The EconomistFebruary 29th 2020 Science & technology 672
1Dr Saxon found that neither performance
on physical standards, such as hikes or
aquatic training, nor physiological mea-
sures of heart rate, work output, hydration,
nutrition and sleep duration predicted
who would throw in the towel. Nor, among
psychological factors, were conscientious-
ness, neuroticism, openness or agreeable-
ness relevant. But extroversion (or, rather,
introversion) was. Using scores for that pa-
rameter and also for positive affect, Dr Sax-
on was able, retrospectively, to predict with
70% accuracy who would drop out.
She also showed when the towel was
most likely to be thrown. A majority of
droppings out happened just before a se-
ries of timed drills, conducted in a deep-
water pool, in full uniform. These drills are
designed to test candidates’ ability to per-
form tasks underwater, holding their
breath, in a chaotic environment.
What the marine corps’ trainers will do
with this information is not yet clear. They
could use it to winnow out likely failures
before the course starts, though that might
seem unfair to introverts who would nev-
ertheless have made it. Or they might
choose to identify those who need a bit of
encouragement to throw themselves into
both the literal and metaphorical deep end,
on the presumption that, having done so,
they will then take the rest of the course in
their stride. Either approach would, pre-
sumably, reduce the drop-out rate. What
you can be sure of, though, is that the
course itself will not be made any easier. 7T
his weekhas seen the publication of
results collected by probes to two heav-
enly bodies: Chang’e 4, a Chinese mission
to the Moon, and InSight, an American mis-
sion to Mars. Chang’e 4landed in January
2019; InSightarrived the previous Novem-
ber. The Chinese team, bowing to the reali-
ties of scientific publishing, have present-
ed their results in Science Advances, an
American journal. The Americans, how-
ever, have chosen Nature Geoscience, a Brit-
ish journal owned by German publishers.
Chang’e 4is China’s second successful
lunar lander, and the first from any country
to touch down intact on the Moon’s far
side—the part never visible from Earth. Its
purpose, other than demonstrating China’s
technological prowess, is to investigate the
geology of Von Kármán crater in the Moon’s
southern hemisphere. To that end it is fit-ted with a ground-penetrating radar which
can peer many metres down.
This radar shows three distinct layers of
rock, the top two each 12 metres thick and
the lowest 16 metres thick. Below that, the
signal is too fuzzy to see what is going on.
The upper layer is composed of regolith—
crushed rock that is the product of zillions
of small meteorite impacts over the course
of several billion years, and which covers
most of the Moon’s surface. The other two,
distinguishable by the coarseness of the
grains within them, are probably discrete
ejecta from separate nearby impacts early
in the Moon’s history that were subse-
quently covered by the regolith.
InSight(pictured above as an artist’s im-
pression) is intended to probe deeper than
this. It is fitted with instruments designed
to measure heat flow from Mars’s interior,
any wobble in the planet’s axis of rotation
(which would probably be caused by an
iron core) and Marsquakes. The heat-flow
instrument has so far been a washout. The
“mole”, a device intended to dig into Mars’s
surface, pulling this instrument with it,
has refused to co-operate—to the point
where the project’s directors are about to
take the time-honoured step of hitting it
with a hammer (or, rather, with the scoop
on the probe’s robot arm) to persuade it to
stay in the hole that it is supposed to be ex-
cavating. And the wobble detector, though
working correctly, has insufficient data to
report. So the release this week is mainly
about the quakes.
InSight’s seismograph recorded 174
quakes between the craft’s landing and the
end of September 2019. The strongest were
between magnitudes three and four—just
powerful enough, had they happened on
Earth, for a human being to notice them.
Quakes are a valuable source of informa-
tion about a planet’s interior. A network ofseismographs, as exists on Earth, allows
their points of origin to be triangulated,
their speed measured and their reflections
from subsurface rock layers observed.
From all this can be deduced those layers’
composition and depth. With but a single
instrument, such deductions are trickier.
InSight’s masters do, though, think that
two of the quakes originated in Cerberus
Fossae, a set of faults 1,600km from the
landing site that are suspected of still being
seismically active. 7The exploration of the Moon and Mars
continues apacePlanetologyBeneath the
surface
On Mars, on Mars, on Mars, on Mars, on MarsI
nternet shopping makes buying
things easier, but has also led to the rise
of a new kind of thief: the porch pirate.
Porch pirates scour door steps for deliv-
eries that have been made when a house-
holder was out, and nab them. Sometimes,
they will stalk delivery vans to do so. Resi-
dents of New York City, for example, lose an
astonishing 90,000 parcels every day to
porch pirates, according to a report in the
New York Times.
Porch piracy is a problem that may be
solved by the spread of parcel-delivering
drones. Because each drone delivery in-
volves a separate journey, rather than hav-
ing to be fitted into a round, it will be easier
for courier and customer to agree on when
a drone should arrive than on the arrival
time of a van. However Nirupam Roy and
Nakul Garg, a pair of engineers at the Uni-As delivery drones get more common,
they may need to protect themselvesDefending delivery dronesIncoming!