9 Compelling Facts About Neptune

NASA
NASA

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.

A Snow Moon—the Year’s Brightest Supermoon—Will Be Visible Next Week

iStock.com/jamesvancouver
iStock.com/jamesvancouver

Save the date: The next supermoon is set to light up skies on Tuesday, February 19. Because of when it's arriving, the event will also be a snow moon—a type of full moon that can only been seen this time of year, USA Today reports.

What is a supermoon?

A supermoon occurs when the moon is at its largest in the night sky. That means the Moon is not only full, but also at the point in its orbit that brings it closest to Earth—a position called perigee. On Tuesday, the Moon will appear 14 percent larger and 30 percent brighter than when it's farthest from our planet, making it the brightest supermoon of 2019.

This next supermoon will also have a fun nickname that fits the season. The full moon of each month has a special name. A harvest moon, the first full moon of September, is the best-known moniker, but there are also strawberry moons (June), sturgeon moons (August), and so on. A snow moon is the name for the full moon in February, alluding to February being the snowiest month of the year in the U.S.

When to watch the next supermoon

If the weather is clear in your area, the best time to see the super snow moon is early Tuesday morning on February 19, when the moon reaches its perigee. The Moon will become officially full six hours later at 10:53 a.m. EST. Sunday, Monday, and Tuesday nights will also offer spectacular views of a seemingly huge, nearly full moon.

Supermoons usually happen just a few times a year, but skygazers won't have to wait long for the next one: There's a super worm moon coming March 21, 2019.

[h/t USA Today]

11 Photos From the Opportunity Rover's Mission on Mars

NASA
NASA

In 2004, the rover Opportunity landed on Mars. Originally intended to serve a mere 90-day mission, the rover instead beamed back scientific discoveries for 15 years. But since a massive dust storm in 2018, the rover Opportunity ceased sending data—and now, NASA has declared its groundbreaking mission complete. (Its twin rover, Spirit, ended its mission in 2011.) Opportunity is the longest-serving robot ever sent to another planet. Let's celebrate Opportunity's Mars mission with a look at the images it captured.

1. Opportunity rover gets its first 360° shot.

Rover Opportunity's 360° photo of Mars
NASA/JPL/Cornell 

This 360° panorama, comprised of 225 frames, shows Mars as it was seen by the Opportunity rover on February 2, 2004. You can see marks made by the rover's airbags, made as Opportunity rolled to a stop. Here's a larger version of the photo.

2. Opportunity rover finds a meteorite.

Opportunity rover's photo of a meteorite on Mars
NASA/JPL/Cornell

This meteorite, found by Opportunity on January 19, 2005, was the first meteorite ever identified on another planet. The rover's spectrometers revealed that the basketball-sized meteorite was composed mostly of iron and nickel.

3. Opportunity rover shoots the Erebus Crater and drifts.

Opportunity rover's photo of Erebus craters and drift
NASA/JPL-Caltech/Cornell

On October 5, 2005—four months after Opportunity got stuck in an area NASA nicknamed "Purgatory Dune"—the rover skirted wind-deposited drifts in the center of the Erebus Crater, heading west along the outcrop (the light-toned rock) on the crater's rim, and snapped this photo with its PanCam.

4. Opportunity rover captures Martian rock layers.

Opportunity rover's photo of layers on Mars
NASA/JPL/Cornell

Located on the western ledge of the Erebus Crater, this ledge—called "Payson"—has a diverse range of primary and secondary sedimentary layers formed billions of years ago. According to NASA, "these structures likely result from an interplay between windblown and water-involved processes." Opportunity snapped this photo on April 5, 2006.

5. Opportunity rover comes to Cape Verde.

Opportunity rover's photo of Cape Verde
NASA/JPL-Caltech/Cornell

On October 20, 2007, Opportunity celebrated its second Martian birthday (one Martian year = 687 Earth days) by snapping this photo of Cape Verde, a promontory that juts out of the wall of the Victoria Crater. Scattered light from dust on the front sapphire window of the rover's camera created the soft quality of the image and the haze in the right corner.

6. and 7. Opportunity rover is hard at work on Marquette Island.

Opportunity rover's photo of Marquette Island
NASA/JPL-Caltech

This photo shows Opportunity approaching a rock called "Marquette Island" on November 5, 2009. Because its dark color made it stick out, the rover team referred to the rock—which investigations suggested was a stony meterorite—as "Sore Thumb." But it was eventually renamed, according to NASA, using "an informal naming convention of choosing island names for the isolated rocks that the rover is finding as it crosses a relatively barren plain on its long trek from Victoria Crater toward Endeavour Crater."

On November 19, 2009, the rover used its rock abrasion tool to analyze a 2-inch diameter area of Marquette, which scientists called "Peck Bay."

8. Opportunity rover encounters SkyLab Crater.

Opportunity rover's photo of SkyLab Crater
NASA/JPL-Caltech

Opportunity snapped a photo of this small crater, informally called Skylab, on May 12, 2011. Scientists estimate that the 30-foot crater was formed within the past 100,000 years. Click the photo for a larger version. You can also see the crater in stereo if you have a pair of anaglyph glasses!

9. Opportunity rover sees its shadow.

Opportunity rover's selfie
NASA/JPL-Caltech

On its 3051st day on Mars (August 23, 2012), Opportunity snapped this photo of its own shadow stretching into the Endeavour Crater.

10. Opportunity rover sees its first dust devil.

Opportunity rover's photo of a dust devil
NASA/JPL-Caltech/Cornell University/Texas A&M

Though its twin rover, Spirit, had seen many dust devils by this point, Opportunity caught sight of one for the first time on July 15, 2010.

11. Opportunity rover snaps a selfie.

Opportunity rover's self-portrait
NASA/JPL-Caltech/Cornell University/Arizona State University

A girl sure can get dusty traversing the Martian plains! Opportunity snapped the images that comprise this self-portrait with its panoramic camera between January 3 and January 6, 2014, a few days after winds blew off some of the dust on its solar panels. The shadow belongs to the mast—which is not in the photo—that the PanCam is mounted on.

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