'
.' *

VOL. 78. so. 20

JOCRS;zL OF GEOPHYSICAL RESE.-ZRCH

JULY 10, 1973

Variable Features on Mars, 2, Ilariner 9
      Global Results

C. SIGAN, J. VEVERKA, P. Fox, R. DUBISCH, R. FRESCH, ASD P. GIERASCH

Laboratory for Planetary Studies, Cornell University, Ithaca, A-ew York l&O

L. @AM, J. LEDERBERG, E. LEVISTHAL, R. TUCKER, ASD B. EROS

  Artificial tntelligence Laboratory and
Department of Genetics, Stanford Xedical School
Stanford L-niz'ersity, Stanford, California 0.@05

J. B. POLLACK

IYAS~~ Ames Research Center, htoffett Field, California  94035

,$-~ternutic Mariner 9 monitoring of the space and time distribution of Martian bright and
dark markings, the streaks and splotches. indicates a range of global correlations. The time-
variable classical dark markings owe their configurations and variability to their constituent
streaks and splotche.s, produced by windblown dust. Streaks and splotches are consistent Kind
direction indicators. Correlation of global streak patterns with general circulation models
shows that. velocities -50 to 90 m/set above the boundary layer are necessary to initiate grain
motion on the surface and to produce strpaks and cplotches. Detailed esamples of changes
in Syrtis Major. Lunae Palus. and Promethei Sinus are generally consistent with removal
of bright sand and dust and uncovering of darker underlying material as the active agent
in such changes, although dark mobile material probably also exists on Mars. The generation
of streaks and the progressive nlbedo changes observed require only threshold velocities of
about. 2 m/set for about 1 day at the grain surface. We propose that the dark collar observed
following the north polar cap in its retreat is produced by the scouring of bright overlying
dust. from the polar peripheral ground by winds driven by the temperature differences
between frosted and unfrosted terrain. The stability of bright streaks and the variability
of dark streaks and splotchesF as well as their contrast, can be the result of size differences
of the constituent particles.

One of the principal objectives of the Mariner
9 mission 15x5 to examine, at high resolution
and extended time b,?seline, the surface albedo
rariations on Mars. The preliminary results of
this inrestigntion have been presented by Sagan
et al. [192; here cnlled paper I]. The time-
variable Martian dark areas and representative
semitone nrens were found commonly to be
resolved into two kinds of fine structure: streaks
nnd q)lotches. Most streaks emanate from
craters, nlthough some begin at positive relief
features. Bright streaks tend to be long and
nnrrow; dark streaks, shorter and broader.
Typicnl streak lengths are tens of kilometers.
Splotches are irregular markings that exhibit

Copyright @ 1973 by the American Geophysical Union.

n significant. tendency to be located inside
craters, often asymmetrically against a crater
wall. Larger splotches may wish over crater
ramparts onto adjoining terrain.

A large variety of splotches and streaks have
been systematically observed during the mission.
In many cases, all three photometric angles
were held nearly constant so that true variations
in the nlbedo of these markings could be sepa-
rated from changes in shadows and the effects
of the surfnce scattering function. These ob-
servations were designed to detect relative
nlbedo changes within the field of view. No
conclusions are based on absolute photometry.
Major variations in splotches and dark streaks
were uncovered with a characteristic time scale
for variations of <:! weeks. Variations on a

4163


time scale of 1 dny were -ought : =uch rapid
\-arintions must, 1.~2 rel:ktively uncommon, a5
none nere di;co\-ered. So \nri:ltions of bright
et reaks, either in production or clis~ip:~tion, vxre
found. In several pl:ice;, most notably S\-rtis
Major, the configuration of dark and bright
streaks corleponds remnrknbly well t 0 the
claszical enrrh-bnied configuration of the dnrk
area that the streaks constitute. Observed time
vsrintions in the di,5tribution of such strenks
correspond to regions in \Thicli the :ilbedo
yarintions were prcvio:l51\- olxerwd from earth.
Paper 1 prolxxecl that the distribution and
time \~?,I'j~lTiOl~ of streaks and 5p!otclics are the
c:llws of the clnsficnl seasonal and Wciil3r Tari-
ntions oi Martinn albedo m:irkingn.
TKO principal hypothe,~es xere propoacd in
pre-llariner 9 clays to explain the.:e \-arinti0il.G:
biology and nindblown dust. .Ilthough con-
vincing evidence agflin<t biological esplanntion~
are not forthcoming, mainly because a wide
range of properties can be proposed for hype-
thetical Martian organisms, the evidence of
paper 1 i.5 strongly in favor of windblown dust
prnchlring .strenks and splotches and their time
variari0n.s. -4 range of ezplnnntions of the ;trenks
and splotches wn mentioned in paper 1. For
esample, bright streaks might be produced 1)~.
bright dust trapped in negative relief dust sink-:
(sue11 as crater bottoms) in the waning stngc.5
of the dust storm, and subsequently deflated
by strong gusts. Or fine dwt deposited uniforml:
by a dust storm may subsequently be stirred
up, suspended, and blown away because of
collisions with snltating grains everywhere but
in the lee of crater walls, where the wind
wlocities are low. Examples of both of thcsc
cased on a smaller scale are known in A4ntnrrtic
dry vnlle\-s [Morris et al., 1921. .4lternntively,
dust darker than the mcan nlhcdo of a given
area might be layered down h\- the wind from
a prevailing direction e\-erywhere but in the
lee of crater ramparts. But in these rnsci, as
with other esplmintions of the strenks, the?
will point in the direction of the wind flow. Thus
it \Yas proposed in paper 1 that the streaks
may be natural wind \-xne5 and porsiblJ
anemometers placed on the Martian surf:tcc.
In this paper, we present global maps of the
streaks , strcnk-splotch correlations, and a com-
parison of wind fiow patterns cleclucecl from
these map:: with results on the general circulation

T1:p pnlire -1lrfnce of Mnrs xv:15 mnpl~etl for
y;re:lk+, bo;h bright acd dark. 1\I:apping was
iwed ;>rimarily on Oznlid mosaics of Iv-id+
3n;if pict1lrc.5 prepared by the z42trogeolog!-
Brnncb, I-.?. Geological Survey. These picrures
;bre 3 con\-enient source. alloving easy mnpping
of ,:treak: Ihat tra\-erie Clc-nngle picture
bolmdaries, but they 3150 limited our effecti\-e
minimum tlctectnble strenli length to :LbOLlt
10 km. There are many smaller streak:

Oil  ixlrron-nngle pictures,  but Mariner 9
did not pro\-ide adequate nnrroly-angle cover-
age of ?iI:lrs to permit useful high-resolution
ztrcnk mapping. The mosaics cover the time
interval lw:ween rcvolulions 101 and 222, corre-
sl)onclin~ to L. = 320" to .35.3", or late summer
in the so~uthern hrmispherc. Our results npyJ?-
only to this season.

