Hello, I'm Dr. Astro, a planetary scientist specializing in the atmospheres and surface conditions of the inner solar system. I've dedicated my career to understanding the extreme environments found on Mercury and Venus, the two planets closest to our Sun.

When discussing the heat of Mercury and Venus, we must consider two key factors: surface temperature and internal temperature.

Let's start with surface temperature. Mercury, the closest planet to the Sun, experiences the most extreme temperature swings in the solar system. Its lack of a significant atmosphere means that there's no way to trap heat, leading to massive temperature differences between day and night. During the day, Mercury's surface can reach a scorching 430 °C (800 °F), hot enough to melt lead. However, as soon as the Sun sets, the temperature plummets to a frigid -180 °C (-290 °F). This drastic fluctuation is due to Mercury's incredibly thin atmosphere, which doesn't provide any insulating effect.

Venus, on the other hand, boasts a dense, toxic atmosphere, primarily composed of carbon dioxide. This thick atmosphere traps heat through a process known as the greenhouse effect, making Venus the hottest planet in our solar system. While Mercury experiences extreme swings in temperature, Venus maintains a remarkably constant surface temperature of about 464 °C (867 °F), regardless of day or night. This extreme heat is primarily driven by the runaway greenhouse effect, where the thick atmosphere traps solar radiation and prevents it from escaping back into space.

Now, let's talk about internal temperature. While surface temperature is influenced by external factors like solar radiation and atmospheric composition, internal temperature is determined by the planet's internal heat source, which primarily comes from radioactive decay within its core. While Mercury and Venus have relatively small cores compared to larger planets like Earth, their internal temperatures are still significant.

Mercury's internal temperature is estimated to be around 1,600 °C (2,900 °F), while Venus's internal temperature is believed to be around 2,500 °C (4,500 °F). This internal heat drives geological activity on both planets, though to a lesser degree than Earth.

To sum it up, Mercury's surface temperature is extremely variable, reaching extreme highs during the day and plummeting to frigid lows at night. However, Venus's dense atmosphere traps heat, resulting in a consistently scorching surface temperature that makes it the hottest planet in our solar system. While both planets have significant internal heat, their surface temperatures are determined by their atmospheric composition and distance from the Sun.

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Mercury sure is hot, but Venus is hotter. Venus is much further from the Sun, orbiting at a distance of more than 108 million kilometers. Average temperature there is a hellish 735 Kelvin, or 462 degrees Celsius -C hot enough to melt lead. Venus remains that same temperature no matter where you go on the planet.read more >>