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Comparative planet data from NASA.

an infographic that shows the past missions to Mars

In this "Ask an Astronomer" episode (03:05), Dr. Carolyn Brinkworth fills us in on what the color of the sky has to do with finding life on distant planets.

There are a couple of things about this one that I think need some careful attention. For one: "A [food]chain will always start with a plant (a primary producer)." That isn't really true for the largest ecosystem on the planet, for example: the oceans. Not only are most algae not considered plants, a large number of these are unicellular and prokaryotic... the "blue green algae/bacteria" or cyanophytes. In fact, there are even deep sea hydrothermal ecosystems, for instance, that do not even rely upon photosynthetic organisms at all. These primary producers are chemosynthetic in the blackness that is the sea floor. So yes, "primary producer" is accurate... but not so for "plant." I'm also anxious to see what kids will place in between the snail and the bird (as pictured) on food chain "B" to complete the "missing link." I honestly had to work the Google to find out that spider-eating snails do exist. I feel like that is pretty obscure.

Electronic Fact Sheets on Over 50 species.