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Thomas J. Wdowiak is an Athena scientist who takes time out of his busy schedule to show kids how to do fun science experiments at home. When he isn't teaching at the University of Alabama at Birmingham or training at the Jet Propulsion Lab in California, he writes for the local newspaper in Birmingham in the "Just for Kids" section. He goes by "Tommy Test Tubes," a nickname given to him when he was a kid. Now "Tommy Test Tubes" contributes his experience and knowledge to the Athena web page with a new column. If you have a question for Tom, click here.

Why is Mars Red?

Asking why Mars is red is a question that can be asked along with "why does the Moon have dark areas?" That's because the answers involve the same thing, the element iron. It also involves an important difference between Mars and the Moon: Mars has an atmosphere and the Moon doesn't!

Iron is pretty interesting cosmic stuff. That's because it's the last element a star can make and still generate energy. This only happens at the end of the lifetimes of certain stars, particularly the "heavyweights".

The simplest element is hydrogen; it's no. 1. This means it has only one piece of a kind of matter, called a proton, in the center and consequently usually has a piece of matter, called an electron, in the outer part. Protons are said to have positive (+) charge, and electrons are said to have negative (-) charge. The rule is that "opposites attract". Also, protons are 1836 times "heavier" than electrons. Sometimes, you can find hydrogen atoms with companions to the proton, a piece of matter called a neutron, which is said to be electrically neutral (neither "+" nor "-").

In the Sun, and other similar stars, the centers of hydrogen atoms are joined together to make a center of another kind of atom. This atom is helium, no. 2, and it has two protons and generally two neutrons in the center and usually two electrons in the outer part. This process of joining centers of atoms together is called fusion. Stars do it, and each time it happens energy is released. This energy becomes starlight (or sunshine in the case of the Sun).

This continues until 26 protons (and a bunch of neutrons) have been joined together, and element no. 26 is produced. This element is iron. Adding a 27th proton does not release any energy (it actually consumes energy!), so this doesn't happen. As a result, iron accumulates inside the stars in which this is going on. Elements beyond no. 26 do get made, but the energy has to come from some process other than fusion.

Iron is pretty abundant stuff. It gets into a lot of things, like planets and even you (remember the iron in your blood). And it has 26 (+) protons and generally 26 (-) electrons. Actually, this is the situation when it is said to be metallic, you know, "shiny". The kind of stuff a lot of things, like cars and refrigerators, are made of. You can even find certain meteorites made of metallic iron, but this only happens about 5% of the time.

Iron atoms easily lose two or three of their electrons. This happens when they encounter other elements like oxygen (which is no. 8). Oxygen really sucks away electrons. When this happens it's called "oxidation".

When metallic iron loses two or three electrons to some other element, it stops being shiny and the iron atom joins with the atom or atoms of the other element to form a molecule (what two or more atoms joined together is called).

Iron-containing molecules where the iron atoms lose two electrons tend to be black or green in color. When three electrons leave the iron atoms, the color is yellowish-orange, and in many cases bright red. We say it's more oxidized when 3 electrons are involved than just 2.

The answer to the question of why Mars is red (and why there are dark areas on the Moon) is first because both worlds contain iron, like Earth contains iron. Secondly, the iron on the surface of Mars is more oxidized than the iron on the Moon, which is why Mars looks red and you see dark places on the Moon (remember, it's often called the "man on the Moon"). Why is iron on Mars more oxidized? Because it has an atmosphere that contains carbon dioxide (CO2) and water (H2O), both of which can be a source of oxygen for oxidizing iron. The Moon on the other hand, has a surface in a vacuum -- no atmosphere, no oxygen to make the iron red.

Here's an experiment you can do: If you can find a piece of rusty iron, carefully remove the red rust with some medium grade sand paper. Just before it gets to be shiny, if you look closely, you will see a thin black layer between the red rust and the shiny metal. That experience will acquaint you with the three forms of iron we've been talking about. When you're doing this, think about the "red planet" and the "man on the Moon".

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