Quite different result:: may apply to other
%x~ollx, inasmllch na only the appearance of
cl:lrk streaks. never the removal of dark streak5
nor the appr:imnce of bright streaks, was
observed during  this time interval. Such 5
yituntion cannot continue indefinitely if Mars
i; to maintain the general nppcnrance to cnrrh
that it has eshibited for more than n century.
On the other hnncl, the frequency of alteration
of ztrenk,< observcd mwt represent some inte-
gration of streaks producctl recently and streaks
l)rotlllccd at some more remote times, perhaps
of the or&r of 1 J.cnr in the past.

Streaks wrc mnly~cd by four coauthors of
this paper, and there was siF;nificnnt o\-erlnp
nmong tlieir counts to gunr:lntce no major
per.<onnl sl.,ytcm:ttic error.+. The relative number
of margin:21 strwks pro1vl to be few, prim:iril!
cncs on the border hctwccn -llort -.-t rwk.5 :rlltl
1011g aplotclw +llin, fl over cr:\trr n:~lls:. The
fin31 dtrwk m:ip5 were c:lrefllll\- lxoofctl ngain;t
the origin;ll coml~il:lticJn~. In the l)rc.>ent AlId!,
IVC arc conccrnctl only \viI II the w:rtlwr \`:\nc,
110t with 11~ Iiyl~otlic~+x~tl :Ili(.lii(,ili(`t(`r`. :i..lwct
of t lie ,2t re:~ks. .\cc*ortlin~l!~ -trc:lk lcn$lli arc

displayed on two scales: the ehort
spend to streaks SO0 km long; the
correspond to streaks 260 km
streaks are represented b\- solid ~a
streaks by dashed arrow. The rc:
played in Figure 1 in Lambert cc
Mercator maps. There are are;l:
number of parallel streaks was 51
given small are3 that represents
streak on maps of this scale woul
impossible (cf. paper 1, Figure 1
regions of great arrow density, o
sentative sampling of streaks is ii
10s.~ in generality for streak dire
from this con\.ention.

Figures 2 and 3 show the streaks
projection on earth-based nlbedo :
9 topographic maps, respectively. 1
of the north polar hood and an ap;
paucity of streaks in the south
region for the L, of these observ:
reason for the blank areas in thl
the absence of streak map? for r
of -CA". In Figures 2 and 3: onl:,, tl
streak direction within each 10"
square is shown. Where there are tv
directions, both are show. AS is
the rosette diagram for the Solis 1
(Figure 1), one or two prevailing d
almost a1wal.s a good approsima
there is a notably high density of
grid square, it is represented by a
Wind directions have been plottt
bright and dark streaks, which in 5
give concordant and in other region
directions, probably because the!
produced at different times.

hIPLIC4TIOSS OF THE STRE.4K

We have prel,iously shown (palx
16) that the configuration of SJ
corresponds well to the distributi
stituent dark streaks. In Figure 5 I
plot the distribution of streaks in
of Solis Lacus, a well-knolvn se
secular variable. The earth-based
Solis Lacw, circa 1969, after the
serwtorl cartography, also is ~1:
sidering the variability cf this f
agreement between the classical CC
and the locus of streaks is excellent
with our previous conclusions. We p


ian atmixphere. WC derive a 1leW
the xvincl yclocities necwnry to
movement on the Martinn surface,
led exunplej of variations in three
Iars, and present nex conclusions
fi:~nism; of wind-initiated nlhCCl0

Sac.4~ ET AL.: M~IUAXR 9 MISSION                 4165

displayed on two scales: the short arrows corre-
spond to streaks <GO km long: the long arrow
correspond to streaks 260 km long. Dark
streaks are represented by solid arrows, bright
streaks by dashed arrows. The results are dis-
played in Figure 1 in Lnmbert conformal and
Mercator maps. There are areas where the
number of parallel streaks was so great in a
given small area that representation of each
streak on maps of this scale would have been
impossible (cf. paper 1, Figure 16). In such
regions of great arrow density, only a repre-
sentative sampling of streaks is indicntecl. So
loss in generality for streak direction result*
from this convention.

Figures 1 and 3 show the streaks in AIercator
projection on earth-baaed nlbedo and Mariner
9 topographic maps, respectively. The existence
of the north polar hood and an apparently real
paucity of streaks in the south circumpolar
region for the L, of these observations is the
reason for the blank areas in the north and
the absence of streak maps for regions south
of -65". In Figures 3 - and 3, only the prevailing
streak direction within each 10" x 10" grid
square is shown. Where there are two prevailing
directions, both are shown. -4s is indicated in
the rosette diagram for the Solis Lacus region
(Figure a), one or two prevailing directions are
almost always a good approsimntion. Khere
there is a notably high density of streaks in a
grid square, it is represented by a thick arrow.
Wind direction5 have been plotted for both
bright and dark streaks, IV nc 1
                1 1 in some regions
give concordant and in other regions discordant
directions, probably because they have been
produced at different times.

IMPLICATIOSS OF THE STREAK 1f.i~~

We have previously sflown (paper 1, Figure
16) that the configuration of Pyrtis %Iajor
corresponds well to the distribution of con-
stituent dark streak. In Figure 5 we similar11
plot the distribution of streaks in the TicinitJ-
of Solk Lucua, a well-known seasonal nncl
secular variable. The earth-based outline of
Solis Lncus, circa 1969, after the Lowell Ob-
servatory cartography, also is shorvn. Con-
sidering the \nri:tbility of this feature, the
agreement between the clzsicnl configuration
and the locus of streaks is escellent, consijtenr
with our prek.w concluion5. Ke propose that

marked secular changes in Solis Laws [e.g.,
A~~tonindi, 1930, p. l-lo] are due to estraordinary
wind regimes, rediztrihuting fine dust in this
area. Other factors being equal, small dark
regions surrounded on all sides by bright areas
~floulcl he more susceptible to eolinn secular
cfianges [Pollnck aftd Sagan, 19Gi]. Ultimntel)
a. reconstruction of several different wind re-
glmea, a kind of eolihn stmtigrnphy, should
be possible from data such as fhat eshibited
in Figure 5. Ke return to this subject else-
where.

In addition to specific cases, such as Syrtis
Major and Solis Lncw, we see from Figure 2
that the global distribution of streaks corre-
~poncls well to tile general configuration of dark
areas as viewed from earth. In these figures
there are many cased where two different flow
directions are in evidence. We interpret these
as the remnants of the flow regimes in the
1Iartian atmosphere at two different epochs,
probably two different seasons. It also is possible
that a subset of flow directions belongs to the
great 1971 dust storm and is not typical of
wind patterns in the absence of global storm
systems.

