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FAQ - Science

1. Whats the difference between rotation and revolution?

You rotate on an axis— spin. You revolve around something— orbit the Sun.

2. How did scientists come to use spectra to understand space/asteroids/planets and other connections?

Objects in space are generally remote, so unless you can physically go there, the only thing that you can do is look at them. As humans, we have the five senses. And when talking about distant objects, we can use our senses to study them. As a side note, space is a vacuum so you cannot hear things in space. So, telescopes enhance our ability to look at objects: make them look bigger (to see more detail), make them brighter (to see fainter objects), let you look at wavelengths that you normally cannot see (to see in the ultraviolet and the infrared), and allow you to look at the colors/spectrum in more detail (look at the way the various minerals reflect and absorb light). This has been done for years with stars, the Moon, and planets.

But in 1969/1970, scientist Tom McCord and others at MIT looked at the visible light of Vesta and several other asteroids using an instrument that allowed them to divide up the light into 24 colors. Scientists were beginning to understand that the meteorites came from the asteroids and so scientists who studied the spectra of meteorites started looking at the spectra of asteroids to see if they could see features similar to what was seen in meteorites. This worked well for Vesta, but not for Ceres. It was not until eight years later, when an infrared spectrum of carbonaceous chondrites at wavelengths about four times longer than visible light was studied, that we realized that there was an absorption feature that was directly related to the presence of clay minerals in meteorites and perhaps, on asteroids. This is when clay minerals (water) were discovered on Ceres!

3. What is an Astronomical Unit?

An Astronomical Unit (AU) is the mean distance from the Earth to the Sun, about 92,556,000 miles or 149,958,000 kilometers.

4. What is differentiation?

Differentiation is the separation of the original mixed planetary material into different layers according to density. Typically, the layers are: iron/nickel at the bottom, dense rocks like peridot in the middle, and light rocks like basalt on top. Differentiation requires that at least most of the materials in the planet were liquid or molten at the time of differentiation. As the planet cools, all of the layers will solidify, preserving the differentiated layers.

5. How do I get rid of caliche in my backyard?

Caliche is sand and gravel that has been cemented by calcium carbonate in a layer below the surface. This layer is common in the desert southwest of the United States because when the many dissolved minerals in the local water supply are precipitated out of solution, it solidifies to form a hard crusty layer at depth. To remove caliche, you will need to dig it up.

6. What is the difference between weathering and erosion?

Weathering is the breakdown of rocks. This can either be done physically (just breaking into smaller pieces) or chemically (changing the composition – conversion of minerals in the rock, e.g. feldspar to clay, not converting one type of rock to another). Erosion is the physical removal of rock – so when we talk about erosional features we are talking about landforms where rock has been removed, most likely after it was weathered.

7. What are the different types of salt deposits in dry lakebeds?

Some of the most common: Halite – NaCl, Gypsum – CaSO4 2H2O, Calcite – CaCO3. Keep in mind there are many others!

8. Why do salt deposits increase in size when they dry?

Salt deposits crystallize out of saline fluid. As the fluid evaporates, the salt crystals precipitate out of solution and keep growing in size as more precipitation occurs.

9. How does suspended load vary in humid vs. arid environments?

In a humid environment, where streams are flowing all of the time, the finer sediment settles out of the water and the water is clear – little or no sediment is carried in suspension. In an arid environment, the water is flowing for only a short time, picking up and carrying everything – lots of sediment being carried in suspension when the water is flowing.

10. What is volume?

We can measure things in three ways: linear (say the diameter of a circle in centimeters), area (say the area of a circle in centimeters squared [cm2]) which is πr2 (r = radius), and the volume (say the volume of a sphere in centimeters cubed [cm3]) which is 4/3 πr3.

11. How can you be sure that the composition of extraterrestrial material is similar or dissimilar to Earth's material and how do you know that those materials are from other planets if we don’t have direct samples to study?

