Anyone who learned “My Very Educated Mother Just Served Us Nine Pizzas” in school had to reassess things back in 2006. That year, the International Astronomical Union declared that Pluto (the “Pizzas” in that famous mnemonic device) was no longer considered a full planet on par with its eight ex-siblings.
In this episode of Misconceptions, host Justin Dodd breaks down the reasoning (and controversy) behind that decision, and discusses one popular myth about each planet in the solar system.
You might think that Mercury is the hottest planet in the solar system, for example. It is, after all, the closest to the sun. Its oval-shaped orbit brings it as near as 29 million miles to the sun and up to 43 million miles away from it. But even at that relatively close proximity, it still has a warmer neighbor.
Mercury’s average daytime temperature can reach 800°F; its nighttime average plunges to -290°F, which is far too cold to sustain life, as far as we know. The main reason for the big swing in temps is the planet’s lack of atmosphere. On Earth, the atmosphere protects us from solar radiation and insulates the planet from extreme temperature variations. Mercury has none of these perks. Instead, it has an exosphere of oxygen, sodium, hydrogen, and other atoms that have been scoured off Mercury’s surface by blasts of solar wind and meteoroid impacts. With no cozy atmospheric blanket to trap heat, Mercury loses the warmth it absorbs during its days. Venus, in contrast, can reach a scorching 900°F.