March 29 – Anniversary of the First Mercury Fly-by

nPostednon March 29, 2016

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nMercurynis one of the four rocky inner planets (and the smallest one – that’s it on the far right), so it seems it would benfairly easy to send robotic space probes to this planet. But Mercury is sonclose to the Sun, it was tricky for the NASA scientists and engineersnto design Mariner 10 to be tough enough to endure that environment.
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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.

nEvennthough the Sun is the ultimate resource necessary for all of Earth’snlife – giving the light and heat that we need – being close tonthe Sun means getting a whole lot of radiation, including way toonmuch heat as well as punishing doses of high-energy radiation.

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nSonthe Mariner needed shielding. It needed thermal blankets andnsunshades. The sunshade scientists devised ended up being aluminizednKapton and glass-fiber sheets covered with Teflon! The solar panels,nof course, could not be covered – their whole purpose was to soaknup the sun’s light so that they could make energy that the spacenprobe needed – but solar panels do not work if they get too hot. Sonscientists created a way to tilt the solar panels so that the rightntemperature was maintained. Finally, the hydrazine rocket nozzle hadnto face the Sun in order to work; the exposed parts of the rocketnnozzle were painted with special paint to reduce the heat flow to thenrest of the probe.

nMarinern10 was launched on November 3, 1973, and it did its first fly-by onnthis date in 1974. n

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nMarinern10 ended up flying past Mercury three times. It mapped between 40%nand 45% of the planet’s surface by taking 2,800 photos. It discoverednthat Mercury has an extremely thin and unstable atmosphere made upnmostly of helium, and it discovered that the planet has a magneticnfield, which shows that it has a large iron-rich core.

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This is one of the Mariner 10 photos
of Mercury.

nThenradiometer readings reveal that Mercury has nighttime temperatures ofn– 183 degrees Celsius ( -297 degrees Fahrenheit) and maximumndaytime temperatures of 187 degrees Celsius (369 degrees Fahrenheit).nSo that’s way more than twice as cold AND twice as hot as Earth.

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Mercury endures the greatest temperature
extremes of any planet in the Solar System.

nYounmay think to yourself, okay, I get the twice as hot part, sincenMercury is so much closer to the Sun. But why are the nights morenthan twice as cold as Earth?

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nThenanswer is that it is Earth’s atmosphere that keeps us relatively warmnat night,ncompared to places with little or no atmosphere – like the Moon andnMercury. In those places, the heat from the rocks radiates away quitenquickly, and then the cold of space is all that is left…

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