Mars once was wet and fertile. It's now bone dry. Something bad happened on Mars. I want to know what happened on Mars so that we may prevent it from happening here on Earth.

A common way to compute density is, of course, to take the ratio of an object's mass to its volume. But other types of densities exist, such as the resistance of somebody's brain to the imparting of common sense.

If you need to invoke your academic pedigree or job title for people to believe what you say, then you need a better argument.

My investment of time, as an educator, in my judgment, is best served teaching people how to think about the world around them. Teach them how to pose a question. How to judge whether one thing is true versus another.

Luckily, there are some rocks left over from our earliest days, asteroids formed during our solar system's birth. Occasionally, some of them drop in on Earth, and when they do, they're called meteorites.

I don't want people to say, 'Something is true because Tyson says it is true.' That's not critical thinking.

Only when you question does society move or advance at all.