Posted by: tyroscenva | March 12, 2008

Why does Mercury get so cold?

Question: Mercury is the closest planet to our sun. So why do nights on Mercury get so extremely cold if it’s closer to the sun than earth or even Venus?

On Mercury temperatures can get as hot as 430 degrees Celsius during the day and as cold as -180 degrees Celsius at night.
Mercury is the planet in our solar system that sits closest to the sun. The distance between Mercury and the sun ranges from 46 million kilometers to 69.8 million kilometers. The earth sits at a comfy 150 million kilometers. This is one reason why it gets so hot on Mercury during the day.

The other reason is that Mercury has a very thin and unstable atmosphere. At a size about a third of the earth and with a mass (what we on earth see as ‘weight’) that is 0.05 times as much as the earth, Mercury just doesn’t have the gravity to keep gases trapped around it, creating an atmosphere. Due to the high temperature, solar winds, and the low gravity (about a third of earth’s gravity), gases keep escaping the planet, quite literally just blowing away.
Atmospheres can trap heat, that’s why it can still be nice and warm at night here on earth.
Mercury’s atmosphere is too thin, unstable and close to the sun to make any notable difference in the temperature.

Space is cold. Space is very cold. So cold in fact, that it can almost reach absolute zero, the point where molecules stop moving (and they always move). In space, the coldest temperature you can get is 2.7 Kelvin, about -270 degrees Celsius.
Sunlight reflected from other planets and moons, gases that move through space, the very thin atmosphere and the surface of Mercury itself are the main reasons that temperatures on Mercury don’t get lower than about -180 °C at night.


  1. Wel… My guess is that the temperature difference has something to do with the absence of an atmosphere. So there is no substance in which heat can be trapped. Therefore the heat build-up will be lost during the night.

  2. It really helps me ona report im doin

  3. Thank you so much, this was amazing!!! It really helped me

  4. this really helped me and my friend

  5. I believe that there is another reason, in addition to the lack of a significant atmosphere, that Mercury gets so cold at night — It’s because Mercury rotates so slowly. A day (one full rotation relative to the sun) on Mercury is about 58 or 59 Earth days. While this means this means much longer “days”, it also means much longer nights. Thus, for any given place on Mercury, the sun is down for about 29 days. By going that long without any sun, it gives that given spot a long time to chill down. Just think — if Earth rotated that slowly, the nights would get much, much colder. Each night, even in the tropics, would probably resemble an Arctic winter!

  6. One more comment — The slow-rotation factor is the only explanation I can think of to account for the following fact: Mercury actually gets a tad colder at night than the moon does during its nights, even though the moon has even less atmosphere than Mercury does (if any at all), and mercury builds up much more heat during its “daytime”. A Mercurian day is about twice as long as a Lunar day.

  7. Very good of this.

  8. Mercury can be up to 800 degrees and as low as 279 degrees

    • why does some part on mercury have really cold parts why? plz anyone answer me

      • bcoz one side iz hot nd other will be cold……….The other reason is that Mercury has a very thin and unstable atmosphere

      • As mentioned above, all provinces on Mercury are exposed to the Sun for almost 90 earth-days at a time, and can reach temperatures over 700 K. Additionally, Mercury has no ambient atmosphere and very low gravity. Water ice on the surface of Mercury is exposed directly to vacuum, and will rapidly sublime and escape into space unless it is kept cold at all times. This implies that the ice can never be exposed to direct sunlight. The only locations on the surface of Mercury where this is possible would seem to be near the poles, where the floors of some craters might be deep enough to afford permanent shading. Whether such permanently shadowed craters exist on Mercury is still problematic. The only close-up images we have of Mercury were taken by the Mariner 10 spacecraft on three close passes in 1974 and 1975. The same hemisphere of Mercury was sunlit on each of these passes, so nearly half the planet has never been imaged, and no determination can be made of what polar areas, if any, are permanently shadowed. However, theoretical studies assuming typical crater dimensions show that craters near the poles should have areas which never rise above about 102 K (4) and that even flat surfaces at the poles would not exceed about 167 K (5). Other studies (6-7) also indicate that water ice in polar craters on Mercury could be stable over the age of the solar system.

  9. this made me cry

  10. Nice answer !

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