Dear Francesco,

Last fall, my friend Lee Kalcsits and I went exploring in the apple orchards of Wenatchee. The apples were ripe and the leaves were changing from green to gold. We plucked a few leaves and took them back to his lab.

Dear curious reader,

Your question reminds me of an experiment: You put a ringing alarm clock in a jar and use a hose to slowly suck out all the air. As the air escapes, the ringing gets quieter until there’s no sound at all.

The inside of the jar becomes what scientists call a vacuum. It’s empty. Just like space.

Dear Aaron,

When I got your question, I headed straight for my friend Jake Leachman’s lab at Washington State University. He’s an engineer who knows a lot about what happens to things when they get super cold.

Dear Jack,

There are all kinds of robots in our world. In fact, you may already have one in your house.

Dear Cynthia,

While walking in the woods with my friend Gary Chastagner, we stumbled upon some old tree stumps. The stumps had so many rings we had to use our magnifying glasses to see them all.

Dear Graylon,

Your question takes us on a journey deep into the Earth. Figuratively speaking, of course. It’s really hot under Earth’s surface. It’s so hot it can melt rock. This melted rock is known as magma. And anything that erupts magma is a volcano.

Dear Jack,

When we dig up fossils from the Earth they can tell us a lot about life in the past.