Question

What are the distinguishing characteristics of Venus?

Answer 1

Hottest planet in the solar system with very dense and thick atmosphere of CO2 thanks to an extreme runaway greenhouse effect

Explanation:

Venus' special qualities compared to Earth:

A great compilation of facts about Venus: http://www.space.com/44-venus-second-planet-from-the-sun-brightest-planet-in-solar-system.html

Much of Venus' high temperature and unique atmosphere is thought to be because of a runaway greenhouse effect: a self-feeding cycle of atmospheric CO2 trapping solar radiation as heat on the planet:

--> raising the temperature
--> boiling away all water (which stored carbon away from the atmosphere and prevented it from trapping heat)
--> releasing more CO2 into the atmosphere
--> trapping more heat
--> until there's an equilibrium between how much heat can escape vs stay trapped on the planet (at a toasty 730 Kelvin surface temperature)