In the latitude b:md betxeen 2O"S and 20"s
(regions MC-S to MC-23) there is a clear
tendency for the flow to be from the SE north
of the equator and from the SK south of the
equator. This pattern corresponds to the zonnll!
averaged surface wincl calculated by Leorsy and
Mintz [19G9] for southern hemisphere summer.
It also appear.5 in the wind field mnps derived
from the Akriner 9 infrared interferometer
spectrometer i Irk) esperiment (Figure 6). The
Iris  wind field5 are determined from the
I,ressure-tempemture profiles ohrnined by in-
version of the infrared emission epecrrum. The
results nbo\-e rhe surface houndlary layer dk-
played in Figure 0 were derir-ed by J. A.
Pirraglin [cf. Hnwl et (II., 1972; Cowath et nl.,
19731 from temperatures during the dust storm.
An approximate dyinmical theory i; used. It
is e5pecinll\- important for our purposes that :
(1) to1lography is neglected, and (2) the results
:Ire most uncertain close to the equntor. Kinds
:It tlw equator are probably overestimated. The
,zenernl confi~nm~ion of the flow pattern ia
probnbl>- correct, however, and the agreement
between the c:~lculnted wincls :lild the streak


i?AGAK ET AL.: !lfhRIl-ER 9 ?dISSIOK

.~
SOUTH                                  SOUTH
MC-2                                  MC-3

SOUTH                                 SOUTH
MC-4                                  MC-5

  ss.Q.              5                                     ;

     i                     :                                     *.
4 so.-
P .-.                                                            *.
                                                            : r.
4s05                                                             . . A.
                                                                  .ul

   6.                                                               :

4%'                                                                -2
  /                                                                :
3s.:                                                    -2>
                                                    i
                                    //;59o
                                 -----G@
               270o                                        200'

              SOUTH                                  SOUTH
               MC-6                                   MC-7
  Fig. 1. Streak maps of Msrs. Solid arrows represent dark streaks; dashed arrows represent
bright streaks. The arrow length is about four times the streak length, but is approximate.
The shortest arrows shown (2O of latitude long) represent streaks 560 km in length. Regions
of the planet north of 50"N could not be mapped for streaks because of obscuration by the
polar hood. The absence of streaks in these regions, evident in Figures 1 and 2, may not be
  real.

NOFTH

0"` --_ -__. ~_i_--_--
IW     170"     160"     1X
               SOUTH
               MC-8

               NORTH
30",~ ------ ~-

SOUTH
MC-IO

NORTH

30"[-----' _.-..- ._.. . .

f I      SOUTH
        MC-12


SION

SOUTH
MC-3

    NORTH      "
-.--- --__ .,4-I . . . ..-

SOUTH
MC-7

streaks; dashed arrows represent
renk length, but is npprosimste.
reaks 560 km in length. Regions
:s because of obscuration by the
in Figures 1 and 2, may not be

S.AG.AS ET AL.: XUUXR 9 ms~ros                4167

               NORTH
30";"  :. ,-------T--...- .-__._ ___ -,--.-

25-E
  i

ok   -    u-.--1 iii ---_-___-
la00     170"     160o     150"     1400
              SOUTH
               MC-6

3(y--r------
1

25oF

NORTH
--_*I -v---r

SOUTH
MC-IO

NORTH
---IT.  -.- .,.____ -

I ,      SOUTH
        MC-12

SOUTH
MC-9

              NORTH
30"---.: --...- -.  .- .-..----T-TTT71m
`,                            i

25":            j
                               i

/

SOUTH
MC-II

NORTH

3O".~F ----. --- -----..-.-- -.--.----

               SOUTH
               !CC-13
1\

Fis. 1. (conrmuea)

275"


SOUTP
MC-14

              NORTH
o"rT ---.. rr-7--,--___-.e-

-30"`u,A,d, ,,, ,, ,,,,,,,,,,,,,,/ .L
183"     170"     1600     1500     140"
               SOUTH
               MC-16

NORTH
  #,I, `I `,`/, ,.,,,

SOUTH
MC-15

NORTH

SOUTH
MC-17

J

i

4
,
i

SOUTH       ,\
MC-18

Fig. 1. (continued)

SOUTH
MC-19

higher latitudes, 2nd the steady component that   is the indication of a steady ensterly flow
Pirrnglia calculates to dominate at low latitudes.  component at latitudes 20" to 40% This is
The streak maps (Figures 1 to 3) support  the latitude range and initial direction of flow
this contention. The flow indicated at high  of the great lOT1 global dust storm, and it is
latitudes does not correspond to thnt predicted  possible that this flow component is a mnrker
either by Pirraglin or by Leovy nnd Iiintz.   of that storm.
An interesting regulnrity nt higher latitude   Other peculiarities may be connected with

              NORTH
00   ~0

SOUTH
NC-M

              NORTH
o'--- --7-~-1---

SOUTH
MC-22

A=
     .--. .-.-.
_b??-; 165'  150" ---
  \@        13;
         SOUTH
         MC-24

topogrnphy. There ii the :~ppcnr:~~
flow away from 3 region ccntel
11O"W. This is the arc:l of Thnwi.5
region on 31x-. The flow mnr:
wind t rnnsport downhill kc, :~ltl


SOUTH
MC-15

SGUTH
MC-17

    .::
    `,%'
   4L ,,
z
.., `..;
..; \ . . `...
-.::. *

<*;, / / _
    300

--g---j~
20"

SOUTH
MC-19

xtion of n steady enjterly flow
nt lntitudes 20" to 40's. This is
range and initial direction of flow
1971 global dust storm, and it is
this flon component is n marker

uliaritier: m:~y bc connected with

SAGAN ET AL.: 11ARISER 9 ~~ISSIOS                 4169

              NORTH
o' -.-- - ..-_ -._  .-_-r-.
      .;
      :
-50                 . . . .

SOUTH    . .
MC-22

MC-24

  NORTH
,      II        
_ _     `, ,,'
`0

-25'         `\

-30'
    310'    3ooo' I.. %". . -. _ -i~j,  ._~
                               2700
                SOUTH
                MC-21

              NORTH
p~T--T--T   "`-`,,   ,,, I."
r                          ,..'
-5't             ;

' SOUTH
MC-23

MC-25

Fig. 1. (continued)

topography. There i.5 the nppe:tr:mce of rndial
flow an-ny from a region centcwtl :jt SOS,  not the predicred flow direction in the yicinit?
                          of ach elevnticxls


     NORTH                                  NORTH
_. . .--------_. .___, _              -_. . ---- --y-----~~

Fiy. 1. (continued)

cation of the flow patterns near 2O"S, llO"W,
seems to be connected with the presence of
rough terrain there (Figure lc) ; the winds
appear to move to avoid the rough region.

