How The Hell Is There Ice On The Closest Planet To The Sun?

We have a very interesting question from the centre of the solar system that has niggled a follower since primary school.

So without further ado...

Stand by for an Ask ARSE in T-3, 2, 1...

"Hey guys, I remember a seriously weird fact from school for some reason that Mercury is colder than Venus for some reason despite being closer to the sun.

A recent article I lost in my newsfeed even said that there was ice on Mercury.

Just wondering if this is true and why/how?

I'm sure there's some reasoning behind it but it's got me itching with only a scratch ARSE can deliver. 

Cheers,
Davo"

A very good question David and one that we find ourselves answering a fair bit.

 

The answer to your query about Mercury and Venus with apparently counterintuitive temperatures is based in part on the composition and shape of either planet.

Understandably, the more distance between a planet and the sun the colder it is. 

Fact.

However, there are factors on the interior and exterior of planets that also plays a role.

Venus.

If you look at Earth, by rights we should be hotter than Mars, and due to our atmosphere - our precious, precious degrading atmosphere - we are lucky to have a type of filtration and trapping system that regulates heat. 

Funnily enough, the angle and lack of atmosphere on Mars has actually made the crusty brown warmer than us despite being 79 million kilometres further from the Sun. 

Although Venus is the second planet in the solar system it is still the hottest in the solar system with temperatures reaching in excess of 464ºC. 

The reason behind such a high temperature is the dense cloud cover surrounding the planet made up almost entirely of carbon dioxide.

This forms a blanket around the planet making it a metaphorical oven and the slight 3-degree tilt allows the temperature to remain fairly constant. 

The Earth's tilt is what gives us seasons, for example. 

Mercury.

Mercury is numero uno from the sun in our solar system and the smallest planet to boot meaning more suns rays envelop the entirety of the planet. 

Although the above is true, Mercury has no atmosphere therefore no heat is trapped making the day-to-day temperatures very extreme on both ends. 

During the day, the Sun will warm the planet to 427ºC in direct sunlight while other parts of the planet will face a chilly -93ºC. 

This means the average temperature of Mercury is just 167ºC. 

This shade and burn contrast to Mars also explains how there can be ice forming on a planet just next door to our sun. 

Funnily enough, the extreme heat on Mercury might actually help the formation of ice on the planet. 

Astronomers believe that the bulk of water on Mercury arrived as a special delivery from asteroids. 

And within the polar regions of Mercury where craters are abundant, ice could stay frozen forever. 

In 2012, David Williams - a team member of the NASA Goddard Space Flight Center said:

"Water 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 Mercury where this is possible would seem to be near the north poles where the floors of some craters might be deep enough to afford permanent shading."

The Messenger spacecraft confirmed the ice deposits on the north pole of Mercury in large craters that never see the sun in 2011.

There are also signs of ice deposits on the south pole of Mercury. 

How does water form on Mercury?

Although 90%of ice on Mercury is attributed to asteroid impacts. to determine the extra 10% means a bit of chemistry is needed.

Solar winds are charged particles that fly outwards from the sun and contain valuable protons that connect with the surface of Mercury. 

Within the planet's surface are groups of atoms called Hydroxyls that have one atom of hydrogen and one atom of oxygen. 

The heat from the sun "excites" these hydroxyls and send them away from the surface to collide forming water and hydrogen which drift around the surface of Mercury. 

A lot of these are degraded by sunlight, but when they are deposited in craters that protect the new water particles from the sun, ice will form. 

As mentioned earlier, the absence of an atmosphere means the dark cold of the crater will stay that way with no insulation from an atmosphere threatening the relatively constant -93ºC.

Should you be interested further, Thom Orlando and Brant Jones of GA Tech are committed to very interesting work in the field of ice formation on Mercury called "Recombinative desorption".

Check it out here.

We hope this has been enlightening for you Dave and all our dedicated readers out there thrusting into the deep unknown!

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