0 WHAT IS THE HOTTEST PLANET IN OUR UNIVERSE?

VENUS!

The surface of Venus is often said to resemble Hell.

Ok, so the universe is too huge for such a question.  As a matter of fact all articles I read pointed to venus... until I came across a more recent artilce -
Scientists discover the hottest planet in the universe... where the temperature is a scorching 3,200C!  - Jan 2011
A planet they called WASP-33b - which now means, if they discovered this hot planet, then they will eventually discover others since, obviously, there are more out there.  However, I'll go on about Venus since it's in our Solar System and a planet with a name we're all familiar this side of our universe!

Now you would think the hottest planet in the universe would be Mercury since it's the planet that orbits closest to the sun.  It receives more sunlight per square meter than any other planet in the Solar System but NO!  The hottest planet is Venus!

The side of Mercury facing the Sun can get as hot as 700 Kelvin (426 degrees Celsius). But without an atmosphere to trap the heat, the side facing away from the Sun gets down to only 100 Kelvin (-173 degrees Celsius).  Venus, on the other hand, has a very dense carbon dioxide atmosphere. The atmosphere acts like a blanket, trapping the heat, and keeping the planet very hot.  The atmospheric mass is 93 times that of Earth's atmosphere while the pressure at the planet's surface is about 92 times that at Earth's surface—a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans. 
The temperature of Venus is 735 Kelvin (461 degrees C) everywhere on the whole planet. And that makes Venus the hottest planet in the Solar System!

Studies have suggested that several billion years ago the Venusian atmosphere was much more like Earth's than it is now, and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.

Fast Fact:

Venus rotates about its axis in the opposite direction to most planets in the Solar System.

Source(s):  universetoday.com, wikipedia,