Which Soviet mission pair deployed balloons in Venus's atmosphere in 1985?

The Soviet mission pair Vega 1 and Vega 2 deployed balloons in Venus’s atmosphere in 1985. Each spacecraft released a descent module containing both a lander and a balloon, then continued onward to study Halley’s Comet.

Vega 1 reached Venus on June 11, 1985, and Vega 2 arrived on June 15. Their helium-filled balloons floated at roughly 54 kilometers above the surface, within an active cloud layer where pressure and temperature were comparatively Earth-like. Instruments measured wind speed, temperature, pressure, and aerosol conditions while the balloons drifted rapidly around the planet.

The balloons were the first uncrewed aircraft to fly on a world beyond Earth. They operated for more than 46 hours, crossing from Venus’s night side toward daylight before their batteries or communications failed. Their tracking also revealed vertical air motions that earlier missions had not detected.

The name “Vega” combines Russian words associated with Venus and Halley. The mission is sometimes confused with Venera, the earlier Soviet Venus program, but Vega’s distinctive contribution was its paired balloon-and-lander descent systems and its later Halley flybys.