Ok, today I’d like to talk about a planet named by the Romans… It’s the planet they observed moving much faster than any other planet… I guess you know I’m talking about Mercury.
Actually, scientists are only recently beginning to learn more about Mercury.
Well, maybe you can start off this discussion by telling me what you know about Mercury.
Okay. Anything else?
I think it’s the size of our moon… Or is that Pluto?
Actually, you’re correct. It is the size of our Moon. Uh, any other comments? … Nothing more?
Well, my point exactly. Many planets are discussed in great length and detail, but most teachers tend to skim over Mercury, because there really isn’t much to say, except that it’s very much like our moon in color, surface area, and lack of atmosphere.
Ok, one big reason why we don’t have a whole lot of information about Mercury is that it’s so close to the Sun.
It’s difficult to observe Mercury from Earth’s telescopes because Mercury appears to be only 28 degrees from the Sun.
So it’s lost in the glare of the Sun much of the time.
What this means is, we can only look at it just before sunrise or a little after sunset.
And even then, Mercury appears very low on the horizon, and that makes it even harder to observe.
Now, it’s true the Mariner 10 visited Mercury 3 times, and took around 2700 pictures.
And from these pictures, scientists were able to make an analysis and give us the most information yet about the planet.
All right, let’s turn to what these photos revealed about Mercury.
First of all, let me say something about what the Mariner 10 learned from its go-round of the planet.
Okay… In the early 1880s, Schiaparelli… let me write this down… Giovanni Schiaparelli determined that Mercury rotates just once each time it orbits around the Sun.
He also believed that as it rotates, it keeps one face directed toward the Sun at all times.
This is the same way the Moon orbits the Earth.
Then in 1965, scientists calculated that Mercury rotated every 59 days, give or take 5 days.
This means that the planet rotates three times for every two times it orbits the Sun.
So the ratio is three to two, not one to one.
The Mariner 10, however, was able to determine, through its specially-designed instruments, that the rotation is actually 58.646 plus or minus 0.0005 days.
So… the technology used on board the Mariner not only confirmed existing knowledge but also made that knowledge more accurate.
Ok… and another thing that the Mariner 10 learned is that Mercury has a magnetic field that is about 100 times weaker than Earth’s.
The interesting thing about this is… for a planet to have a magnetic field, it has to have a core that is partially molten, that is, liquid metal or rock.
But scientists had assumed that Mercury’s iron core had become cold and solid after all these billions of years.
So, remember that a solid core does not produce a magnetic field.
But the Mariner 10 did detect a magnetic field, yeah, a weak one, it’s true, but nevertheless there was a magnetic field coming from Mercury.
But… scientists can’t really say for sure what’s causing this.
Another point is… a planet with a magnetic field should exhibit some geological activity… you know, earthquakes, plate tectonics, or volcanic eruptions… But Mercury has none of this activity.
Actually there is currently no volcanic activity.
At some point perhaps billions of years ago there might have been volcanoes… because Mercury has hardened lava flows today.
Anyway, the Mariner 10’s flybys did unearth new information about Mercury, but it sure did raise other questions as well.
All right, I wanna talk about the pictures now.
The pictures that Mariner 10 took covered about 45 percent of the surface of Mercury.
That may not seem like much… I mean, that’s less than half of the planet, but the pictures remind us a lot of the Moon, I mean basically, the surface of Mercury resembles lunar terrain.
In fact, if you compare the pictures I have up on the board, it may be difficult to tell the difference unless you’re really familiar with the terrain of both these spheres.
So… as you can see, Mercury’s surface is pockmarked with craters, lava flows, and very large multi-ring basins.
Ok, let me point out a few other similarities between the Moon and Mercury.
They both have thin atmospheres, and this makes them easy targets for meteorites and other debris… So you can see why they both look pockmarked and kind of cratered.
Both also have temperature extremes… Mercury goes down to minus 170 degrees Celsius at night and 350 degrees Celsius during the day, and the Moon’s temperature also ranges from minus 100 to 340.
So, they’re really similar, huh?
Now, the only big difference between them is density.
OK, so the moon’s lower density suggests that it’s made of mostly igneous rock from lava flows.
But Mercury’s higher density means that it has an iron core.
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