Having an NTSC monitor next to my workstation, I can now watch
NASA Select while "working". Here are notes I typed in from today's
Magellan briefing. Please don't ask me for further details,
because I can't provide them. I do not vouch for the absolute
accuracy of this material, I'm not a stenographer and it was going
by pretty quickly.
Jon (leech@cs.unc.edu)__@/
Notes from Magellan Science Briefing on NASA Select - 10/29/91
==============================================================
Wes Huntress - Division Director, Solar System & Exploration
Division
Venus superficially similar to Earth, but "stunningly different".
Magellan good for understanding geological differences from Earth
and verifying theories about why it's different.
Project has completed processing first cycle data. 1/2 mapping
data available on 22 CD-ROMS, remainder by end of year. "Digital
treasure chest."
More than halfway through second cycle; filling in gaps. Looking
at new angles to clarify interpretation. Conducting special tests:
3D stereo radar imagery. Very successful, plan to cover 70% in 3D
stereo in cycle 3 starting Jan. 15.
Measuring internal structure by mapping gravity field.
Maat Mons lacks radar reflective surface - is it a new structure?
New surface maps from radar altimeter + radio science to study
deep into atmosphere.
Steve Saunders, JPL - Magellan Project Scientist
Cycle 2 mapping south pole - about 3/4 done. Fill in gap at
superior conjunction (about 80% done). On orbit 3000 since starting
mapping.
Global mosaic & projection onto a sphere, looking down from N.
pole. Topography + other properties from altimetry data set. Can
see geologic patterns on a global basis. 6 maps: N/S/4 hemispheres.
Large equatorial fracture system including largest volcanoes -
Matt Mons, Beta Regio - like rift systems on Earth. Totally
different features elsewhere - small scale scarp features like
subduction scarps in W. Pacific - seeing stretching & compression
- brittle structure case -> buckling.
Global look at volcanic features. Prof. Hedd & students @ Brown
Smallest domes to largest shield volcanoes.
Jerry Schwaber (sp?) mapped impact craters - randomly
distributed. [they look to number in low hundreds on slide - Jon]
Are we seeing catastrophically resrufaced Venus (~800 My) or
continuing process with small amounts of vulcanism?
Mapped fracture zones. Map major parts giving only an equatorial
distribution - what's going on? Puzzle. More extensional features
in N/S, compressional in E/W. Another puzzle - would expect them
to be paired.
Landslides - Peter Ford of MIT produced cycle 1/cycle 2 (low
incidence) image. Still somewhat ambiguous; investigators favor
radar layover explanation. (Two possible interpretations for
left-looking data, right looking hard to match up). i) Steep slope,
top closer to radar appears overlapping ii) Actual slumping.
Stereo pair - L sensitive to albedo variation, R to volcanic
domes.
Another presentation form - anaglyph - R/B prints (in press
package). Giant trought 800m deep, 10km across.
Channels on plains - intruiging feature. plains are 85% of
surface, history of plains is history of Venus in last few 100 My
as far as we can see. Apparently carved by some sort of fluid
lava. Don't see on Earth, certainly not of this length (100s of
kms, longest 800 km). Similar morphology along their entire
lengths.
Perspective views to understand relationship of some features -
combine imaging & topography & reproject in computer. Same
technique used for video. Crater farm, Gula Mons (sp?) 3km high.
Matt Mons - 9km high. Recent lava flows pouring over plains.
Surface of volcano is not bright; this is an exception.
Corona Artemis - circular feature 2600km in diameter. Little
relief in interior, margin is trough 150 km across, 3-4 km deep.
Flyaround animation coming. Other chasms to N like Pacific
subduction areas.
Zooming in on trough in next few slides. "Amazingly uniform
feature." Models include mantle plumes rising & spreading,
interacting with external part of crust causing subduction-like
patterns.
Computer generated film of radar mapping results - Artemis &
eastern Aphrodite Terra. Simulated color & radarclinometry to
enhance small scale features. Mitchell crater into trough, Diana,
Dali chasms. Ascend for view of Artemis @ end.
Artemis first seen in radar @ Goldstone. Complex topograhy
(arcuate scarps) at margin. 20x vertical exaggeration. One of the
most useful scientific videos for visualizing scientific videos.
John Woods, SAO - Radar Investigator.
Maxwell Montes - highest on Venus. Generally displays very high
reflectivity (observed by Pioneer Venus, confirmed by Magellan).
Appears to require that surface has some special mineral component
which helps reflectivity - opposite of Stealth Bomber. Where would
mineral have come from? Most surface material is not rock; has
weathered into soil (exposed to warm, chemically reactive
atmosphere for 100My forming different minerals). On Earth, turns
into clay & quartz & oxides (soil). On Venus, different kind of
soil. Venus is much hotter at low altitude than on mountaintops
(170 degrees F) which controls composition of minerals in soil.