The preceding re,qlts provide us with n new
cstimnte of the threshold velocity necessaq
to initiate q:rin motion on the ?IInrtinn surfttcc.
There is :I. modest v:trintion :~mong various
recent estin1:tte.s of the critical velocity I' above
the surface boundary layer newwwy to initiate
grain motion on the surf:tce. Sagajf nntl Pollack
[19Gi, 1969: see nl~o pnpcr l] estimated this
velocity nt :tbout 65 in,,`3cr for a l&nib surface
lm%ure level, about 50 m/set for 10 mb, and
;tbout 110 iii,/.sec for 5 nib. Golitsyz [ 10731
lxol~o~ed th:tt thwe \xlue,; may be reduced b)
about 3t.l:: by introducing sharl~ rou~hne~.~
gradients. IIcss ]l!liS], recttlculsting the
probkili, drrivCs 1' for Xl S-IlllJ ~llrf3CC pws5llre
to be between X ;III~ GO IX/CCC, depending on

the velocity distribution function through the
boundary layer. Yet another independent esti-
mate by Gierasch a& Goody [1X3] is about
ZO m/set for a surface pressure of 5 nib. The
range among these models is about :I factor of
2 for comparable `surface presaureS for the
t!n-eshold velocity V,, to initiate grain motion
at the ground but rises to :t factor of almost
4 for the velocity above the boundary layer
due to differences amorq the models in the
nesumed functional form of the velocity dis-
tribution through the boundary hiyer. Dis-
tinpishing niiiong thede results is a matter
of some import:nwe for understanding the
greneration of dust storms and eoli:tn transport
on Mars. It also has a more practical im-
portance: Lower velocities present 110 problem
to a lander mission such RS \.iking, whereas
the higher velocities po.~r grave hazards.

The  esktencc of a  40" wide equatorial

--.--- 1.. ---  _--. - .-...... ---..- _.____.________.___-*__, Fr*i

Fig. 2. Prevailing streak direct
Lowell Observatory earth-based a
areas.

latitude band in which the streal
follow strikingI!. the mean general
with significant deviations outside
indicates that the globnl wind veloci
borders of the band are npprosii-
velocities appropriate for initiating g
ment on the surfnce. From the I

-w--m... ~...s"...--,l. ----

Fig. 3.  P revnilin:: &reali tlirwtion
                 hI:uG

-7_-.


;ION       I                                                           4171

      NORTH
___,~-~~--------
      ----, b
  F/
       `\                ;
                       /

NORTH

Fig. 2. Prwailing streak directions (averaged over 10" by 10' - ccp~lres) ~uperin~po~ed on n
Lowell Observatory earth-based alhedo rnll!) of Mar.;. Thick rlrrows indicl~te hen\ily strenked
areas.


geiicml circulntion, but the high-\7locity t:iil
of tile di-tril,utiun fmctiun uf tlic gener:d
circulntion winds thnt mu-t Le olmative. Time
velocities lie in the middle of the rnnge tmmm-

Fig. 7. The north polar c'np of 31:
     Ixtc spring in the nortll<


I ilcrivcd from qlkitr tlificrcnt con-

oreovcr, :I recent rc\.i>ion of the
at these altitude-: :(I the start of
n, for the numrriv:~l circulation
:`!I at~cl Miotz [ 1969], r:tises these
1 60 m,`scc :tt cqu:Ltori:J latitudes
19i3], 17elocitics derived from the
f lee \wve clouds [Leouy et al.,
is 5:1me order.

mentioned, few wind indicators
very high kitirudes, both because
and l,ossibly because of efficient
e p:Acles from the polar regions.
tch density in the south circum-
I come zenbe compensates for the
trcak tlcnsity ; there is :I marked
3k; in the most heavily splotched
Sewrthele+, there nre a. few
in the north (LIxrc .4cidalium,
1 the ~33~1th (1lare Au-trnle, MC-
Ann?- streaks arc directed awva>
. This i5 h:rrdly an invnrinble high-
3mcnon (there is :d50 2 westerly
cunIpo11ent i ,  CIJ  in~prction of
C-24 to XC-??) clearly shows;
eles seems noteworthy. The most
,d cslkuxltion would be in terms
cap trmperclture gradient winds

postuhtetl 1,~ Lro~y/ et al. [ l!U], The pole-
fleeing &rcnks in Xlrc Acidulirnr~ nrc intcrcsting
because this mnre i:: one of t hc fen tlnrk :lreas
at thrse lntitudes for which een-`onnl clktngcs
nrr csl~ectcd nt the okerl-ed awson. It is
posiblc th2t sxsonrd nlbedo vnrintions nt hi$
lutitudcs nre driven b!. such polnr winds. The
most likely mechanism woultl be the eolinn
removal of bright overlying clust, revealingr the
darker material underneath, ~15 lw5tuI:itcd for
se\.eral varieties of ,5en:onnl change5 [Sagarl curl
Pollack, 1967, 1969; Saqm et al.. 151: paper
11.'

4 related phenomenon may be the north polnr
collar. This dark band, surrounding :cnd follow-
ing the northern ice cap in its summer retreat
to the pole, hns been reported by nmnp visual
observers [e.g., de Vawouleua, 1954; Dollf~s,
19i3]. Because of possible ps~choph~~iologicnl
contrast effects, nnd especially beeawe of the
interpretation  of the  northern  collnr   a s
moistened ground, the very esisence of the
collar has been cnlled into question in rcecnt
years. Mariner 9 estended mission .photograph>

-I

!

I - >, / , , i :\\\k..-----/, ----
.m  r/i. I iilL\.--,,,, ,
I, I i'\`.\..-- -,,, .: ,`, (!`L:;
  `liii\.---r ,,,,t'..---*~

:iiiiiiiii~~-~iriii:iiiiit~ I
     : I > a   .<_.. .`"C '     )I it I.

Fig. 6. Iris wind fields determined from pres-
aurc-tenlpcmturc profiles of the Martian atmo-
sphere. The season is summer in the southern
hemisphere. The wind direction is into the grid
points; a wind vector equal in length to one grid
sl)acing corresponds to n velocity 0i SO m/set
(courtesy of F. A. Pirraglin).

hns demon:tr:lted unnmbiguouJy (Figure i)
the esktence of the north polar collar. Under
the circumstances, the report by earth-based
vieunl observers that the collar follow the
retreating polar cal) toward the pole mu5 now
be taken seriously.


