A Day on Venus

Colorized perspective image mosaic of Vesusian surface from Venera 9. Photos by Venera 9 team, processing by Don P. MitchellCompared to Earth, our astronomical next-door neighbor Venus is 95 percent as large, 28 percent closer to the sun, and almost identical in planetary composition. However, if one wished to spend a day on Venus’s surface–from one sunrise to the next–one would be confronted with a considerable array of hindrances and novelties.

Assuming one could weather the journey through sulfuric acid clouds to reach the surface, survive the lead-melting heat, withstand the air pressure comparable to an ocean depth of 800 meters, and remain stationary against the constant thick breeze, the sun would not actually be visible as a single point, because all sunlight is diffused by a planet-wide cover of nearly opaque clouds.

The sun would be rising in the west rather than the east because Venus is “retrograde,” rotating in the direction opposite the sun and most of the other planets in the solar system. One hypothesis suggests that the planet was once “prograde” like most of the others, but that its spin was reversed by two massive planetoid impacts billions of years ago. Another hypothesis suggests that Venus’s original prograde spin was unstable due to the fact that the planet’s core, mantle, and atmosphere all move at different rates. Friction between these layers may have induced an increasing wobble on the entire planet, ultimately causing Venus to flip over. If that hypothesis is accurate, Venus is upside-down rather than backwards.

Venus’s rotation is also very slow. A full-day visit to Venus’s equator would include 1,401 hours of uninterrupted sunlight–or about 58 Earth days. At this rate, a fast jog would be enough to keep the sun-blob stationary in the sky. After sunset, one would observe another 1,401 hours of darkness, though there would be no change in temperature after dark–Venus has become isothermal due to the greenhouse effect, having an average temperature of 788°F (420°C) at every point on the planet: both poles and the equator, day and night. The coolest point on the planet’s surface is at the peak of its tallest mountain, Maxwell Montes, where the temperature drops to about 719°F (382°C). There, one might observe a heavy metal “snow” of lead sulfide and bismuth sulfide.

Venus completes an orbit of the Sun every 224.7 Earth days, so a Venusian year is almost–but not quite–two Venusian days in length.

Venera 9In the 1970s, the Soviet Union sent a series of ‘Venera’ probes to Venus with various scientific instruments. The heat and pressure plagued the probes with problems, and their operating times on the surface were measured in mere minutes. On 22 October 1975, Venera 9 became the first probe to return images from the surface of another planet, surviving for almost an hour, owing to a sophisticated liquid cooling system.

During the space race, the United States also had a Venus visit in mind. In the mid-1960s, NASA designed a manned flyby mission to Venus using modified Apollo hardware. Launch was scheduled for Halloween 1973, with a Venus fly-by set for 03 March 1974, and return to Earth on 01 December 1974. After liftoff, the astronauts would have a roughly one hour window to abort the mission in the event of a problem, after which time they would lack the fuel to return to Earth by any means other than a slingshot around Venus. The mission was scrapped due to budget constraints.

In 2020 scientists reported the discovery of phosphine in Venus’s atmosphere, which could be an indicator for airborne microbial life. However these data did not fare well in subsequent review, so it remains likely that Venus is a lifeless planet.

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