Night Owls

Giuseppe Piazzi at the Palermo observatory has found a slow-moving star-like object, at first taken for a comet. Named Ceres, it was given a planetary symbol and listed as a planet in astronomy books, along with Pallas, Juno and Vesta, for about half a century. Only when many similar bodies turned up in the same region did astronomers start to treat them as a separate class, the asteroids. Source

Clyde Tombaugh, a young assistant at the Lowell Observatory in Flagstaff, Arizona, found a faint moving object on photographic plates taken in January 1930, confirming it on 18 February. The discovery is announced by telegram to Harvard College Observatory on 13 March. The new planet is named Pluto on the suggestion of Venetia Burney, an 11-year-old girl in Oxford, and is at first thought to be large. Source

David Jewitt and Jane Luu, observing from Mauna Kea in Hawaii, have found a small body orbiting the Sun beyond Neptune, designated 1992 QB1. It is the first trans-Neptunian object found since Pluto and its moon Charon, and supports the old idea of a belt of icy bodies in that region, now called the Kuiper belt. Some press reports call it a possible tenth planet. Source

The International Astronomical Union says that no proposal to change Pluto's status as the ninth planet has been made by any of its bodies. Astronomers had discussed giving Pluto a number in a technical list of objects beyond Neptune, but this was never meant to change its status, and the committee concerned has decided not to give Pluto a minor-planet number. The IAU says reports to the contrary caused needless public concern. Source

The Hayden Planetarium in New York shows a model of the solar system with only eight planets, leaving Pluto out. Astrophysicist Neil deGrasse Tyson, its director, later receives angry letters from schoolchildren about it. Source

Mike Brown of Caltech, with Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale, says they have found an object larger than Pluto orbiting the Sun about three times as far out, nearly 100 times the Earth-Sun distance. It is catalogued as 2003 UB313 and was first spotted on images from the Samuel Oschin Telescope at Palomar on 8 January 2005. NASA and the discoverers call it the tenth planet; it has no official name yet. Source

Astronomers using the Hubble Space Telescope have found two small moons around Pluto besides Charon, which was found in 1978. The search was made by members of the team preparing NASA's New Horizons mission. The new moons, many thousands of times fainter than Pluto, are provisionally called S/2005 P1 and S/2005 P2. Source

NASA's New Horizons probe, about the size of a piano, has been launched on an Atlas V rocket from Cape Canaveral, Florida. It is the first mission to Pluto and is due to fly past Pluto and its moon Charon in July 2015. Source

Hubble images from December 2005 show 2003 UB313, nicknamed Xena, to be about 2,400 km (1,490 miles) across, against about 2,290 km (1,422 miles) for Pluto. Ground-based estimates had put it about 30 percent bigger than Pluto. Because it is smaller than thought but bright, its surface must be very reflective, possibly from fresh methane frost. Source

Brian Marsden, director of the IAU's Minor Planet Center, says the IAU working group that has discussed the definition of a planet for years was divided, so another committee, including non-scientists, has been formed. It is to meet in the coming weeks and make a recommendation to the General Assembly in Prague in August, where members may be allowed to vote. Marsden himself would accept eight planets. Source

NPR reports that the IAU panel set up to define 'planet', seven people led by Harvard historian of astronomy Owen Gingerich, met in Paris in June and reached a unanimous view. Sources say Pluto would keep its title in a new class of small planets, and other bodies might join. Gingerich will not give details but says the result will please the 'Plutocrats' and the children of the United States. Panel member Iwan Williams talks of 'no more than four or five new planets'. An IAU executive member, Bob Williams, is not sure members in Prague will approve it. Source

The International Astronomical Union opens a 12-day General Assembly in Prague on Monday, and one question is whether the solar system has eight, nine or more planets. There is still no official definition of 'planet'. Alan Stern of the Southwest Research Institute says it is embarrassing that astronomers do not have one. Brian Marsden says life would be simpler with eight planets. Alan Boss suggests Pluto could be an 'ice dwarf planet'. Mike Brown, who found 2003 UB313, says he is agnostic. Source