Venera 7 (1970): The First Landing on Another Planet

Venera 7 was a Soviet space probe that made the first soft landing on another planet when its capsule touched down on Venus on 15 December 1970. For about 23 minutes it sent back faint signals from a surface hotter than an oven and crushed by a dense carbon dioxide atmosphere. The mission proved that a machine could survive on Venus, and it set the pattern for a decade of Soviet exploration of the planet.

Background: the race to reach Venus

Venus is Earth’s nearest planetary neighbour and was long imagined as a warm, perhaps swampy twin of our own world. Radio observations in the late 1950s and the American Mariner 2 flyby of 1962 suggested something very different: a scorching surface hidden under thick cloud.

The Soviet Union made Venus a priority target. After a string of failures in the early 1960s, Venera 4 entered the atmosphere in October 1967 and returned the first direct measurements from inside it. It stopped transmitting high above the ground, apparently overwhelmed by pressure far greater than its designers had expected. Venera 5 and Venera 6 repeated the feat in May 1969, and they too fell silent before reaching the surface.

Those missions showed that the atmosphere was overwhelmingly carbon dioxide and that pressure at the ground might be close to 100 times that on Earth. The engineers at the Lavochkin design bureau, led by chief designer Georgy Babakin, set out to build a capsule strong enough to land.

Building a capsule for Venus

The new descent capsule was a heavily reinforced titanium sphere of roughly 500 kilograms, designed to withstand about 180 atmospheres of pressure and temperatures of around 540 °C. To save weight for the strengthened hull, the scientific payload was kept very simple: chiefly sensors for temperature and pressure.

Before release, the capsule was cooled by the mother spacecraft so that it would start its descent as cold as possible and last longer in the heat. A small parachute, made to resist high temperatures, would slow it during the final fall through the dense lower atmosphere.

Two identical spacecraft were prepared for the 1970 launch window. The first, launched on 17 August 1970 from the Baikonur Cosmodrome in Kazakhstan on a Molniya rocket, became Venera 7. The second, launched a few days later, was stranded in Earth orbit by an upper-stage failure and was given the cover name Kosmos 359.

The landing on 15 December 1970

After a cruise of about four months, Venera 7 reached Venus on 15 December 1970. The capsule separated, plunged into the atmosphere on the night side of the planet, and deployed its parachute for a descent that lasted about 35 minutes.

Things did not go entirely to plan. Telemetry suggests that the parachute tore or collapsed partly during the descent, so the capsule fell faster than intended. It hit the ground at an estimated 16–17 metres per second, a hard impact for a landing probe. The signal received on Earth then seemed to vanish, and controllers at first believed the mission had failed at touchdown.

Only when scientists reprocessed the magnetic tape recordings in the following weeks did they find that a very weak signal, about 1 per cent of its normal strength, had continued for roughly 23 minutes after the impact. The most likely explanation is that the capsule bounced and came to rest on its side, with its antenna pointing away from Earth.

What Venera 7 measured

A fault in the switching system meant that the capsule sent back only temperature readings during its descent and on the ground. The surface temperature was about 475 °C, plus or minus around 20 °C, hot enough to melt lead.

Pressure was not measured directly at the surface. Scientists combined the temperature profile, the known composition of the atmosphere and the rate of descent to estimate a surface pressure of about 90 atmospheres, with a margin of roughly 15 either way. That is comparable to the pressure about 900 metres deep in Earth’s oceans.

These figures confirmed that Venus was no tropical twin of Earth. Its thick carbon dioxide atmosphere traps heat in a runaway greenhouse effect, making it the hottest planet in the Solar System even though Mercury is closer to the Sun.

Consequences and later Venera missions

Venera 7 showed that a well-built capsule could survive the trip to the surface, and the Soviet programme followed up quickly. Venera 8 landed on the day side in July 1972 and transmitted for about 50 minutes, measuring sunlight levels at the ground.

In October 1975, Venera 9 and Venera 10 sent back the first photographs from the surface of another planet, showing flat, broken rocks under a dim orange sky. Later landers, up to Venera 13 and 14 in 1982, returned colour images and analysed the soil. The Soviet missions remain the only spacecraft to have operated on the surface of Venus.

The achievement belongs to a wider series of Soviet firsts, from Sputnik 1 to Luna 9, the first soft landing on the Moon. Six years later, NASA’s Viking 1 completed the first fully successful landing on Mars.

Timeline

• 1967, 18 October: Venera 4 returns the first data from inside the atmosphere of Venus.
• 1969, 16–17 May: Venera 5 and Venera 6 descend through the atmosphere but fall silent before landing.
• 1970, 17 August: Venera 7 is launched from the Baikonur Cosmodrome.
• 1970, 22 August: Its twin is stranded in Earth orbit and named Kosmos 359.
• 1970, 15 December: The Venera 7 capsule lands on Venus and transmits for about 23 minutes.
• 1972, 22 July: Venera 8 lands on the day side of Venus.
• 1975, 22 October: Venera 9 returns the first images from the surface of Venus.

Why it matters

Venera 7 was the first spacecraft to land on another planet and report back. Its few minutes of faint data turned Venus from a cloudy mystery into a known extreme, and they gave scientists a vivid real-world example of a runaway greenhouse effect.