We all know that Mercury's surface temperature varies a lot from day to night, from 427 °C in a day dropping down to −173 °C at night.

Mercury has a hot molten outer core inside it. How can it suddenly change its surface temperature in the night time? Is its inner core made of metal with icy water, methane and ammonia similar to Neptune?

  • $\begingroup$ It's not exactly sudden - have you checked how long a day is on Mercury? $\endgroup$ – M. Enns Jul 22 '16 at 15:35
  • $\begingroup$ i actually mean the dark side of mercury. $\endgroup$ – Nani Hari Jul 22 '16 at 15:37
  • $\begingroup$ Maybe you can get (even) more answers if you ask this question on astronomy.stackexchange.com too. :) $\endgroup$ – Kevin Jul 22 '16 at 15:45
  • $\begingroup$ @NaniHari, does my answer properly answer your question? $\endgroup$ – heather Jul 22 '16 at 15:52
  • $\begingroup$ No, did not a find proper answer. $\endgroup$ – Nani Hari Jul 22 '16 at 16:02

So, scientists were surprised when they found that Mercury has a molten core. Since small planets (like Mercury) cool rapidly, the core should've frozen a while ago.

In a nutshell, though, whether or not the core stays molten over time depends on the composition of the core...as this website says,

Maintaining a molten core over billions of years requires that it also contain a lighter element, such as sulfur, to lower the melting temperature of the core material.

Mercury's core is also known to have an impressively high iron content. The interior structure of Mercury is shown below...the core is a significant portion of Mercury.

mercury interior

Then, for why Mercury's surface temperature can change - think of Earth, real quick. We have a molten core too, but it can get pretty cold or hot on Earth's surface...and that's with a stable atmosphere that helps regulate things and our prime position (not to far and not to close to the sun). The temperature difference would be even wilder on Mercury where there isn't a protective atmosphere and it's really close to the Sun.

Hope this helps! This website has a lot of useful information about Mercury.

  • $\begingroup$ Yes,Mercury is so very close to sun, to change temperature with that difference, i feel it must a Mental inner core like Neptune covered with a molten outer core may be made up of sulfur. $\endgroup$ – Nani Hari Jul 22 '16 at 15:56
  • $\begingroup$ @NaniHari, from the little research I've done, I doubt the core is much like Neptune's. $\endgroup$ – heather Jul 22 '16 at 16:06

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