2020-03-14_The_Economist_UserUpload.Net

(Barré) #1
The EconomistMarch 14th 2020 Science & technology 65

O


ccasionally,a fossilturnsupthat
remindspeopleofhowlittleisreally
knownaboutthepast.This,perhaps,is
sucha discovery.It istheskull,a mere
7mmlong,ofa tiny,yetfull-growndino-
saur,preservedinamberfroma deposit
innorthernMyanmarwhichis99myears
old.Thatdatesit tothemiddleofthe
Cretaceous,morethan30myearsbefore
thisperiod’smorefamousdinosaurian
denizens,Ankylosaurus,Triceratopsand
Tyrannosaurus, bestrodewhatisnow
NorthAmerica.
Extrapolatingfromitsskull,Oculu-
dentaviskhaungraaewouldhavebeen
aboutthesizeofa beehummingbird,the
smallestbirdnowalive.And—confus-
inglytomodernsensibilities,whichare
usedtothinkingof“dinosaurs”and
“birds”asseparatecategories—itwasa

bird,too.It belongedtoa groupcalledthe
Enantiornithes,whichweresimilarto
modernbirds,theNeornithes,except
thatevolutiondidnotdeprivethemof
eithertheirteethortheclawsontheir
forelimbs,eventhoughthoseforelimbs
werefullyfunctionalwings.
TheEnantiornithesperishedalong
withmostotherdinosaurs(andabout
three-quartersoftherestoftheplanet’s
animalandplantspecies)ina collision,
66myearsago,betweenEarthandan
asteroid.TheNeornithes,though,sur-
vivedthiscatastropheandwentonto
become,in1758,theclassofanimals
calledAvesinLinnaeus’s“SystemaNatu-
rae”.Thisclassificationpredatedthe
discoveryoffossildinosaurs(indeed,it
predatedtherealisationthatEarthisfar
olderthansuggestedbyBiblicaland
othermythicaltraditions).That,andthe
everydayfamilarityofbirds,hasmadeit
hardtograspthattheAvestrulyarea
groupofdinosaurs.
TheformaldescriptionofO.khaun-
graaewaspublishedthisweekinNature
byXingLidaoftheChinaUniversityof
Geosciences,inBeijing,whohasmany
previousdiscoveriesfromthenorth-
Burmeseambertohisname.Thereis
evidencethattheareainwhichit lived
was,atthetime,anislandinanarchipel-
agoina vanishedoceancalledTethys.Dr
Xingandhiscolleaguesthereforespecu-
latethatit mayhavebeena productof
islanddwarfism—atendencyofinsular
speciestoshrink,comparedtotheir
mainlandrelatives.Whatevertheexpla-
nationforitssize,though,O.khaungraae
nowshareswiththebeehummingbird
(whichisnota productofislanddwar-
fism,butratherofitshabitoffeedingon
thenectarofflowers)thetitleof“small-
estdinosaurknown”.

Thesmallestdinosaur?


Palaeontology

AnotherintriguingdiscoveryfromtheamberminesofMyanmar

Small,butperfectlypreserved

W


ar zones are dangerous places.
Where better, then, for a nuclear reac-
tor? On March 9th America’s government
awarded a trio of firms $39.7m to design
“microreactors” that can supply a few
megawatts of power to remote military
bases, and be moved quickly by road, rail,
sea and air.
The idea of small reactors is as old as nu-
clear power itself. In July 1951, five months
before a reactor in Idaho became the first in
the world to produce usable electricity
through fission, America began building
uss Nautilus, a nuclear-powered subma-
rine. In the 1960s and 1970s small reactors
powered bases in Alaska and Greenland, a
radar facility in Wyoming, a research sta-
tion in Antarctica and—from a cargo ship—
the Panama Canal Zone. America still uses
nuclear-powered submarines and aircraft-
carriers. But land-based mini-reactors
proved unreliable and expensive and have
fallen out of favour.
Interest has been revived by recent
wars, in which American forces proved ex-
traordinarily hungry for energy. Early in
the Iraq war, fuel made up over a third of
the tonnage transported to the region. Be-
tween 2001 and 2010, over half of American
casualties in Iraq and Afghanistan oc-
curred during land-transport missions,
many involving fuel deliveries to remote
outposts. Portable reactors could substi-
tute for unreliable power grids or the gen-
erators that often take their place.
America’s armed forces use about 30
terawatt-hours of electricity per year—
about the same as Ireland—and more than
35m litres of fuel per day. In 2016 a report by
the Defence Science Board, a committee of
experts, concluded that demand would
surge as new power-hungry weapons, like
lasers and rail-guns, come to maturity. Ve-
hicles are also moving away from fossil fu-
els: America expects to have all-electric bri-
gades within the decade. A report by the
army in 2018 said that Holos, a prototype
mobile nuclear reactor, would be 62%
cheaper than using liquid fuel.
It is not just American troops experi-
menting with mobile nuclear power. nasa
is developing smaller “Kilopower” reactors
for space missions, designed to power
small lunar outposts. Russia already uses
larger floating reactors for its nuclear-pow-
ered icebreakers. China plans to install
similar devices on disputed islands in the
South China Sea.

But the planned microreactors would
be distinct in several ways. They are in-
tended to be assembled in a factory and
shipped in one piece, doing away with the
need for tricky engineering in remote
places. They should weigh under 40 tonnes
and fit onto the back of an articulated lorry.
And they are supposed to run themselves,
with “minimal monitoring” from afar.
The risks are manageable, say propo-
nents. Designs feature “passive safety” sys-
tems, which keep working even if electric-
ity is lost or a component breaks. Cooling
pumps can be replaced by natural convec-
tion currents, for instance. The reactors

use “tristructural isotropic particle fuel”, in
which blobs of fissile uranium (along with
oxygen and carbon) are wrapped in layers
of carbon and silicon carbide. The pellets
can withstand high temperatures, contain
radioactive contamination and limit the
impact of accidents. The reactors them-
selves “would be shielded and protected,
and possibly placed in a hole in the
ground”, says Bill Lee, a nuclear engineer
and materials scientist at Bangor Universi-
ty, in Wales. A nuclear meltdown should be
“physically impossible”, says the Pentagon.
The grunts on the ground will be hoping
that is right. 7

Nuclear power plants are coming to a
battlefield near you

Atomic energy

Fun-sized fission

Free download pdf