[meteorite-list] Venus Express Gets Ready To Take The Plunge
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 16 May 2014 22:32:44 -0700 (PDT)
Venus Express Gets Ready To Take The Plunge
European Space Agency
16 May 2014
After eight years in orbit, ESA's Venus Express has completed routine
science observations and is preparing for a daring plunge into the planet's
Venus Express was launched on a Soyuz-Fregat from the Russian Baikonur
Cosmodrome in Kazakhstan on 9 November 2005, and arrived at Venus on 11
It has been orbiting Venus in an elliptical 24-hour loop that takes it
from a distant 66 000 km over the south pole - affording incredible
global views - to an altitude of around 250 km above the surface at
the north pole, close to the top of the planet's atmosphere.
With a suite of seven instruments, the spacecraft has provided a comprehensive
study of the ionosphere, atmosphere and surface of Venus.
"Venus Express has taught us just how variable the planet is on all
timescales and, furthermore, has given us clues as to how it might have
changed since its formation 4.6 billion years ago," says Hakan Svedhem,
ESA's project scientist.
"This information is helping us decipher how Earth and Venus came to
lead such dramatically different lives, but we've also noticed that
there are some fundamental similarities."
Venus has a surface temperature of over 450??C, far hotter than a normal
kitchen oven, and an extremely dense, choking mixture of noxious gases
for an atmosphere. But from the mission's infrared survey of the chemical
composition of the rocky surface, we have learned that Venus might have
once had a plate tectonics system like Earth, and even an ocean of water.
Just like Earth, Venus is losing parts of its upper atmosphere to space
and Venus Express measured twice as many hydrogen atoms escaping out of
the atmosphere than oxygen. Because water is made of two hydrogen atoms
and one oxygen atom, the observed escape indicates that water is being
broken up in the atmosphere.
Today, the total amount of water on Earth is 100 000 times that on Venus.
But because the two planets are about the same size and formed at the
same time, both may have had similar amounts of the precious liquid in
their early years.
Meanwhile, the spacecraft's cameras have tracked thousands of features
in the cloud tops some 70 km above the planet's surface, including an
enormous swirling vortex at the planet's south pole that shares similarities
with hurricanes on Earth. The spacecraft also recorded bursts of lightning
- identified by their electromagnetic signature - generated in clouds
of sulphuric acid.
Is Venus volcanically active?
Studies of the planet's "super-rotating" atmosphere - it whips
around the planet in just four Earth-days, much faster than the 243 days
the planet takes to complete one rotation about its axis - also turned
up some intriguing surprises. In one study, average wind speeds were found
to have increased from roughly 300 km/h to 400 km/h over a period of six
Conversely, a separate study found that the rotation of the planet had
slowed by 6.5 minutes since NASA's Magellan, which completed its 5-year
mission at Venus 20 years ago, measured it.
However, it remains unknown if there is a relationship between the increasing
wind speeds and the slowing rotation.
Magellan's radar survey of the planet revealed that its surface was
heavily altered in the past by a large number of volcanoes. But Venus
Express has provided tantalising hints that the planet may well be still
geologically active today. One study found numerous lava flows that must
have been created no more than 2.5 million years ago, just yesterday on
geological timescales, and perhaps much more recently.
Indeed, measurements of sulphur dioxide in the upper atmosphere have shown
large variations over the course of the mission. Although peculiarities
in the atmospheric circulation may produce a similar result, it is the
most convincing argument to date of present-day active volcanism.
Venus Express aerobraking
Now, after eight years in orbit, the fuel supplies necessary to maintain
the elliptical orbit are running low and will soon be exhausted. Thus,
routine science operations concluded this week, and the spacecraft is
being prepared for one final mission: to make a controlled plunge deeper
into the atmosphere than ever before attempted.
"We have performed previous short "aerodrag" campaigns where we've
skimmed the thin upper layers of the atmosphere at about 165 km, but we
want to go deeper, perhaps as deep as 130 km, maybe even lower," says
Patrick Martin, Venus Express mission manager.
"It is only by carrying out daring operations like these that we can
gain new insights, not only about usually inaccessible regions of the
planet's atmosphere, but also how the spacecraft and its components
respond to such a hostile environment.
This "experimental aerobraking" phase is planned for 18 June - 11
July, during which time some limited science measurements with the spacecraft's
magnetic field, solar wind and atom analysing instruments will be possible.
Also, temperature and pressure sensors will record the conditions that
the spacecraft is experiencing.
"The campaign also provides the opportunity to develop and practise
the critical operations techniques required for aerobraking, an experience
that will be precious for the preparation of future planetary missions
that may require it operationally," says Paolo Ferri, head of mission
Aerobraking can be used as a way of getting into orbit around planets
without having to carry quite so much fuel, thus reducing the launch mass.
It is possible that the remaining fuel in Venus Express will be exhausted
during this phase or that the spacecraft does not survive these risky
operations. But if the spacecraft is still healthy afterwards, its orbit
will be raised again and limited operations will continue for several
more months, fuel permitting.
However, by the end of the year, it is likely that Venus Express will
have made its final descent into the atmosphere of the planet, bringing
a fantastic scientific endeavour to an end.
"Venus Express has penetrated deeper into the mysteries of this veiled
planet than anyone ever dreamed, and will no doubt continue to surprise
us down to the last minute," adds Hakan.
Prior to and during the aerobraking campaign, short updates will be published
via _at_esaoperations and/or the Rocket Science blog whenever they are available.
A final report will be published on the ESA Portal soon after the aerobraking
Eight mission highlights for eight years in orbit - read more about
these key mission discoveries:
Shape-shifting polar vortices
Spinning Venus is slowing down
Super-rotation is speeding up
Snow on Venus?
A magnetic surprise
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer at esa.int
ESA Venus Express project scientist
Email: hakan.svedhem at esa.int
ESA Venus Express mission manager
Email: pmartin at sciops.esa.int
Head of ESA mission operations
Email: paolo.ferri at esa.int
Received on Sat 17 May 2014 01:32:44 AM PDT