Sky and Telescope - April 2015 - 14

News Notes

MARS I Curiosity Finds Organics . . .
On December 16th, team members with
NASA's Mars Science Laboratory reported
the detection of methane and other
organic compounds on Mars.
Organics are molecules made up of
carbon atoms linked to other elements.
They can arise both biologically and abiotically, such as by raining down from space
as micrometeoritic dust. Organics would
break down fast in the hostile Martian
environment, destroyed by solar UV rays
or by the strongly oxidizing soil, so scientists have struggled to detect them.
Curiosity's organics detection comes
from the Cumberland sample, which
the rover drilled on May 19, 2013. The
compound identiﬁed is chlorobenzene
(C6H5Cl), at a level at least four times the
upper levels inferred from previous samples. It's unclear whether the compound is
actually present in the rock as chlorobenzene or as something else, such as benzilic
acid (C14H12O3), that's transformed by the
roving lab's processing.
The methane detection came with a
surge in atmospheric levels in November
2013. Planetary scientists have debated
methane's presence on Mars for decades,

and Curiosity's iﬀ y detection in 2012 -
which placed an upper limit of 1.3 parts
per billion by volume (ppbv) - didn't help.
But in fact methane is there. "We were
completely surprised, we suddenly saw 5½
ppbv methane," says Chris Webster (JPL).
"It was an Oh My Gosh moment."
A week later it had risen to 7 ppbv; a
month later it was still 7 ppbv. A fourth test
3 weeks after that detected 9 ppbv. Then 6
weeks later, it had completely disappeared.
The average over the 2-month period
is 7.2 + 2.1 ppbv, about 10 times the average background level, the team reported
December 16th at the American Geophysical Union and in Science.
The signal's sudden appearance and
disappearance, coupled with the low
background levels and wind patterns, suggest that the methane came from a small,
localized source either within Gale crater or
just outside and to the north of it. It could
either come from a modern source or be
ancient methane leaked from a subsurface
reservoir. The team will monitor methane
levels and work with India's Mars Orbiter
Mission to try to catch another spurt.
■ CAMILLE M. CARLISLE

. . . and Studies Mars's Dry-out
Samples taken from two drill holes on
Mars support the idea that the Red Planet
lost a whole lot of water early in its history.
Mars had wet conditions in the ﬁrst few
hundred million years of its existence. But
the planet had turned cold and dry by 3
billion years ago. Scientists investigate what
happened in part by looking at the ratio of
hydrogen (H) to its heavier form, deuterium (D). The D:H ratio leans more in favor
of deuterium if the parent world loses a lot
of hydrogen (and, therefore, water) to space.
The D:H ratio in Mars's atmosphere
today is roughly 6 times the average in
Earth's oceans. But primitive mantle material in a Martian meteorite called Yamato
980459 has a ratio similar to Earth's.
Scientists with NASA's Curiosity rover
investigated Mars's water loss by drilling into clay minerals that solidiﬁed in
standing water roughly 3.8 billion years
14

April 2015 sky & telescope

ago. They found that the water released
from the heated samples had a D:H ratio
three times that of Earth's. The value is
higher than expected for early Mars, Paul
Mahaﬀ y (NASA Goddard) and colleagues
report December 16th in Science.
If the samples reﬂect the planet-wide
D:H levels at that time, then Mars has lost
to space 100% to 150% as much water as it
currently has in its surface and subsurface.
But if the planet has multiple water
reservoirs that have been isolated from
one another for a long time - such as ice
embedded in sediments that hasn't interacted with the atmosphere - then the
samples only reveal how much water that
particular reservoir lost. NASA's MAVEN
orbiter will reveal whether the current
atmospheric loss rates imply the same history of loss for the planet.
■ CAMILLE M. CARLISLE

COSMOLOGY I BOSS
Ruler for the Universe
Astronomers have announced the most
precise standard ruler yet for cosmological
distances. The Baryon Oscillation Spectroscopic Survey (BOSS) covered 25% of
the sky over the past 7 years as part of the
Sloan Digital Sky Survey (SDSS). The goal:
detect the imprint of primordial sound
waves, called baryon acoustic oscillations,
which sloshed around the primordial universe's plasma and left their mark in the
distribution of matter in the universe.
This mark appears in huge statistical
samples as galaxies' slight preference to
lie 500 million light-years apart. Although
BOSS's ﬁnal data analysis isn't expected
until later this year, the 85% of the data
already analyzed conﬁrms the primordial
sound waves' ﬁngerprint to 10 sigma, or
having a 1 in 1023 chance of being a ﬂuke.
BOSS detected ripples by looking at
populations of relatively nearby galaxies, divided into two groups whose light
has traveled for 3.5 billion and 5.7 billion
years, respectively, and by looking at more
distant quasars, whose light has traveled
11 billion years to Earth. These two data
sets sandwich the era when the universe's
expansion began accelerating.
Normally, astronomers need to calculate distances to these objects using their
redshifts. But that requires models of how
fast the universe is expanding. On the
other hand, if astronomers know how big
the primordial ripples should be (found
in cosmic microwave background ﬂuctuations), and they measure how big the ripples appear on the sky, they can measure
the distance directly. These distances are
now known to an accuracy of 1%, BOSS
scientists announced at the winter American Astronomical Society meeting in Seattle. Alternatively, you can forgo the cosmic
microwave background measurements and
just calculate relative ripple sizes at diﬀerent distances to see how quickly the ruler
expands over cosmic time. Both measurements agree with the leading cosmological
model, including a constant dark energy.
■ MONICA YOUNG

Sky and Telescope - April 2015

Table of Contents for the Digital Edition of Sky and Telescope - April 2015