Friday, March 18, 2011
Originally thought to be two different planets, Apollo visible around dawn, and Hermes which could be seen at dusk. The Romans eventually named it Mercury after the God they equated with Hermes and the rest is celestial history.
It's so close to the Sun that the surface temps are in the 400C range on the bright side, and -170C in the shady part, and at the poles. Heavy, with a huge iron core at its center, Mercury moves very quickly. Its orbit around the sun takes 88 Earth days.
Because of the solar glare, very little was known about Mercury until it was mapped, 45% worth anyway, by Mariner 10 back in the mid 70s. That's when we found out with certainty that its cratered surface resembles our own Moon. Until then it was a crescent on the morning and evening horizons.
Because of the solar glare, very few people have ever seen Mercury outside of the usual suspects in the field. When you combine it's proximity to the sun, and the fact that you can only see Mercury when its orbit has taken it to either side of the sun, and then only when the sun has dipped just below our own horizon (with traditional equipment I mean, without a solar filter), it's not hard to understand why Mercury is elusive from an amateur astronomer's standpoint.
I find it fascinating that we've got a rocky inner planet that we know next to nothing about.
We know its size is small in relation to the other inner planets, (Saturn's moon Titan and Jupiter's Ganymede are larger) that it's got craters and maria like our Moon, that Mercury has no moon of its own, and the stuff about its magnetic poles and orbital mechanics. We know it has an equatorial radius of a little less than 2500 miles.
I know there are other details but those are the rough ones and that's really all we know, with certainty, about Mercury.
On August 3, 2004 NASA launched the spacecraft Messenger atop a Boeing Delta II rocket. Its voyage would carry it 5.9 billion miles, with a total of 15 trips around the Sun, once around Earth, a reasonably close first fly-by of the target in 2008, twice around Venus, with the final destination being the planet Mercury. Can't just fire a rocket at Mercury and hope to get there I guess, something to do with gravitational slingshots and changing trajectories but that shit makes my head hurt.
All I know is that there are people who do understand that stuff, and that those people calculated correctly, because at 9PM ET last night Messenger achieved orbital insertion around the planet Mercury.
And that is a first. Outward bound is the usual direction for the exploration of our solar system, and even with Venus it's more like next door. Even planetary missions that required a swing around the sun were eventually destined for out that-a-way.
Mercury is unique in this way. The mission is unique. They're going to map the remainder of the surface (30% was mapped 3 years ago when Messenger did it 1st fly-by of the planet), as well as look for traces of ice at the perma-shade points near the poles. Pretty weird to think ice could exist in a pizza oven, but there is that shadow line where 400C meets -175C.
What a bizarre environment Messenger entered last night.
The designers at Johns Hopkins University's Applied Physics Laboratory had to come up with a craft that could withstand the sun's rays in extremely close proximity, as well as enormous heat reflected by Mercury's planet surface. Messenger is rugged. It is shielded front at back by, essentially, heat screens that protect the scientific package contained within.
Messenger weighed a little over 2100 lbs when it launched in Aug. 2004, and over 1300 lbs of that was propellant required to slow the spacecraft as it approached Mercury and allow for orbital insertion. That doesn't leave much weight allowance for scientific instruments.
The mission itself hopes to finish mapping Mercury (in color), to examine its surface composition, its magnetic field and core, its magnetosphere, its atmosphere, and its polar regions.
Very ambitious to say the least, but nothing would have meant a damned thing if they hadn't pulled off one of the truly astounding feats of space rendezvous last night.
No do-overs, no fly-bys, no take-it-around and let's try a little steeper descent angle this time. One chance, and one chance only to correctly send signals from the Earth, which would fire Messenger's thrusters, and slow the thing down enough so that it could gently settle into orbit and not get sucked into the gigantic ball of hydrogen and helium glowing right next door.
Last night at 9PM ET, exquisite engineering and practically perfect mathematical calculations combined to accomplish a first in human history. We have arrived at Mercury.
Noteworthy I'd say.
Here I am, arrived at last to swoop around you
Like a glass and metal hawk, my electronic claws
Reaching down to snatch up data as I sweep o'er
Your mountains and meandering rupes.
Bathed in the flares billowing off this so-close star
Head down against the gusts of its golden solar wind
I am here to steal your secrets, reveal
The mercurial mysteries you have teased us with
For far too long, hiding here in the sun's blinding glare
Daring us, to stare at you.
I hope you have enjoyed your isolation, your surreptitious
Solitude, laying low here in Sol's radiation-thick glow
For I have come to finally Know you.
Unlike others of my kind, who find beauty in the billowing
Clouds of a bloated ball of gas, I am in love with stone.
So I am here to take countless two-tone portraits
Of your asteroid-blasted plains; lovingly paint
The great bulls-eye of Caloris in a million pixel shades
And immortalise your craters and canyons
In 21st century jpeg glory, for all those on the Waterworld to see.
Stuart Atkinson 2011