Transcript Gale Crater MSL Candidate Landing Site in Context

Gale Crater
MSL Candidate Landing Site
in Context
by K. Edgett
April 2010
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 1
What do I mean by “Context”?
• How will the things we can learn at this landing site inform
us about the rest of Mars?
• How do things we can observe with MSL fit into the bigger
picture?
• My focus here is on key aspects of Mars geology and
geologic history. Granted, there are many minor areas that
could be discussed, as well as some non-geological topics.
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 2
What aspects of Gale connect with the rest of Mars?
• Liquid water
• Layered “fill” in an impact crater
• The so-called “Medusae Fossae Formation”
• Mineralogy remote sensing ground truth
• Eolian dunes
• Relative age
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 3
Liquid Water (or other liquid)
• Liquid cut channel on northwest wall and deposited sediment in the
proposed MSL landing ellipse.
• Liquid cut gorges into the layered rocks of the lower part of the Gale
mound. Some sediments from they might still be present.
• Materials date back to a time when liquid was flowing at the surface of
Mars.
• Materials present opportunity to study clasts transported by flowing
liquid.
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 4
Liquid Water (or other liquid)
Channel cutting rocks of lower Gale
mound in an area accessible to MSL
channel “fill” material
MOC M03-01521, looking westward
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 5
Layered “fill” in Impact Craters
•
Thousands of Mars craters of sizes from meters to hundreds of kilometers in diameter
have been filled or partially filled with material.
•
Some were filled and then buried.
•
Some were exhumed or partially exhumed.
•
Many remain filled and buried and are either completely unknown to us, or only vaguely
recognized (or speculated to be there) by the presence of a circular depression.
•
Gale is of the broad family of craters that have exposures of layered fill materials (usually
lithified) in them— these include examples where the fill is expressed today as an eroded
mound, but there are other expressions, too.
•
The processes that deposit the fill, lithify it, and erode it, may be similar all over Mars—
what we learn at Gale applies to all.
•
If some of the fill is lake sediment (or not!) then we learn a lot about these fill materials all
across the planet. Were there lakes in any of the martian craters? Gale is a large, deep
crater. If there was never a lake, that is as major a result as if there was a lake.
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 6
Layered “fill” in Impact Craters
Gale is part of a
family of craters with
interior layered
mounds or other
interior layered “fill”.
Henry
Capen
Gale ~155 km diameter
mound
note this “fill” has broken-up
Tuscaloosa
Schiaparelli
Gale
Pollack
Knobel
Lasswitz
Wien
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 7
Layered “fill” in Impact Craters
Asimov & neighbors
Henry Crater
Gale Crater
Becquerel Crater
The scale is the same in these Viking image mosaics.
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 8
Layered “fill” in Impact Craters
Even Gale’s “little buddy” has layered fill material (and a fan).
HiRISE ESP_013329_1745
landing ellipse
fan
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 9
So-Called “Medusae Fossae Formation”
•
Unit named in global Viking-era “geologic” mapping by Scott and Tanaka
(1986).
•
Yardang-forming material, generally superimposed on cratered terrain and lava
flow plains.
•
Outcrops across 25% of Mars equator between Tharsis and Gale
•
Interpretations vary; most “popular” is volcaniclastic, particularly airfall tephra
and ignimbrites; could be eolian dust or something else altogether.
•
A few investigators have suggested the Gale mound, or some part of the
mound (e.g., upper materials) are remnants of a formerly more extensive
“blanket” of “Medusae Fossae Formation” materials
(e.g., Scott and Chapman 1995; Zimbelman et al. 2009).
•
Others disagree.
MSL Science Team Landing Sites Discussions — Gale Crater
Scott and Tanaka (1986) USGS Map I-1802-A
Scott and Chapman (1995) USGS Map I-2397
Zimbelman et al. (2009) GSA Annual Meeting Abstract #95-1
Edgett, p. 10
So-Called “Medusae Fossae Formation”
Zimbelman (2010) map — This is new/preliminary work. He suggests there
are Medusae Fossae Formation remnants/outliers near and in Gale.
he says the light blue and purple units are “MFF”
“MFF”
GALE
these “MFF”
units have a
plethora of
fluvial
landforms,
mainly in the
form of inverted
stream
channels.
