The next time you look at a bright full moon, think about this: no one knows exactly where the moon came from.
“We have no idea why the moon is here,” science writer Rebecca Boyle said on Inexplicable – Vox’s podcast that explores big mysteries, unanswered questions and everything in between we learn by diving into the unknown. “I think for a lot of people [the moon] is taken for granted, it’s that mundane stuff, and galaxies, nebulae, stars, and planets are more intriguing.
It’s true that some of the most epic questions in science lie in the outer reaches of space – how and when did the first galaxies form, what happens inside a hole? black – but equally epic questions exist here, in our celestial neighborhood, in our own solar system.
To explore our own solar system – the moons and planets it contains – is to better understand what is possible in the far reaches of the universe. Everything we find or discover in our own cosmic backyard will help us understand what is possible in the larger universe. If evidence of ancient life is found on a hostile world like Mars, we might better understand just how common life might be in other solar systems. If we understand how a possibly once vibrant world like Venus fell to ruin, we might understand how often similar planets around other stars die in an apocalypse.
The solar system’s most provocative mysteries help us understand why we’re here, how long we have left, and what we might be leaving behind. Here are some of the solar system mysteries we encountered on Inexplicable.
For more mysteries, listen and follow Inexplicable 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 almost entirely made up of carbon dioxide, which generates a very 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 greater than what you would feel at sea level on Earth.
Yet some scientists suspect Venus is Earth-like, with an ocean of liquid water like those that support life on our planet. This raises an existential question for life on Earth.
“Venus and Earth are planetary sisters,” says Robin George Andrews, volcanologist and author of Super Volcanoes: What They Reveal About Earth and Worlds Beyond. “They were made at the same time and made of the same material, but Venus is apocalyptic and awful in every way possible. Earth is a paradise. So why do we have a paradise next to a lost paradise?
There are two main assumptions. The first is that the sun baked Venus to death. The other is that volcanoes did it.
Further reading: Venus could have been a paradise but turned into a hellish landscape. Earthlings, be careful.
Where the hell did the moon come from?
Before the moon landings, scientists thought they knew how the moon was formed. The prevailing theory was that it formed much like the planets: bits of matter left over from the formation of the sun, coming together. But then Apollo astronauts brought back samples from the lunar surface, and those rocks told an entirely different story.
“Geologists had discovered that the moon was covered with a particular type of rock called anorthosite”, Inexplicable says senior producer Meradith Hoddinott on the show. “Glittering, shining and reflective, it is the rock that makes the white moon shine in the night sky. And at the time, it was thought, this rock could only form in a very specific way. Magma.”
But magma means the moon must have formed in some kind of epic cataclysm. “Something that poured so much energy into the moon that it literally melted,” says Hoddinott. Scientists don’t know exactly how it all happened. But each scenario is a cinematic story of fiery apocalyptic proportions.
Further reading: How Apollo’s moon rocks reveal the epic story of the cosmos
Is there anything alive in the human shit left on the moon?
During the Apollo missions to the Moon, astronauts traveled to the Moon and, to save weight for the return to Earth, they dumped their trash behind them. In all the Apollo missions, the astronauts left 96 Bags human waste on the moon, and they pose a fascinating astrobiological question.
Human waste – and especially feces – is teeming with microbial life. With the Apollo moon landings, we took microbial life to Earth into the most extreme environment it has ever been in. Which means littering on the moon represents a natural, albeit unintended, experience.
The question the experiment could answer: how resilient is life to the harsh environment of the moon? And besides, if microbes can survive on the moon, can they survive interplanetary or interstellar travel? If they can survive, then it may be possible for life to spread from planet to planet, riding on the backs of asteroids or other space junk.
Further reading: Apollo astronauts left their poo on the moon. We have to go back for this shit.
Was there an advanced civilization on Earth before humans?
Many scientists have long wondered: is there intelligent life in the depths of space? But climatologist Gavin Schmidt and astrophysicist Adam Frank have another question: Was there intelligent life deep within Earth’s history? Could we find evidence of an advanced non-human civilization that lived perhaps hundreds of millions of years ago, buried in the earth’s crust?
It’s not strictly a “solar system” mystery, but it does have cosmic significance. At the heart of it, Schmidt and Frank ask themselves: what is the likelihood that intelligent life on any planet – here or in the depths of space – will leave a mark, a sign that it once existed? ? And by the way: Hundreds of millions of years from now, will some extraterrestrial explorers landing on Earth be able to find traces of humans if we’re long gone?
Further reading: The Silurian hypothesis: would it be possible to detect an industrial civilization in the geological archives?
Can we push an asteroid off a collision course with Earth?
Many disasters – volcanic eruptions, earthquakes, hurricanes, tornadoes – are unavoidable. Scientists talk about when, not if, they will strike. Although humans make some calamities worse, natural disasters have occurred long before we got here. They are part of life on Earth. But one type of disaster is not necessarily inevitable: a collision between an asteroid or a comet and the Earth.
The problem is this: we’ve never tried to deflect an asteroid and we don’t know if a plan to do so would work.
To help answer this question, NASA last year launched the Double Asteroid Redirection Test (DART), which is a car-sized box fitted with solar panels. It is currently en route to a 160 meter asteroid called Dimorphos. In the fall, DART will crash into Dimorphos at 24,000 kilometers per hour (about 15,000 miles per hour) in pursuit of a big question: Can the collision push the asteroid into an orbit? slightly different?
Further reading: The quest to avoid an asteroid apocalypse is going surprisingly well
Was there ever life on Mars?
Mars today is a desert, devoid of any obvious signs of life. But over the years, scientists have uncovered evidence of a long-lost Mars that might have looked much more like Earth.
“Mars is a very different place today than it was 4 billion years ago, but you can see evidence of what it was,” says NASA astrobiologist Lindsay Hays. “You see things like the remnants of a huge river delta, which indicates not only that you had water flowing, but that you probably had a lot of water flowing over a long period of time that has continued to deposit sediment.”
And where there was water, there could have been life. Last year, a new rover landed on Mars, and this is our best chance to answer the question “was there ever life on Mars?” If the answer is “yes,” it could change our understanding of everyday life in the universe.
The Inexplicable episode on Mars aired June 22.
Further reading: NASA’s latest rover is our best chance of finding life on Mars
Is there a real ninth planet lurking in the darkness?
In 2006, the International Astronomical Union voted to change the definition of what constitutes a planet, and Pluto was dropped. There were no longer nine official planets in the solar system, but eight.
But then “we started to realize that there really was something else out there – and a real giant planet that we think still lurks far beyond Neptune, waiting to be found”, said astronomer Mike Brown on Inexplicable. Astronomers haven’t detected this planet yet, but they suspect it’s there: other distant objects in the solar system appear to be impacted by its gravity.
Could these clues lead us to a real new ninth planet? Maybe. But it will be hard to find.
“It’s kind of like taking a little grain of black sand and throwing it on the beach,” Brown says of the research. “It would be a bit difficult to find that one in the sea of all the others. And that’s the problem with Planet Nine.
Further reading: The Hunt for Planet 9
If you have ideas for topics for future shows, email us at firstname.lastname@example.org.