About 300 years ago during another pandemic, there was a person named Sir Isaac Newton who spent a lot of time at home thinking about the universe.

Guy Worthey

That’s what I found out from my friend Guy Worthey, an astronomer at Washington State University. Gravity plays a big part in the answer to your question, and we’ll explore that in just a moment.

“I remember when I was a kid, the textbooks said that Pluto was twice the mass of Earth,” Worthey said.

It turns out some planets, such as Venus and Mercury, do not have an orbiting object like a moon. It wasn’t until humans were able to send satellites to these planets that we were finally able to gather precise information about gravity and learn about mass.

You know, gravity is an important force. It’s what makes things fall. It’s what keeps planets in orbit. It’s what keeps us on the ground. While we may not have a scale to weigh planets, we can use what we know about gravity and mass to make all sorts of calculations and investigate questions about our universe.

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