New Scientist - USA (2019-06-08)

8 June 2019 | New Scientist | 15

TEN thousand years from now,
humanity decides to settle
100,000 stars in the galaxy, and
the race is on to see who can
spread through our cosmic
neighbourhood the fastest.
That is the premise of the 10th
Global Trajectory Optimization
Competition currently being
run by NASA, in which teams of
astrophysicists and engineers
attempt to plot out a course for the
human race to fulfil this dream.
It assumes we have access to
large spacecraft that can support
life long enough to travel to
other stars, but not at the near
instantaneous speeds seen in
science fiction. “I guess you can
imagine these vessels to be like
the spaceships shown in [the
Disney film] WALL. E,” s ay s
Nathalie Hager, a member of a
team from Columbia University
in New York, one of 73 groups
from around the world competing
in the month-long challenge.
There are a few rules. The first
settlers must depart from our
solar system within 10 million
years. They then have up to
90 million years to fan out across

the galaxy. There is a bonus for

solutions submitted earliest to

mimic the need for an urgent

settlement plan due to humanity’s

supposed dwindling resources.

The fleet at the disposal of the

competitors includes three

mother ships, which each carry up

to 10 settlement pods that may be

released when passing a star. Up to

three new settler ships can then

fan out from each of these stars,

so long as two million years have

passed since arrival – a limitation

that reflects the need to rebuild

resources, but that also makes

the game more manageable, says

Anastassios Petropoulos at NASA’s

Jet Propulsion Laboratory in

California, one of the organisers.

The game is a bit like solving the

mathematics puzzle known as the

travelling salesman problem, in

which you must find the shortest

route that visits several cities. But

this is the travelling salesman on a

galactic scale. “Here you have

multiple salesmen and the targets

are all moving,” says Petropoulos.

Jacob Irwin, one of the Columbia

University team members, says

they started with an animated

simulation of the movement of all

100,000 stars, and then broke up

into smaller groups to solve each

part of the problem – the number

of ships to send out, the speed at

which they should travel, and the

next star they would visit.

So why do this? First, because

it is fun, says Petropoulos. But it is

also a chance to learn something,

even if the scenario seems

far-fetched right now. “I don’t

think that settling other stars is

something we’ll need to seriously

plan in the next centuries,” says

Hager. “That being said, many

technological advances have often

existed in people’s imaginations

long before they have been

implemented in reality.” ❚

PLASTIC waste has spread just
about everywhere on the planet.
But some animals seem to have
adapted to our litterbug ways: a
bees’ nest has been found made
entirely of this material.
At the end of 2017 and the
beginning of 2018, Mariana
Allasino of the National Agricultural
Technology Institute in Argentina
and her colleagues were studying
chicory pollinators in the city of San

Juan, Argentina. At the edges of crop

plots, they put 63 trap nests made

of wood with holes where bees can

use foraged material to build brood

cells – enclosures for raising young.

The team checked the trap nests

monthly. Just three were used. Two

had brood cells made of petals and

mud, but the cells in the third nest

were made entirely of two types of

plastic: thin, blue strips that could

be from disposable shopping bags

and slightly thicker white pieces.

In this nest, one brood cell

contained a dead larva, one was

empty and may have housed

a larva that emerged as an

adult and one was unfinished

(Apidologie, doi.org/c6kj).

“I find it rather sad, but

interesting. It begs for a choice-test

in an enclosure to determine why

this plastic might be more appealing

or adaptive than use of natural

materials,” says Theresa Pitts-

Singer at the US Department of

Agriculture. She says it will be

important to determine whether

plastic lining in brood cells can

harm bees, because it traps more

moisture which can lead to higher

pathogen levels. Plastic may also

be toxic as it breaks down.

Although which species built the

plastic nest isn’t known for certain,

the team says it may be Megachile

rotundata, also known as the alfalfa

leafcutting bee. There are earlier

reports of it foraging plastic for nest

building, though previously it was

used alongside natural materials. ❚

Bees’ nest made

entirely out of

plastic discovered

Pollution

Megachile

rotundata

normally uses

leaves and other

organic material

to line its nests

“Teams must work out the

best way for humans to fan

out and occupy a large part

of the Milky Way”

How to settle the galaxy

A NASA competition is seeking the best way to reach the stars

Space flight

Chelsea Whyte

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To go interstellar,

we will need

large spaceships

Chelsea Whyte