The Economist 29Feb2020

The EconomistFebruary 29th 2020 Science & technology 65

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DrSaxonfoundthatneitherperformance

onphysical standards,suchashikes or

aquatictraining, norphysiologicalmea-

suresofheartrate,workoutput,hydration,

nutrition and sleep duration predicted

whowouldthrowinthetowel.Nor,among

psychologicalfactors,wereconscientious-

ness,neuroticism,opennessoragreeable-

nessrelevant.Butextroversion(or,rather,

introversion)was.Usingscoresforthatpa-

rameterandalsoforpositiveaffect,DrSax-

onwasable,retrospectively,topredictwith

70%accuracywhowoulddropout.

Shealsoshowedwhenthetowelwas

mostlikelyto bethrown. A majorityof

droppingsouthappenedjustbeforea se-

riesoftimeddrills,conductedina deep-

waterpool,infulluniform.Thesedrillsare

designedtotestcandidates’abilitytoper-

form tasks underwater, holding their

breath,ina chaoticenvironment.

Whatthemarinecorps’trainerswilldo

withthisinformationisnotyetclear.They

coulduseittowinnowoutlikelyfailures

beforethecoursestarts,thoughthatmight

seemunfairtointrovertswhowouldnev-

ertheless have made it. Or they might

choosetoidentifythosewhoneeda bitof

encouragementtothrowthemselvesinto

boththeliteralandmetaphoricaldeepend,

onthepresumptionthat,havingdoneso,

theywillthentaketherestofthecoursein

theirstride.Eitherapproachwould,pre-

sumably,reducethedrop-outrate.What

you can be sure of, though, is thatthe

courseitselfwillnotbemadeanyeasier. 7

T

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-

tedwitha ground-penetratingradarwhich

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 of

seismographs, 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. 7

The exploration of the Moon and Mars

continues apace

Planetology

Beneath the

surface

On Mars, on Mars, on Mars, on Mars, on Mars

I

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 themselves

Defending delivery drones

Incoming!