Buzz
Why is it that the planets in our solar system always steal the spotlight? There are still so many mysteries about our Moon, with new revelations emerging even decades after the historic Apollo 11 mission landed the first humans on it.
Some moons might support life or reveal dramatic events that reshaped the solar system’s very foundation. And then there are moons like Charon that are nothing short of extraordinary. Curious about Charon?
10. Charon, Pluto’s Moon, Has No Observable Rise or Set
Pluto and its largest moon, Charon, are gravitationally locked in a dance where they always present the same face to one another. Why does this matter? Well, it means that an astronaut on Pluto will either see Charon constantly above them or not at all.
Our Moon is also gravitationally locked to Earth, which is why we never get a glimpse of its far side. The key difference is that Earth is much larger than the Moon, so it’s only the Moon that is locked. In contrast, Pluto and Charon are nearly the same size, so they both remain locked to each other. One fascinating consequence of this is that if you’re on Pluto’s far side, Charon is completely out of sight. On the near side, it appears about seven times larger than our Moon, just hanging there in the sky and completing its phases in a little over six days.
Speaking of our Moon…
9. Our Moon Is Mostly Dormant, But Not Entirely
Part of the excitement surrounding the Apollo missions was that astronauts were stepping onto an untouched lunar surface that had been cold and lifeless for billions of years. While Apollo 15 and 17 recorded unusually high heat readings, it was suspected to be a result of instrument error, and no one believed in the possibility of active volcanoes. However, it now seems that dinosaurs, around 70 million years ago, and later Earth life—like elephants and horses, which emerged 33 million years ago—probably witnessed glowing lava flows on the Moon. One day, we may get to witness it as well.
When Apollo 15 astronauts captured images of unusual rocky patches on the basalt plains of the Moon, no one knew what they were. It wasn’t until 2009, with improved imaging technology, that scientists discovered these irregular mare patches (IMPs) are surprisingly young volcanoes. So far, 70 IMPs have been identified. This finding suggests that the Moon’s interior remained hotter for much longer than originally believed, and it may still be partially molten.
8. The Moon Reflects Life On Earth
There’s another light visible on the Moon: the soft glow on the dark side of a crescent moon. Known as “earthshine,” it comes from the light of a fully illuminated Earth in the Moon’s sky, reflecting off the lunar surface. Scientists have analyzed this earthshine with a spectrometer and found “biosignatures” from our atmosphere and plants. These biosignatures appear as unique spikes on the spectrum of earthshine, caused by sunlight reflecting off Earth’s oceans, vegetation, and cloud cover. Yes, NASA spacecraft have confirmed there is life on Earth, and it was well worth the investment of taxpayer money.
Now that astronomers know what to look for, they can search for biosignatures in the planetshine of distant exoplanets. While they’re not ready to make contact with extraterrestrials just yet, the discovery of earthshine as a spectral reflection of life is a significant step toward that goal.
7. Venus Might Hold Clues About Our Moon’s Origins
Many scientists believe the Moon was formed when an object roughly the size of Mars collided with Earth during the early days of our solar system. This theory helps explain why the Moon’s chemistry is so similar to Earth’s, but some experts remain unconvinced. At a recent conference on the Moon’s origins, the question was raised repeatedly, “What’s Venus made out of?” It’s a valid point. Venus and Earth formed close to each other in the same dust cloud that gave birth to our solar system. They are nearly the same size, so why does Earth have a Moon, yet Venus doesn’t?
The answer remains unclear. All our knowledge of Venus comes from images and data gathered by orbiting spacecraft. Without surface samples, we can’t determine whether Venus has a different chemical composition than Earth and the Moon (which would support the impact theory for the Moon’s formation). But if Venus shares similar geochemistry with Earth, the question remains: where did the Moon actually come from... Venus or Earth?
6. Irregular Moons Suggest Giant Planets May Have Shifted Orbits
Astronomers classify our Moon as a “regular” moon because its orbit is nearly circular and doesn’t tilt at extreme angles. However, there are also “irregular” moons orbiting the giant planets—Jupiter, Saturn, Uranus, and Neptune—that follow strange and erratic paths with unusual angles.
