Australian Sky & Telescope - May 2018

10 AUSTRALIANSKY & TELESCOPEMay| Juune 2018

me planets are bigger

n they seem

Nearby stars can make some exoplanet

didates look smaller than they really

says Carl Ziegler (University of North

olina, Chapel Hill. The conclusion

e from data obtained with the Robo-

system, which is following up on some

0 candidate exoplanets from NASA’s

ler mission. The automated laser-

ed adaptive optics system took rapid-

ire images of each target star, looking for

lar companions that might mess up the

. Of 3,857 stars observed with Robo-
almost 600 had stellar companions.
The extra stars’ light contaminated
exoplanet transits, making their dips
appear smaller and thus giving the
ression that the planets themselves
smaller. Generally, having another
in the system makes planets twice
wide as they irst appear. Because of
contamination, 8 of the 26 potentially
rocky, habitable-zone worlds studied
might actually be gaseous. Among them
are the conirmed planets Kepler-438b
and Kepler-437b, which could be 2 to 3
times larger than estimated if they orbit
their system’s secondary star.
■CAMILLE M. CARLISLE

THICK SHEETS OF water ice, some

barely buried beneath the surface and

more than 100 metres thick, have been

spotted on several Martian cliff faces.

The widely scattered outcrops —

seven in the southern hemisphere and

one in the north — lie far from the

planet’s icy polar caps.

Colin Dundas (U.S. Geological

Survey, Flagstaff) led the team

that made the discovery using two

instruments aboard NASA’s Mars

Reconnaissance Orbiter. First, detailed

enhanced-colour images from the

spacecraft’s HIRISE camera revealed

bluish layers in the scarps’ steep faces.

Then near-infrared maps from the

CRISM spectrometer confirmed that the

layers are enriched with water ice. The

layers appear to persist year-round.

Planetary scientists have realised for

more than a decade that vast deposits

of water ice must lie just below the

planet’s dusty surface. Radar scans from

orbit have revealed huge glaciers of ice

There’s water beneath those Martian cliffs

within 20 metres of the surface over

roughly a third of the Martian surface.

But these newfound outcrops, reported

in the January 12 issue of Science, open

an unprecedented window into Martian

climatic and geologic history.

The team surmises that the icy layers

started out as dusty snow or frost laid

down over time. The deposits eventually

compacted and recrystallised. As exposed

ice gradually sublimates, the rocky cliff

face crumbles and erodes, revealing fresh

exposures of previously buried ice.

The water ice begins within a few

metres of the surface and can extend

down to more than 100 metres. Given

the planet’s thin atmosphere and

temperature swings, geophysicists

calculate that water ice on Mars at the

scarps’ locations should be stable at

depths of as little as 10 cm. Being able

to access water so easily would be a

huge boon to future human exploration

of the planet.

■ J. KELLY BEATTY

T A thick sheet of underground water ice (blue in this enhanced-colour image) lies exposed

along a steep slope at latitude 57°S. The ground at the top of the image is about 130 metres

higher than the ground at the bottom.

NASA / JPL / UNIV. OF ARIZONA / USGS

NEWS NOTES

NASA’s new nuclear

power source

NASA has announced the development

of a new nuclear generator, one that

may become a permanent ixture on

lunar outposts or deep space missions

in the coming decades. The Kilopower

ission reactor will generate 10 kilowatts

of electricity for a minimum of 10 years

— more than enough to run several

typical Australian househoulds. The

new technology offers a more eficient,

portable power source that opens new

areas for space exploration, such as high

latitudes on Mars. Launching nuclear

generators into space isn’t without its

issues, of course, but tests show that if a

Kilopower reactor were lost and the core

breached during a launch, the peak dose

from exposure to unissioned uranium

for people on the ground would be less

than a millirem, and would more likely

be in the microrem range, according

to Pat McClure (Los Alamos National

Laboratory). The average Australian

receives about 620 millirems per year

from background radiation.

■ DAVID DICKINSON