Claim: The terrestrial planet with the densest atmosphere is Venus.

Venus is the second planet from the Sun , orbiting it every 224.7 Earth days . It has the longest rotation period -LRB- 243 days -RRB- of any planet in the Solar System and rotates in the opposite direction to most other planets . It has no natural satellites . It is named after the Roman goddess of love and beauty . It is the second-brightest natural object in the night sky after the Moon , reaching an apparent magnitude of − 4.6 , bright enough to cast shadows at night and , though rare , occasionally be visible in broad daylight . Because Venus orbits within Earth 's orbit it is an inferior planet and never appears to venture far from the Sun ; its maximum angular distance from the Sun -LRB- elongation -RRB- is 47.8 ° .   Venus is a terrestrial planet and is sometimes called Earth 's `` sister planet '' because of their similar size , mass , proximity to the Sun , and bulk composition . It is radically different from Earth in other respects . It has the densest atmosphere of the four terrestrial planets , consisting of more than 96 % carbon dioxide . The atmospheric pressure at the planet 's surface is 92 times that of Earth , or roughly the pressure found 900 m underwater on Earth . Venus is by far the hottest planet in the Solar System , with a mean surface temperature of 735 K , even though Mercury is closer to the Sun . Venus is shrouded by an opaque layer of highly reflective clouds of sulfuric acid , preventing its surface from being seen from space in visible light . It may have had water oceans in the past , but these would have vaporized as the temperature rose due to a runaway greenhouse effect . The water has probably photodissociated , and the free hydrogen has been swept into interplanetary space by the solar wind because of the lack of a planetary magnetic field . Venus 's surface is a dry desertscape interspersed with slab-like rocks and is periodically resurfaced by volcanism .   As one of the brightest objects in the sky , Venus has been a major fixture in human culture for as long as records have existed . It has been made sacred to gods of many cultures , and has been a prime inspiration for writers and poets as the `` morning star '' and `` evening star '' . Venus was the first planet to have its motions plotted across the sky , as early as the second millennium BC .   As the closest planet to Earth , Venus has been a prime target for early interplanetary exploration . It was the first planet beyond Earth visited by a spacecraft -LRB- Mariner 2 in 1962 -RRB- , and the first to be successfully landed on -LRB- by Venera 7 in 1970 -RRB- . Venus 's thick clouds render observation of its surface impossible in visible light , and the first detailed maps did not emerge until the arrival of the Magellan orbiter in 1991 . Plans have been proposed for rovers or more complex missions , but they are hindered by Venus 's hostile surface conditions .