Helps explain different radar reflectivity behavior. Pyritite (iron
sulfide) appears only at >5km above plains. Electrically conductive
mineral -> increase reflectivity, appears to be responsible to
radar bright summits of high mountaintops.
All except Maat Mons (volcanic peak at E end of Aphrodite Terra,
second highest peak on planet).
Slide of confusing region - Maat Mons + Alpha Regio. Much higher
than surrounding bright region, yet it's dark. Can clearly see
volcanic outflows - no question it's a volcanic edifice, unlike
Maxwell, which is a tectonic structure. Has a radar bright area at
low altitudes; highest are quite radar dark. Why would this be the
case? Hypothesis: Maat Mons has not been weathered. Why not? Hasn't
had time - fresh lava poured out relatively recently. High temp ->
very young (may still be active). Best candidate for currently
active volcano. High priority given to examining second cycle
images taken just last week. Images being processed now.
Gordon Pettengill, MIT - Principal Investigator
First global topography map; contrasted to Pioneer Venus. About
10x resolution, covering further into S and N than PV did.
Distinictive feature - Aphrodite Terra ("Scorpion" for two jaws),
lowest region, Maxwell (W. edge showing rise of 7-8 km with steep
slopes (> 30 degrees) - obvious result of strong tectonic forces).
Maat is ~8km above mean. Can now see true height of such small
volcanic features that weren't resolved by Pioneer. Putting
material into context, allows understanding of interconnections.
Next slide shows global emissivity - related to brightness from
temperature & ability to emit - inverse of reflectivity. A few deep
blue areas (~30% emissivity, corresponding to ~70% reflectivity),
related to Dr. Wood's discussion. Still some S. polar gaps, which
will be filled in.
Special experiment done on Oct. 5 - using telemetry at 2-3 cm
X-Band and 10 cm S-band (normally used for tracking & radar data)
to probe atmosphere (beam bent by atmosphere). At ~32km (20 mi) up,
density gradient so high that curvature of ray matches curvature of
planet - ray is captured! Can get close to this. Advantage
compared to earlier observations is about 10x more sensitivity with
Magellan's large antenna & higher transmited power in X-band - goes
several km lower than previously achieved, and more sensitive to
attentuation. Hope to place levels on sulfuric acid vapor and
monitor amount (indicating amount of volcanic activity). Adds info
on vertical structure and hope to get handle on a different
constituent of atmosphere.
Q&A session:
Plate tectonics controversy?
Saunder: don't think they've seen features predicted from
pre-Magellan data. Not plate spreading, but subduction & folding.
Probably doesn't go on in quite the same way as on Earth, where
plates are dragged along, but it may be taking up some of the
spreading motions seen at ridges.
Amount of data? Interpretation of radar overlay -> what
confidence in correct interpretation of radar data?
Saunders: 8 orbits of test data analyzed by radar experts &
geologists. Layover almost nonexistent in chosen geometries except
in a few areas, a very small fraction of data set.
Terabits of data - approaching double amount of imaging data.
Better global map of Venus than of the Earth (oceans poorly
mapped).
[Q about weathering I didn't catch - Jon]
Wood: Weathering of Maat Mons would proceed in just a few years
(<10). Controversial view. Wouldn't bet a lot on it. Not only
candidate for active volcano, just most prominent - high, stands
out. May be many others that don't come to attention as rapidly.
Can quantify reflectivity vs. other materials?
Gordon: need dielectric of ~80. Only normal candidate is water.
Require unusual mineral, like metallic meterorites.
What are 5-6 most interesting spots for onsite analysis?
Saunders: Alpha Regio, parts of Aphrodite Terra that stand up
high - may be ancient crustal materials formed by differentiation.
Finding feldspar would be interesting. Typical plains area -
fundamentally different from volcanoes, much more extensive, will
tell much more about geochemistry of planet. Pancake volcanoes -
steep sided features. Very dark areas - what are they? Glassy
material? Fine powder? What interaction of surface is going on?
Guess on when we might see landers?
Huntress: Next century. No particular plans to return to Venus in
this decade. Waiting on results of Magellan before deciding what
next step should be. Measure trace elements/isotopic ratios in
atmosphere? Geological sites/geochemistry? Both at once? As we
learn more, will develop ideas on what to do next.
Future Magellan plans?
Gravity data. Measure crust. Models indicate thick crust, but
they're just models.
What has been learned that wouldn't be known 3 years ago?
