Two National Space Club summer 2003 interns in the Geodynamics Branch submitted papers based on their research on martian gullies to the Intel Science Talent Search competition. Joshua Stern (Montgomery Blair High School) and Erin Frey (South River High School) both made the initial cut to semi-finalists, part of a group of 400 selected from over 1560 entries nationwide. The selection results in a $1000 prize to both the student and the student's school. Both students will present their work at the Lunar and Planetary Science Conference in Houston, March 15-17, 2004.
Water Indicators in Sirenum Terra and Around the
Argyre Impact Basin, Mars was the subject of Josh
Stern's paper. Working with Herb Frey, Stern looked
at the relative percentages of craters that displayed
rampart form, thought to indicate the presence of
volatile material at the time the (probably ancient)
craters formed, and had gullies in their walls. Gullies
are cited as evidence of geologically recent water
seepage. He compared these percentages in two areas which differ in their present-day near-surface hydrogen abundance as measured from the Mars Odyssey Gamma Ray Spectrometer. The hydrogen is thought to be derived from water within the upper meter of the surface of Mars. In both areas, non-rampart craters have gullies in about 25% of the cases. Among rampart craters, however, the "wetter" of the two regions (Sirenum) has a much higher percentage of gullies than the drier region (Argyre).
The gullied craters in Sirenum
all have a depth-diameter ratio
greater than 0.5, whereas the
non-gullied craters in both areas
have a much wider range of d/D
(see figure below). Stern also
found that gullied craters tend to
cluster near tectonic structures,
which may have an influence on
how the water that later gave rise
to the gullies became localized.
Erin Frey, working with her mentor Susan Sakimoto,
extended her study "Water on Mars: Where was it,
where is it today" which had won awards at the
International Science and Engineering Fair in May
2003. In her earlier work, Frey had found that gullies
form at greater depths in areas where near surface
hydrogen (as determined from the Mars Odyssey
Gamma Ray Spectrometer) was scarce and that
where there was abundant water in the upper meter of the soil, gullies tended to form close to the surface. This summer she found observation evidence in THEMIS data to support one model for gully formation. Comparing night and daytime IR imagery she found what may be an impervious layer which could trap subsurface water and give rise to the seepage which many think is responsible for formation of the gullies. See the figure. Although this
could explain the formation of gullies
when they form at significant depth, it
may not apply in those "wetter" areas
where gullies form within 50 m of the
surface. Her paper discussed other
possible models of gully formation.
Recently Frey has found a way to
estimate the depth of some gullies,
and is now trying to determine the
volume of water and the possible
volume of ice that was responsible
for the formation of the gullies.
Back to Geodynamics Science Highlights
Responsible NASA official: Dr. Herbert Frey