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Keck telescope captures Jupiter's Red Spot Jr. as it zips pastplanet's Great Red Spot (Forwarded)



 
 
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Old July 31st 06, 02:13 AM posted to sci.astro
Andrew Yee
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Default Keck telescope captures Jupiter's Red Spot Jr. as it zips pastplanet's Great Red Spot (Forwarded)

W. M. Keck Observatory
Kamuela, Hawaii

Media Contact:
Robert Sanders, 808.885.7887

July 29th, 2006

Keck telescope captures Jupiter's Red Spot Jr. as it zips past planet's
Great Red Spot

Kamuela, Hawaii -- Astronomers from the University of California,
Berkeley, and the W. M. Keck Observatory in Hawaii this month snapped
high-resolution near-infrared images of the Great Red Spot, a persistent,
high-pressure storm on Jupiter, as a smaller storm, Red Spot Jr., breezed
by it on its race around the planet.

The image, which also shows Jupiter's moon Io, was taken on July 20 Hawaii
time (July 21 Universal Time) by the Keck II telescope on Mauna Kea using
adaptive optics (AO) to sharpen the image.

The spots are of interest to astronomers because Red Spot Jr. formed from
the merger of three white spots only recently, between 1998 and 2000, and
in December 2005 turned red like the much older Great Red Spot. While the
new red spot is about the size of Earth, the Great Red Spot is nearly
twice that diameter and has been circling the planet for at least 342
years.

The images captured by the second-generation Near Infrared Camera (NIRC2)
on Keck II show that, though the two red spots are about the same color
when seen in visible wavelengths (see Christopher Go's optical image from
July 20 UT, http://redspotjr.christone.net/cg07200611-18c.jpg), they
differ markedly at infrared wavelengths. When the astronomers viewed the
planet through a narrow-band filter centered on the 1.58 micron,
near-infrared wavelength, Red Spot Jr., which was called Oval BA before it
changed from white to red, was a lot darker, indicating that the tops of
the storm clouds may be lower than those of the Great Red Spot. With more
atmosphere above its cloud tops, more infrared light is absorbed by
molecules like methane in the atmosphere.

"Red Spot Jr. is either not as high as the Great Red Spot, or it's just
not as reflective, that is, as dense," said lead astronomer Imke de Pater,
professor of astronomy at UC Berkeley. "These images will put some
constraints on the altitude of Red Spot Jr."

The Great Red Spot is thought to tower about 8 kilometers (5 miles) above
the surrounding cloud deck. The fact that Red Spot Jr. turned red may
indicate its swirling storm clouds are rising higher also, though
apparently they are not as high as those of its larger companion, or the
clouds are thinner.

Why the spots are red is a subject of great debate. Some people think the
hurricane-like winds in the Great Red Spot, which can reach 400 miles per
hour, dredge up material from deeper in the planet's atmosphere that, when
exposed to ultraviolet light, turns red. One candidate is phosphine gas,
PH3, which has been detected on Jupiter. Ultraviolet light might catalyze
its conversion to red phosphorus, P4, according to one of the leading
theories. Other, more complicated theories have phosphine interacting in
the atmosphere with chemicals such as methane or ammonia to form complex
compounds such as methylphosphane or phosphaethyne.

Recent studies suggest that the red color also may be attributed to sulfur
allotropes, that is, different molecular configurations, including chains
and rings, of pure sulfur, such as S3-S20. The new work hypothesizes that
ammonium hydrosulfide particles are carried upwards in the Great Red Spot
and are broken up by ultraviolet light. Subsequent chemical reactions
ultimately lead to long-chained sulfur allotropes , which can vary in
color from red to yellow.

"The jury is still out on the exact processes that lead to the red
coloration of the Great Red Spot -- and Oval BA," de Pater is quoted as
saying in the August 2006 issue of Sky & Telescope magazine.

Christopher Go, an amateur astronomer who first noticed the coloration
change of Red Spot Jr., joined de Pater's team earlier this year. He noted
that during the close encounter between the two spots, Red Spot Jr. was
squashed slightly, stretching in its direction of motion. The same thing
happened in 2002 and 2004 when the Great Red Spot and Red Spot Jr. passed
one another, though then Junior was white.

The Great Red Spot rotates westward, opposite to the eastward rotation of
the planet. Because alternating bands on the Jovian surface move in
opposite directions, the adjacent Red Spot Jr. moves eastward. The planet
rotates about once every 10 hours.

Another of de Pater's colleagues, UC Berkeley mechanical engineering
professor Philip Marcus, predicted several years ago that Jupiter's
climate was changing, based on the disappearance of the cyclonic storms or
spots within the bands. The mixing of the atmosphere by these cyclones
keeps the temperature about the same over the entire planet, he argued, so
loss of this mixing will cause the equator to heat up and the poles to
cool.

