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Near infrared images of Neptune taken by Keck II show best detail yet of planet's icy atmosphere
25 Oct 2000

By Robert Sanders, Media Relations


Pasadena - Astronomers taking advantage of new adaptive optics on the W. M. Keck II Telescope in Hawaii have obtained the best pictures yet of the planet Neptune, showing an atmosphere rich with dynamic features such as vortices, waves and narrowly spaced bands of clouds 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 - captured near infrared pictures of the giant ice planet on five nights between June 8 and 28. They hoped to track characteristics of very bright features previously seen on the planet, but 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 UC Berkeley. "This shows us how much structure there is in the planet's atmosphere, how dynamic it is - as dynamic as Jupiter."

De Pater and her team will present the pictures and data this week in Pasadena at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society, both at a Wed., Oct. 25, media briefing and at a Friday, Oct. 27, scientific session. The team, which collaborates through the National Science Foundation's Center for Adaptive Optics at UC Santa Cruz, consisted of UC 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 inner rings around that planet, that is, the rings inside the bright epsilon ring.

Adaptive optics is a relatively new technology which compensates for blurring caused by turbulence in the atmosphere. Such a system was recently installed at the Keck telescope, and works extremely well, said Macintosh of LLNL. 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, UC Berkeley's Martin said, showing signs of transient storms and wind speeds reaching 400 meters/second at the equator - 30 times the wind speeds on Jupiter. The team has yet to explain most of the 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 even indications 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. The methane condenses into methane cloud layers in the same way water condenses into clouds in Earth's atmosphere.

Using the same 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 a 40-some year 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.


NOTE: Photos of Neptune and Uranus are available for download