Why is Mercury the hottest and coldest planet in the solar system?

[Rob B]

I've read that Mercury is actually the hottest and coldest planet in the solar system since it always has the same face to the sun. I occured to me, however, that with Mercury being as small as it is and composed largely of iron, wouldn't the radiant heat from the sun facing side warm the surface sufficiently so that it would be at least warmer than say Neptune which is much further from the sun?

[Mr S]

A: It's not the hottest, Venus is.

B: It's not the coldest, Neptune is.

[sandmanboys]

1. Closest to the sun

2. No atmosphere

[RationalThinker]

Neptune generates it's own heat through atmospheric friction though.

[EVERYTHING]

1. Mercury is closest to sun
2. sun is a star, so at night it's a cold star. That's it's very cold there.

[Carlos_dfc]

Mercury isn't the hottest or coldest planet - but it does get close to both, and has the greatest temperature variation of all the planets by far.

Mercury has a day which lasts about 59 Earth days - this causes the surface to bake in the hot Sun for almost a month, and then face awy from the Sun, and freeze for almost a month.
Max temp gets to about 700K (about 627°C)
Min temp is around 100K (about -173°C)

Due to runaway greenhouse effect, Venus is about 735K (662°C)
Neptune averages about 85K (-188°C)
Uranus Averages about only a few degrees more than Neptune
And even Saturn can drop to -190°C in places