417-1             8.4G.43 ET AL.: 11ARISEI< 9 ~IIssION

I;otli tltc csi51cttcc of I110 coll:tr :ind its retrent.
wn 1~ undvr.~iootl in term:: of polnr winds,  Ark Spl0t~ll~ ierrxin tll:it follows tltc \wtting

dCfl3iillC :t Illill. IIl'i~llt .*llrf:lVC l:l!-Pr Of dLl?t  l~criphcr~~ of the cap. The tr;uwl)ortctl bright

in the imtnc~linte \,ivinity of the northern polar  rnntcrinl i.5 ktycrcd tlo~vn sonic\vlt:tt equator-
                   ward, 1)roducing bright circutnpular strc&.
C:I~ rdgc. But why did 1I:triner 9 find no  High polar xinds are al.50 cot&tent \vith the
c\.idcwce for 3 SourIt polnr collar? If the south
coll:tr \-i:ibilitv indeed follows the curve of  ltrohnbly eoli:tn etch pits sren cxcltt3i\-vly in
                      pol:tr region,<.
tic ~`a~cco~t/c~ws [ 1!154, Figure 311, peak visibilit!
cwrcq~ottds io L, v -310". Xtriner 9 did not   Cotwx.3TIos~ OF STIE.~~S .~SD SNATCIIES
ol)st,rw 1IarS ncx this L,.            We tlbo 113~ nial~lxd the distribution of
.Inotltcr curious circttmst~lncf is tltat the
wutlirrtt circuml~olar strcnks are, almost, nitlt-  cr:tter sl~lotclies over the entire SI3rti:tn surfnce,
                      wing the tccltniquen 2nd cnutions dcxrihed
o11t  ~~wq~tion,  d:trk streaky, wheta. the  :lbOVC  ior the  streak txtppittg
norihern :trenk. :1n11 especially the Alarc                           progrxn.
                       Splotches
~kaidnlium ,-tre:tks,                  .qGlling over crater ramparts :tnd
        are largely bright during  ~q~lotcltc3 unconnected with craters were not
1f:triner 9 observations.

One possible esplntintion of form.2 of three  mapped. Streaks and splotches in five repre-

l~ltettotnenn is the following: The steep tetnpera-  .zntative regions of IJars arc displ:tyed in
                       Figures 8 through 12. The convention for
tttre gradient between frosted and unfrosted  representing  ,5t renks  is described above.
terrnins at the edge of the retreating polar ice
cap produces               Splotches are represented by sketches nitltin
       strong winds. These winds de-
flnte fine, bright surficinl dust, uncorering the  crater boundaries showing the nlqxosimnte
                   configurations of the splotches. Only craters

0

0

0
0

Fig. 8. Splotch-streak map of the MC-IO region. This is the area surrounding Lunne Palm.
Ml cmtcrs I:trgcr than about 50 km in diameter nnd all dark crater splotches are sho\vn. Solid
arrows indicate the dircctiona of dark crnter tnils; d:Ated :~rrows, bright. crater t :~ils;. The XI'-
row length is approximately four times the length of the toil. The shortest arrows shown are
3" (of latitude) and rqxesent crater tails <60 km in length.

,/
r"



6

Fig. 9. Splotch-stre

O'C

C


,ION

y terrnin that follows the waning
the cap. The tmnaported bright
nycred down somen-hnt equntor-
ring bright circunipolnr strcoks.
vinds are 01~0 con&tent with the
inn etch pits seen exclusively in

INS OF STREAKS AND SPLOTCHES
lnw mapped the distribution of
1133 over the entire Martinn surface,
vlmiques and cnutions described
the  streak mapping  program.
illing over crater ramparts and
connected with craters were not
cnks and splotches in five repre-
<ions of Mars are displayed in
hrough 12. The convention for
streaks  is  described  above.
e represented by sketches within
clnries showing the approximate
J of the splotches. Only craters

I " " I " "I""

0

    0
    0


@

SAGAN ET AL.: MARISER 9 MIssIos                 4175

30. , , , , , , , ,`,     /           NORTH
             ,


                                      .
                                  -..,
    Fig. Il. Splotch-streak map of the MC-22 region Mare T~rrl~cn~~m-Bc.~~~eri~.
                                NORTH
Ok,,,,,,,,,,,,,,,,,,,,,,,, ,,,, ,,   I""""`4
                                                         /'

lnrger thnn about 50 km are shol
that splotches tend to be localized
face of the containing crater (cf.
There is, nt lesst. in many cases,
for splotches in adjacent craters to
in the same face of their respect
This face tends to be the direct
which the wind has been blowing, 3
the predominant nearby streak n-ir
indicators.

As is usual in our present ignorance
surface processes, there are two E
of this correlation, each the obvc
other. In the first view, the winds
dark material into the craters, VA
accumulated against the leeward rz
the second view, the winds have pr
deflated bright material off the leewai
of the craters, exposing the underl!
material, possibly basement rock. Tl
streaks would then bear a closer
to Saharan sand streamers, describe1
[I9631 as `relatively thin, ribbon- or
accumulations of sand downwind fro
source areas or from topographic cc
Where long, straight, parallel and
by relatively sand-free strips, the:
indicate consistency and direction
moving winds.'

Accordingly, we postulate some
Mars in which dark mobile mate
crater floors is overlain with bril
material, perhsps as a consequent
or global dust storms. Subsequent c
the crater produces long, bright.
streaks emanating from the crater, a
ally exposes underlying dark matex
interior leeward side of the crater. I
winds, possibly from another direr
can deflate the exposed dark material,
incipient dark tails. Dark splat
associated dark tails are knowi, e.g., i
[paper 1, Figure 271. The developme
crater tails from craters with pre-esis
tails is also known, e.g., in Heeperia
Figure 231. These views are consi
the conclusions that we will dra\
detailed study of nlbedo variation:
selected regions, Syrtis Major, LUI
and Promethei Sinus. In other cases
splotchy material ma\. be bedrock
dark streaks may be produced by d
overlying bright material.


SAGAN ET AL.: MARISER 9 Mrss~ox                41ii

larger. than about 50 km are shown. We see
that splotches tend to be localized toward one
face of the containing crater (cf. paper 1).
There is, at least in many cases, a tendenc?
for splotches in adjacent craters to be localized
in the same face of their respective craters.
This face tends to be the direction toward
which the wind has been blowing, according to
the predominant nearby streak wind direction
indicators.

As is usual in our present ignorance of Xartinn
surface processes, there are two explanations
of this correlation, each the obverse of the
other. In the first view, the winds have blown
dark material into the craters, where it has
accumulated against the leeward ramparts. In
the second view, the winds have preferentially
deflated bright material off the leeward ramparts
of the craters, exposing the underlying darker
material, possibly basement rock. The resulting
streaks would then bear a closer relationship
to Saharan sand streamers, described by Smith
[1963] as `relatively thin, ribbon- or banner-like
accumulations of sand downwind from localized
source areas or from topographic constrictions.
Where long, straight, parallel and separated
by relatively sand-free strips, they serve to
indicate consistency and direction of snnd-
moving winds.'

.4ccordingly, we postulate some cases on
Xlars in which dark mobile material within
crater floors is overlain with bright mobile
material, perhaps as a consequence of local
or global dust storms. Subsequent deflation of
the crater produces long, bright dowwind
streaks emanating from the crater, and eventu-
ally exposes underlying dark material on the
interior leeward side of the crater. Subsequent
winds, possibly from another direction, then
can deflate the esposed dark material, producing
incipient dark tails. Dark splotches with
associated dark tails are knovn, e.g., in Bosporus
[paper 1, Figure 271. The development of dark
crater tails from craters with pre-existing bright
tails is also known, e.g., in Hes,peria [paper 1,
Figure 231. These views are consistent with
the conclusions that we \vill draw from a
detailed study of nlbedo variations in three
selected regions, Syrti,s Major, Llmne Pnlus,
and Promethei Sinus. In other ca.ses, the dark
splotchy material may be bedrock, and the
dark streaks may be produced hy deflation of
overlying bright material.

