Archive | May, 2016

Size Matters D.5.31

31 May

If a planet is larger, because it’s bigger, because it has more gravity, the escape velocity is lower and so whatever atmosphere you do make tends to stay with you because it gets harder to escape.

The other thing about being large enough to have a still warm core is you drive convection in the interior, and if the planet is rotating quick enough, then you get a protective magnetic field, which puts your atmosphere in a cocoon. This shields it from the solar wind from stripping away your atmosphere as well. So, there’s a whole host of a litany of benefits from being larger rather than smaller for a terrestrial planet.

Planet Size D.5.30

29 May

Start with size. Essentially, larger planets retain their heat allowing them to have volcanism, and plate tectonics, erase impact craters, all of that. For example, a small terrestrial planet where the interior cools relatively quickly – Once the interior cools that becomes the end of volcanism and plate tectonics.

Once you end volcanism then that ends the outgassing of gas from the interior; in other words it ends the atmosphere building process. Then because you’re relatively small, the escape velocity for particles going out is relatively low so any atmosphere that you do have is lost to thermal escape.

And so we have a couple of good examples of that in our solar system, Mercury and the moon are like this, Mars in on its way – Being relatively smaller planets and everything that that implies.

On the other hand, on larger terrestrial planets, something like Venus or Earth, that are large enough that they are still warm in their interior with the molten iron core, which causes convection, which causes heat, which then drives volcanism and plate tectonics. It drives an active erosion process, where the ancient craters are erased. Because you’ve got volcanism going on, you’ve got the process of outgassing happening, so you’re building your atmosphere around the planet.

Geological Processes D.5.29

28 May

Erosion takes place much more easily on a world that has a significant atmosphere or had a significant atmosphere. For example Mars had a more significant atmosphere. When erosion was a lot more prevalent you could see what looks like a river bed – A river bed delta from the Mars Global Surveyor.

There are our four processes that shape geological processes, that shape planetary surfaces.

We have impact crater.

We have volcanism.

We have tectonics.

And we have erosion.

There are basically three reasons why the terrestrial planets have different histories. Size, distance from the sun, and rotation.

Erosion Break Downs D.5.28

27 May

Erosion is the break down and the transport of rocks by volatiles. Volatiles mean that something evaporates easily. Examples of volatiles include things like water, H2O, carbon dioxide, CO2, and methane, CH4.

Gasses, liquids or solids – Erosion breaks down existing geological features such as mountains, river beds, ultimately a little bit of Meteor Crater as it begins to erode. You can see how water has run down the sides starting the process of erosion at the Meteor Crater.

But besides breaking down features it can also build new features that can build things like sand dunes, glacial deposits. One of the real prime examples of erosion on Earth is located at the Grand Canyon. You can see some spectacular evidence of erosion of water cutting through rock over the last few 100 millions of years or so.

Tectonic Activities D.5.27

26 May

Tectonic activity on earth is always accompanied by earthquakes. The Ring Of Fire around the world on the South America up through North America, on over Alaska, on over to Russia, down through Japan and over across the South Pacific islands. This is a region of very high tectonic activity, and hence a lot of volcanic activity. And anybody who lives on the west coast of the USA or the west coast of South America is certainly familiar with that tectonic activity.

Undoubtedly, planet quakes occur on other worlds, and so geologists are often quite interested in placing a little modern Micro seismometers on other planets to measure those quakes. Those have been placed on the Moon, and so we can measure the seismic activity of the Moon and Mars as well. Some of those have been placed on some of the Martian rovers that have come on down.

And the Mountain Ranges D.5.26

25 May

If the convection cells come together you can cause compression stresses and this can make mountain ranges. This is as that material comes together.

Another way to cause stresses on a planet’s surface is through the temperature. So if either you heat the surface up through, for example, radioactive decay, or you cool it down, just because a planet is dying of its internal heat, it’s losing its internal heat you can crinkle the surface.

Mercury is a good example of this. Mercury has lost most of its internal heat and so that surface is crumpling, sort of like tin foil or paper, around the surface of the planet. And you see evidence of this on what are called scarps. A very sharp like cliff structure caused from the planet basically shrinking, its skin wrinkling around its core as it goes on cooling down.

The rolling of Convections D.5.25

24 May

So on planets with convections it has this internal convection rolling. The hot stuff rises up cools off at higher elevation or higher depth and then it cools off and it flows back down and you get this flowing of molten rock convection through the Earth’s interior.

And those stresses is that material wells on up. This can cause stresses on the surface of the planets. This is a tectonics of sorts. And it’s those stresses that can either as they come on up and spread this way, you can spread material. This is like where a sea floor spreading comes from because the material is coming on up and overturns go that way and you push the continents apart so the mid Atlantic ridge is a good example of, for example Europe and USA being pushed apart as that sea floor in the Mid Atlantic spreads out.

Volcanism D.5.24

23 May

Volcanism is more likely on a planet that has high internal temperatures so that you can get the molten lava going, so you can get the convection rolling. And it also helps if you have a thin lithosphere, so that the magna does not have a lot of material that it does not have to plough on through to come on up to the surface.

So the structure of a lava flow depends on its viscosity. And a viscosity is a measure of how easily a fluid flows. Water has a very low viscosity, whereas something like honey or molasses has a much thicker, much higher viscosity because the material doesn’t flow as well. So with regards to lava, if you have a sort of very runny lava, this is what you see on the moon when you take a look at the lunar Maria, those dark areas that fill in on the moon. That’s very low viscosity lava and that tends to make flat plain like structures.

On the other hand if the viscosity of the lava is a little bit higher than you can make shield volcanoes. And at the other extreme if you have this really thick heavy type of lava then you make what are known as stratovolcanoes and a good example of that is Mount St. Helen and there because the lava is so thick it freezes out before it flows much and so you get these very steep angled stratovolcanoes.

Underwater Volcano D.5.23

22 May

The underwater volcano is a process of that squeezing of the more buoyant magnet coming up and creating islands, in the ocean. The trapped gases within magma rise. This can lead to some pretty dramatic explosions, mainly because that gas that’s coming up is under a very high pressure. When it reaches the surface it bursts on open, and on occasion, you can get lightning.

Lightning associated with those tapped gases, and the dust and dirt coming on up where you have volcanic eruption with gases coming out, and then lightning forming within that and striking back down onto the volcano.

Volcanos Erupt D.5.22

21 May

Why do volcanos erupt? The answer to this would be that volcanos erupt when magma finds a path through the lithosphere. And the magma rises because it’s molten rock and so it’s less dense and so it’s buoyant and so it wants to rise on up. And it can also be squeezed upwards by the pressure of the tectonic forces.

It is a simple explanation but often a deadly one.