We're getting a better look at our planetary next door neighbor,
courtesy of the ESA.
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Probe peers into Venusian secrets
By Molly Bentley
Pasadena
Venus is an enigma, wrapped in a mystery, inside a dense cloud of carbon
dioxide (CO2).
But a suite of orbiting instruments is proving its ability to penetrate
the thick atmosphere and create a new and dynamic picture of Earth's
sister planet.
Scientists at the Division of Planetary Sciences meeting in Pasadena,
California, this week said that data streaming from the Venus Express
probe had provided unprecedented detail of the Venusian atmosphere and
the first-ever peek at its lower strata.
They hope the spacecraft will help answer fundamental questions about
the planet's atmospheric composition and dynamics, as well as solve key
Venus puzzles: what drives its "super-rotation"; are its volcanoes
active; and just what is the strange ultraviolet-absorbing substance
swirling at the cloud tops?
From what we have now, this will be like going from a 19th Century
topographical map to the Weather Channel
David Grinspoon, mission scientist
But for now, scientists are happy to report that all the instruments are
in good working order and beaming back massive amounts of data.
"It's a treasure trove of information," said David Grinspoon, a
participating scientist with the mission, "and we've barely opened the
chest and looked in."
Open 'slots'
The seven instruments on the spacecraft, in obit around Venus since
April, are examining the planet over a wide swath of the spectrum: from
ultraviolet to visible, to infrared, and even radio wavelengths.
"Our main objective is to do a comprehensive study of the atmosphere,"
said Hakan Svedhem, Venus Express project scientist.
The instruments provide a look at Venus at different depths.
The Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS), for
example, allows scientists to penetrate the otherwise opaque upper
atmosphere of Venus and study the chemistry below it.
It takes advantage of "infrared windows", the few narrow wavelengths
that carbon dioxide does not absorb.
"It's like looking through gaps in a picket fence for the first time and
seeing through," said Dr Grinspoon.
Unlike Mars, Venus is a close planetary neighbour of Earth that remains
relatively unexplored.
The dense atmosphere has shielded it from scrutiny, but scientists
speculate that Venus once had vast oceans, similar to Earth. The oceans
have since disappeared.
"The closest analogy to Venus today is the Achaean Earth, prior to life,
when Earth's atmosphere was primarily CO2 and a lot of sulphur," said
Frank Mills, a supporting investigator on the mission.
Mystery pattern
Scientists want to understand the evolutionary divergence of the sister
planets - what happened to the oceans on Venus, and what triggered its
runaway greenhouse?
Some clues may be found in understanding the role and amount of sulphur
dioxide (SO2) in the atmosphere, said Dr Mills. When oxidised, it
produces sulphuric acid, the main component of Venusian clouds and a
tremendous greenhouse gas.
The gas is also a product of volcanoes. Previous measurements of Venus
from ground-based instruments and the Pioneer spacecraft have showed a
spike of sulphur dioxide followed by a gradual decrease, suggesting that
the planet's volcanoes are not dormant.
But the last measurements of SO2 were 20 years ago. VIRTIS will provide
a long-needed update.
Meanwhile, the Visible Monitoring Camera (VMC) may solve another
Venusian mystery.
The VMC produces visible and ultraviolet images of the planet. In the
visible range, the Venus surface remains opaque. But in the ultraviolet,
a swirling weather pattern appears. It is unclear what it is made of.
Some guess an aerosol or small crystals.
"It is some substance absorbing the ultraviolet, that's not CO2," said
Dr Svedhem.
"People have tried to identify it and have failed, and it's really
strange," added Dr Grinspoon; "it's dubbed the 'unknown ultraviolet
absorber'. "
In the eye
As if the composition of the Venusian atmosphere is not intriguing
enough, scientists hope Venus Express will also help explain why it is
spinning faster than the planetary body beneath it.
While winds on Earth flow in Easterly and Westerly directions, on Venus
they seem to flow only Eastward, and at speeds faster than the planet's
rotation.
Scientists don't know what's causing the super-rotation, or even how to
describe it.
"Is it contributing to the planet's spin? Why doesn't it break down?"
pondered Sanjay Limaye, a planetary scientist with the mission. "We just
don't know."
He is pleased by the new images that VIRTIS has returned of the double
vortex that sits like twin cyclones at the eye of the southern
hemispheric circulation.
"Venus Express can help us define the depth and the structure of the
vortex, and how the whole circulation is maintained," said Dr Limaye.
As Venus Express continues to beam back data over the next few years,
scientists will create a new dynamic map of the planet's once
impenetrable atmosphere.
"From what we have now, this will be like going from a 19th Century
topographical map to the Weather Channel," said Dr Grinspoon.
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http://news.bbc.co.uk/2/hi/science/nature/6041570.stm
--
John Hachmann aa #1782
"Those who can make you believe absurdities can make you commit atrocities"
-Voltaire
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