Sky and Telescope - September 2018 - 9

Methane
(parts per billion)

SOLAR SYSTEM

0.7

Apollo Astronauts Warmed the Moon

0.6
0.5

of molecules or the structural patterns
usually created biologically.
The sulfur might have protected the
organics in these samples from degradation by acting as a "sacrificial element,"
Eigenbrode says, serving as a chemical
victim in Mars's oxidizing environment
in place of the carbon.
A separate paper by Christopher
Webster (NASA Jet Propulsion Laboratory) and colleagues details the Martian
methane cycle. Curiosity has detected
methane before, including a startling
spike back in 2013 (S&T: Apr. 2015,
p. 14), but the new result reveals a
clear seasonal trend, with a peak in the
northern hemisphere's late summer.
The researchers think the gas comes
from the subsurface, perhaps via rock
fissures; surface temperature may govern its release.

A NEW FIND HAS SOLVED an old mystery: What
slightly warmed the Moon in the 1970s?
During the Apollo 15 and 17 missions in 1971 and
1972, astronauts placed Heat Flow Experiment (HFE)
monitors a few meters into the lunar surface to
p This image of Apollo 15's
ALSEP setup shows the HFE
measure the temperature of soil undisturbed by the
power box in the foreground.
month-long day/night cycle. Lunar scientists planned
Cords to the detectors snake
to use the data to measure the heat flow from the
off to the lower right. The
Moon's core, characterizing geological activity.
foreground shadow is that of
To their surprise, investigators saw the temperaastronaut David Scott.
ture increase gradually at both the Apollo 15 and
Apollo 17 sites, by 1° to 2°C (2° to 4°F). The warming continued until the sensors fell silent in 1977.
A study published in the May issue of the Journal of Geophysical Research:
Planets reveals the cause of this heating: the astronauts themselves. As the astronauts traveled, they disturbed the smooth surface of the Moon. The rumpled
surface better absorbed heat from the sunlight.
The study wouldn't have been possible without some detective work. NASA
had recorded data from 1971 to 1974, storing it on open-reel magnetic tapes, but
data collected in later years had gone missing. After some digging, researchers
recovered a set of 440 archival tapes at the Washington National Records Center. With additional legwork, they also discovered hundreds of weekly logs with
temperature readings that filled in the gaps in the remaining years, confirming
that warming continued through 1977.
Key evidence also came from the Lunar Reconnaisance Orbiter's images of
the Apollo landing sites, which showed that the places where the astronauts had
traveled appeared darker, showing that they absorb more solar heat than the surrounding regolith. The finding may affect future Moon exploration.

■ CAMILLE M. CARLISLE

■ DAVID DICKINSON

0.4
0.3
0.2

Spring

Summer Autumn
Mars Year: 1

2

Winter

3

ME TH A NE CYCLE: N ASA / JPL- CA LTECH; A LSEP: N ASA; G A L A X Y CLUSTER: INSE T: A LM A (ESO /
N AOJ / NR AO) / H ASHIM OTO E T A L., BACKG ROUND: N ASA / ESA HUBBLE SPACE TELESCOPE / W.
ZHENG (JHU) / M. POST M A N (STSCI) / CL ASH TE A M

p Methane cycle on Mars

p The galaxy cluster MACS J1149.5+2223
(background) magnifies the young galaxy
MACS 1149-JD1 (inset), in which ALMA detected oxygen (green).

oxygen, and other heavy elements into
the cosmos that the universe's inventory
of elements increased. The detection of
oxygen 550 million years after the Big
Bang suggests that a generation of stars
had already formed and died.

The results are in line with a tentative result from the EDGES experiment
(S&T: June 2018, p. 8), which found a
signal from stars forming just 180 million years after the Big Bang. However,
the EDGES result still awaits confirmation from other groups performing
similar experiments.
Hashimoto and colleagues used data
from the Hubble and Spitzer Space Telescopes to gauge the galaxy's star-formation history. The observations indicate
that starbirth kicked off strong, tapered
off, then restarted. That's different
from the slow start and exponential
growth that simulations of high-mass
galaxies in the early universe predict.
"It may mean that we don't really
understand the first generation of
galaxies sufficiently well," says coauthor Erik Zackrisson (Uppsala Univer-

sity, Sweden). "There might be some
ingredient that is missing from the
simulations." That missing ingredient
could come in the form of powerful
supernovae or a ravenous supermassive
black hole, either of which could have
unleashed powerful winds and suppressed further star formation.
Rychard Bouwens (Leiden University,
The Netherlands), who was not involved
in the study, argues that the paper's
conclusions are reliable but uncertain,
only because the team is peering so far
back into the universe's history. "It's
always this way when you're at the cutting edge," he says. "It might be providing us with important clues to what
happened at very early times in the
universe, but we can't be sure until we
observe more objects."
■ SHANNON HALL
sk yandtelescope.com * S E P TE M B E R 2 018

9

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

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