The “fluorescent
green” markings
are indicators that
he interprets the
presence of
layered material.
this map was “blown up” from a tiny figure in the LPSC abstract; the unit labels are not readable in the original.
MSL Science Team Landing Sites Discussions — Gale Crater
Zimbelman (2010) LPSC abstract #1157
Edgett, p. 11
Mineralogy Remote Sensing Ground Truth
•
Investigators working with TES, THEMIS, OMEGA, CRISM, and other orbiter data have
made interpretations regarding the presence of various minerals in Gale Crater.
•
Layered phyllosilicate-bearing rock in the mound.
•
Layered sulfate-bearing rock in the mound.
•
Pyroxene-bearing materials in or near the mound.
•
Olivine-bearing mafic materials in the dark eolian dunes.
–
(called “olivine basalt” by the THEMIS investigators that report this, but I prefer to avoid saying “basalt” because
this implies the genesis of the materials is known to be extrusive igneous or very shallow intrusive igneous)
•
Like all of the MSL landing sites, Gale offers “ground truth” to check our mineralogical
results interpreted from orbiter data.
•
This includes an opportunity to explore the “abundance” of these minerals—for example,
when someone says they see “sulfates” in CRISM spectra, how much of the material is
not sulfate? This is important.
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 12
Eolian Dunes
•
Gale offers something not available at all 4 landing sites: a look at low-albedo eolian dunes.
•
These are located in and between the landing ellipse and the mound.
•
Similar dunes occur all over Mars and we can compare the properties of these dunes with all the
others observed from orbit to understand how similar or different they are.
•
And then we can use the Gale dunes to “ground truth” our understanding of both particle size and
composition as inferred from remote sensing data (particularly thermal- and near-infrared).
CTX stereo anaglyph, Gale dunes, images B06_011984_1754_XN_04S222W & B07_012340_1750_XN_05S222W
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 13
Relative Age
•
Independent of whether certain materials in Gale can be interpreted as being Noachian, Hesperian, or Amazonian —
and independent of whether these 3 epochs can be tied to an absolute date via models of past cratering rate — we can
say some key things about where Gale falls in the sense relative timing of events on Mars.
•
Water. Materials in the landing ellipse and on the lower mound date back to a time when a liquid could flow across the
surface of Mars, cut channels, and transport sediment.
•
Sedimentary rock. The layered rocks of the lower Gale mound were deposited, lithified, then eroded by fluvial (and
probably other) processes. The sedimentation, then, was a long time ago and pre-dates the gorges cut into the lower
mound.
•
Crater “fill”. The layered rocks of the Gale mound, furthermore, date back to a time when conditions prevailed over all
(or much of) Mars such that large craters could become filled—even buried—by materials. This does not seem to be a
process that has acted in more recent times.
•
Erosion. The rocks that make up the Gale mound not only lithified a long time ago, they were eroded a long time ago
(and might still be eroding today). Layers formerly extending to the crater walls were broken-up and removed such that
the mound is all that is left today. This happened so long ago that there is no clear indication as to “how did the stuff get
out of the hole?” This is a huge mystery, one that Gale shares with many other craters on Mars that have these
mounds and interior layered rock outcrops.
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 14
Take-Home Points
• Each of the 4 MSL candidate landing sites has
things we’ll learn via Curiosity’s field study that
inform our larger view of Mars.
• Gale could inform us about…
– the liquid that carved channels, etc., on Mars
– the general nature of light-toned, layered, “sedimentary
rock” crater-filling material
– were there lakes in these craters at some point?
– ground truth for remotely-sensed mineralogy
– general nature of eolian dunes
– what was Mars like back at this time when liquid “water”
could flow across the surface and “stuff” was filling the
craters?
MSL Science Team Landing Sites Discussions — Gale Crater
Edgett, p. 15