More from the 31st DPS Meeting (reported from in the
last update) in Abano, Italy
Mars' magnetic stripes: Good bye, plate
tectonics?
Much debate was caused in the Martian community by a bizarre
discovery from the Mars Global Surveyor's magnetometer: The
magnetic anomalies on the planet were concentrated in the
Southern hemisphere - and they came in long stripes of changing
polarity (see Update # 129 small stuff).
This at first looked like a relic from ancient plate tectonics,
because the - ongoing - sea-floor spreading on Earth causes such
a stripe pattern as well (together with rather regular polarity
switches of the Earth's field). But the details were very different
on Earth and Mars which also lacked any other traces of plate
tectonics.
This has led to a search for alternative explanations of Mars'
magnetic stripes, and it was the PI of the MGS magnetometer who
has now come up with what may be a more convincing
explanation. What if there was a homogeneous magnetization of
the surface of early Mars, and then some magma came from below
and cracked it along various lines? Just like a bar magnet broken
in two forms two new poles at the crack, the pattern of field lines
would change - in much the way it's being observed today by MGS.
The magma intrusion and cracking (that even seems to be
indicated in the topography) could be related to the formation of
the Tharsis volcanoes - a kind of 'one-shot plate tectonics'.
(Poster and press conference on Oct. 14, 1999, by
M. Acuna)
"No ancient shorelines on Mars" argument flawed? The widely
reported conclusion from MGS imagery that there are no old shorelines
on Mars (where they were suspected at Viking resolution) and that
therefore there is no evidence for an ocean on young Mars (see
Update # 149 sidebar of lead) may be wrong,
says Bill Hartmann: Sometimes you need the larger, low-res view, to
spot subtle, eroded structures in aerial views, while close-up views
mislead! Therefore the MGS pictures can't close the case... (same
press conference on Oct. 14)
Mars' altimetry gets better all the time while the MOLA laser
altimeter on the MGS continues to deliver tons of data - the famous
maps from May (see Update # 132 story 3) are
already superseded. Now we have altimetry for every quarter of a
degree, and 1/2 degree block is added every month. In the public
domain so far is an altimetry data set of 1 degree resolution that
already contains a lot of information on Mars' history. The Northern
hemisphere, e.g. is 6 km lower than the Southern - one-plume
convection or major impacts could be to blame. (Smith at the same
news conference on Oct. 14)
|
In other Mars news:
An interview with the JPL boss and a Mars Surveyor manager
on the MCO loss and MPL prospects:
Space Daily.
Mars Surveyor 2001 payload the most complex ever flown to
another planet - the orbiter, the lander and the rover (a clone
of Sojourner) are full of instruments, both for science and for
the preparation of any human mission that might follow. The APEX
(Athena Precursor) in particular is a highly integrated
payload. (Talk by Saunders at the DPS Meeting on Oct. 12 +
Mission Homepage +
APEX Homepage)
Choice of landing site for 2001 now reduced to two:
Space Daily.
Mars Express gives Mars'96 payload a 2nd chance:
Nearly all instruments on ESA's first mission to Mars are derived
from hardware that vanished with Russia's Mars'96, only one payload
(MARSIS) is new. The orbiter promises global hi-res photography at
10 m, global mineralogy at 100 m and subsurface sounding at 1 km
resolution, while the lander Beagle 2 (that is now most likely to
fly) carries the usual instruments plus some exobiological
detectors - and a 'mole' to dig below the surface. (News
conference by Ferri at the DPS Meeting on Oct. 11 +
Mission Homepage +
Beagle 2 Homepage)
With 'Micro Missions' to Mars and onwards:
NASA is busily planning for a series of 'micro missions'
to Mars that will cost less than 30 million dollars per
mission and will launch as auxilliary payloads on the
Ariane 5 and make it to their target via the Moon. The
launch mass limit is 220 kg, the science payload restricted
to 5...10 kg at Mars - nonetheless various concepts of
airplanes, landers and penetrators are pondered. And there
could be micromissions to Venus, Mercury and asteroids as
well! (Talk by Wilson at the DPS Meeting on Oct. 12)
Yet another Mars movie is being planned, this time "Ghosts on
Mars" by John Carpenter:
Space.com.
|
What the sulfuric acid on Europa means
The discovery by Galileo's NIMS instrument that there is a lot of
sulfuric acid mixed into the icy surface of the Jovian moon Europa
(see Update # 149) supersedes the earlier
interpretation of the NIMS spectra as evidence for various salts.
Laboratory experiments on icy mixtures have since been performed that
make it all but certain that hydrated sulfuric acid is a major
constituent of Europa's surface and can explain all the distortions
seen in the water absorption bands in the NIMS spectra "pretty darn
good". Europa's surface composition varies widely, though, with some
regions being pure ice and others predominantly hydrated and
everything inbetween.
Spectral maps of Europa show furthermore that the presence of
sulfuric acid correlates nicely with the darkness of the surface (for
which polymerized molecules are responsible), and some
of the largest dark bands even show up in the NIMS map. While the
sulfur most likely came from elsewhere in the Jovian system as ions
and was implanted into the ice (and then turned to H2SO4 by radiation),
there must also be geological processes going on that concentrate the
acid in certain areas. The connection with the dark bands makes it
likely that here upwelling waterice lava has freed sulfur compounds
embedded in the crust and exposed them in a concentrated fashion.
