Sky and Telescope - September 2018 - 8

NEWS NOTES
SOLAR SYSTEM

Methane and Other
Organics on Mars
IN THE JUNE 8TH SCIENCE, team

Dunes on Pluto
p New Horizons imaged the mountain range on the edge of the Sputnik Planitia ice plain.
Dune formations are clearly visible in the bottom half of the picture.

USING DATA SENT BACK from NASA's New Horizons spacecraft after its

2015 flyby of Pluto, planetary scientists think they've found evidence of
wind-built ripples of methane ice on the world's surface. The results appear in
the June 1st Science.
Matt Telfer (University of Plymouth, UK) and colleagues discovered a wide
swath of parallel ripples on the western edge of Sputnik Planitia, the vast
plain of molecular nitrogen-rich ice at Pluto's equator. This edge abuts the
Al-Idrisi Montes, a mountain range that reaches up to 5 km (3 mi). The series
of ripples runs largely parallel to the mountain-plain boundary. From there, it
extends some 75 km before fading out. This pattern is just what you'd expect
if the ridges are dunes formed by wind coming off the mountains and sweeping across Sputnik Planitia.
But winds are gentle on Pluto, reaching 10 m/s (20 mph) at the gustiest.
Such breezes could carry grains through the air once aloft, but it's hard for
them to pick grains up off the ground.
The team thinks Sputnik Planitia is to blame. Its molecular nitrogen ice
sublimates in daily, intense bouts that could loft nearby grains. Methane
mixed in with the nitrogen may exacerbate the gasification: Although the
methane doesn't sublimate, it warms in sunlight and would transfer that
heat to the surrounding nitrogen - which would then in turn launch the
methane grains. Once in the air, the grains would be caught by the wind
and do a hopping dance across the surface, called saltation, kicking up more
grains and building undulating dunes.
How long the dunes remain once they're in place, or if they're undergoing
erosion, is unclear. But given the time it takes Sputnik Planitia's convecting
cells of ice to turn over, the features can be no older than 500,000 years.
■ CAMILLE M. CARLISLE

* Learn more about the dunes and the origin of Sputnik Planitia's nitrogen-rich
ice at https://is.gd/plutodunes. Also, see Cosmic Relief on page 12.
8

S E P TE M B E R 2 018 * SK Y & TELESCOPE

COSMOLOGY

Early Star Formation Presents New Cosmic Mystery
NEW OBSERVATIONS SUGGEST that
stars began forming just 250 million
years after the Big Bang - a recordbreaker that will likely open a new line
of cosmological inquiry.
Reporting in the May 17th Nature,
Takuya Hashimoto (Osaka Sangyo
University, Japan) and colleagues used
the Atacama Large Millimeter/submillimeter Array to detect doubly ionized
oxygen in a galaxy that existed just
550 million years after the Big Bang (at
a redshift of 9.1).
Because only hydrogen, helium, and
a little lithium emerged from the Big
Bang, it wasn't until the first generation
of stars exploded and breathed carbon,

N ASA / JOHNS HOPK INS UNIV. A PL / SOU THWEST RESE A RCH INSTIT U TE

SOLAR SYSTEM

members from NASA's Curiosity rover
mission reported the presence of several
organic compounds in ancient mudstones on Mars, as well as the conclusive detection of a seasonal methane
cycle. (Organics are molecules that
contain carbon and hydrogen.) Neither
of these results means we've found
Martian life, but they do make the
question of whether it ever existed a
more reasonable one to ask.
The studies used Curiosity's Sample
Analysis at Mars, a suite of instruments
in the rover's body. For the mudstone
study, Jennifer Eigenbrode (NASA Goddard) and colleagues heated pulverized
rock to nearly 900°C (1,600°F), catching the gases released as the rock molecules underwent chemical reactions
or broke down. The rover then analyzed
these gases to determine their molecular masses and components.
Based on these data, the researchers
determined that the mudstones contained organic compounds containing
carbon, hydrogen, and sulfur. However,
the compounds don't show the diversity


https://www.is.gd/plutodunes

Table of Contents for the Digital Edition of Sky and Telescope - September 2018

Contents
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