* Astronomy

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RE: Pluto

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Charon

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RE: Pluto

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Pluto should have its status as a planet reinstated, leading astronomers have said.
Senior space scientists, including experts from Nasa, will this week attack a controversial decision by the International Astronomical Union, the body responsible for astronomy nomenclature, to redefine what constitutes a planet.

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PLUTO

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This week the New Horizons mission team celebrates the 30th anniversary of the discovery of Plutos largest and first moon, Charon, by U.S. Naval Observatory astronomers James Christy and Robert Harrington.
Charon, whose discovery was officially announced on July 7, 1978, orbits nearly 18,220 kilometres from Plutos surface and has a diameter of about 1,210 kilometres. At half the diameter of Pluto, Charon is the largest moon relative to its planet in our solar system.

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Plutoid

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RE: Pluto

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Frost has been seen vaporising on Pluto for the first time, though the pictures of it were taken in the 1930s, soon after the dwarf planet was discovered.
A team led by Bradley Schaefer from Louisiana State University in Baton Rouge measured Pluto's brightness on 32 photographic plates taken at US observatories in 1933 and 1934. Using modern techniques, the team was able to measure Pluto's brightness far more accurately than at the time.
Comparing the results with observations from the early 1950s, the team showed that Pluto darkened by about 5 per cent in the intervening years. The results will be reported in the journal Icarus.

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Title: Pluto's Light Curve in 1933-1934
Authors: Bradley E. Schaefer, Marc W. Buie, Luke Timothy Smith

We are reporting on a new accurate photographic light curve of Pluto for 1933-1934 when the heliocentric distance was 40 AU. We used 43 B-band and V-band images of Pluto on 32 plates taken on 15 nights from 19 March 1933 to 10 March 1934. Most of these plates were taken with the Mount Wilson 60" and 100" telescopes, but 7 of the plates (now at the Harvard College Observatory) were taken with the 12" and 16" Metcalf doublets at Oak Ridge. The plates were measured with an iris diaphragm photometer, which has an average one-sigma photometric error on these plates of 0.08 mag as measured by the repeatability of constant comparison stars. The modern B and V magnitudes for the comparison stars were measured with the Lowell Observatory Hall 1.1-m telescope. The magnitudes in the plate's photographic system were converted to the Johnson B- and V-system after correction with colour terms, even though they are small in size. We find that the average B-band mean opposition magnitude of Pluto in 1933-1934 was 15.73 +- 0.01, and we see a roughly sinusoidal modulation on the rotational period (6.38 days) with a peak-to-peak amplitude of 0.11 +- 0.03 mag. With this, we show that Pluto darkened by 5% from 1933-1934 to 1953-1955. This darkening from 1933-1934 to 1953-1955 cannot be due to changing viewing geometry (as both epochs had identical sub-Earth latitudes), so our observations must record a real albedo change over the southern hemisphere. The later darkening trend from 1954 to the 1980s has been explained by changing viewing geometry (as more of the darker northern hemisphere comes into view). Thus, we now have strong evidence for albedo changes on the surface of Pluto, and these are most easily explained by the systematic sublimation of frosts from the sunward pole that led to a drop in the mean surface albedo.

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