> Which planet's poisonous atmosphere is attributed to the "runaway greenhouseeffect?"> And the answer: Venus. Photo credit: NASA.The second closest planet to the sun, Venus is also thehottest and brightest planet in our solar system. It has a toxic atmospherefilled with carbon dioxide and is shrouded in clouds of sulfuric acid.Venus is one of the most unique planets in our solar system. Not only is itsatmosphere toxic, hot and barren, but it is a planet which takes longer torotate on its axis than it does around the sun. Effectively, this means that aday on Venus is longer than a year. On top of that, Venus is hotter thanneighboring planet Mercury— which is closer to the sun. This is due to the highamount of carbon dioxide which gets trapped in the atmosphere. But wait: the Venus fun facts don't end there. This peculiar planet doesn't justrotate around its axis slowly— it actually rotates in a direction unlike everyother planet in our solar system. While all other planets spin counterclockwiseon their axis and orbit the Sun in a counterclockwise direction, Venus orbitsthe Sun counterclockwise... and spins clockwise! This unusual axis rotation isactually due to the fact that the planet is upside down– it was knocked off itsupright position earlier in its history! The only other planet to spin in astrange direction is Uranus, which spins on its side. Both of these events arebelieved to be the result of another collision early on in the planets' life.Venus is also the second-brightest natural object in the night sky, after theMoon. It turns out that those clouds of sulfuric gas actually do serve somegood— the planet is able to reflect light with ease, making it appear bright andshiny in the night sky. For this reason, Venus was the first planet to have itsmotions plotted across the sky as far back as 2 BCE.Learn more about Venus here[https://solarsystem.nasa.gov/planets/venus/overview/].