MAUNA KEA – 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 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 (OCT. 25, 2000) at the American Astronomical
Societyís 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 UC 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 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 rings around
that planet.

 



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
micro-meters 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. (CREDIT: Imke de Pater/UC Berkeley)

 

Adaptive optics is a relatively new technology that compensates for
blurring caused by turbulence in Earthís atmosphere. Such a system was
installed at the Keck telescope in 1999, and works extremely well, said
Livermoreís Macintosh.

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 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.



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
micro-meters 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 teh 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. (CREDIT: Imke de Pater/UC
Berkeley)

 

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. Neptuneís methane condenses into methane cloud layers in 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. 

NOTE: Photos of Neptune and Uranus can be downloaded from the UC Berkeley
website:

 http://www.berkeley.edu/news/media/download/nep_index.html

-30-