The theories
Is there really
something big and
influential somewhere
out there causing
mass extinctions?Above left:
An infrared
sky survey
by WISE
failed to
discover
evidence of
NemesisAbove
right:
Binary star
systems
are not
uncommon
–the
closest to
us is Alpha
Centauri
AandB,
along with
faint red
dwarf CThe Nemesis theory
RichardA.Muller'stheory
suggests the Sun has a
companion red dwarf star
named Nemesis which
has an unusual orbit and
causes mass extinctions
on Earth every 26 million
years or so by having a
chaotic impact on bodies
in the Oort Cloud.Our dangerous Sun
In2008,acomputer
simulation by researchers
at Cardiff University
suggested our Solar
System bounces up
and down through the
plane of the galaxy.
Gravitational forces may
dislodge comets from
the Oort Cloud and send
them cascading inwards.A brown dwarf
Nemesismaynotbea
reddwarf,butabrown
one. If that was the case
then it would go some
way towards explaining
why astronomers have
struggledtoseeit:
brown dwarfs have a
low intrinsic brightness,
making them harder
to discover.Other planets
There is an acceptance
that there are other
planets in the outer
region of the Solar
System. These have never
been found, although
computer simulations
continue to rule in the
possibility that they are
out there exerting a
gravitational influence.Gas giant Tyche
Scientific analyses
suggest extinctions
on Earth don't happen
at regular, repeating
intervals. Some
astrophysicists propose a
less disruptive gas giant
in the Oort Cloud instead,
dubbed Tyche – a Greek
goddesswhowasthe
‘good sister’ of Nemesis.stability of Nemesis' proposed orbit. They said the
star would come within the gravitational pull of
otherstarsmovingthroughthegalaxy.Otherscast
doubt that extinction events follow a set cycle.
“There is a tendency for people to find patterns in
nature that do not exist,” said Coryn Bailer-Jones
from the Max Planck Institute for Astronomy in- “Unfortunately, in certain situations traditional
statistics plays to that particular weakness.”
Bailer-Jones said the impact rate of asteroids and
comets had been judged to be steadily increasing
over the past 250 million years on the basis of the
numberofcratersofdifferentages.Butheargued
that periodic variations could be ruled out: “From
the crater record, there is no evidence for Nemesis,”
he concluded. “What remains is the intriguing
question of whether or not impacts have become
ever more frequent over the past 250 million years.”
Onthatbasisitissurelyamatterof‘caseclosed’.
Here we have an intriguing idea that many of us
wouldwishtobetrue,andyetinrealityitsounds
merely fantastical, with evidence that is flaky
at best.
Butthatisn'ttellingthefullstory,andtherehas
beenalittlematterofadwarfplanetcalledSedna
to consider, which some astronomers reckoned
was additional proof of a twin for the Sun. It is, at 8
billion miles away, one of the most distant bodies
in the Solar System, and it pursues an extremely
elongated orbit. Discovered in 2003 by a team led
by Mike Brown, an astronomer at the California
Institute of Technology, it has certainly caught the
imagination,butwhatdoesitreallyprove?
Well,therehasbeenatheorythatSedna's
wonky orbit could only be the result of a large and
distant binary companion to the Sun pulling it
out to such a distance. What else, scientists argue,
could take the dwarf some 200-times further from
the Sun than Neptune every 11,400 years? A study
in 2015 seemed to lend credence to this argument© Alamy
© Tobias Roetsch
© NASA/ESA©TyrogthekreeperThe Sun Nemesis
Many stars in the Solar
System are born with a
companion star including
our nearest neighbour,
AlphaCentauri,whichisa
triplet star system.Red dwarf stars are the most
common type of star in the
universe. They are smaller and
less massive than the Sun.After a million
years after
their birth,
60 per cent
of companion
stars split up;
the rest move
closer to each
other.Sun-like stars
outshine 90
per cent of
other stars in
the Milky Way.Nemesis