How hot is Mercury? Well, that depends on where you are on the planet’s surface. There is a tenuous, at best, atmosphere on Mercury. That means that the planet does not retain the heat it receives from the Sun as it rotates. The side facing the Sun is amazingly hot, around 700 Kelvin (430 °C), yet that same place on the planet can plunge to 110 Kelvin (-163 °C) when it is on the dark side. Due to the planets axial tilt, some parts of the poles never receive sunlight and can stay at 90 Kelvin (-183 °C). Given those figures, the average(median) temperature of the Mercurian surface is 452 Kelvin (179 °C).
Mercury is the smallest planet in the Solar System and orbits the Sun every 87.969 Earth days. At this time it does not have a moon, but some scientists speculate that it may have had a moon in the ancient past. It is their contention that the orbit of Mercury’s moon decayed and it impacted the surface of the planet. The planets has an apparent magnitude that ranges from 2.3 to 5.7 and would easily be seen with the unaided eye if it were not so close to the Sun.
Scientists are very interested in Mercury. It is one of the least understood planets in the Solar System. Mariner 10 was the first spacecraft to visit the planet, but could only map a small portion of its surface. The MESSENGER spacecraft is currently in orbit around Mercury and is sending back images that are revealing a great deal of information. Scientists had hoped to find evidence of water ice at the frozen polar regions. That has not happened, yet, but they have found evidence of water in the exosphere, visual evidence of past volcanic activity, and evidence of a liquid planetary core.
How can there be water on a planet that nearly boils in the solar wind? NASA scientist Thomas Zurburchen notes three possibilities: First, there may be reservoirs of water ice in small areas of Mercury’s poles(this water could be as old as the Solar System). Next, comets may have deposited. Third, chemical sputtering could create water from the solar wind and Mercurian rock.
Well, not only do you have the answer to how hot is Mercury’s surface, but a few interesting facts that could impress your friends and teachers.
We’ve also recorded an entire episode of Astronomy Cast all about Mercury. Listen here, Episode 49: Mercury.