14 DAY TRIAL // During an occultation event that occurred in November 2010, the dwarf planet Eris passed in front of a distant star. On standby, astronomers conducted a series of measurements of the object as this happened, and learned that this celestial body is Pluto's twin brother in terms of size.
Using a number of telescopes based in the Chilean Andes, the research team was able to compile the first exact measurement of Eris' diameter. Due to the fact that the object orbits very far from the Sun, inside the Kuiper Belt, direct observations and analyses are very difficult to perform.
As such, astronomers only had access to estimative figures until now. During the investigation, they also used the Belgian TRAPPIST telescope, which is located at the La Silla Observatory, in Chile. The facility is operated by the European Southern Observatory (ESO).
One of the most interesting things that the science team learned was that Eris most likely has a very reflective surface. Many now hypothesize that the object is in fact covered in a thin layer of ice, which helps reflect a great deal of whatever light manages to reach that faraway location.
It could be that the ice sheet is the frozen remnant of a solidified atmosphere. Researchers will present their discoveries and theories in length in a paper to be published today, October 27, in the top scientific journal Nature.
In order to determine a star suited for analyzing Eris through occultation, the researchers browsed through data collected by the MPG/ESO 2.2-meter telescope at La Silla. Experts from French, Belgian, Spanish and Brazilian universities then analyzed the star win great detail.
The TRAnsiting Planets and PlanetesImals Small Telescope (TRAPPIST) played a significant role in these observations. “Observing occultations by the tiny bodies beyond Neptune in the Solar System requires great precision and very careful planning,” lead study author Bruno Sicardy explains.
“This is the best way to measure Eris’s size, short of actually going there,” he adds. Occultations are however very rare. In the case of Eris, the next instance when its diameter will be analyzed in this manner will be in 2013.
“It is extraordinary how much we can find out about a small and distant object such as Eris by watching it pass in front of a faint star, using relatively small telescopes,” the investigator adds.
“Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members,” he adds. TRAPPIST and two other telescopes in San Pedro de Atacama were the only observatories out of 26 participants to observe the actual occultation.
The study also revealed that temperatures on the Sun-facing side of Eris reach around minus 238 degrees Celsius (minus 396.4 degrees Fahrenheit). These values drop even further for the dwarf planet's night side.