The Economist UK - 14.03.2020

74 Science & technology The EconomistMarch 14th 2020

O

ccasionally, a fossilturns up that

reminds people of how little is really

known about the past. This, perhaps, is

such a discovery. It is the skull, a mere

7mm long, of a tiny, yet full-grown dino-

saur, preserved in amber from a deposit

in northern Myanmar which is 99m years

old. That dates it to the middle of the

Cretaceous, more than 30m years before

this period’s more famous dinosaurian

denizens,Ankylosaurus,Triceratopsand

Tyrannosaurus, bestrode what is now

North America.

Extrapolating from its skull,Oculu-

dentavis khaungraaewould have been

about the size of a bee hummingbird, the

smallest bird now alive. And—confus-

ingly to modern sensibilities, which are

used to thinking of “dinosaurs” and

“birds” as separate categories—it was a

bird, too. It belonged to a group called the

Enantiornithes, which were similar to

modern birds, theNeornithes,except

that evolution did not deprive them of

either their teeth or the claws on their

forelimbs, even though those forelimbs

were fully functional wings.

The Enantiornithes perished along

with most other dinosaurs (and about

three-quarters of the rest of the planet’s

animal and plant species) in a collision,

66m years ago, between Earth and an

asteroid. The Neornithes, though, sur-

vived this catastrophe and went on to

become, in 1758, the class of animals

called Aves in Linnaeus’s “Systema Natu-

rae”. This classification predated the

discovery of fossil dinosaurs (indeed, it

predated the realisation that Earth is far

older than suggested by Biblical and

other mythical traditions). That, and the

everyday familarity of birds, has made it

hard to grasp that the Aves truly are a

group of dinosaurs.

The formal description ofO. khaun-

graaewas published this week inNature

by Xing Lida of the China University of

Geosciences, in Beijing, who has many

previous discoveries from the north-

Burmese amber to his name. There is

evidence that the area in which it lived

was, at the time, an island in an archipel-

ago in a vanished ocean called Tethys. Dr

Xing and his colleagues therefore specu-

late that it may have been a product of

island dwarfism—a tendency of insular

species to shrink, compared to their

mainland relatives. Whatever the expla-

nation for its size, though,O. khaungraae

now shares with the bee hummingbird

(which is not a product of island dwar-

fism, but rather of its habit of feeding on

the nectar of flowers) the title of “small-

est dinosaur known”.

The smallest dinosaur?

Palaeontology

Another intriguing discovery from the amber mines of Myanmar

Small, but perfectly preserved

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

ussNautilus, 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