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9 Compelling Facts About Neptune

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Neptune is like a celestial paint swatch: a stunning royal blue that demands attention. The eighth planet in the solar system, it is one half of the ice-giant system (the other half being Uranus), and among the most mysterious worlds circling our Sun. Mental Floss spoke to Mark Hofstadter, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, to learn more about this lesser-known planet. Here are a few things you might not know.

1. IT HAS SIX RINGS AND 14 MOONS, ONE OF WHICH HAS GEYSERS BLASTING INTO SPACE.

Neptune is about 30 times farther than we are from the Sun (2.8 billion miles to our 93 million miles)—the farthest in the solar system (aside from the dwarf planets). Its effective temperature, according to NASA, is -353°F. Its mass is 17.1 times that of Earth, and it's big (but not Jupiter big), with an equatorial radius of 15,300 miles. Neptune is circled by six rings and has 14 moons, one of which is geologically active and blasting geysers into space. (Plumes are ideal for sampling; rather than building a lander, you can just fly a science spacecraft right through them.) A Neptunian day is short, at 16.11 hours long, but its years are a different story.

2. IN 2011, HUMANITY MARKED NEPTUNE'S "FIRST" BIRTHDAY.

It is impossible to see Neptune with the naked eye. Galileo first recorded its existence with his telescope, though he identified it as a star, misled by its slow orbit. In the 19th century, astronomers noticed an aberration in the orbit of Uranus, and Urbain Joseph Le Verrier, a French mathematician, went to work on the problem. With a pen and paper, he worked out not only the existence of a planet, but also its mass and position. In 1846, Johann Gottfried Galle made the observation at the request of Le Verrier, and sure enough, found a planet. A couple of weeks later, he also observed Triton, Neptune's largest moon.

It took 165 years for a full Neptunian year to elapse. That's why we celebrated Neptune's "first" birthday in 2011.

3. IT'S CALLED AN ICE GIANT … BUT IT DOESN'T HAVE MUCH ICE.

Hofstadter tells Mental Floss that until the Voyager 2 spacecraft visited Neptune and Uranus in the late 1980s, the two planets were thought to be small Jupiters. "It turns out they are fundamentally different than Jupiter," he says. "They are around two-thirds water by mass, and then they have some rock and an atmosphere of hydrogen and helium."

The "ice" in "ice giants" refers to their formation in the interstellar medium. "When modeling the formation of the solar system, things are more or less sorted into three categories: gas, rock, or ice," says Hofstadter. In interstellar space, helium or hydrogen will not exist as a solid or liquid, so they are the gases. They form planets like Jupiter. Silicates and irons, meanwhile, are solid, and exist as dust particles blown out from such things as supernovae. They form places like Earth. Then there are "in between" molecules, such as water, methane, or ammonia. Depending on the local temperatures and pressure, they might be water vapor or solid ice. Those are called—you guessed it—the ices.

"When planetary scientists found that, wow, Neptune and Uranus seem to be mostly stuff like water and methane, they called them 'ice giants,'" Hofstadter explains. But the name is misleading, because today there is very little ice in those planets. "When they formed, the water was probably coming in as ice," he says. "Now, however, it's hot enough in the interior that almost all of the water there is liquid."

Neptune's blue hue? That's due to the methane in its atmosphere.

4. IT HAS A SOLID CORE SURROUNDED BY AN OCEAN. THE REST IS A MYSTERY.

… but not liquid water like you find on Earth. The interior structures of Neptune and Uranus are among the biggest questions facing planetary scientists today. The conventional thinking is that there is a rocky core at each of their centers, surrounded by an extensive region of ocean. A hydrogen and helium atmosphere comprises the outer layer. "There's a lot of atmosphere to get through before you hit the ocean," says Hofstadter. "It is deep enough that it is under extremely high pressure and temperatures. It is probably a highly reactive ionic ocean." The water exists in what is called a supercritical state: "It doesn't behave in the same way that water in our oceans behave. It's probably conducting and has a lot of free electrons in it."

