While Mercury is the closest planet to the Sun, it is not the hottest. The hottest planet in our solar system is Venus, a world farther from the Sun. This highlights the factors that govern a planet’s surface temperature.
Mercury’s Extreme Temperatures
Mercury orbits closer to the Sun than any other planet. During the day, temperatures can soar to 430 degrees Celsius (800 degrees Fahrenheit) due to direct solar radiation. However, Mercury possesses an incredibly thin atmosphere. Without a substantial atmosphere to trap heat, warmth rapidly escapes into space at night. This results in nighttime temperatures plummeting to -180 degrees Celsius (-290 degrees Fahrenheit), creating the most dramatic temperature swings in the solar system.
Venus’s Scorching Surface
Venus, the second planet from the Sun, is located at an average distance of about 108 million kilometers (67 million miles). While it receives less solar radiation than Mercury, its surface temperature is consistently higher. Venus holds the record for the hottest planet, with an average surface temperature of around 462 to 475 degrees Celsius (863 to 900 degrees Fahrenheit). This temperature is hot enough to melt lead.
The planet’s atmosphere is remarkably dense and is primarily composed of carbon dioxide, accounting for about 96.5% of its atmospheric gases. Thick clouds of sulfuric acid perpetually shroud the planet, contributing to its distinct appearance. The atmospheric pressure at the surface of Venus is also extreme, being approximately 90 to 92 times greater than Earth’s atmospheric pressure at sea level.
The Atmospheric Anomaly
The stark contrast in temperatures between Mercury and Venus can be attributed primarily to their atmospheres. Mercury’s virtually non-existent atmosphere offers no insulation, allowing any absorbed solar energy to quickly radiate back into space. This leads to its drastic temperature fluctuations between day and night. The planet essentially has no thermal blanket to retain heat.
In contrast, Venus’s thick, carbon dioxide-rich atmosphere acts as a highly effective insulator. This dense atmospheric blanket traps solar heat, preventing it from escaping back into space in a process known as the greenhouse effect. Even though Venus’s thick clouds reflect a significant portion of incoming sunlight, the heat that does penetrate is efficiently retained. This continuous heat trapping mechanism is the reason for Venus’s consistently high and stable surface temperatures, day and night. The immense atmospheric pressure also contributes to its ability to retain heat.