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Tue Nov 27, 2012, 02:07 PM

Mercury’s Shadowy North Pole



Many MDIS images were averaged together to create a mosaic of Mercury’s polar region, which this stereographic projection is centered on.

The largest centrally-peaked crater near the center is Prokofiev, named after a 20th-century Russian composer. Approximately 110 km (68 mi.) in diameter, its permanently-shadowed interior is home to radar-bright deposits that are thought to contain water ice.

Even though Mercury is almost three times closer to the Sun than Earth is and hosts searing daytime temperatures of 425ºC (800ºF), there’s virtually no atmosphere to hold or transmit that heat. Nighttime temperatures can reach as low as -185ºC (-300ºF), and since a day on Mercury is 176 Earth days long it gets very cold for quite a long time!
Also, because Mercury’s axis of rotation isn’t tilted like Earth’s, low elevation areas near the poles receive literally no sunlight. Unless vaporized by a meteorite impact any ice gathered inside these deep craters would remain permanently frozen.


Read more: http://www.universetoday.com/98651/mercurys-north-pole/

10 replies, 2194 views

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Always highlight: 10 newest replies | Replies posted after I mark a forum
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Arrow 10 replies Author Time Post
Reply Mercury’s Shadowy North Pole (Original post)
n2doc Nov 2012 OP
krispos42 Nov 2012 #1
1620rock Nov 2012 #2
Up2Late Nov 2012 #3
Thor_MN Nov 2012 #4
Art_from_Ark Nov 2012 #5
muriel_volestrangler Nov 2012 #6
reACTIONary Nov 2012 #8
muriel_volestrangler Nov 2012 #9
reACTIONary Dec 2012 #10
gtar100 Nov 2012 #7

Response to n2doc (Original post)

Tue Nov 27, 2012, 08:52 PM

1. There is an older Larry Niven short story...

...about a spaceship going to the coldest spot in the Solar System... the dark side of Mercury.


This was when it was believed that Mercury was tidally locked to the Sun.




So we could build an outpost at one of Mercury's poles in the permanent shadow of a crater wall, then arrange mirrors to point just enough sunlight at the colony to make it warm and comfy and well-lit!

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Response to n2doc (Original post)

Wed Nov 28, 2012, 10:13 PM

2. Could a spaceship approach that close to the sun to land at Mecury's pole?

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Response to 1620rock (Reply #2)

Thu Nov 29, 2012, 04:48 AM

3. Doubt it

...if you are talking a maned spacecraft. Not only is it hot, but their is probably a ton of solar radiation too.

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Response to n2doc (Original post)

Thu Nov 29, 2012, 08:32 AM

4. The Goldilocks crater

Just enough shadow, just enough sunlight..

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Response to n2doc (Original post)

Thu Nov 29, 2012, 09:49 AM

5. This is so fascinating

I have always been interested in space exploration, ever since the days of the Gemini and Apollo missions. Thanks for posting this

However, I think a correction is in order in the original article-- a day on Mercury is about 58 earth days, meaning that there is the equivalent of 29+ Earth days of uninterrupted sunshine and then 29+ Earth days of uninterrupted darkness.

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Response to Art_from_Ark (Reply #5)

Thu Nov 29, 2012, 11:09 AM

6. 58 days is the sidereal rotation period

ie the time for a star (effectively at infinite distance) to come back to the same position in the sky. But since Mercury's orbit period is 88 days, it takes longer than either for the Sun to get back to the same position in the sky, ie midday to midday - by the time Mercury has rotated once, relative to the stars, it's gone 2/3rds through its orbit, so it would have to rotate another 2/3rds to get the Sun in a similar position, ie another 39 days, and then a bit more to make up for how much further it went in that orbit, etc. The end result is the solar day is 176 days long. And for the purposes of the heating from the Sun, that's the day we're interested in.

Here's the NASA figures:

http://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html

--------------------------- Mercury Earth -- Ratio (Mercury/Earth)
- Sidereal orbit period (days) 87.969 365.256 0.241
Sidereal rotation period (hrs) 1407.6 23.9345 58.785
------- Length of day (hrs) 4222.6 24.0000 175.942

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Response to muriel_volestrangler (Reply #6)

Thu Nov 29, 2012, 10:12 PM

8. AND the Sun goes retrograde...

... from the surface of Mercury, the sun rises, progress higher in the sky, then goes BACKWARD back toward the sun rise point, then FORWARD again, higher in the sky and on down the other side for sunset.

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Response to reACTIONary (Reply #8)

Fri Nov 30, 2012, 04:16 AM

9. I'd never heard of that, but I see what you mean

because the orbit is very eccentric, Mercury's angular velocity around the Sun is more, for a short time, than its rotational angular velocity, so the Sun would appears to go backwards. The Wikipedia explanation:

At certain points on Mercury's surface, an observer would be able to see the Sun rise about halfway, then reverse and set before rising again, all within the same Mercurian day. This is because approximately four Earth days before perihelion, Mercury's angular orbital velocity exactly equals its angular rotational velocity so that the Sun's apparent motion ceases; at perihelion, Mercury's angular orbital velocity then exceeds the angular rotational velocity. Thus, to a hypothetical observer on Mercury, the Sun appears to move in a retrograde direction. Four days after perihelion, the Sun’s normal apparent motion resumes at these points.

http://en.wikipedia.org/wiki/Mercury_%28planet%29

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Response to muriel_volestrangler (Reply #9)

Sat Dec 1, 2012, 02:34 PM

10. Didn't understand the dynamics - Thanks for the explanation! (NT)

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Response to n2doc (Original post)

Thu Nov 29, 2012, 09:45 PM

7. If it's 800 degrees in the daytime and -300 degrees at night,

then at some point in the morning and evening it is a pleasant 72 degrees. Now if we could just hover around in one of those regions, we'd be all right (bring your own oxygen, of course).

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