another planet and study it. No one had succeeded before. The Soviet Venera 1 lost contact on its way to Venus in 1961, and Mariner 1 failed at launch. Once Mariner 2 had succeeded, the way was open for spacecraft to Mars, Mercury and the planets farther out.
Mariner 2 confirmed something important about the Sun as well as about Venus. Throughout its cruise it measured a constant flow of electrically charged particles streaming out from the Sun, known as the ‘solar wind’. In a 1958 paper the American physicist Eugene Parker had predicted that such a wind blows all the time; the paper was published by the journal’s editor even though the scientists who reviewed it objected. Mariner 2’s measurements showed directly, out in space, that Parker was right.
Finding Venus so hot also changed how people saw the planet. Because Venus is close to Earth in size and mass, it had sometimes been called ‘Earth’s twin’. After Mariner 2, however, it came to be seen as a world with conditions completely unlike Earth’s and very hard for life. Scientists explain the heat as a greenhouse effect, in which the thick atmosphere traps warmth.
Mission chronology and background
Mariner 2 was a small spacecraft weighing 203 kg, built in a hurry by adapting the frame of the Ranger lunar probe. The best time to travel from Earth to Venus, called a ‘launch window’, comes around only about every 19 months. To make the 1962 window, the team went from design to launch in less than a year.
After Mariner 2, the Soviet Union led the way at Venus. In 1970 Venera 7 landed and sent the first data from the surface, and in 1975 Venera 9 sent back the first pictures of the surface. The United States returned with Pioneer Venus in 1978 and with Magellan in 1990, which mapped the whole planet by radar. These missions showed that the average surface temperature of Venus is about 465 °C.
Mariner 2’s success established the Jet Propulsion Laboratory (JPL) in California as a leader in planetary exploration. The missions that followed, Mariner 4 to Mars, Mariner 10 to Mercury, and spacecraft such as Voyager, Galileo and Cassini, were all led by the same laboratory. Mariner 2 opened the first chapter of that long history of planetary exploration.
Other milestones of this mission
Where to see it — sky and simulator
Mariner 2 is thought to be still circling the Sun, but there has been no contact since 1963 and it is far too small and distant to be seen from the ground. The replay in the orbit view instead follows its route in time order, from leaving Earth on 27 August 1962 to passing Venus on 14 December. The replay slows down at the moment of closest approach to Venus.
Venus is the easiest planet to find in the night sky. It appears as the brightest point after the Moon, either in the west just after sunset or in the east before sunrise. Choosing Venus in the sky view works out whether it is in the evening or the morning sky from your location and how high it rises. Moving the time back to December 1962 reproduces where Venus stood when Mariner 2 flew past.
Through binoculars or a small telescope Venus shows phases, growing and shrinking like the Moon. No telescope, however, can show its ground, because thick clouds cover the surface completely. That is why Mariner 2 measured the temperature with microwaves, which pass through the clouds, rather than with visible light.
See this for yourself — replay the moment in the orbit view
FAQ
How close did it get to Venus?
On 14 December 1962 it passed about 34,773 km from Venus and observed it for about 42 minutes.
What did it find?
That the surface of Venus is hotter than 400 °C with no clear magnetic field, and that the solar wind blows out from the Sun all the time.
Why did Mariner 1 fail?
About five minutes after launch it strayed from its path and was destroyed for safety. A single missing symbol in the rocket’s guidance equations is usually given as the cause.
Where is it now?
It is thought to be circling the Sun. Contact was lost on 3 January 1963.
Related
- Venera 7 — first landing on another planet
- Parker at closest approach
- Mariner 4 — first close-ups of Mars
- Venus — object index
- The Sun — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.