Venera 7 — first soft landing on another planet

The spacecraft that fell toward Venus on 15 December 1970 had been kept deliberately cold, chilled to minus 8 degrees Celsius by its carrier bus before entry, because every degree bought seconds of life below. Venera 7's lander was a sealed titanium sphere built to survive 180 atmospheres of pressure, engineered against a planet that had crushed or silenced every probe sent into its depths before. Its parachute opened about 60 kilometres up, in air the instruments confirmed was 97 percent carbon dioxide, and the probe began radioing temperatures as it sank.

Then the descent went wrong. Minutes after deploying fully, the parachute began to fail and finally collapsed. The probe fell free and struck the surface at about 16.5 metres per second, roughly 60 kilometres per hour, and apparently bounced onto its side, leaving its antenna aimed away from Earth. The signal seemed to die at impact. In Moscow the mission looked like another agonizing near miss, one more Venus probe lost at the last moment. But the ground stations' tape recorders had kept rolling.

Weeks later, radio scientist Oleg Rzhiga, combing through the recordings, found something buried in the noise: 23 more minutes of telemetry at about one percent of normal signal strength, transmitted from the surface itself. A stuck telemetry switch meant only the temperature channel had come home, 475 plus or minus 20 degrees Celsius, from which a surface pressure of roughly 90 atmospheres was later derived. Faint, garbled and very nearly lost, it was the first signal human beings had ever received from the surface of another planet.