6 | New Scientist | 10 August 2019
THE sails have been hoisted,
the sunlight streamed strong
and we have begun to sail through
space. The LightSail 2 craft has
demonstrated controlled solar
sailing in orbit around Earth for
the first time, but that isn’t the
end of the voyage.
The small craft was developed
by the Planetary Society, a space
advocacy group, and launched
aboard a SpaceX Falcon Heavy
rocket on 25 June. On 31 July, the
society announced that operators
had raised the spacecraft’s orbit by
about 1.7 kilometres, completing
its main mission of demonstrating
that solar sails work and can
be steered. Its predecessor,
LightSail 1, launched in 2015, but
only unfolded its sail – it didn’t
do any controlled manoeuvring.
Solar sails are propelled by
sunlight bouncing off lightweight,
mirrored sails. As particles of light
hit the sails, these photons impart
a small amount of energy that
pushes the craft forward, like
wind in a sail at sea.
LightSail 2’s sails are a mere
4.5 micrometres thick – thinner
than a human hair – and their totalsurface area is 32 square metres.
Each photon imparts a minuscule
amount of energy to the sails, but
over time the momentum adds
up, causing the spacecraft, which
itself is about the size of a loaf of
bread, to continually accelerate.
Light sails are an old idea, first
dreamed up by astronomer
Johannes Kepler in 1608. Othercraft are set to follow LightSail 2.
NASA’s Near-Earth Asteroid Scout
mission is planned to launch
on the first flight of the Space
Launch System rocket, currently
scheduled for 2021. Members of
that mission have been consulting
the LightSail 2 engineers to inform
the development and operation of
their own solar sail, which will take
a craft past a nearby asteroid.
The grand dream is for light
sails to eventually take us to other
solar systems. They don’t carry
fuel and aren’t limited by how fastthey can shoot out exhaust like
traditional propulsion systems,
so light sails could, in theory,
accelerate to an appreciable
fraction of the speed of light to
get us to another star far faster.
However, that will take much
more technology than LightSail 2
has demonstrated, from larger
sails to giant lasers to accelerate
them more efficiently than
sunlight could.
So far, we have taken one baby
step on a long journey towards
using light sails for interstellar
travel, says Avi Loeb of Harvard
University. He is chair of the
Breakthrough Starshot project’s
advisory committee, an initiative
that aims to send a fleet of tiny
spacecraft to our solar system’s
closest star using light sails.
“If I’m being realistic, it will be
several decades at a minimum.”
Craft like LightSail 2 could
take us out among the planets,
but much more work is needed
before we can reach the stars. ❚Space flightLeah CraneTHE PLANETARY SOCIETYNews
“ The grand dream is
that light sails will
eventually take us to
other solar systems”Sailing through space
A solar sail has been successfully steered for the first time
Extreme weatherClimate change
made heatwave
more likelyIF YOU struggled during last month’s
record-smashing heatwave across
Europe, there is bad news. Such
events are the new normal for
countries like the UK, and we can
expect even more extreme ones
in the next few years.
Friederike Otto at the University
of Oxford and her colleagues used
computer models to assess how
global warming has altered the
likelihood of events like the Julyheatwave in Europe. During this, the
UK, Germany, Belgium, Luxembourg
and the Netherlands experienced
all-time highs. Only the UK
remained below 40°C.
The researchers found that
temperatures in all locations would
have been 1.5°C to 3°C cooler had
this event occurred in pre-industrial
times. It is highly unlikely that
France and the Netherlands would
have seen such a heatwave at all
without global warming – it would
be expected to happen less than
once every 1000 years.
For the UK and Germany, the
heatwave wasn’t quite as unlikely.It could have happened around once
every 100 years in a pre-industrial
climate. In today’s climate, such
heatwaves are now expected
around once every eight years.
“Every heatwave analysed so far
in Europe in recent years was found
to be made much more likely andmore intense due to human-
induced climate change,” says the
study, which was published by the
World Weather Attribution initiative.
Globally, July equalled or
surpassed the hottest recorded
month, according to the World
Meteorological Organization and
the EU’s Copernicus Climate Change
Programme. The hot air that caused
the European heatwave later moved
over Greenland, resulting in record
levels of surface melting.
Meanwhile, forest fires
continue to rage across Greenland,
Alaska, Canada and Siberia. ❚
Michael Le PageWith the world
still warming,
heatwaves such
as July’s are likely
to continue -
and to get even
more extreme
BERTRAND GUAY/AFP/GETTY IMAGESLightSail 2 took this
shot as it deployed its
sail in Earth orbit