At Mariner 9 resolution, the classical albedo
feature Syrtia Major is outlined by a concen-
tration of bright and dark streaks. The bright
streaks dominate near the Ivestern (stable) edge
of Syrtis Major. The dark streaks outline the
eastern, variable edge (Figure 13) of Syrtis
Major (paper 1). Telescopic evidence suggests
that the eastern boundary of Syrtis Major
varies seasonally [rintoniadi, 19301.

Since the end of the 1971 dust storm, Mariner
9 photography has revealed a gradual darken-
ing of Svrtis Major at resolutions of the wide-
angle camera (Figures 1-l to 16) and the nnrrow-
angle camera (Figures 17 to 20). This darkening
resulted largely from the appearance, develop-
ment, and merging of dark crater tails of the
type seen in Figure lQ, which are characteristic
of Syrtis Major. In other arena, dark tails do
not have the patchy, discontinuous appearance
of the Syrtis Major tails. This nonuniform
patchiness of the tails and their tendency to
shed tangentially from topographic protuber-
ances such as crater walls suggest that they are
produced by eolisn erosion of extensive, but
very thin, deposits of bright material, resulting
in the exposure of dark, w-ind-resratant, under-
lying material. Radar evidence suggests that
the region of Figure 13 is a relatively smooth
surface, sloping from west to east (left to right
on Figure 13), making it a likely locale for
eolian transport.

\t'e assume that, after the 1971 dusr storm,
much of this slope was col.ered by a thin layer
of bright dust. Subsequent ninds, bloning pre-
dominantly donnslope, ha1.e scoured OE this
material, especinliy in regions where wind speed
are intensified by topography. d cio-e esami-
nation of the high-resolution  rxrrow-angle
pictures (Figures 17 to 20) is e+&ll!- in-
structive in this contest. Many iwtnnces of
d.trk tails or sections of dark tnils shedding
off crater\` can be seen. This i.5 especialI\
evident in Figure 20.

Ke po-tnlnre efficient microtraps for the dust
aroliretl off in the abo1.e manner. Our model
predicts that Fyrri.s 1Injor n-ill continue to
darken iintil i: is afirered by either a local or
global dli;t storm. The contra-t;  involved
het\veen t.he d.irk and bright portion; of Syrtiz
\Iajor are 5m:ill, heing t!-picnll!- nhollt 105
I ior the a!hw!n rn:~rkin~~ in Fiel:rr !I.


Fig. 13.  Grneral I-ien of Syrtis RI:ljor. This wide-an& picture. centered at 13"N, 2S30w,
        is about 360 km wross (hlTS:S 4181X2, DAS 07147333).

at u-i&-nnglc cnniern rcaolution between revo-
lutions 1'23 nnd ICiO, but n \-cry pronounced
tl:lrkclling occurred sometime during the 30-dal
iiitcrvnl betnrcn  rcvollltionc 1GO 2nd 239
(Figlirr 28).

channel Seen in thr figuw. The view I
was obtsined on rcwlu~ion 1ll.j: r!l
right, 17 days later on revolution
change that 11:~s occ:uwtl in this reck
el.ident in Fiyre Zi,, which shon-a
scaled, similsrl!- projeered, and alir
of the region ~;lrrcliiiiciin~ llir three
Figure 23. The 11~0 d:lrl< rol:nd 5;~
1 km) can be seen ju;t lXl0W the ce!




ure, centered nt 13"S, 2S3'I\w,
J 071473S3).

cdmer:~ rc-ollltion between revo-
lltl INO, b11' 3 T.FT!' p'"tlO"tlced
urred ~:ornetimc during the XLdn
\-em  rcvohltiow  160 and 235

                SAGAX ET .4L.: ;\I~RI~ER 9 ~Irssxos                413
channel seen in the figure. The viex on the left  xvindon in the left (revolution 325) and middle
was obtained on revolution 133 ; thnt on the  (re\`olution IGO) wcriow of Fiylrc 3G. SimilnrlJ
right, 17 days later on revolution 1GO. The  the charncteri.4ic lwti,l in the ch:mncl occurs at
change that ha.5 occurred in this region is mnde  the bottom left corner of both sections. The
evident in Figure 26, which shows rectified,  right seciion of Figure 21; ,~Irons a picture-
scaled, similarly projected, and aligned views  element by Ilicturc-rlemcnt dlffcrence of the
of the region surrounding the three arrow in  two sections on the left. Soticc that the two
Figure 25. The two dark round spots (about  round spots cnnnot be xrn in the difference,
1 km) can be seen just below the center of the  a.3 the)- have not cli2nged Eimi!:Lrly the channel

Fiyv. 11. Dnrlicning of SJ,i-tis


Fig. 16. Darkening of Syrtis hlxjor at wide-angle ramem rrsoluiion. The arra :-horn is
RbOll' 250 !;m ""?C'S an<] :"
          a L15 ccntcrcd at 14.6"X and SS?.S"`\T-. It corresponds to the upper half
of Figure 13. Left to right : revolution 155, wvolution 430. re\.olutions 430 minus 155. Bccsuv
the photometric geomctm diffcr- 3 nppreciahly between rc\.olutions 155 and 430. topographic
detail has not hcen cancelled successfully in the picture diffrrence (Stanford AIL Picture
Product STXOl91, 1021011.

Fig. 17. Darkening of FTrtis Major at narrow-angle cnmcra rt<olution. Thr area aho\vn
is nhout 50 km across and I wntered at 13.2"s and 2S2.9"\\s. Lrft to right: re\.olution 233.
rc\.olution ,430. rr\-olutinnz 430 minus 233. Thr photometric. peomctry (IifIcrs conG~i~-i~aI~I~
hctwwn the two \icws. and topogr:iphic detail remains in ihr l~ir~turc tliffcrcncc (c.g.. 111~
cr:ilcr at lower right) (Stanford .\II. Picture Product STS 0191. 102111).

Fig. 18. Another example of tl
lution. The area shown is about
row (leit to right) : revolution 155,
to right): revolutions 233 and 4:
factory alignment. could not be c
geometry between the two pirtr


I resolution. The area shown is
corresponds to thr loner left of
lutions 233 minus 155 (Stanford

1 rr;olution. Thr area shown is
It corrcspond~ to the upper half
:olutions 430 minw 155. Because
l.!!iox 1.55 and 430. !opogrtlphic
ifirrcncf (3:nniorci AIL Picture

SATAN ET AL.: MARIXER 0 XIIsaIos                 4181

Fig. 18. Another example of the darkening of Syrtis Major at narrow-angle camera reso-

lution. The area shown is about 50 km across and is centered at 10.8"S nnd 283.6"\\~. `l`op
row (left to right) : revolution 155, revolution 233, revolutions 233 minus 155. Bot,tom row (left
to right): revolutions 233 and 430. These two pictures were not differenrrd because satis-
factory alignment could not be obtained olvin g to a significant change in the photometric
geometry between the two pictures (Stanford AIL Picture  Product STS 0191. lo"113).


