ASTRONEWS
ORIGIN STORY. The first meteorites found to contain both liquid water and complex organic compounds may have
originated from a dwarf planet in the asteroid belt, such as Ceres.
MASSIVE ICE DEPOSITS FOUND ON MARS
E
ven though Mars’ atmosphere is just
1 percent as dense as Earth’s, the
Red Planet’s surface still experiences
plenty of weathering and erosion. In
2008, researchers captured a full-
scale avalanche on Mars as material
plunged down a 2,300-foot (700 meters)
slope into a valley. These types of geological
events often expose structures beneath the
martian surface, revealing layers of rock,
dry (carbon dioxide) ice, and even water ice.
In a study published January 11 in
Science, researchers using the Mars
Reconnaissance Orbiter investigated eight
steep and eroded slopes, known as scarps, at
various sites across Mars. At each spot, they
found thick shelves of relatively pure water
ice as little as 3 feet (1 m) below the surface.
Some of these ice deposits were massive —
more than 330 feet (100 m) thick.
Scientists have spotted frozen water on
Mars’ surface many times before, but this
is the first time observations have revealed
so much about its layering, thickness,
purity, and prevalence.
According to the paper, “the ice exposed
by the scarps likely originated as snow that
transformed into massive ice sheets, now
preserved beneath less than one to two
[meters] of dry and ice-cemented dust or
regolith near ±55° latitude.” In 2008, the
Phoenix Mars lander discovered similar ice
deposits along martian scarps, but they
were in regions much closer to the planet’s
north pole.
Since the ice deposits highlighted in the
study were found intact along the scarps’
DEEP BLUE. In this color-enhanced image of an eroding cliff on Mars taken from above, water ice appears in
blue. The top third of the image shows the martian surface leading up to the cliff’s edge, while the bottom third
is the valley below. NASA/JPL/UNIVERSITY OF ARIZONA/USGS
weathered slopes, the researchers believe
the ice is “cohesive and strong.” The team
also found that the ice appears banded,
showing layered variations in its blue color.
This suggests that the massive ice deposits
are composed of many distinct layers that
have been squished together over time, pre-
serving a record of Mars’ climate history.
However, because there are few craters near
these sites, the authors suggest the ice was
formed relatively recently, in the past mil-
lion years or so.
Although the deposits formed quickly
(geologically speaking), they also recede a
tiny bit each summer, the researchers say.
In one scarp, the team found that over the
course of only three martian years, multiple
meter-wide boulders had dislodged them-
selves from the ice deposits, tumbling into
the valley below. Based on this, the
researchers estimated the ice is retreating
horizontally at a rate of a few millimeters
each year, likely because of exposed ice sub-
limating (transforming directly from a solid
to a gas) as it contacts the thin martian air.
The discovery of these large reservoirs of
pure water ice adds yet another piece of
evidence supporting the increasingly held
theory that water ice not only remains on
Mars, but also is surprisingly common.
Although the ice sheets could obviously
serve as sources of water for future manned
missions to Mars, scientists still need to
characterize them and estimate their size
first. But with the Mars 2020 rover just a
few years away, the discovery of eight more
tantalizing sites ripe for investigation is still
an exciting find. — Jake Parks
Stellar disks
can form rings
without planets
12
2 arcseconds
22 billion miles
(35 billion kilometers)
A ST R O N O M Y • MAY 2018
NO PLANET REQUIRED. Astronomers spot
disks of gas and dust around young stars by
placing a “mask” (the dark region in the image’s
center) over the star to block its light. This disk
around the star HD 141569A shows complex
structure; rings and other patterns are often used
as proxies for forming exoplanets, which are
thought to carve out lanes as they grow. But new
simulations using NASA’s Discover supercomputing
cluster show that planets are not needed for such
rings to arise. Instead, disk material can develop
structure as a result of exposure to ultraviolet
light from the star. The discovery was announced
January 11 at the American Astronomical Society
meeting in Washington, D.C. — Alison Klesman