(Carlson & al., Science of Oct. 1st, 1999, 97-99 +
news conference by Carlson at the DPS Meeting on Oct. 13th)
|
Earlier
JPL News Release on the identification of the H2SO4 and
CNN and
SpaceViews
stories.
Related:
The details of NASA's Europa Orbiter are already well
defined - especially the fact that there will be only 20 kg of
payload while 565 kg of propellant will dominate the spacecraft.
After a Nov. 2003 launch the Orbiter will arrive in the Jovian
system in Aug. 2006 but in Europa's orbit only in 2008 - whether
the 2 years among the other moons can be used for science depends
on the precise orbits (reaching Europa in the safest manner has
priority). When in the final orbit the science objectives are to
determine whether there is an ocean, to map the distribution
of any liquid water and to understand how Europa's surface works,
which is now generally thought to be only 10...100 Myr old. The
whole Europa orbit activities are limited by the radiation
environment, and the primary mission there lasts only 30 days
(though an extension seems likely). (Talk by Johnson at
the DPS Meeting on Oct. 12 + Space News of Oct. 25 +
Europa
Orbiter Homepage)
|
SMART-1 will fly - here is why
At its last meeting in September the Science Programme
Committee of the European Space Agency has finally given green
light for the first mission of a new kind: SMART stands for
Small Missions for Advanced Research in Technology,
basically the European answer to NASA's New Millennium
Program that tests innovative technologies for possible use in
later scientific missions. And SMART-1 resembles the Deep Space
1 mission at first glance: It's primary objective is to qualify an ion
engine for deep space missions, in particular the BepiColombo
Mercury orbiter (see Update # 149).
But the spacecraft is more complex than DS1 and carries more
instruments which make it a really mixed tech & science project
from the beginning.
SMART-1 will be launched in late 2002 as an auxilliary payload on
an Ariane 5 (the exact launch date depends on when the -
probably commercial - main payload is ready) - and the travel to
its target, the Moon, will take 14 to 17 (!) months! Little fuel will be
spent and the Moon's gravity used in multiple weak gravity
assists, and the long cruise phase will be used for X-ray
astronomy with one of the 3 1/2 real science instruments. Only
15 kg are allocated for the payload, so miniaturization of
nonetheless powerful instruments is another objective of the
SMART-1 mission. The spacecraft (with a launch mass around
350 kg) carries
- for diagnostics of the ion engine and for other
technological experiments an Electric Propulsion
Diagnostic Package (EPDP) with various plasma sensors,
- KaTE, an X/Ka-band Telemetry & Telecommand
experiment,
- for both tech & science use an Spacecraft
Potential, Electron and Dust Experiment (SPEDE) that
completes the EPDP package and also monitors the spatio-
temporal variations of the spacecraft's plasma, electron & dust
environment during cruise and in the lunar orbit,
- for science use (but also to demonstrate new
detector designs for future missions) the Demonstration of a
Compact Imaging X-ray Spectrometer (D-CIXS) to provide X-
ray spectroscopy of the Moon with 30 km resolution and to
monitor celestial sources during the cruise.
- AMIE, the extremely miniaturized Asteroid-Moon
Imaging Experiment with a CCD camera with a FOV of 5.3 degrees,
and
- SIR, the SMART-1 IR Spectrometer with a
wavelength range of 0.9 to 2.4 microns.
Two further experiments will use AMIE (to look for laser flashes
sent up from an ESA telescope on Tenerife) and KaTE plus AMIE
(RSIS, the Radio Science Investigation with SMART-1, that will
allow precise navigation and even measurements of the Moon's
rotation). Further SMART missions haven't been defined yet, but
ESA's planners would like to have about one every three years:
Decisions hinge on what innovations the future 'cornerstone'
missions demand. (Nature of Sept. 30, 1999, p. 414 +
Racca & al., paper IAA-99-IAA.11.2.09 from the 50th Int'l
Astronautical Congress Oct. 4-8, 1999 + various talks +
posters at the DPS Meeting)
|
SMART Homepage.
A report on the SPC Meeting from ESA's Science pages - that
has exactly zero content regarding any decisions made of the meeting
or questions raised there. Why does ESA never disclose these
right away and why do we always have to wait for the Nature
or Science or Space News articles about them???
The decision on the next Cornerstone mission of ESA's
science program won't come before next June. The choice is now
down to the Mercury orbiter BepiColombo and the space
interferometer GAIA for high-precision astrometry. This
Hipparcos-successor would be even more ambitious than the just
selected NASA mission FAME (see last
Update). If BepiColombo wins, its three components would
probably be launched at two different times: That would stretch
the cost somewhat.
Next September ESA will also select two more 'flexi missions',
smaller projects that balance the cornerstones. One choice will
probably be a substantial ESA contribution to NASA's Next
Generation Space Telescope, while the choice of the other mission
will depend on which cornerstone is selected.
At the SPC meeting also certain concerns were voiced about
unnecessary duplications: Do the U.S., Europe and Japan have to
have each a Mercury mission and a big X-ray satellite of their
own? While the missions are often complementary and not identical,
more coordination between the space agencies would be good, the
ESA delegates stated - and in the case of the Mercury missions
such talks apparently have happened already.
|
