* Astronomy

Die-hard Pluto fans still seeking redemption for their demoted planet have cause for despair this week. New data shows that the dwarf planet Eris is 27 percent more massive than Pluto, thereby strengthening the decree last year that there are eight planets in the solar system and a growing list of dwarf planets.
According to Mike Brown, the discoverer of Eris, and his graduate student Emily Schaller, the data confirms that Eris weighs 16.6 billion trillion kilograms. They know this because of the time it takes Eris's moon, Dysnomia, to complete an orbit.

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In 2005, Michael Brown of the California Institute of Technology and his team discovered a large body in the outer solar system. It was not the first distant object that had been found in the Kuiper Belt -- that region encircling our solar system is composed of hundreds of icy objects. But it was the largest known Kuiper Belt object, just beating out Pluto in terms of size, and so their discovery was heralded as “the tenth planet.”
Brown’s discovery, now named “Eris,” has since been demoted by the International Astronomical Union to a “dwarf planet,” along with the former ninth planet, Pluto. This re-categorization came about partly because scientists think we will discover many planet-sized globes in the Kuiper Belt. Recent discoveries of many unusual extrasolar planets in other solar systems also raised questions about what should and shouldn’t be called a planet.

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Still mourning the loss of Pluto as a planet? Blame Caltech astronomer Michael Brown. His 2005 discovery of Eris, a new "planet" past Pluto, prompted other astronomers to redefine what makes a planet, and eventually rule out Pluto and Eris and settle on eight true planets. Pluto and Eris now have the new designation of dwarf planet.
Brown will present the 25th annual Bunyan Lecture at Kresge Auditorium on Wednesday, Oct. 25, at 7:30 p.m., telling the story of his discovery and explaining why it prompted changing the definition of a planet. His talk, titled "Pluto, Eris and the Dwarf Planets of the Solar System," is free and open to the public. The Astronomy Program in the Department of Physics will host the event.

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Eris, the largest dwarf planet known, was discovered in an ongoing survey at Palomar Observatory's Samuel Oschin telescope by astronomers Mike Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University). We officially suggested the name on 6 September 2006, and it was accepted and announced on 13 September 2006. In Greek mythology, Eris is the goddess of warfare and strife. She stirs up jealousy and envy to cause fighting and anger among men. At the wedding of Peleus and Thetis, the parents of the Greek hero Achilles, all the gods with the exception of Eris were invited, and, enraged at her exclusion, she spitefully caused a quarrel among the goddesses that led to the Trojan war. In the astronomical world, Eris stirred up a great deal of trouble among the international astronomical community when the question of its proper designation led to a raucous meeting of the IAU in Prague. At the end of the conference, IAU members voted to demote Pluto and Eris to dwarf-planet status, leaving the solar system with only eight planets.

The satellite of Eris has received the offical name Dysnomia, who in Greek mythology is Eris' daughter and the demon spirit of lawlessness. As Dysnomia is a bit of a mouthful, we tend to simply call the satellite Dy, for short.
As promised for the past year, the name Xena (and satellite Gabrielle) were simply placeholders while awaiting the IAU's decision on how an official name was to be proposed. As that process dragged on, however, many people got to know Xena and Gabrielle as the real names of these objects and are sad to see them change. We admit to some sadness ourselves. We used the names for almost two years now and are having a hard time switching. But for those who miss Xena, look for the obvious nod in the new name of the moon of Eris.

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