In 2005, astronomer Mike Brown and his colleagues Chad Trujillo and David Rabinowitz announced the discovery of a previously unknown asteroid in the Kuiper belt beyond the orbit of Neptune. The researchers named the object Eris, after the Greek personification of strife and discord, which was assigned by the IAU a year later. Along with Haumea and Makemake, which they also observed in 2004 and 2005 (respectively), this object sparked the Great Planetary Debate, which continues to this day. Meanwhile, astronomers have continued to study the trans-Neptunian region to learn more about these objects.
Subsequent observations have allowed astronomers to get a better idea of Eris’ size and mass, but there are still many unanswered questions about the dwarf planet’s structure and how it compares to Pluto.in recent researchMike Brown, Professor, University of California, Santa Cruz francis nimo present a series of models based on new mass estimates for Eris’ moon Dysnomia. According to their results, Eris is likely to have a convective icy shell and a rocky core, distinct from Pluto’s conductive shell.
Their paper, “Eris’ internal structure inferred from the evolution of its rotation and orbit‘ was recently published in a magazine. scientific progress. This research began when Nimmo visited Professor Brown at the California Institute of Technology and realized that some of his unpublished data could help reveal information about Ellis’ properties. . We now know that Eris is about the same size and mass as Pluto, and has a highly eccentric orbit around the Sun, ranging from 38.271 AU at perihelion to 97.457 AU at aphelion. This is nearly twice the eccentricity of Pluto’s orbit, which puts it about 50% farther from the Sun.
For several months, Brown and Nimmo worked on Ellis’ model, which incorporated two important pieces of information. The first concerned Eris’ only known moon, Dysnomia, and how the two objects always point in the same direction. “This happens because the large planet rotates due to the ebb and flow of the tides caused by the small moon,” Nimmo said recently at UCSC. press release. “The bigger the moon, the faster the planet spins. So as soon as we know that, we can start doing the actual calculations.”
Astronomers can use the rotation and orbital characteristics of planets and moons to infer certain properties, such as their internal structure. But until recently, scientists had no estimates of dysnomia’s size, mass, or density. Fortunately, Brown and his colleague, National Radio Astronomy Observatory (NRAO) researcher Brian J. Butler, recently used the Atacama Large Millimeter-Submillimeter Array (ALMA) to study Dysnomia and Eris (as well as Orcus and its satellites). Vance) was observed. Based on their findings, Planetary Science JournalDysnomia has a diameter of approximately 615 km (382 miles), and the Dysnomia to Eris mass ratio is 0.0085.
This upper mass limit provided a second important piece of information about Eris’ internal structure. A major (but unexpected) result of the Brown and Nimmo model is that Ellis is surprisingly dissipative. This is a concept in thermodynamics in which a system operates out of equilibrium. From this, they determined that Eris has a rocky core surrounded by a crust that may be convecting with layers of ice. “Rocks contain radioactive elements that generate heat,” Nimmo said. “And that heat has to escape somehow. So as the heat escapes, it promotes slow agitation within the ice.”
This is distinguished from Pluto, which has a conductive shell, as revealed by: new horizons Mission. Brown and Nimmo hope to have more precise measurements of Dysnomia’s mass in the near future, which will provide additional data on Eris’ shape. Because of the distance, Eris appears as a single pixel of light, while Dysnomia appears as a faint speck next to it (see below). Therefore, astronomers must watch Eris pass in front of the background star to reconstruct its shape. This is similar to the transit method used by astronomers to detect exoplanets and limit their size.
as nemo summarizedThese measurements will help refine the model he and Brown created.
“If Dysnomia is smaller than that, Eris is squishier. I would argue that Eris must be fairly smooth, because if there is terrain on the surface, the ice will flow and that terrain will disappear. Therefore, if Eris is It would be good to be able to measure what the shape is, because if it’s very irregular, it won’t match our model.”
“When the stars flash and then come back, you can see how wide Eris is at that point. And when you do that with a lot of stars, you can actually reconstruct the shape. People I hope they actually do that, but I don’t know if they actually do that.”