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Keck Images of Neptune Best Ever Captured: Reveal New Details of Giant Planet's Icy Atmosphere

Mauna Kea, Hawaii – October 25, 2000:   Astronomers observing with the adaptive optics instrument on the Keck II Telescope have obtained the best pictures yet of the planet Neptune, showing an upper atmosphere rich with moving features such as vortices, waves and narrowly spaced bands of clouds  
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  similar to those present around Jupiter.

The team – which included astronomers from the University of California, Berkeley; Lawrence Livermore National Laboratory (LLNL); the California Institute of Technology, or Caltech; and UCLA – presented the near-infrared images of the giant ice planet today at the American Astronomical Society’s Division of Planetary Sciences meeting in Pasadena, Cal.

The team captured the Neptune images on five nights of observing on Keck II between June 8 and 28 of this year. They had hoped to track characteristics of very bright features previously seen on the planet, but the detail in the images were beyond their expectations.

"We've never seen the detail we see now," said team leader Imke de Pater, a professor of astronomy and of earth and planetary science at the University of California, Berkeley. "This shows us how much structure there is in the planet's atmosphere, how dynamic it is – as dynamic as Jupiter."

The team, which collaborates through the National Science Foundation's Center for Adaptive Optics at the University of California, Santa Cruz, consisted of University of California, Berkeley graduate students Shuleen Chau Martin and Henry Roe, and LLNL physicists Claire Max, Bruce Macintosh and Seran Gibbard.

The team also is presenting new near infrared pictures of the planet Uranus that mark the first ground-based detection of the faint rings around that planet.

Adaptive optics is a relatively new technology that compensates for blurring caused by turbulence in Earth’s atmosphere. Such a system was installed at the Keck telescope in 1999, and works extremely well, said Livermore’s Macintosh.
Neptune Image of planet Neptune taken using the new adaptive optics system at the 10-meter diameter Keck II Telescope on the Mauna Kea volcano in Hawaii. The image uses infrared light with a wavelength of 2 µm to outline the planet in reflected sunlight. The bright bands are haze layers in Neptune's upper atmosphere. By compensating for the blurring effects of turbulence in the earth's atmosphere, adaptive optics has shown much more detail in the haze bands than has been previously observed from earth-bound telescopes.
The dark stripe is a very narrow slit through which light was directed onto a spectrograph in order to characterize the chemical composition of Neptune's atmosphere and the heights of the haze layers. These images were obtained on June 17th.
 Image:   I. de Pater/UC Berkeley
Science With Adaptive Optics, Brandner
Thanks to this technology, the team was able to see not only the large-scale bright features on Neptune but also a wealth of small-scale features: narrow bands of brightness encircling the planet, waves within those bands, and regions where the bands move apart and come together as if they were separated by a vortex. Similar structures appear in infrared images of Jupiter, around structures that correspond to vortices in visible images.
Neptune's atmosphere is a puzzle, University of California, Berkeley's Martin said, showing signs of transient storms and wind speeds reaching more than 1,100 miles per hour at the equator. The eighth planet from the Sun, Neptune is about 2.7 billion miles distant and has a cloud-surface temperature of about −330°F.

The team has yet to explain most of the newly-discovered features, such as what causes the brightest features (often referred to as storms), why wind speeds are so high on Neptune and what tremendous energy source is driving weather on the planet. These are the types of questions researchers hope analysis of these data will answer.

An exciting prospect for this research is the opportunity to track the atmospheric features of Neptune over time using ground-based telescopes. Previous wind speed measurements were based on
Voyager spacecraft data and data from the Hubble Space Telescope. Preliminary analyses of the June data indicate that wind speed measurements are similar to those made by Voyager.

Ultimately, these data, along with fluid dynamical models of the atmosphere, may give some hints as to the internal structure of Neptune and perhaps some insight of its formation and history. Such questions are of particular interest since extra-solar planet hunters are seeing hints of many solar systems with multiple planets orbiting their sun.
The team also took spectral measurements of Neptune to obtain information about the composition of the atmosphere.

Neptune, the eighth planet from the Sun, has an atmosphere composed primarily of hydrogen, helium and methane and is 17 times as massive as the Earth. Neptune’s methane condenses into methane cloud layers n the same way water condenses into clouds in Earth's atmosphere.

Using the same Keck adaptive-optics system, the team also made the first ground-based detection of the faint rings around Uranus on June 17. The faint rings are those encircling the planet closer than the bright epsilon ring. According to de Pater, the researchers also saw numerous small cloud features well above, in altitude, the south polar methane haze layer.

These features, located at high northern latitudes in regions of the atmosphere which only recently emerged into sunlight after 40-plus years of darkness, could be tracked during several hours. The derived wind speeds suggest the winds at high northern latitudes to be similar in strength to those at high southern latitudes. The overall wind profile is strikingly similar to that derived for Neptune from Voyager data, except that the extreme wind speeds on Uranus are roughly half those found on Neptune.

Among the team's other collaborators were Professors Michael Brown of Caltech and Andrea Ghez of UCLA.

This research was supported in part by the National Science Foundation and in part by the U.S. Department of Energy at Lawrence Livermore National Laboratory.  
The W.M. Keck Observatory, located atop Mauna Kea in Hawaii, is operated as a scientific partnership among Caltech, the University of California and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W.M. Keck Foundation.

Uranus Image of the planet Uranus taken using the new adaptive optics system at the 10-meter diameter Keck II Telescope on the Mauna Kea volcano in Hawaii. The image uses infrared light with a wavelength of 2 µm to outline the planet and its rings in reflected sunlight. The planet itself is artificially darkened by a factor of 20. Clearly visible are the methane haze layer on Uranus's south polar cap and the tiny cloud features at high northern latitudes. The latter features are located well above the methane haze in altitude. Inside the bright epsilon ring, three fainter rings can be discerned, which consist of multiple ringlets. These are barely resolved in the image. These images were obtained on June 18, 2000.
 Image:   I. de Pater/UC Berkeley
S.G. Gibbard, I. de Pater, H.G. Roe, S. Martin, B.A. Macintosh and C.E. Max, "The altitude of Neptune cloud features from high-spatial-resolution near-infrared spectra," Icarus 166, 359–374 (2003)

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