Hence, IAU recommendations should rest on well-established scientific facts and have a broad consensus in the community concerned. Such decisions and recommendations are not enforceable by any national or international law rather they establish conventions that are meant to help our understanding of astronomical objects and processes. ![]() As Professor Ron Ekers, former President of the IAU, explained in the newspaper of the 2006 IAU General Assembly: The IAU has been responsible for naming planetary bodies and their satellites since the early 1900s. These discoveries prompted astronomers to ask the question: "What constitutes a planet?" The process of defining a planet The team found several objects that did not resemble any of the 8 planets we consider today but were large enough to be compared to Pluto. Subsequent observations (Brown, 2006) showed that the new object, initially named 2003 UB 313 according to the IAU's naming protocol, was more massive than Pluto and that it, too, had a satellite. Later analysis showed that they discovered another cold world: slightly larger than Pluto and orbiting the Sun (Brown et al., 2004). They imaged a region of the sky that showed an object moving relative to the background stars, just as Clyde Tombaugh did decades earlier. In 2003, Mike Brown (Caltech), Chad Trujillo (International Gemini Observatory) and David Rabinowitz (Yale University) searched the edge of our Solar System from the Palomar Observatory in the United States. Today, we know of more than 1000 objects that orbit in the so-called transneptunian region these bodies are often referred to as Trans-Neptunian Objects (TNOs).ĭue to the influx of TNO discoveries, it was inevitable that one or more might be found to rival Pluto in size. They discovered (Jewitt and Luu 1993) the first in a special class of objects orbiting beyond Neptune, known as Kuiper Belt Objects, which have major implications for Solar System formation theory. In 1992, this was finally validated by David Jewitt and Jane Luu from the University of Hawaii. In the decades following Pluto’s discovery, astronomers postulated that there might be a belt of objects beyond the orbit of Neptune. 2018) and are officially named Nix, Hydra, Kerberos and Styx by the IAU (Aksnes, 2006 Showalter et al., 2013). The smaller four were discovered using the Hubble Space Telescope between 20 (Stern et al. The largest, Charon, was discovered in 1978 (Buie et al., 2006). But Pluto is not alone: its five satellites were later discovered. It is a frigid world, billions of kilometres from the Sun, and 30 times less massive than the then-smallest known planet, Mercury. The object Tombaugh discovered was eventually named Pluto, a name officially adopted by the American Astronomical Society, the Royal Astronomical Society in the UK, and the International Astronomical Union. Tombaugh had found his new planet! (Stern & Mitton, 2005) The developing landscape of the Solar System While comparing two photographic plates to search for this slight movement, Tombaugh noticed a small object moving only a few millimetres near the constellation Gemini. ![]() Tombaugh was continuing the search for an elusive planet - Planet X - that astronomers of the time had incorrectly believed to be responsible for perturbing the orbits of Uranus and Neptune.Īfter spending numerous nights at the telescope and months tediously scanning his data for the telltale signs of a planet – slight movements of the same body between two images (in those days, on photographic plates) of the sky taken at different times - Tombaugh made a discovery. The young astronomer was Clyde Tombaugh, an observing assistant working at the observatory made famous by the great astronomer Percival Lowell. In early 1930, an astronomer working at the Lowell Observatory in the United States made a discovery that would ultimately initiate a dramatic change in the way we look at our Solar System. The developing landscape of our Solar System.
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