The surface of Mercury is a many-splendored thing. Let me put us into context: Mercury, the first planet in our Solar System, named for the messenger of the gods because of its fleet-footed movements across the sky.

Mercury is extremely difficult to view by telescope because it is so close to the sun. That means that whenever Mercury rises in the night sky, the sun is close behind it, or in front of it, making it extremely difficult to see. The giant, looming sun also poses the greatest difficulty in sending a spacecraft to the planet, which is the other reason that so little of it has been seen or mapped even though its existence has been known since thousands of years B.C. According to the people on the MESSENGER mission, the sun on Mercury would appear about three times as large as it does here on the Earth and would be 11 times as bright.

To send a spacecraft into orbit around Mercury requires incredible precision and a lot of planning. Mariner 10, the first spacecraft to view Mercury, was a flyby mission, meaning that it went into orbit around the sun at an orbit comparable to Mercury's, and then took pictures of the planet every time their two orbits intersected. This was over 30 years ago, and it was the first time that anyone had used the gravity of another planet (in this case Venus) to help the spacecraft along its way and to save the fuel it would take for course corrections.

It wouldn't take very long to fly a spacecraft straight at Mercury. However, by the time it arrived, it would be traveling at a tremendous speed, and the amount of fuel it would take to fight the ever-growing gravitational pull of the sun (which scales as a square to the inverse radius) would be unfeasible. Instead, the spacecraft travels towards Mercury in circles around the sun with ever lessening radii. In the case of MESSENGER, at the moment that the spacecraft was launched, it is traveling the same speed as the Earth, which is a little bit less than 70,000 mph. After making some changes in its speed and direction, it flies for a year before encountering the speeding Earth again. This time it uses the gravity well of the Earth to help modify its speed and direction, and it makes a slightly smaller circle which lines it up to intersect with the planet Venus. MESSENGER had two Venus flybys, each about a year apart and each modifying the trajectory just a bit, until it finally moved into the orbit of Mercury. You can control the way that a planet affects your flight path by planning how fast you will be going with respect to the planet (You can change this by changing your angle of approach) and how far away you are when you fly by (which changes the magnitude of the change that the planet can make in your trajectory).

On January 14th, the spacecraft flew by Mercury in the first of three flybys that it will complete before orbital insertion. Each flyby will slow down the spacecraft and prepare it to burn its thrusters and be captured by the gravity of the small planet. It is a great difficulty to avoid being drawn in by the immense gravity of the sun and to catch the gravity of the tiny planet Mercury.

um... I'll have to continue this later...

Please do.
I never quite new the details of interplanetary probes. Thanks!
» middaymoon on 2008-01-21 01:00:38

Please do.
I never quite knew the details of interplanetary probes. Thanks!
» middaymoon on 2008-01-21 01:00:45

.. x_x; will it still be over my head then?
» Dilated on 2008-01-21 06:19:21

You should write a book... or an article for a popular science magazine!

I like your writing, Zanzi. It is very interesting.
» jinyu on 2008-01-21 06:35:52

hey thanks for the comment, i wish i had read it that day i would've felt a lot better :)

and WOW, that was an amazing entry. i got lost a couple times in the paragraph about the messenger but it was still really interesting!! is this what you do for a living?
» chocobopnai on 2008-01-23 11:04:02

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