Earlier this year, on April 16, de Pater and her team captured
near-infrared, ultraviolet and visible light photos of the planet using
the Hubble Space Telescope to look more closely at the two red spots. The
observations with the Keck Telescope were a follow-up study to try to
measure the speeds of the swirling winds in the spots. Jupiter's
brightness, however, confused the adaptive optics system, forcing the
astronomers to miss some good shots of the planet as the guide star was
being positioned optimally relative to Jupiter.

"This was probably the most challenging observation ever tried with the AO
system at Keck," said de Pater, referring to use of the laser guide star
system next to an object as bright as Jupiter. Adaptive optics can take
the twinkle out of an object caused by thermal motion in the atmosphere,
but to do this well, the target must be near another bright object that
can serve as a reference. For some of the images, Jupiter's moon Io was
used as the reference "star." But until Io got close enough for this, a
laser guide star was created near Jupiter to serve this purpose.

"This was our first attempt using the laser to obtain AO-corrected images
of Jupiter's surface," said Dr. Al Conrad, a support astronomer at the
Keck Observatory. "The technique shows promise and, if we perfect it, will
provide us with many more opportunities to observe this fascinating,
ever-changing object."

The team also obtained a close-up of the two spots through a narrow-band
filter centered on 5 microns, which samples thermal radiation from deep in
the cloud layer. Both spots appear dark because the clouds completely
block heat emanating from lower elevations, though narrow regions around
the spots that are devoid of clouds show leakage of this heat out into
space.

"These 5 micron images reveal details in the cloud opacity not seen at the
other wavelengths and will help unravel the vertical structure of the
spots," UC Berkeley team member Michael Wong added. "The smooth, narrow
arcs visible to the south of each spot probably result from the
interaction between the spots and high-speed winds that are deflected
around them."

The resolution using both the narrow and wide views on the camera was
about 0.1 arcseconds, or only half as good as can be obtained on a clear
night with optimal seeing.

The W. M. Keck Observatory operates twin 10-meter telescopes located on
the summit of Mauna Kea on the island of Hawaii and is managed by the
California Association for Research in Astronomy, a non-profit corporation
whose board of directors includes representatives from Caltech, the
University of California and NASA. For more information, please visit
http://www.keckobservatory.org

IMAGE CAPTION:


[Left,
http://astro.berkeley.edu/~imke/Jupi...posite-986.jpg
(123KB)]:
A false-color composite near-infrared image of Jupiter and its moon Io,
taken July 20 Hawaii time (July 21 UT) by the Keck II telescope on Mauna
Kea using adaptive optics (AO) to sharpen the image.

Images taken in narrow band filters centered at 1.29 and 1.58 microns
(shown in gold in this image) detect sunlight reflected off Jupiter's
upper cloud deck -- the same clouds that are seen in visible light. The
narrow band image at 1.65 micron (shown in blue) shows sunlight reflected
back from hazes lying just above these clouds. The image was sharpened
using the RegiStax software, developed by Cor Berrevoets.

The planet Jupiter is 143,000 km (90,000 miles) across. The Great Red Spot
is about twice the diameter of Earth, while Red Spot Jr. has a diameter
nearly equal to that of Earth. Resolution is about 0.1 arcseconds, or 370
kilometers (250 miles). The AO system used the satellite Io as its
reference star. Io itself is visible in the upper right corner in the
green, red and blue colors of the 1.29, 1.58 and 1.65 micron filters,
respectively. The motion of the satellite with respect to Jupiter during
the observing sequence is clearly seen.

Red Spot Jr., which is below the Great Red Spot, is not as bright, either
because its clouds are less dense and thus reflect less light, or because
the tops of the clouds are not as high as those of the larger spot. The
red outline shows the approximate area covered by the 5-micron band mosaic
shown on the right.

[Right,
http://astro.berkeley.edu/~imke/Jupi...mosaic-900.jpg
(86KB)]
A closeup of the two red spots through a 5-micron filter, which samples
thermal radiation from deep in the cloud layer. Both spots appear dark
because the clouds completely block heat emanating from lower elevations,
though narrow regions around the spots that are devoid of clouds show
leakage of heat into space. This 5-micron mosaic image reveals details in
the cloud opacity not seen at the other wavelengths, and will help unravel
the vertical structure of the spots.

Credit: Imke de Pater, Michael Wong (UC Berkeley); Al Conrad (Keck), and
Chris Go (Cebu, Philippines)


 




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