An image combining orbital imagery with 3-D modeling shows flows that appear in spring and summer on a slope inside Mars’ Newton crater. Sequences of observations recording the seasonal changes at this site and a few others with similar flows might be evidence of salty liquid water active on Mars today. Image credit: NASA/JPL-Caltech/Univ. of Arizona
Observations from NASA’s Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars.
Mars Exploration Program keeps bringing us closer to determining
whether the Red Planet could harbor life in some form,” NASA
Administrator Charles Bolden said, “and it reaffirms Mars as an
important future destination for human exploration.”
finger-like features appear and extend down some Martian slopes during
late spring through summer, fade in winter, and return during the next
spring. Repeated observations have tracked the seasonal changes in these
recurring features on several steep slopes in the middle latitudes of
Mars’ southern hemisphere.
best explanation for these observations so far is the flow of briny
water,” said Alfred McEwen of the University of Arizona, Tucson. McEwen
is the principal investigator for the orbiter’s High Resolution Imaging
Science Experiment (HiRISE) and lead author of a report about the
recurring flows published in Thursday’s edition of the journal Science.
aspects of the observations still puzzle researchers, but flows of
liquid brine fit the features’ characteristics better than alternate
hypotheses. Saltiness lowers the freezing temperature of water. Sites
with active flows get warm enough, even in the shallow subsurface, to
sustain liquid water that is about as salty as Earth’s oceans, while
pure water would freeze at the observed temperatures.
dark lineations are different from other types of features on Martian
slopes,” said Mars Reconnaissance Orbiter Project Scientist Richard
Zurek of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “Repeated
observations show they extend ever farther downhill with time during the
features imaged are only about 0.5 to 5 yards or meters wide, with
lengths up to hundreds of yards. The width is much narrower than
previously reported gullies on Martian slopes. However, some of those
locations display more than 1,000 individual flows. Also, while gullies
are abundant on cold, pole-facing slopes, these dark flows are on
warmer, equator-facing slopes.
This map of Mars shows relative locations of three types of findings related to salt or frozen water, plus a new type of finding that may be related to both salt and water. Coloring of the map is coded to concentrations of shallow subsurface water ice found by the Gamma Ray Spectrometer – Neutron Spectrometer on NASA’s Mars Odyssey orbiter. Blue, at high latitudes north and south, indicates higher concentrations of water ice (deduced from detection of hydrogen); orange designates lowest concentrations. Some hydrogen, possibly in the form of bound water, is close to the surface even at middle latitudes.
images show flows lengthen and darken on rocky equator-facing slopes
from late spring to early fall. The seasonality, latitude distribution
and brightness changes suggest a volatile material is involved, but
there is no direct detection of one. The settings are too warm for
carbon-dioxide frost and, at some sites, too cold for pure water. This
suggests the action of brines, which have lower freezing points. Salt
deposits over much of Mars indicate brines were abundant in Mars’ past.
These recent observations suggest brines still may form near the surface
today in limited times and places.
researchers checked flow-marked slopes with the orbiter’s Compact
Reconnaissance Imaging Spectrometer for Mars (CRISM), no sign of water
appeared. The features may quickly dry on the surface or could be
shallow subsurface flows.
“The flows are not dark because of being wet,” McEwen said. “They are dark for some other reason.”
flow initiated by briny water could rearrange grains or change surface
roughness in a way that darkens the appearance. How the features
brighten again when temperatures drop is harder to explain.
“It’s a mystery now, but I think it’s a solvable mystery with further observations and laboratory experiments,” McEwen said.
This image contrasts gullies and recurring warm-season slope flows appearing in the same crater, in the middle southern latitudes of Mars. It was taken Nov. 27, 2007, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter. Image Credit: NASA/JPL-Caltech/University of Arizona
results are the closest scientists have come to finding evidence of
liquid water on the planet’s surface today. Frozen water, however has
been detected near the surface in many middle to high-latitude regions.
Fresh-looking gullies suggest slope movements in geologically recent
times, perhaps aided by water. Purported droplets of brine also appeared
on struts of the Phoenix Mars Lander. If further study of the recurring
dark flows supports evidence of brines, these could be the first known
Martian locations with liquid water.
Mars Reconnaissance Orbiter is managed by JPL for NASA’s Science
Mission Directorate in Washington. The University of Arizona’s Lunar and
Planetary Laboratory operates HiRISE. The camera was built by Ball
Aerospace & Technologies Corp. in Boulder, Colo. Johns Hopkins
University Applied Physics Laboratory in Laurel, Md., provided and
operates CRISM. JPL is a division of the California Institute of
Technology in Pasadena.