Fig. 20. Development of dark tnils at narrow-angle caner3 resolution in the region of
Fipllre 10. Top row (Jcfl to right) : revolution 155. re\-olntion 233, re\~olutions 233 minus 15;.
Rliddlc roiv: wvoluiion 23i, revolution 130. rcl-olutions 430 minus 237. Bottom row: revolution
Ij5, rc\.olurion 4.30, rc\-olulions 430 minu 155, The ghotomelric geometl? is similar for
rcvolurions 155 find 233. brat. differ.: significnntly for revolution 330. The area is nbollt 50 I;m
aeros,+ nnd is ccntcrcd at li.O"S. %I.D"]V (Stanford -411, Pictllre Products STY 0191, 10211-1,
102115. 102116. 102117).


ern resolution in the region of
233. rei-olutions 233 minus 155.
nud 237. Bottom row: revolution
metric gEornetr-~. is zimilsr ior
n X0. The nrrn i:' about 50 km
urc Products 6TS 0191. 10'2111.

~AC..IN ET AL.: lI,\RISER 0 1IISSIOS                4183


Fig. 24. Snrrow-angle wmcrn \.iew of the region outlined in Figure 22. Revolution 160.
       Centered at 22"N, GO\V; n-idth = 75 km (IPL 1329, lS5SO2).


SAC.AS ET AL.: MARISER 9 1IrssIos                -I%

`I, in Figure 22. Revolution 160.
1329. lS5SOS).

bottom in Figure 25, n-hirh woulcl
111 n-it11 th:lt infcrrcd from the
:plotclies within the two craters. In
c cl:!rB scnllopetl ~plotchc- could be
ns imtlcrl>kg, !Yind-resistnnt clrlrk
po-14 by 5courin.g ofi bright olw-
i:ll. Ot!lcr intf2rpre:;~rion.s arc dis-
: nmt .scction. The contrnst ljet\vet:l
nil kirk spl0tche.s in this region is

Fig. 25, Ri&t: revolution 160. Exne area. as in Figure 21. but shown in orthographic
projection. Lpft : Snme region. seen on revolution 12.5. Theze tn-o views do not ox-erlap
csnctly and xc not aligned with respect to each other. In enrh view. rhc Ilpyr tn-11 ~rro\vs
poinf, to n pair oi &xi; spots. ::nti the borrom arrow points to :: chnmcteristiC bend i!~ ;llr
smsll channel (IPL Roll 1329, 121209).


Corporntion's 14foot cn~~ironmcnt:il s
Akmhienr condition; were 5X-%.i mb
i and room rempernture. TKO q~cimens
i ing Nnrtinn .surf:lce mntcrixl wre usccl
i fl our with p3rt irk diameteri Inrgcl\-
\ betneen 1 nnd 1010 pm, nntl :: lvhite :I,
with piricIe &x~ieters I;irgrly ranpi
; 100 to 700 pm. Pilc5 of t1lc.c 17oxder.s
: cm thick vxw plnccd on smooth n
plates at the orifice of :k rvind tan
! ve!ocities mexured wre ;it nn flltituc
the surince bonn~.lnr~- !:t\.cr :\nti rnn~ed
m/set. Thr resulting mori!holopy of n.j
dust spprent!!- depended much more (
cle Fize 2nd layer thicknes th:m up
velocity.

In Figure .?G xrr shone heforc n
photognphs of :i layer of sugar snnd ES
these winds for nhouf 100 min. Here A

Fip. 27.  \Yitle-nnplr V:~IUCTU view of Promethei Sinus, centered at Tl"S, 269"\Y! ant1 shout
750 I<111 :rr~rw~. Tlic> ?oli<l outline aho\vs the ;~VR of Figure 28 (SITES 1211-g. DiiS OSOOSO3S).


SAGaN ET AL.: hfAHISEH 9 lhSSIOh-                4157

eretl at il"S, 26O"W, and about
(AlTYi: Qll-9, DAS OSOOSOSS).

Corporation's I+foot environmental simulator.
Ambient conditions were 5.35-16.7 mb pressure
and room temperature. Two specimens simulnt-
ing 1Iartinn surfnce material were used: a silica
flour with particle diameters largely ranging
between 1 and 100 pm, and a white sugar sand
with particle diameters largely ranging from
100 to 700 pm. Piles of the.se powders about 1
cm thick were placed on smooth aluminum
plates at the orifice of a wind tunnel. The
velocities measured were at an altitude within
the surface bounclar~- layer and ranged up to 30
m/se?. The resulting morphology of windblown
dust apparently depended much more on pnrti-
cle size and layer thickness than upon wind
velocity.

In Figure 36 are shown before and after
photographs of a layer of sugar sand exposed to
these winds for about 100 min. Here a marked

rmhayment is produced by the removal of
bright material, revealing underlying dark ma-
terinl; the wind direction is into the figure, and
the extent of the remaining bright material has
decreased because of remo\.nl. Figure 37 shows
n nearly identical experiment with a layer of
silica flour exposed to these winds for about
100 min, but with the base plate inclined at
an angle of 30'. Long strenmrrs are produced
opposite the direction of wind flow, possibly
because of the backward gravitational displace-
ment of particles. The scalloped material in
Promethei Sinus resembles Figure 36 much
more than Figure 37.

Figure 3S shows the results of an esperiment
performed on sugar sand for less than 10 min,
but at velocities at the surface significantly
above the threshold velocities for grain motion.
The resulting pattern, like that in Figure 3G


1


                 s.\~~.~~ ET AI,.: x~l~rst~l~ 9 h+ros                 41s9
less, it is unfortunatr that, with informntion  L:lcrl.- region cslk~in.~ it.< 5wccptihility to secular
avnilnhlc both on the motion of thr scnllolv  cl1:qcs [rl~itovinrli. 1930; Po?lack and Sagan,
and the direction of the prevailing wind.;, WE  19X], c.~perinlly ~1x1~ it i.5 realized that the
are still nt this timr unnhle to decide whcthcr  dark 5trwki arc rc.yon.~ihle for the major
it is bright or dark mobile mntcrkl thflt i.:  alhrdo mnrking in the 3re:l (see Figure 5).
primnril>* rcaponsil)lc for the ph~nornena oh-   Gcncr:~lIy apfxiking. nlbrdo markings nre not
served in Promethci Sinus.            closely corrclntcd with topogrsphy: nlbedo

