Most extreme temperature fluctuation Though mercury is the closest to the sun still it is the second most hottest planet of our solar system , but it does have the most extreme temperature fluctuations in the solar system. The temperature during the day can reach 840 degrees Fahrenheit (450 degrees Celsius), but at night, temperatures can get as low as minus 275 F (minus 170 C). That equals to a temperature difference of more than 1,100 F (600 C), the largest of any planet in the solar system. 2. Mercury has water ice and organic compounds This may sound surprising given that the planet is so close to the Sun, but the ice is in permanently shadowed craters that don’t receive any sunlight. Organics, a building block for life, were also found on the planet’s surface. While Mercury doesn’t have enough atmosphere and is too hot for life as we know it, finding organics there demonstrates how those compounds were distributed throughout the solar system. There’s also quite a bit of sul...