Comet 10P/Tempel 2’s Nucleus Rotation Determined to Within 10 Seconds
October 6, 2009 – 11:00 am
When professional astronomers study a comet carefully enough and they are patient enough to do so every chance they get, the results can be astonishing. This type of result is just what Lowell Observatory astronomers and colleagues have with research on Comet 10P/Tempel 2. Lowell astronomer David Schleicher led a team that made the best measurement of the comet’s rotation period, showing that the rotation period of Tempel 2’s nucleus has lengthened, or the comet has slowed down, by about 10 seconds every five years.
“We’ve made the definitive determination,” said Schleicher. “We first measured it in 1988 and then in 1999 and we have a lot of data over many months.” The research team measured the brightness of Tempel 2’s nucleus including how the brightness increases and decreases as the nucleus rotates. The results, Nucleus and Coma Properties of Comet 10P/Tempel 2 During Its 1999 Apparition, are being presented today at the American Astronomical Society’s Division of Planetary Sciences meeting in Puerto Rico.
As the comet rotates, the cross section that reflects sunlight back to the Earth changes. Think of it as a football tumbling—when you are looking at it end on you see less of it than if you look at it from the side. By measuring subtle changes in the comet’s brightness the team could determine when they were seeing a smaller or larger portion of the nucleus. With enough data, they can determine not only the rotation period, but also the approximate ratio of the long and short axes, and the tilt of the comet’s rotation axis.
During the comet’s 1999-2000 apparition the astronomers carried out an intensive observational campaign obtaining 31 nights of data using Lowell telescopes over 11 months. Summer student Eddie Schwieterman, a senior at Florida Institute of Technology, helped to process the data from 1999 and to compare the rotation period determined by the Lowell team with the results other astronomers obtained in studies from 1987-1994. By combining the large number of observations made by other astronomers with the precise data obtained by the Lowell Observatory team in 1999, Schleicher and his colleagues were able to conclusively show that the rotation period had changed since 1988. Other research goals for the comet are an ongoing effort to determine its mass and to try to locate where the jet of material is coming from on the surface of the nucleus.
“It is a fairly anemic comet,” said Schleicher. “It doesn’t have a lot of activity. You might think of it as an older comet that is nearly entirely crusted over.” Schleicher noted that Comet 10P/Tempel 2 will be back next spring. And Lowell astronomers have been studying it since 1988 when they measured the comet’s size. “Twenty years later and we’re still working to put all the pieces together,” said Schleicher.
image: Lowell Observatory has a long history of observing comets, including studies of Halley’s Comet in 1910 (pictured in this computer reconstructed image); the first observation of a comet in IR wavelengths (Comet Skjellerup, 1927 IX = 1927 k = 1927 X1); and an ongoing study that has characterized the physical properties of more than 160 comets since 1976. Lowell Observatory/NOAO/AURA/NSF