Posted
on March 29, 2016
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| The fact that Mercury is so close to the Sun makes it difficult for us to see it in our skies. It tends to be lost -- or almost lost -- in the Sun's glow during dawns and sunsets. |
Even
though the Sun is the ultimate resource necessary for all of Earth's
life – giving the light and heat that we need – being close to
the Sun means getting a whole lot of radiation, including way too
much heat as well as punishing doses of high-energy radiation.
So
the Mariner needed shielding. It needed thermal blankets and
sunshades. The sunshade scientists devised ended up being aluminized
Kapton and glass-fiber sheets covered with Teflon! The solar panels,
of course, could not be covered – their whole purpose was to soak
up the sun's light so that they could make energy that the space
probe needed – but solar panels do not work if they get too hot. So
scientists created a way to tilt the solar panels so that the right
temperature was maintained. Finally, the hydrazine rocket nozzle had
to face the Sun in order to work; the exposed parts of the rocket
nozzle were painted with special paint to reduce the heat flow to the
rest of the probe.
Mariner
10 was launched on November 3, 1973, and it did its first fly-by on
this date in 1974.
Mariner
10 ended up flying past Mercury three times. It mapped between 40%
and 45% of the planet's surface by taking 2,800 photos. It discovered
that Mercury has an extremely thin and unstable atmosphere made up
mostly of helium, and it discovered that the planet has a magnetic
field, which shows that it has a large iron-rich core.
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| This is one of the Mariner 10 photos of Mercury. |
The
radiometer readings reveal that Mercury has nighttime temperatures of
– 183 degrees Celsius ( -297 degrees Fahrenheit) and maximum
daytime temperatures of 187 degrees Celsius (369 degrees Fahrenheit).
So that's way more than twice as cold AND twice as hot as Earth.
 |
| Mercury endures the greatest temperature extremes of any planet in the Solar System. |
You
may think to yourself, okay, I get the twice as hot part, since
Mercury is so much closer to the Sun. But why are the nights more
than twice as cold as Earth?
The
answer is that it is Earth's atmosphere that keeps us relatively warm
at night,
compared to places with little or no atmosphere – like the Moon and
Mercury. In those places, the heat from the rocks radiates away quite
quickly, and then the cold of space is all that is left...
Also
on this date:
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ahead:
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