5. NEPTUNE'S FORMATION IS ONE OF THE GREAT CELESTIAL UNKNOWNS.

When planets form, solids first come together. When a solid ball gets big enough, it can gravitationally trap gas—and there's a lot more gas around than there is rock. Hydrogen is the most abundant thing in the universe. "Once you get a rocky core that's big enough to trap gas, a planet can grow very rapidly and can grow very big," says Hofstadter. In the inner solar system, where there was not as much gas, or ices were not solid, you got the terrestrial planets. In the outer solar system, where there was rock and solid ice, large cores formed quickly and started sucking up all the gas around them. That's how you get monster planets like Jupiter and Saturn.

How this relates to Neptune (and Uranus): A star, as it is forming, has a phase during which it has a tremendously strong stellar wind and effectively blows away all the gas. "If Jupiter and Saturn had been in an environment with an endless supply of gas, they would have grown big enough to eventually become stars," says Hofstadter. "But the idea is, the Sun kind of turned on and blew away all the gas, and Jupiter and Saturn had their growth cut off."

Neptune and Uranus have large cores big enough to trap gas. So the question is, why didn't they become like Jupiter and Saturn? "Jupiter and Saturn are 80 percent gas, by mass. Why are Uranus and Neptune something like 10 percent gas? Why didn't they trap more?"

The first theory involves luck. "The idea is, well, for Uranus and Neptune, their cores got big enough to trap gas precisely at the time when the Sun started blowing away all the gas. There wasn't enough, and they couldn't trap more," Hofstadter says. It's possible that could happen once or perhaps twice in a solar system's formation, explaining Uranus and Neptune. But the study of exoplanets have upended this thinking. "When you look around in our galaxy and see how many ice giants there are, it's hard to believe that every solar system out there was lucky enough to have planets forming large cores just as their stars started blowing away all the gas," he points out. "So this is a fundamental question: How do ice giants form? And we don't understand."

6. NEPTUNE'S RINGS ARE CLUMPY.

Unlike the rings of Saturn, the six Neptunian rings are thin, young, and dark. Their color is due to their composition: radiation-processed organic material. One of the rings features three thick, distinct clumps named Liberty, Equality, and Fraternity. The clumps are something of a mystery: The laws of physics dictate that they should be spread out evenly, as you see at Uranus, but there they are, little lumps in space. (Before Voyager 2 visited, only the clumps were visible, and were called arcs, part of an incomplete ring.) The most likely cause for the ring irregularity is gravitational meddling by the moon Galatea.

7. MORE ABOUT THAT MOON WITH GEYSERS …

Triton, Neptune's largest moon, is thought to be something like Pluto: an object from the Kuiper Belt (the ring of icy bodies beyond Neptune). "It happened to be gravitationally captured by Neptune," says Hofstadter. "It is a fascinating object to study because it's a Kuiper Belt object, but it's also interesting because it is active. We see a lot of geology on Triton just like we see on Pluto. When Voyager flew by—in just a few minutes—it happened to see geysers spouting off."

When Triton was captured into orbit around Neptune—you can see it circling the planet in the video above—it caused all the native Neptunian satellites to be destroyed. They either impacted Neptune and were absorbed, or they were ejected from the Neptunian system.

8. IT HAS A "GREAT DARK SPOT."

Just as Jupiter has a Great Red Spot, Neptune has a Great Dark Spot. They are both anticyclonic storms, though while Jupiter's spot is centuries old, Neptune's spot is short lived. It seems to come and go. Notably, the Great Dark Spot even generated stunning white clouds over Neptune much in the way that cirrus clouds form from cyclones on Earth.

9. WE'VE BEEN THERE ONCE BUT WANT TO GO BACK.

Only one spacecraft has visited Neptune: Voyager 2, in 1989. The photo of Neptune at top was taken during that mission; in fact, it's likely the source of any image of Neptune you've ever seen. Pretty much everything scientists know about the world comes from that flyby, and from telescopic observation. The James Webb Space Telescope [PDF], which launches in 2019, will unlock new ice-giant science, including mapping cloud structures, observing auroras, and studying post-impact atmospheric dynamics.

