16 November 2019 | New Scientist | 9Marine life SpaceBrian Owens Leah CraneMOSQUITO nets designed to stop
the transmission of malaria are
finding a new use: fishing. However,
the way they are used could have
destructive consequences for food
security and coastal ecosystems.
Although it was known that
mosquito nets are repurposed this
way in many countries, little was
known about the amount and type
of fish they caught. So Benjamin
Jones at Stockholm University in
Sweden and Richard Unsworth
at Swansea University in the UK
decided to investigate the practice
at 10 sites in Mozambique.
The pair found that the nets are
extremely effective. A single sweep
can bring in almost half of the
daily average catch by weight of
a traditional net, by scooping up
everything in its path, including
juveniles (Ambio, doi.org/ddzg).
That could be a problem, both
for people and the local ecosystem,
says Jones. Removing so many
juveniles could reduce fish numbers
in the future. And the seagrass
meadows, which bind the sediment
along the coast and are a vital
carbon sink, rely on fish to stay
healthy. Remove too many fish
and they could collapse, he says.
For many people, the nets are
their only chance to provide foodfor their families. “The people using
the nets are the poorest in society,”
says Jones.
A traditional net can be very
expensive compared with how
much people earn, but mosquito
nets are provided free by many
governments and charities. ❚Using mosquito
nets for fishing is
far too effectiveIT IS a dangerous universe
out there. Astronomers have
spotted the aftermath of an
enormous collision between
two distant planets, and their
studies indicate that such
violence could ruin the chances
for life on planets that could
otherwise be similar to Earth.
Almost 400 light years away,
two nearly identical dwarf stars
orbit one another. Around those
stars sits a strange disc of dust.
That dust is far warmer than it
ought to be, given that we would
have expected it to have cooled
in the past billion years since
the star system formed.
Maggie Thompson at the
University of California, Santa
Cruz, and her colleagues suspect
that a planetary calamity heated
things up (The Astrophysical
Journal, doi.org/dd2b).
“The only thing that we
could think of that could
cause something like this is a
recent collision between two
planetary-sized bodies,” says
Thompson. The team doesn’t
know when the collision took
place, but suspect it was within
the past 80,000 years.
These kinds of collisions
probably happen all the time,
particularly in systems with gasgiants like Jupiter, according to
Renata Frelikh at the University
of California, Santa Cruz.
Huge planets that orbit fairly
close to their stars often have
elongated orbits instead of
circular ones. Looking at a
sample of 311 planets, Frelikhand her colleagues have found
that the planets with the most
elongated paths tend to orbit
a type of star that we know can
produce lots of massive planets.
Her team’s simulations
show that these strange orbits
could be the signature of a
period of planetary chaos in
the systems’ history, where
large worlds smashed into
one another or gravitationally
slingshotted each other away
into space (The Astrophysical
Journal Letters, doi.org/dd2c).
Despite these extreme
systems being very different
to our own, something similar
probably happened here, says
Frelikh. “This phase might be
a sort of common unifying
feature in all planetary systems.”If so, that might be a bad
sign for alien life, she says.
“This violent phase might
disrupt smaller planets,
they might collide with the
Jupiter-like planet or get
thrown out of the system.”
To investigate how such
instability would affect a
smaller planet in the habitable
zone around a star where
surface water can remain
liquid, Giorgi Kokaia at Lund
University in Sweden and his
colleagues ran simulations of
34 nearby planetary systems.
They found that, in most cases,
the instability in the orbits of
the giant planets would almost
definitely destroy any chances
of life on the smaller worlds.
“The outer planets go unstable
and send your habitable planet
careening into the star, and that
would not be very good for life
on that planet,” says Kokaia.
Only seven of the 34 systems
were likely to have planets that
could stay in the habitable zone
despite changes in the orbits
of the giant planets (arxiv.org/
abs/1910.07573). But for those
that remain, a period of huge
collisions and instability may
be important. “These impacts
can be really bad for planets
and their habitability, but also
sort of a blessing in disguise,”
says Thompson.
On Earth, for example,
a huge collision created the
moon, which is important to life
here, and impacts may also have
brought water to the planet.
Studying these impacts not
only helps us figure out where
in the galaxy we should look for
life, but also puts our own solar
system in perspective. ❚Planetary smash-ups are
bad news for alien life
NASA/JP
L-CALTEC
H.Collisions may happen
frequently in systems
with giant planets“ Your habitable planet
careens into the star,
and that would not be
very good for life”BE
NJA
MIN
L.^
JON
ES
Two men carry
a large net made
from mosquito
nets and
traditional
fishing nets