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Our Solar System - Mercury

By Edited Feb 2, 2016 1 1

This is part of a mini-series of articles about the planets in our Solar System


               You might not be able to hitchhike a spaceship to Mercury for the next 200 years, unless you have 100 billion dollars on your hands to fund the mission on your own, but here's the story of Mercury.

      1. How do we know about it ?

                 Since ancient times, astronomers have observed Mercury as a planet and gave it names. The chinese called it Chen Xing (the Hour Star), the Greeks called it Apollo and Hermes, because they thought they were seeing two different planets. However, they later realised it was really the same planet they were observing. The name of Mercury was given by the Romans, because it was the fastest moving planet on the sky. The earliest known observation comes from the Assyrians around the 14th century BC.

                 Now since human beings are so curious about stuff and want to know more about everything and experiment with things (which sometimes go "boom"), we've started studying the planets in great detail in the 2nd half of the 20th century. Radar was used to determine the rotation period of Mercury, which was thought to be 88 days, which meant that one side of Mercury would always face the Sun and the other always stayed in the dark, but they found out that the actual rotation period was 59 days.

      2. Facts about it

                It's time for a nice fact session (if you read fat session, read again):

Diameter:  4,878km (3,032 miles) at its equator

Orbit: 57,910,000 km (0.38 AU) from Sun. Orbiting the Sun once every 88 days.

Average Distance: About 58 million km (36 million miles)

Time to Rotate: 58.6 days

Mass: 5.5% of Earth's

                Now that's all great to know, but if you really want to go for some sightseeing, you should know, there's not much to see. First of all, we don't know much about it up close. But we do know it's way too close to the sun. Here's a picture to have a better idea about just how close:

Mercury in front of the sun

Photograph courtesy of NASA Goddard Space Flight Center

                 Because it's so close, Mercury is a furnace on one side and a freezer on the other. Average temperature ? 168 degrees Celsius. But here's a place where average doesn't give a good idea of the reality. The maximum temperature is 426 degrees Celsius, and the minimum is -173 degrees Celsius. Now, based on this, you might want to choose a landing site on the dark side of the planet, where you'll encounter ice and extreme auroras forming due to the sun's bombardment of the planet and the lack of appropriate atmosphere.

                 If that last sentence gave you a hint that there might be a tiny atmosphere around Mercury, you're right. Mercury retains particles that the sun blasts with each solar wind. It doesn't retain much, and it definetely doesn't hold on to them for long. So what Mercury actually has is an exosphere. And the sun is eating it away. Because of this and the lack of any worth-mentioning gravity, Mercury loses it's exosphere at a rate which allows for the creation of a comet-like tail, about 56000km long.

         3. On the ground! What should I wear?  Jeans ?

                Nah, you might want something like an actual space suit. I know it's not this year's fashion design, but hey, you need to breath and you need to cope with the cold temperatures, since we've established that going on the side facing the sun will make you into a not-so-nice human puddle. And you might want a few training trips to the moon to get aquainted with the low-gravity environment.

                 Sightseeing ? Sure, we've already mentioned the beautiful auroras that are forming on the dark side, but that's about it. But, bear in mind the surface. Mercury is one of the most asteroid-hit planets in the solar system. It has so many impact craters that it's simply useless to start counting them up. You'll probably look at a crater that is inside a crater and you'd probably be in a much larger crater that you can't even distinguish. Probably even the small rocks on the surface have impact craters on them. The planet surface is really old, and because there's no activity on the surface, other than objects impacting the surface, the craters are very well preserved over billions of years.

          4. Any way to get surface pictures without actually going ?

                  Not really, no. There haven't been many missions to Mercury and no probes have ever landed on the surface. There just isn't anything particular to see while on the surface that can't be observed from the orbit. And it's really hard to get there with a space probe. Reaching the planet consumes more fuel than it would be needed to escape the entire Solar System. Only two space probes have been to Mercury so far, with a third planned by the European Space Agency in joint cooperation with Japan. The second space probe sent, MESSENGER, was launched from the Earth in 2004 and it needed two close fly-bys of Mercury before being able to establish an orbit around it on March 18th 2011. Here's the image obtained on March 29:

Mercury from orbit 2011

First image from the orbit of Mercury, obtained by MESSENGER

Courtesy of NASA


                      You might want to wait before actually going there, maybe until you've actually visited all the other planets in the vicinity of the Earth. But hey, if you want the ultimate place to build a house where no one will ever bother you (just as long as it's under ground), this is the place to do it.




Jul 18, 2013 7:01am
Great article.The two contrasting temperatures,furnance and freezer creates the impression that the planet does not rotate on its axis.
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