10 Facts About the Dwarf Planet Eris

An artist's rendering of the dwarf planet Eris
An artist's rendering of the dwarf planet Eris
ESO/L. Calçada and Nick Risinger (skysurvey.org) // CC BY 4.0

Far beyond the orbit of Pluto exists a celestial body that’s a little smaller, a little colder, and a little denser—the dwarf planet Eris. In Greek mythology, Eris is the goddess of strife, and never was there a more appropriately named body in the solar system. When astronomer Mike Brown of Caltech and his team discovered Eris in 2005, the finding set off a chain reaction that would see the planetary status of Pluto called into question. Here are 10 things you might not know about Eris.

1. An Eridian day is just slightly longer than Earth's.

If you were an astronaut, you wouldn’t find an Eridian day, at 25.9 hours, too disconcerting. This compares favorably with, say, Venus, whose day lasts 5832 hours (admittedly, it's an outlier). An Eridian year is a bit longer than what we're used to, with the dwarf planet completing an orbit of the Sun every 557 Earth years. And that orbit is not along the relatively flat plane with the orbits of most of the other planets of the solar system. Imagine your elementary school solar system model of planets on wires around a light bulb: Instead of a path neatly aligned with the other planets, Eris’s orbit is tilted at a 44 degree angle.

2. Eris was once thought to be bigger than Pluto.

After Eris’s discovery, the best measurements then available placed it as slightly larger than Pluto, with a radius of 722 miles. But after the initial spacecraft reconnaissance of Pluto by New Horizons in 2015, Pluto’s ranking as the ninth-largest planetary object orbiting the Sun was restored; it is now known to have a radius of 736 miles. In comparison, Earth’s Moon has a radius of 1079 miles. Ganymede, Callisto, Io, and Europa (Jupiter’s largest moons), Titan (Saturn’s largest moon), and Triton (Neptune’s largest moon) are also bigger than Pluto. On the other hand, Eris is 34 percent denser than Pluto.

3. Eris is responsible for the big debate over the definition of "planet."

When Brown’s team discovered Eris, it was initially hailed as either the 10th planet of the solar system, or a big problem for scientists who like nicely ordered celestial objects. The discovery of Eris came on the heels of the discoveries of Sedna and Quaoar, both beyond the orbit of Neptune. Astronomers were looking at the possibility of a dozen planets in the solar system or more, because—based on these three—who knew how many Pluto-sized bodies were out there? The International Astronomical Union eventually defined a planet in our solar system as something that has achieved hydrostatic equilibrium (in other words, it's round), orbits the Sun, and has “cleared its neighborhood” (i.e., is gravitationally dominant in its orbit). Yet the debate continues [PDF].

4. It has its own moon.

Eris has a moon called Dysnomia that circles the dwarf planet every 16 days. In Greek mythology, Dysnomia is the name of one of Eris’s daughters and means “anarchy.”

5. Initially, Eris was called Xena.

Before it was called Eris, it was called 2003 UB313 (a provisional designation by the International Astronomical Union). But before that, Brown’s team of astronomers named it Xena—yes, of Warrior Princess fame. “We always wanted to name something Xena,” Brown told The New York Times in 2005 after the discovery. Among Brown’s colleagues, Dysnomia was called Gabrielle, who was, of course, Xena’s sidekick.

6. Its surface is like Pluto's heart.

The primary way to analyze the composition of the surface of a celestial body is through spectroscopy, which is basically looking at an object and seeing how much light comes back at you as a function of wavelength. Many materials have characteristic absorptions of light at certain frequencies, and so less light will come back to you at that frequency.

“Eris has very, very strong methane ice absorption bands,” Will Grundy, a planetary scientist at Lowell Observatory and a member of the New Horizons team, tells Mental Floss. “They are much stronger than Pluto’s, and of course we’ve seen methane all over the place on Pluto, so I think it’ll be more ubiquitous on Eris’s surface.” The implication is that Eris is more than just a dead ice rock in space, because methane degrades very quickly in a space environment, darkening and forming heavier hydrocarbons. “The fact that it’s bright and covered with methane ice says it’s refreshing its surface relatively rapidly, and there are any number of ways it can do that. One is the methane just periodically sublimates underneath the atmosphere and then re-condenses somewhere else, just sort of painting on top of whatever dark stuff that forms,” Grundy says.

7. Pluto data enriches our understanding of Eris.

Pluto data returned from the New Horizons spacecraft give scientists new ideas about the processes that might be at work on Eris. “One of the things the Pluto flyby showed us that nobody really talked about, even in wild speculations, was something like Sputnik Planitia: this big, bright, teardrop-shaped region on the encounter hemisphere. Volatile ices there are trapped in a deep basin and they are just convectively overturning, like a simmering pot of soup,” Grundy says.

That process might be happening writ large on Eris. It might be, in a sense, an ice lava lamp planet. “I’ve called it a Sputnik planet,” Grundy says, “but nature is much more clever than scientists at coming up with new ways of doing things with the same old ingredients. Who knows, we might get there and find out it’s doing something completely different than Pluto was doing to refresh its surface. The real lesson is that activity on a lot of different timescales is possible, even on a tiny little planet that’s at frigid temperatures, far away from the sun.”

