When faraway Eris blocked the light of a star beyond it during a rare occultation event in November 2010, astronomers were able to accurately measure the shape and size of this dwarf planet, which was identified as a large object in our solar system in 2005.
Eris’ discovery was one of the reasons Pluto was relegated to dwarf planet status in 2006. Currently, Eris is three times further from the sun than Pluto, and was believed to be around 25 percent larger until this new research showed the two dwarfs to be about the same size.
Prior to the occultation, an international team of experts prepared to gather observations from 26 sites worldwide that they thought would be able to follow Eris’s shadow as it hid the star’s light, but only two of these captured the event directly, both in Chile.
One was the TRAPPIST telescope at La Silla Observatory, while the other was at San Pedro de Atacama using two telescopes combined. Together, the three devices detected a sudden decrease in the distant star’s brightness as Eris passed in front of it.
“Observing occultations by the tiny bodies beyond Neptune in the solar system requires great precision and very careful planning,” said study lead author Bruno Sicardy at Pierre and Marie Curie University in Paris in a press release.
“This is the best way to measure Eris’s size, short of actually going there.”
The results show that Eris is almost spherical, with its diameter measured at 2,326 kilometers (1,145 miles) to an accuracy of 12 kilometers (7 miles), compared with Pluto’s less precise diameter measurement of 2,300 to 2,400 kilometers (1,430 to 1,490 miles).
Due to Pluto’s atmosphere which makes its edge impossible to detect via occultations, its diameter is more difficult to measure precisely.
To measure Eris’s mass, the movement of its moon Dysnomia was tracked. According to this information, Eris is 27 percent heavier than Pluto with an estimated density of 2.52 grams per cm3.
“This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” said study co-author Emmanuel Jehin at Belgium’s University of Liège in the release.
Eris has a highly reflective surface, emitting 96 percent of the light that hits it, which makes it one of the most reflective objects in our solar system, like Saturn’s snowy satellite Enceladus.
This reflectivity is probably due to a thin coating of nitrogen-rich ice and frozen methane that is less than one millimeter thick, and may evaporate as Eris draws closer to the sun towards the closest point in its orbit around 5.7 billion kilometers away from our star.
“This layer of ice could result from the dwarf planet’s nitrogen or methane atmosphere condensing as frost onto its surface as it moves away from the sun in its elongated orbit and into an increasingly cold environment,” Jehin explained.
The data also enabled measurements of Eris’ surface temperature which is estimated at -238 degrees Celsius maximum on the dwarf planet’s sunny side, and even less on its night side.
“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,” Sicardy said.
“Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members.”
Eris’ discovery was one of the reasons Pluto was relegated to dwarf planet status in 2006. Currently, Eris is three times further from the sun than Pluto, and was believed to be around 25 percent larger until this new research showed the two dwarfs to be about the same size.
Prior to the occultation, an international team of experts prepared to gather observations from 26 sites worldwide that they thought would be able to follow Eris’s shadow as it hid the star’s light, but only two of these captured the event directly, both in Chile.
One was the TRAPPIST telescope at La Silla Observatory, while the other was at San Pedro de Atacama using two telescopes combined. Together, the three devices detected a sudden decrease in the distant star’s brightness as Eris passed in front of it.
“Observing occultations by the tiny bodies beyond Neptune in the solar system requires great precision and very careful planning,” said study lead author Bruno Sicardy at Pierre and Marie Curie University in Paris in a press release.
“This is the best way to measure Eris’s size, short of actually going there.”
The results show that Eris is almost spherical, with its diameter measured at 2,326 kilometers (1,145 miles) to an accuracy of 12 kilometers (7 miles), compared with Pluto’s less precise diameter measurement of 2,300 to 2,400 kilometers (1,430 to 1,490 miles).
Due to Pluto’s atmosphere which makes its edge impossible to detect via occultations, its diameter is more difficult to measure precisely.
To measure Eris’s mass, the movement of its moon Dysnomia was tracked. According to this information, Eris is 27 percent heavier than Pluto with an estimated density of 2.52 grams per cm3.
“This density means that Eris is probably a large rocky body covered in a relatively thin mantle of ice,” said study co-author Emmanuel Jehin at Belgium’s University of Liège in the release.
Eris has a highly reflective surface, emitting 96 percent of the light that hits it, which makes it one of the most reflective objects in our solar system, like Saturn’s snowy satellite Enceladus.
This reflectivity is probably due to a thin coating of nitrogen-rich ice and frozen methane that is less than one millimeter thick, and may evaporate as Eris draws closer to the sun towards the closest point in its orbit around 5.7 billion kilometers away from our star.
“This layer of ice could result from the dwarf planet’s nitrogen or methane atmosphere condensing as frost onto its surface as it moves away from the sun in its elongated orbit and into an increasingly cold environment,” Jehin explained.
The data also enabled measurements of Eris’ surface temperature which is estimated at -238 degrees Celsius maximum on the dwarf planet’s sunny side, and even less on its night side.
“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,” Sicardy said.
“Five years after the creation of the new class of dwarf planets, we are finally really getting to know one of its founding members.”
