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
EMBARGOED
FOR RELEASE UNTIL 10:30 A.M. PDT WED., OCT. 25, TO COINCIDE
WITH MEDIA BRIEFING AT THE ANNUAL MEETING OF THE DIVISION
FOR PLANETARY SCIENCES, AMERICAN ASTRONOMICAL ASSOCIATION,
IN PASADENA.
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
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