CL.ASSIC.U, Y.ARI.ABI,F: FE.ATGRER FROM THE    mnrking.5 arc quite srqwrficinl. There are, how-
                                  ever:
      ~IARISER 9 I'ERBPECTIIT          n fen intcrwtinr[ trrnd.s: large dcpres-
                       Pion. euch as the Coprate; rift vnlley 2nd the
Certain seculnr chnngcs cm be correlated to  cncloaed dcprrs~ion  Jwcntne Fons tend to
Martian topogrnpliy, while no convinriiig topo-  nlqxxr as dnrk nll~ctlo features from earth. In
graphic connection can be forind for others.   the Coprates rift vallq-, one can invoke scour-
In the first category is thr dnrkcning of  inp of fines l)!. chnnncled winds 3s in the Lunate
Phnsis in lS'ii-lSi9 [Antoniadi, 1X30] near  Pnlus cnn\-on. hut whnt is the erplanation for
Solis Lncus. The nrcn affected is n wedgelike .Juventne Fowl
extension of rllggtxl terrain into the otherwise   Ako, in general, strong seculnrly variable
smooth region of Solis Lnclrs (cf. Figure 3).    fenturcs tend to lie in smooth regions. Esnmples
The smoothness and kolation of the Solis  are the Polk Locus region 2nd Syrtis hlnjor


On the other hsnd. no

, -


.
. . .

Fis. 32. Ch:lnecs in r&on D. Top rox (Icft to right): revolution 126. ret-olution 181,


Fig. 33. Changes in region E. Top roxv (left to right): revolution 126, revolution lS1,
revolutions lS1 minus 126. Middle row: revolution 179: revolution lS1, revolutions 181 minus
179. Bottom row: revolution lS1, re\-olution 220. revolutions 220 minus 161. The window is
about 45 km across xnd is centered :it 69S"S, 252.5'W (Stanford AIL Picture Products STT
01i3,0G1112,061113, 061114).

Fig. 34. Chnngcs in region F arc shown in the bottom row. Left to right: revolution 181,
wyolrlrion 220. rc>\-olutions 220 minus Sl. This window is about 40 km acrops and is centered nt
6Q.G"S, 231.S"\\T (.`;t:iuford AIL Picture Pro11uc.t STS 0173, 061104). Tllc lop row ~1~0~s chungcs
111 rcgiun-; 13. I). E over tlie s:inic :imc into r\.:11. I.cEt to righr : revolution 1Sl. rc~voluliun 220,
rcvoliitious 220 Il>inrl.s lS1. Tllo loll \vintlow is: :il,out GO km xcrw8, :~n~l is wntercd :I( 696's.
253.1"\V (std0d AIL l'icturc Product dTS OlGG. OU905).

Fig. 35.  Ch:anges: at wicle-angle r(
re\~oluiion 1X. rt,\.olution 151. revolu
TilJll L'L'U. I/ \~illl~ii!ll. 2'20 I,,,,,, 1: Ii!).
i2.1"s. 267 2"\V: ire outline is show
STS Olil. 061306. OG130i).


:  rpvnlution  126. revolution 181,
,iut?nn lhl, rr\-oiutions 181 minus
1s 220 minus 1Sl. The window is
oford AIL Picture Products STX

Fig. 35. Changes at \vide-nngle resolution in adjoinin g regions. Top row (left to right):
revolution 179. rc~volution ISI. revolutions IS1 minus 179. Bottom row: revolution 179. revolu-
tioil 220. rt I 0lutir,n.5 220 Initlll.G 1X. Tllr, wintluw i.5 about ?20 !irn i1(`ro'.> ant1 i< ~`11: i,r;::I at
72.4"S, 267.2"!1-; its outline is shown dashed in Figure 2i (Stanford .AIL Picture Products
STX 0174. 061306. 061307).


4194             S.4G.4X ET AL.: hIr\RISER 9 ~&ION
strong pre\-ailing character for about 1 day, not  mnge from 3 x IO-" g cm' sec.' to 3 x 10-j g
an unlikely requirement.                cm-' SCC`~. Thus a layer of dust 1 cm thick
On earth snltating particles can induce creep  could easily be removed in 1 1Iarti;in day under
in surface grains many times their olvn diam-  conditions of moderately high xindr, a result
eter. For Mars the diameter ratio should be  quite consistent n-ith that just derived on the
even larger. T!:us small bright particles can  time scale for the generation of streaks, The.se
induce creep in large dark particles. On earth,  numbers imply typical dust, removal rates for
typical sandstorm creep velocities are about 1  an area the size of the leaf in Promerhei Sinus of
cm/set [Ba.grrold, lg.%]; on Mars they should  about 100 tonsjec, most of v&ich, being in
be correspondingly larger. Thus. during 1 da>  saltnting particles, ITill be immediately rede-
on Mars. creep of about 1 km is possible. It is  po&ed.
curious, therefore, that the same velocities for   Deflntion of dust out of gravitational poten-
the same periods of time can account by salta-  tial II-ells such as craters probably requires
tion for The production of bright streaks and by  velocities > V,., ; in this case also transport
creep for the motions of dark material in places  times are reduced. The high values of I,`,,
like Promet!lei Sinus.             deduced here and elsewhere have important
Hertz'er [ 1966b] estimated eolian transport  consequences for eolian erosion rates on Mars?
rates under typical Martian conditions IT-hen the  as is discussed in a separate publication.
threshold stress is eweeded. Typical values   The contrasts that we find between adjacent

Fig. 37. Results of a wind tunnel experiment similar to that in Figure 36, but \vith the
bnse plate inclined at 20" to the wind. Wind direction is from right to left [from Herlzler,
1966n, bl.


SSION

3 X lo-" g cm-' see-' to 3 X IO-" g
Thus a layer of dust 1 cm thick
. be removed in 1 Martian day under
of moderately high winds, a result
stent with that just derived on the
for the generation of streaks. These
nply typical dust removal rates for
`size of the leaf in Promethei Sinus of
tons/see, most of which, being in
particles, vi11 be immediately rede-

1 of dust out of gravitational poten-
such as craters probably requires
>v*,;  in this case also transport
reduced. The high values of V,,
lere and elsewhere have important
:es for eolian erosion rates on Mars,
ssed in a separate publication.
trasts that we find between adjacent

to that in Figure 36; hut with the
from right to left Lfrom Hertzler,


fl%               SAGAS ET .iL.: 11.4

to .1. T. Young, B. .A. smith. C. 1~eol.y. :mcl J.
McCauley for useful discussions: and to ihe scien-
tists and engineers of the Jet, Propukon Lnb-
oratorv who made this mission possible. .X11 pic-
ture differencing in this paper was performed b\
Lynn Quam and the staff of Staniord's .Jrtifici:tl
Intelligence Laboratory.

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(Received February i. 1973;
revked March 9, 1X3.)