One theory suggests that much of Earth’s water came from comets. In the early solar system, Earth was too hot to hold onto its water, so comets—icy visitors from the outer solar system—may have delivered it through countless impacts. Some comets have a similar ratio of deuterium (heavy hydrogen) to regular hydrogen as Earth’s oceans, supporting the idea that comets played a key role in making our planet habitable.

Enjoyed this article?

Get daily 10-minute PDFs about astronomy to read before bed!
Sign up for our upcoming micro-learning service where you will learn something new about space and beyond every day while winding down.

Join the Waitlist

Be the first to receive our daily 10-minute astronomy PDFs and help shape our launch!

Please enter a valid email address

You're on the list!

Thank you for joining our waitlist. We'll send you an email as soon as we launch our astronomy PDFs.