Scientists believe these irregular moons are all similar in size, and each of the giant planets hosts roughly the same number of them. Computer simulations suggest that these irregulars could have originally been comets, captured around four billion years ago, if the giant planets had swapped orbits back in the day. This theory also proposes that the planets' orbital shuffle led to a surge of comets and other debris being hurled into the inner solar system, triggering the event known as the Late Heavy Bombardment.
With so much chaos unfolding, it’s likely that some moons acquired their own little moonlets along the way. But they didn’t keep them for long…
5. Moons Can Have Moons (In Theory)
At least one asteroid has a moon, which is unusual. The Sun, being much larger, should have easily pulled the asteroid’s moon away. However, this asteroid is far enough from the Sun for an effect called a “Hill sphere” to come into play. A Hill sphere occurs when the gravity from an object (like Earth) is stronger than the gravity from a more massive but distant object (like the Sun). Our Moon stays in orbit around Earth due to Earth’s Hill sphere.
In theory, any moon that orbits far enough from its planet could have moonlets within its Hill sphere, but none have been observed so far. Maybe we just haven’t spotted any yet. However, other forces, like slight variations in gravity called tidal forces, could cause moonlets to crash or break apart. So perhaps there simply aren’t any moonlets left.
4. Saturn Hosts Trojan Moons
Saturn is the only planet in our solar system that has moons sharing an orbit with another moon. Tethys and Dione aren't alone as they circle Saturn. Positioned 60 degrees ahead and behind each moon is another, smaller moon, also orbiting Saturn along the same path. That’s right—two orbital tracks, each hosting three moons.
This phenomenon has nothing to do with Hill spheres. Instead, it involves stable Lagrangian points, located 60 degrees ahead and behind Tethys and Dione. At these points, the inward gravitational pull perfectly balances the outward centripetal force on the smaller Trojan moons, which are moving faster than their size suggests. What happened to other moons that weren’t in stable Lagrangian points? They likely escaped or collided, contributing material to Saturn’s rings.
3. Europa Might Be Home to Life
Europa is one of Jupiter’s icy moons that is believed to harbor a subsurface ocean. Unlike Ganymede, however, Europa has large patches of orange-brown material scattered across its surface, alongside white ice. NASA refers to these orange-brown regions as 'non-ice components' because their exact composition is unknown. Interestingly, a NASA astrogeologist used infrared light to compare this material with extreme bacteria found on Earth, and was quite surprised to discover a close, though not exact, match.
No, life hasn’t been conclusively found on Europa. The only way to be certain is by obtaining samples, but Europa is incredibly distant and perilous to visit due to radiation from Jupiter. However, NASA is contemplating a Europa Clipper mission, which might involve halting a lunar orbiter as well as the Opportunity rover on Mars.
Because discovering extraterrestrial life is *that* significant.
2. Titan Produces the Basic Ingredients for Plastic
It turns out George Carlin was mistaken: Nature doesn’t need humans to make plastic. Saturn’s largest moon, Titan, is already doing it on its own.
Titan is the only moon in our solar system known to have a substantial atmosphere. The weather there is far from pleasant, with constant methane rain and other hydrocarbons. If scientists are correct in suggesting that Titan’s atmosphere resembles Earth’s early one, it seems like Earth has made substantial progress. When sunlight interacts with hydrocarbons in Titan’s atmosphere, they break down and create other molecules, a process akin to how we refine hydrocarbons on Earth to obtain plastic ingredients. In fact, NASA’s Cassini spacecraft detected both propylene and ethane on Titan—exactly what plastic manufacturers use to produce polypropylene and polyethylene.
1. Ganymede Features A ‘Club Sandwich’ Ocean Structure That Could Support Life
In the 1990s, NASA’s Galileo spacecraft observed that beneath Ganymede’s icy surface, there’s likely a highly saline ocean, hundreds of kilometers deep. Initially, scientists thought that the extreme cold and immense pressure at the ocean’s bottom would freeze the water, making it an unlikely habitat for life.
New research proposes that Ganymede’s ocean might have a 'club sandwich' structure, consisting of up to three layers of ice, each alternating with water. The deepest layer is a particularly salty ocean. Since extremophiles prefer living in water over ice, and with the possibility of hydrothermal vents beneath the surface—similar to those on Earth—this new model raises the possibility of life on Ganymede.
In 2022, the European Space Agency plans to send a spacecraft to study Ganymede, possibly even landing on it to further investigate.