Some things, however, such as a detailed atmospheric composition or a study of its satellites, can only be done by a spacecraft at the system. Planetary scientists are today developing flagship-class missions to visit both Neptune and Uranus. An ice-giants mission is considered a top priority of the planetary science community, after a Mars sample return mission and a Europa orbiter. Mars 2020, which launches in its namesake year, is a sample-caching rover (returning those samples to Earth awaits a future mission); meanwhile, the Europa Clipper was approved by NASA and is well into development. That puts Neptune and Uranus next in line. A mission to these planets would have to launch no later than 2034 lest their orbits place them beyond easy reach.

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Look Up! Residents of Maine and Michigan Might Catch a Glimpse of the Northern Lights Tonight
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The aurora borealis, a celestial show usually reserved for spectators near the arctic circle, could potentially appear over parts of the continental U.S. on the night of February 15. As Newsweek reports, a solar storm is on track to illuminate the skies above Maine and Michigan.

The Northern Lights (and the Southern Lights) are caused by electrons from the sun colliding with gases in the Earth’s atmosphere. The solar particles transfer some of their energy to oxygen and nitrogen molecules on contact, and as these excited molecules settle back to their normal states they release light particles. The results are glowing waves of blue, green, purple, and pink light creating a spectacle for viewers on Earth.

The more solar particles pelt the atmosphere, the more vivid these lights become. Following a moderate solar flare that burst from the sun on Monday, the NOAA Space Weather Prediction Center forecast a solar light show for tonight. While the Northern Lights are most visible from higher latitudes where the planet’s magnetic field is strongest, northern states are occasionally treated to a view. This is because the magnetic North Pole is closer to the U.S. than the geographic North Pole.

This Thursday night into Friday morning is expected to be one of those occasions. To catch a glimpse of the phenomena from your backyard, wait for the sun to go down and look toward the sky. People living in places with little cloud cover and light pollution will have the best chance of spotting it.

[h/t Newsweek]

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10 Facts About the Dwarf Planet Haumea
Kevin Gill, Flickr // CC BY-2.0
Kevin Gill, Flickr // CC BY-2.0

In terms of sheer weirdness, few objects in the solar system can compete with the dwarf planet Haumea. It has a strange shape, unusual brightness, two moons, and a wild rotation. Its unique features, however, can tell astronomers a lot about the formation of the solar system and the chaotic early years that characterized it. Here are a few things you need to know about Haumea, the tiny world beyond Neptune.

1. THREE HAUMEAS COULD FIT SIDE BY SIDE IN EARTH.

Haumea is a trans-Neptunian object; its orbit, in other words, is beyond that of the farthest ice giant in the solar system. Its discovery was reported to the International Astronomical Union in 2005, and its status as a dwarf planet—the fifth, after Ceres, Eris, Makemake, and Pluto—was made official three years later. Dwarf planets have the mass of a planet and have achieved hydrostatic equilibrium (i.e., they're round), but have not "cleared their neighborhoods" (meaning their gravity is not dominant in their orbit). Haumea is notable for the large amount of water ice on its surface, and for its size: Only Pluto and Eris are larger in the trans-Neptunian region, and Pluto only slightly, with a 1475-mile diameter versus Haumea's 1442-mile diameter. That means three Haumeas could fit sit by side in Earth—and yet it only has 1/1400th of the mass of our planet.

2. HAUMEA'S DISCOVERY WAS CONTROVERSIAL.

There is some disagreement over who discovered Haumea. A team of astronomers at the Sierra Nevada Observatory in Spain first reported its discovery to the Minor Planet Center of the International Astronomical Union on July 27, 2005. A team led by Mike Brown from the Palomar Observatory in California had discovered the object earlier, but had not reported their results, waiting to develop the science and present it at a conference. They later discovered that their files had been accessed by the Spanish team the night before the announcement was made. The Spanish team says that, yes, they did run across those files, having found them in a Google search before making their report to the Minor Planet Center, but that it was happenstance—the result of due diligence to make sure the object had never been reported. In the end, the IAU gave credit for the discovery to the Spanish team—but used the name proposed by the Caltech team.

