Astronomy

ASTRONEWS

12 ASTRONOMY • MAY 2018

Stellar disks

can form rings

without planets

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.

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’

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

MASSIVE ICE DEPOSITS FOUND ON MARS

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

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

NASA/HUBBLE/KONISHI ET AL. 2016

2 arcseconds

22 billion miles

(35 billion kilometers)