8. Its neighborhood is a potential gold mine of information.

In comparative planetology, scientists use planets to understand other planets. By studying Venus, which is similar to Earth in terms of size, mass, and basic composition, scientists can better understand how our planet operates and evolved. The objects in Eris’s celestial neighborhood work the same way. “The Kuiper Belt”—a region rich in rocky and icy objects beyond Neptune’s orbit—“is an incredibly rich environment for comparative planetology because there are so just many of these tiny planets out there,” Grundy says. “It’s going to take a while to discover them all, let alone explore them all, but that’s what is exciting about it.” The New Horizons data from Pluto are helping planetary scientists develop models to tease out the secrets of Eris.

9. Geologists could learn a lot, too.

“If you work out the surface area of, say, objects there that are bigger than 100 kilometers, based on extrapolation, the Kuiper Belt has more solid geology surface area than of all of the planets in the solar system—including the terrestrial planets—combined,” Grundy explains, adding that it holds true even if you wanted to include the ocean floor on Earth. “If you like geology—and especially if you like exotic, cryogenic temperature geology—this is the place to explore, and there’s just so much territory to explore out there.”

10. A mission to Eris will take a while.

It took New Horizons, one of the fastest spacecrafts ever built, nine years to get to Pluto. Eris is currently three times farther from the Sun than Pluto (though due to a highly elliptical orbit, this number changes), so if a mission is ever approved, don’t expect to find out how it all ends. “It takes decades to pull something like that together, so if you want to be around to see the results, you’ve got to start young,” Grundy says. A possible future Kuiper Belt mission might be part of a flyby mission to Uranus or Neptune, after which the spacecraft would continue into that region of space. It will be a very long time before technology allows an Earth-centric telescope—in space or otherwise—to take pictures of the geology of Eris.

Keep Your Cat Busy With a Board Game That Doubles as a Scratch Pad

Cheerble
Cheerble

No matter how much you love playing with your cat, waving a feather toy in front of its face can get monotonous after a while (for the both of you). To shake up playtime, the Cheerble three-in-one board game looks to provide your feline housemate with hours of hands-free entertainment.

Cheerble's board game, which is currently raising money on Kickstarter, is designed to keep even the most restless cats stimulated. The first component of the game is the electronic Cheerble ball, which rolls on its own when your cat touches it with their paw or nose—no remote control required. And on days when your cat is especially energetic, you can adjust the ball's settings to roll and bounce in a way that matches their stamina.

Cheerable cat toy on Kickstarter.
Cheerble

The Cheerble balls are meant to pair with the Cheerble game board, which consists of a box that has plenty of room for balls to roll around. The board is also covered on one side with a platform that has holes big enough for your cat to fit their paws through, so they can hunt the balls like a game of Whack-a-Mole. And if your cat ever loses interest in chasing the ball, the board also includes a built-in scratch pad and fluffy wand toy to slap around. A simplified version of the board game includes the scratch pad without the wand or hole maze, so you can tailor your purchase for your cat's interests.

Cheerble cat board game.
Cheerble

Since launching its campaign on Kickstarter on April 23, Cheerble has raised over $128,000, already blowing past its initial goal of $6416. You can back the Kickstarter today to claim a Cheerble product, with $32 getting you a ball and $58 getting you the board game. You can make your pledge here, with shipping estimated for July 2020.

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Where to Watch SpaceX’s Historic Astronaut Launch Live

Joe Raedle/Getty Images
Joe Raedle/Getty Images

SpaceX will make history today when it launches its first crewed spacecraft from Cape Canaveral, Florida, at 4:33 p.m. EDT. Powered by a Falcon 9 rocket, the Crew Dragon spacecraft will transport NASA astronauts Doug Hurley and Bob Behnken to the International Space Station, marking the company's first-ever crewed mission and the first crewed launch from the U.S. since 2011. If you want to watch the momentous event from home, there are plenty of ways to stream it live online.

Both SpaceX and NASA will be hosting livestreams of the May 27 launch. NASA's webcast kicks off at 12:15 p.m. EDT today with live looks at the Crew Dragon and Falcon 9 rocket at the Kennedy Space Center. The feed will continue streaming until late in the morning of Thursday, May 28, when the spacecraft is set to dock at the International Space Station. You can catch the coverage on NASA's website, its social media channels, or on the NASA TV channel through cable or satellite. SpaceX's stream also starts at 12:15 p.m. EDT, and it will be broadcast on the company's YouTube channel. (You can watch the video below).

Several television networks will be covering the event, with ABC and National Geographic airing "Launch America: Mission to Space Live" at 3 p.m., and Discovery and the Science Channel showing "Space Launch Live: America Returns to Space" at 2 p.m. If you're looking for more online streaming options, the American Museum of Natural History and Intrepid Museum in New York City will be hosting live events to celebrate the launch this afternoon on YouTube.

The launch has been scheduled down to the minute, but SpaceX still has time to change that depending on the weather. If today's launch doesn't happen according to plan, there are windows on May 30 and May 31 set aside for second attempts.

[h/t TechCrunch]