Friday, July 17, 2015 0

Today the NASA spacecraft sped past (the planet?) Pluto and made it’s closet approach at an altitude of around 12,500km. To date, nothing groundbreaking has been found out about Pluto although plenty of new information about the planet is due to be beamed back in the upcoming hour and days.

However, the event reminded me of a discussion I have most years with my students when I am teaching about solids, liquids and gases and the gas laws (you will now cover this part of the course in topic 1, Stoichiometric Relationships).

What we do know about Pluto is that it is a very cold world, with an average surface temperature of -228 oC or 45K and we also know that Pluto has an atmospheric pressure of 0.3Pa (compared to around 101,000Pa on Earth – making it around 330,000 times less than the pressure on Earth.

On a side note, I was mildly surprised at how ‘warm’ the plant actually is – given that space has a temperature of 2.7K or -270.3 oC – this means Pluto is around 40K or 4 oC warmer than space, which (to me) implies there must be some sort of atmosphere insulating the surface … but with such a low atmospheric pressure, would this be enough to warm up the planet so much? – but I digress, maybe I’ll ask a Physicist.

So linking back to the states of matter and the gas laws I pose my students this hypothetical question. If you were to stand on the surface of Pluto without a space suit on you would die (nobody disputes this) – but how would you die?

There are two possible scenarios:

1, As the temperature is so low, all the liquid in your body would free – your blood would freeze and so would your muscles. Your heart couldn’t pump your blood. Anybody finding you would find a frozen you.

Or,

2, As the pressure is so low you would explode – the air in your lungs and oxygen and nitrogen in your blood would expand rapidly – blowing you apart – there wouldn’t be much of you left for anyone to find.

So what do you think would happen? It would be great to read your thought below.

I do sometimes offer a third alternative – would somehow the effect of low temperature and low pressure cancel each other out and would you somehow be left with a (dead) person with liquid air in their lungs?

What do you think?

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