Materials reflect light. Certain minerals absorb different wavelengths of light in very characteristic ways. So, we can use this (using telescopes) to compare what we see on, say, Mars, to the rocks we have on Earth. We also have lunar samples brought back by the astronauts, as well as meteorites which appear to be from the Moon and Mars (again, the way they reflect light and other characteristics help support this). While there may be slightly different minerals on other planets, from what we can see, the geologic processes on other planets are similar to what we see on Earth, so we do not expect to see very different minerals: a rock is a rock!

12. If you use a model to determine how something occurred on another planet based on what we know about the Earth, what do you have to take into consideration?

If one is talking about liquid water, then is the temperature warm enough? Is there enough atmosphere to have liquid water be stable? If the temperature is too low, as on Saturn's moon Titan, what other liquid could act like water (methane, nitrogen, etc.)? If you see what appears to be volcanic features, are there volcanoes? Is it likely that the interior is/was warm enough to make lava? If you see what appears to be sand dunes, is the surface dusty/sandy? Is there enough atmosphere to move dust around?

13. Heavy elements forming the core makes sense, but how does this create gravitational pull?

When the Earth was molten, the heavy elements (e.g., iron and nickel) "sank" to the bottom (the core) due to gravity. If you hold something in the air and drop it, it will fall faster and faster until it hits something—potential energy is converted to kinetic energy which in turn is converted into other forms of energy when it hits the surface (heat, etc.). When the heavy elements sank, their potential energy was converted to heat energy (friction with the surrounding molten material), heating up the Earth. No additional gravitational pull was created, the mass of the Earth stayed the same. In physics, from the outside, a sphere can be thought of as a point mass. Standing on the surface of the Earth, the gravitational pull of the Earth would not change even if all of the mass were concentrated in the center (just as long as you stayed the same distance from the center).

14. What is a "heat budget"?

Heat budget has to do with how heat energy (i.e., the Sun's solar energy) entering the Earth is distributed. In the picture below (left), 30% of the energy from the Sun is reflected back into space and 70% is absorbed by the ocean, land, atmosphere, and clouds. In an ideal world, when the ground and ocean warm up, they re-radiate all of the heat back into space and the Earth stays at a stable temperature. However, add greenhouse gases and the heat generated by burning fuels, this is no longer the case. Greenhouse gasses trap heat and it cannot escape (something like your car in the summer or in a greenhouse). If it gets out of control, you have a runaway greenhouse effect and you get what happened to Venus!

In terms of planetary processes (and planet formation), there is another meaning to this (figure below, right): when a planet is formed, a lot of heat is generated when the material that formed the planets came together (kinetic energy turns to heat). Then when a core is formed, heat is generated as the heavier materials, such as iron, "rain" down into the interior (converting potential energy into heat). Finally, there is heat still being generated by radioactive decay. Now, you have a warm body that has to "get rid of" all of this heat into cold space. Depending on how much heat is being generated over time, the material that makes up a planet (or moon), and the size of the object, heat is brought to the surface by conduction or convection (like a boiling pot of water). At the surface, this heat can then be radiated into space.


15. What is really out there besides planets?

Objects in the solar system:

1) Orbiting the Sun: dwarf planets, asteroids, comets, meteoroids (small asteroids), interplanetary dust particles (what you eventually see as meteors, the material that comes off of comets and we see as the coma and tail of comets), Kuiper Belt Objects/Trans-Neptunian Objects (icy asteroids, may become comets), and Oort Cloud objects (objects very far from the Sun and the source of long-period comets; its existence is only a theory, but based on observations of comets).

2) Orbiting the planets: satellites (also called moons).

3) Beyond the Solar System: other stars, white dwarfs, black holes, neutron stars, dust and gas clouds, extrasolar planets, etc.

16. What are tides? I can visualize ocean tides, but you are referring to a force between planets (moons). How does that affect the planet/moon?

Tides are deformities in the shape of a body caused by another object. They are caused by the gravity of the other object (one tidal bulge) and by the fact that both objects are orbiting around a common center of mass (the opposite tidal bulge, caused by inertia/centrifugal force). Since Earth is essentially covered in water we usually think of tides in the ocean. But tides also occur in objects composed entirely of rock, like Earth's Moon and Jupiter's moon Io. In fact, tides occur in Earth's rocky crust too, but the deformation is not detectable without sensitive instruments.

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