The next time you look up at a bright full moon, think about this: No one knows, precisely, where the moon came from.
“We have no idea why the moon is here,” science writer Rebecca Boyle says on Unexplainable — Vox’s podcast that explores big mysteries, unanswered questions, and all the things we learn by diving into the unknown. “I think for a lot of people [the moon] is taken for granted, it’s this sort of humdrum thing, and galaxies and nebula and stars and planets are more intriguing.”
It’s true that some of the most epic questions in science are found in the farthest reaches of space — how and when did the first galaxies form, what happens inside a black hole — but equally epic questions exist right here in our celestial neighborhood, in our own solar system.
To explore our own solar system — the moons and planets in it — is to better understand what’s possible in the farthest reaches of the universe. Anything we find or discover in our own cosmic backyard will help us understand what’s possible in the broader universe. If evidence of ancient life is found on a hostile world like Mars, we might better understand how common life might be in other solar systems. If we understand how a possibly once-vibrant world like Venus fell into ruin, we might understand how often similar planets around other stars die in an apocalypse.
The most provocative solar system mysteries help us understand why we are here, how long we might have left, and what we might leave behind. Here are some of the solar system mysteries we’ve encountered on Unexplainable.
For more mysteries, listen to and follow Unexplainable wherever you listen to podcasts.
What killed Venus?
“Hellscape” is the most appropriate word to describe the surface of Venus, the second planet from the sun. At 900 degrees Fahrenheit, it’s the hottest planet in the solar system, thanks to an atmosphere that’s almost entirely made up of carbon dioxide, which generates a really strong greenhouse effect. Clouds made of highly corrosive sulfuric acid are draped over a volcanic landscape of razor-sharp volcanic rock. The pressure on the surface of Venus is about 92 times what you’d feel at sea level on Earth.
Yet some scientists suspect Venus was once much like Earth, with a liquid water ocean like the ones that support life on our planet. This prompts an existential question for life on Earth.
“Venus and Earth are planetary siblings,” says Robin George Andrews, volcanologist and author of Super Volcanoes: What They Reveal about Earth and the Worlds Beyond. “They were made at the same time and made of the same stuff, yet Venus is apocalyptic and awful in every possible way. Earth is a paradise. So why do we have a paradise next to a paradise lost?”
There are two leading hypotheses. One is that the sun cooked Venus to death. The other is that volcanoes did.
Further reading: Venus could have been a paradise but turned into a hellscape. Earthlings, pay attention.
Where the heck did the moon come from?
Before the moon landings, scientists thought they knew how the moon formed. The prevailing theory was that it formed a lot like the planets did: bits of material left over from the formation of the sun, lumping together. But then, Apollo astronauts brought samples back from the lunar surface, and those rocks told a totally different story.
“Geologists had found that the moon was covered in a special kind of rock called anorthosite,” Unexplainable senior producer…
Read More: Unexplainable podcast: 7 solar system mysteries scientists haven’t solved yet