EMBARGOED—NOT FOR PUBLIC RELEASE BEFORE:
Monday, March 23, 2015
 3:00 PM US Eastern Daylight Time
 7:00 PM Greenwich Mean Time
Tuesday, March 24, 2015
 4:00 AM Japanese Standard Time
 6:00 AM Australian Eastern Time
The full PNAS embargo policy is available here:
http://www.pnas.org/site/misc/journalist.shtml
Indigenous fixed nitrogen in martian deposits
A study reports the presence of indigenous fixed nitrogen in martian rocks and sediments.
Jennifer Stern and colleagues report that the Mars Science Laboratory Curiosity Rover has
detected the presence of oxidized nitrogen-bearing compounds in deposits within Mars’s
Gale Crater. Nitrogen species were detected in samples from three sites, with total nitrogen
concentrations ranging from 20-250 nmol per sample. The samples contained more nitrogen
than could be accounted for from known terrestrial instrument sources, and the bulk of the
nitrogen detected across the three samples was in the form of nitric oxide (NO). The authors
suggest that the NO may have been released from decomposition of nitrates as the sample
was heated during analysis. The presence of nitrates in different types of deposits,
representing both the martian dust and soil reservoir, and a potential ancient lakebed,
suggests that the residues resulted from nitrogen fixation generated by thermal shock from
lightning or impact on ancient Mars. Terrestrial life requires a fixed form of nitrogen for
synthesis of crucial biomolecules, and the discovery of indigenous fixed nitrogen in martian
rocks and sediments has implications for the past habitability potential of Mars, according to
the authors. Fixed nitrogen could have facilitated the development of a primitive nitrogen
cycle on the surface of ancient Mars, potentially providing a biochemically accessible source
of nitrogen, the authors suggest.
Article #14-20932: “Evidence for indigenous nitrogen in sedimentary and aeolian deposits
from the Curiosity rover investigations at Gale crater, Mars,” by Jennifer C. Stern et al.
MEDIA CONTACT: Jennifer C. Stern, NASA Goddard Space Flight Center, Greenbelt, MD;
tel: 301-614-6062, 850-294-9189; e-mail: <jennifer.c.stern@nasa.gov>
An image accompanying this article is available.
http://www.eurekalert.org/jrnls/pnas/14-20932.htm
AFTER THIS ARTICLE PUBLISHES, it will be available at
http://www.pnas.org/cgi/doi/10.1073/pnas.1420932112
Carbon monoxide as potential energy source on Mars
Atmospheric carbon monoxide could potentially sustain microbial communities on Mars, a
study suggests. Although the search for past or current life on Mars has focused primarily on
finding liquid water, researchers have not identified an energy source that could fuel
metabolism by microbes living on or near the planet’s surface. Gary King suggests that
carbon monoxide (CO), an abundant gas in the martian atmosphere, could potentially serve
as a metabolic source at conditions likely found in the past and present. Drawing parallels
with locations on Earth such as the Bonneville Salt Flats in Utah, the author suggests that
CO oxidation could occur on local scales in martian brines, features thought to form
seasonally and that explain narrow, dark-toned streaks observed from the Mars
Reconnaissance Orbiter. In addition, the author suggests that two terrestrial microbes,
halophilic CO-oxidizing Proteobacteria and a recently identified extremely halophilic COoxidizing Euryarchaeota, represent models for how the martian atmosphere could support
microbial communities. The findings suggest a framework whereby microbial CO oxidation
can potentially occur at local scales on contemporary Mars and at large scales earlier in the
planet’s history.
Article #14-24989: “Carbon monoxide as a metabolic energy source for extremely halophilic
microbes: Implications for microbial activity in Mars regolith,” by Gary M. King.
MEDIA CONTACT: Gary M. King, Department of Biological Sciences, Louisiana State
University, Baton Rouge, LA; tel: 225-578-1901; e-mail: <gkingme@gmail.com>; Alison
Satake, Louisiana State University, Baton Rouge, LA; tel: 225-578-3870; e-mail:
<asatake@lsu.edu>
http://www.eurekalert.org/jrnls/pnas/14-24989.htm
AFTER THIS ARTICLE PUBLISHES, it will be available at
http://www.pnas.org/cgi/doi/10.1073/pnas.1424989112