3. IT'S NAMED FOR A HAWAIIAN GODDESS.

In Hawaiian mythology, Haumea is the goddess of fertility and childbirth. The name was proposed by the astronomers at Caltech to honor the place where Haumea's moon was discovered: the Keck Observatory on Mauna Kea, Hawaii. Its moons—Hi'iaka and Namaka—are named for two of Haumea's children.

4. HAUMEA HAS RINGS—AND THAT'S STRANGE.

Haumea is the farthest known object in the solar system to possess a ring system. This discovery was recently published in the journal Nature. But why does it have rings? And how? "It is not entirely clear to us yet," says lead author Jose-Luis Ortiz, a researcher at the Institute of Astrophysics of Andalusia and leader of the Spanish team of astronomers who discovered Haumea.

5. HAUMEA'S SURFACE IS EXTREMELY BRIGHT.

In addition to being extremely fast, oddly shaped, and ringed, Haumea is very bright. This brightness is a result of the dwarf planet's composition. On the inside, it's rocky. On the outside, it is covered by a thin film of crystalline water ice [PDF]—the same kind of ice that's in your freezer. That gives Haumea a high albedo, or reflectiveness. It's about as bright as a snow-covered frozen lake on a sunny day.

6. HAUMEA HAS ONE OF THE SHORTEST DAYS IN THE ENTIRE SOLAR SYSTEM.

If you lived to be a year old on Haumea, you would be 284 years old back on Earth. And if you think a Haumean year is unusual, that's nothing next to the length of a Haumean day. It takes 3.9 hours for Haumea to make a full rotation, which means it has by far the fastest spin, and thus shortest day, of any object in the solar system larger than 62 miles.

7. HAUMEA'S HIGH SPEED SQUISHES IT INTO A SHAPE LIKE A RUGBY BALL.

haumea rotation gif
Stephanie Hoover, Wikipedia // Public Domain

As a result of this tornadic rotation, Haumea has an odd shape; its speed compresses it so much that rather than taking a spherical, soccer ball shape, it is flattened and elongated into looking something like a rugby ball.

8. HIGH-SPEED COLLISIONS MAY EXPLAIN HAUMEA'S TWO MOONS.

Ortiz says there are several mechanisms that can have led to rings around the dwarf planet: "One of our favorite scenarios has to do with collisions on Haumea, which can release material from the surface and send it to orbit." Part of the material that remains closer to Haumea can form a ring, and material further away can help form moons. "Because Haumea spins so quickly," Ortiz adds, "it is also possible that material is shed from the surface due to the centrifugal force, or maybe small collisions can trigger ejections of mass. This can also give rise to a ring and moons."

9. ONE MOON HAS WATER ICE—JUST LIKE HAUMEA.

Ortiz says that while the rings haven't transformed scientists' understanding of Haumea, they have clarified the orbit of its largest moon, Hi'iaka—it is equatorial, meaning it circles around Haumea's equator. Hi'iaka is notable for the crystalline water ice on its surface, similar to that on its parent body.

10. TRYING TO SEE HAUMEA FROM EARTH IS LIKE TRYING TO LOOK AT A COIN MORE THAN 100 MILES AWAY.

It's not easy to study Haumea. The dwarf planet, and other objects at that distance from the Sun, are indiscernible to all but the largest telescopes. One technique used by astronomers to study such objects is called "stellar occultation," in which the object is observed as it crosses in front of a star, causing the star to temporarily dim. (This is how exoplanets—those planets orbiting other stars—are also often located and studied.) This technique doesn't always work for objects beyond the orbit of Neptune, however; astronomers must know the objects' orbits and the position of the would-be eclipsed stars to astounding levels of accuracy, which is not always the case. Moreover, Ortiz says, their sizes are oftentimes very small, "comparable to the size of a small coin viewed at a distance of a couple hundred kilometers."

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