Saunders: Knew a lot from Pioneer & Venera at 1-2 km resolution.
Now have global picture to 120m resolution. Details of vulcanism &
tectonic features seen fuzzily before. Have focused on details of
processes, know types of volcanoes, can categorize, know there are
impact craters. Confidence in determining relative surface age
globally. Know there are surface wind patterns caused by slow,
sluggish surface winds moving sand and dust around.
What surprises seen in planet as a whole?
Saunders: impact crater morphology - appears very unmodified from
oldest to youngest, for as much as 500-700My or more. Use craters
for determining relative ages of terrains on other bodies.
Expected to find crater aging on Venus, but seems well preserved
everywhere.
Will we see new volcanic flows?
Wood: probably not. Timescale too short even for active
volcanoes.
Evidence for continuous vs. catastrophic evolution?
We see a random distribution of impact crater. Both sides use
same data. Similar crater morphology, 5-6% at most showing
modification from volcanic activity, 10% by tectonics. Enormous
amounts of modification by plains volcanic activity. Support
resurfacing over large regions continually, OR very large event
(duration up to 100My) covering entire planet, followed by small
amounts of modification.
What further evidence to support one or the other?
Sophisticated development of statistical arguments, depending on
detailed geologic arguments & mapping that haven't been done yet.
Will take many scientist & student hours to develop evidence.
Start/stop dates for 1/2/3 mapping cycles?
Saunders:
9/16/90 - start mapping 5/15/91 - end cycle 1 1/15/92 - end cycle
2 cycle 3 will do left-side mapping - similar viewing geometries to
cycle 1. right now in low-shade geometries, don't get as much
mapping time. Will get stereo & quantitative data. 9/15/92 - end
that phase. Could lower periapsis to 185 km & do gravity tracking -
would get 360 degrees of tracking (geophysicists want this).
Health of spacecraft & budget for cycle 3 & beyond?
Saunders: spacecraft is very healthy, no problems. One tape
recorder lost. Lost exciter for 1 X-Band transmitter. Would not
have redundancy if lost another, would lose radar mapping but not
gravity. One reason to wait for thermally benvolent cycle 3 to do
more imaging. Plenty of hydrazine for any kind of manuever desired.
120 kg initially, 100 kg left.
Huntress - budgets decided on year-by-year basis. Came out in
fairly good shape for '92. Plan to continue through 3rd cycle. For
FY '93, depends on OMB and Congress.
Status of Pioneer Venus? Doing co-observations?
Pettengill - orbiter will reenter in late '92. Very interested in
revealed variability & height structure of atmosphere - may use
drag to circularize Magellan orbit.
If active volcanoes, will Magellan see it in real time like
Voyager?
Saunders: radar gives a snapshot. Image once/8 months and look
for changes - can't see motion directly. Io vulcanism seen in
profile looking at planet limb, radar looks down.
Shape of typical ejecta in terms of dipole length, reflective
characteristics? What is special about Magellan that allowed
discovering Maat Mons?
Wood: Maat Mons is right at equator. Venera didn't go that far
south. Pioneer had too low resolution to see it.
Pettengill - might have seen from Earth-based radar, but geometry
was poor.
Galileo gives indirect evidence for lightning. How does this
correlate with Maat Mons being active?
Saunders: Galileo scientists don't feel there's any correlation.
No link from scientific view.
What would cause rapid weathering?
Wood: weathering is chemical transformation. Igneous rock not in
equilibrium after it cools. Weathering -> change in chemical
character. Erosion -> change in physical character. Speed
exponentially dependent on temperature, Venus is very hot and
atmosphere is reactive (SO2, high water content (~1/10 atm. H20
vapor pressure)). These tend to accelerate reactions.
What does Magellan say about past existence of oceans on Venus?
Saunders: craters indicate surface is unchanged for as far back
as we can see. Smallest are ~3km -> size of smallest bodies that
can get through thick atmosphere -> suggests atmosphere unchanged
for ~800My with greenhouse at 900 degrees F, disallowing open
water.
What is impact of budget pressures on new probes?
Huntress: CRAF survived FY '92 process, but allocated far less
than requested, mandating delay in both CRAF (1 year) and Cassini
(depending on FY '93) 1-2 years, with no effect on Saturn arrival
date. Mars Observer on track for 9/92 launch, has operating budget.
Magellan planned continuing operations. Galileo working on getting
antenna to unfold. CRAF penetrator deleted 1 year ago.
-- Jon Leech (leech@cs.unc.edu) __
``You looked so innocent and vulnerable, I wanted to use
everything I knew about radar astronomy to protect you.''
- Dr. Steve Mills in _My Stepmother is an Alien_