October 27, 2011 23:38
Astronomers have for the first time were able to accurately measure the diameter of Eris because the dwarf planet eclipsed star.
Such cases are very rare cover and watch their hard as dwarf planets are far away and have a small size. The next such event involving Eris is not expected before 2013. But the cover — it is the most accurate and often the only way to measure the shape and size of distant solar system bodies.
Star candidate for coating was determined by studying the images taken by the 2.2-meter telescope of the MPG / ESO, which is located at La Silla Observatory. The observations were carefully planned and executed a group of astronomers from several (mostly French, Belgian, Spanish and Brazilian) universities under the guidance of Bruno Sicard of the Paris Observatory.
The studies were conducted at the end of 2010 in 26 locations around the world — where the earth slipped unseen shadow dwarf planet. The project involved not only professionals but also amateurs. But only two places failed direct observations — both times in Chile: a telescope TRAPPIST La Silla observatory and two telescopes at San Pedro de Atacama.
The combined data showed that the shape of Eris is close to spherical. Distort the results would big mountains, but they are unlikely to such a large icy objects.
Previous work by other methods led to assume that Eris is about 25% larger than Pluto, that is, its diameter is about three thousand kilometers. If we believe the new data, it is equal to 2326 ± 12 km (Pluto — 2 300-2 400 km, the diameter of Pluto is harder to measure, since the presence of the atmosphere does not identify the exact boundaries in coatings).
To estimate the mass of Eris, scientists have used motion Dysnomia, her companion. Found that a celestial body is 27% heavier than Pluto (1.66 × 10? Kg, ie 22% of the mass of the Moon).
Accordingly, the density of Eris is 2.52 g / cm (Compared to the density of the Moon — 3.3 g / cm). From this it follows that the dwarf planet is 85% composed of hardwood and 15% — of water ice. The latter, apparently, is the mantle layer thickness of 100 km. Above it is a millimeter layer of frozen atmosphere.
The surface of Eris, as it turned out, highly reflective — 0.96. It is brighter than fresh snow (compared to the visible albedo of the Moon — .136, almost like coal). So, this is one of the brightest objects in the solar system, along with Saturn's moon Enceladus, which is also covered with ice. The surface of Eris is likely to consist of nitrogen-rich ice mixed with frozen methane, as evidenced by the range of the object.
The new data also allowed the scientists to re-measure the surface temperature of the dwarf planet. The side facing the sun, heated to 35 K.
Pluto's twin sister Eris has a "blinking" atmosphere