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.

Stardust Created 7 Billion Years Ago Is the Oldest Stuff on Earth

NASA/JPL-Caltech/Harvard-Smithsonian CfA
NASA/JPL-Caltech/Harvard-Smithsonian CfA

Between 5 and 7 billion years ago, a dying star shot an explosion of particles through space. Some of that stardust ended up in a meteorite that landed in Murchison, Australia, in 1969. And according to new research, it's officially the oldest known solid material on Earth.

For the new study, published in the journal Proceedings of the National Academy of Sciences 30 years after the research began, scientists pulverized fragments of the meteorite to determine its age. The resulting paste-like substance reportedly smelled like "rotten peanut butter." The strange aroma "comes from byproducts of the breakdown of the abiotic organic molecules—molecules that didn't form from life—in the Murchison meteorite," lead author Philipp R. Heck, a curator at Chicago's Field Museum, tells Mental Floss.

Heck used acid to further break down the rock and isolate the grains of stardust, which are smaller than the period at the end of this sentence. To date the particles, the team measured neon isotopes that formed when cosmic rays hit the solid matter making up the stardust. The older the stardust is, the more cosmic rays it has been exposed to, so the amount of neon isotopes it contains can be used to estimate its age. Heck compares the method to collecting water in a bucket to determine how long it's been raining.

The team found that the meteorite contained particles older than 5.5 billion years and possibly as old as 7 billion years. The Earth has only been around for 4.5 billion years, and the sun for 4.6 billion. The formation of this super-old stardust is believed to have occurred during an "astral baby boom," according to a statement released by the Field Museum, in which an uptick in stellar activity literally created the matter that shapes the world we know today.

When the grains formed, "most stars that we see tonight in the sky didn’t exist," Heck says. "The bright stars that would have been shining through our galaxy were the previous generation of stars, our parent stars. [They] formed the elements that later became fuel and ingredients for the solar system, Earth, and us. These stars formed the material that we are made out of."

While the grains in the Murchison meteorite are the oldest solid material on the planet, many of the gases on Earth are much older. Some of the hydrogen in your body, for example, may have originated with the Big Bang 13.7 billion years ago.

17-Year-Old NASA Intern Helped Discover Twin-Starred 'Tatooine' Planet

NASA's Goddard Space Flight Center/Chris Smith
NASA's Goddard Space Flight Center/Chris Smith

On January 6, NASA announced that it had detected an Earth-sized planet, TOI 700 d, 100 light-years away from Earth that could be capable of hosting life. The same mission also led to the discovery of a rare planet with twin suns courtesy of a 17-year-old intern.

As CNN reports, high school student Wolf Cukier was combing through data collected by NASA's Transiting Exoplanet Survey Satellite, or TESS, when he noticed something strange about one binary star system. The system TOI 1338 consists of two stars that orbit each other once every 15 days. When the smaller of the two stars passes across the larger one, it's known as a stellar eclipse. But one signal that had been flagged as a stellar eclipse wasn't an eclipse at all; just three days into his internship at NASA's Goddard Space Flight Center, Cukier had found a planet orbiting the two stars.

The planet, since dubbed TOI 1338 b, is like a real-life version of Luke Skywalker's home planet Tatooine from the Star Wars movies. It's located roughly 1300 light-years away in the Pictor constellation and is somewhere between Neptune and Saturn in size. Twin-starred planets are rare, and this marks this first one detected through NASA's planet-hunting TESS mission.

TESS launched in 2018 with the goal of finding new planets outside our own solar system. Planets are typically discovered by recording stars over time and looking for dips in their brightness that indicate passing planets. This system becomes complicated when dealing with binary star systems, as dips in light caused by a planet in transit can get confused with an eclipsing star and vice versa. Without Cukier's keen eye, this latest discovery may have gone undetected.

It may have the same number of stars as Tatooine, but the similarities TOI 1338 b shares with the planet from Star Wars end there. So far, TOI 700 d is the only planet discovered by TESS that has a chance of being habitable.

[h/t CNN]

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