You know, I want to blog on deep-space tracking stations, but to do that I needed to review deep-space missions and before that I need to…Yeah. It’s a big subject so I’m going to break things down a bit just so I don’t get too out of control. Let’s just start with the planets in our solar system, and their moons. Don’t forget about the moons because they’re cool too.
Mercury is the closest planet to the sun and its orbit is highly elliptical, I mean all the planet’s orbits are elliptical, but Mercury is really, really elliptical with its aphelion, or furthest point being 69,816,900 km from the sun and its closest point or perihelion being 46,001,200. The cool animation below shows Mercury, Venus, and Earth orbiting the sun. Probably not to scale, but it shows a good comparison between Earth and Mercury orbit shapes.
Animation courtesy wikipedia: http://en.wikipedia.org/wiki/Mercury_%28planet%29
Mercury is way way smaller than Earth at 2439.km radius it is only 0.3289 Earths. Even though it’s small for a planet it is dense and has an iron core like earth. Two moons in the solar system are larger, Ganymede (a moon of Jupiter) and Titan (a moon of Saturn) but they don’t have as much mass. Mercury is dense since it’s made up of rock and metal – kind of like a gigantic asteroid.
Mercury’s surface resembles the surface of our moon – rocky and pock-marked. It experiences the greatest temperature swings between day and night at its equator: 800 deg F during the day and -280 deg F at night. At the poles, it never gets above -136 deg F. And we’re pretty sure there’s ice at the poles. And how do we know this?
We checked it out with ultra-cool space probes – the first one was Mariner 10 launched 11-03-1973 and it got this great shot of Mercury from 703 km away on 03-29-74:
First photo of Mercury by Mariner 10 – Kindly placed in the public domain by NASA.
“Mariner 10 was the first spacecraft to make use of an interplanetary gravitational slingshot maneuver, using Venus to bend its flight path and bring its perihelion down to the level of Mercury’s orbit. This maneuver, inspired by the orbital mechanics calculations of the Italian scientist Giuseppe Colombo, put the spacecraft into an orbit that repeatedly brought it back to Mercury. Mariner 10 used the solar radiation pressure on its solar panels and its high-gain antenna as a means of attitude control during flight, the first spacecraft to use active solar pressure control.” http://en.wikipedia.org/wiki/Mariner_10
Back then was when we figured out that Mercury was far more massive than we previously thought and has an iron core. It also has a magnetic field like Earth, but Mercury’s is far weaker than Earth’s. So Mercury has an iron core; and Earth has an iron core. And they both have magnetic fields. Well, ends up that the iron core on Mercury, and the iron core on Earth are very different; the magnetic fields generated by those cores depend on a different process…and it gets freaking complicated so Google it for extra-credit!
The point is, we learned a lot about Mercury from Mariner 10. But not enough. So we sent up MESSENGER August 3, 2004, (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft.
Image courtesy NASA.
And if you want to view the surface of Mercury as if you were riding along on MESSENGER, check out the video:
This is so amazing it is almost decadent. Think about it. You can sit at home or better yet, work, and cruise over Mercury. No, really, that’s Mercury.
NASA released this fact sheet at MESSENGER’s 10 year anniversary. Says it all.
And yes, it looks like there is ice at the poles. Where did it come from?