On which planet in our solar system is a year shorter than a day?
And the answer: Venus.
The rotation of Venus is the slowest of all of the planets in our solar system, taking 243 Earth days to make one rotation on its axis. But it takes only 225 Earth days to fully orbit the sun. This makes a year on Venus shorter than its day.
Scientists generally define a solar day as a single rotation of a planet around its axis. An orbit, on the other hand, is defined as the time it takes for a planet to make one complete round about the sun. Although Venus is very close in size to Earth, it is closer to the sun and therefore completes an orbit in less time (not only does it have less distance to go, it is also closer to the sun’s gravity, which keeps it moving relatively quickly).
Venus’ slow rotation is not its only quality that sets it apart from the bunch. It also rotates along its axis backward, or in the opposite direction that Earth rotates. This means that you could watch the sun rise in the west and set in the east on Venus!
However, the sun doesn't rise and set each "day" on Venus like it does on most other planets. On Venus, one day-night cycle takes 117 Earth days because Venus rotates in the direction opposite of its orbital revolution around the Sun.
Even though Venus isn’t the closest to the sun, it is the hottest planet in our solar system. Its thick atmosphere, full of carbon dioxide and sulfuric acid, traps heat to keep the surface of the planet burning hot. In fact, it’s so hot on Venus that metals like lead would quickly become puddles of melted liquid.