When the end of the world comes,
we'll know what to blame. Scientists have found compelling
evidence that the Sun has a baby brother, a dark star whose
eccentric orbit is responsible for periodically showering the
Earth with comets and meteorites.
The dark star - named Nemesis by astronomers - is thought
to be a "brown dwarf" that spins round the Sun in an orbit so
large it is measured in light years, the distance light travels
in a year, equivalent to about 6,000 billion miles.
The research suggests that, every 26m years, the star's
eccentric orbit brings it within one light year of the solar
system. There it causes havoc in the Oort Cloud, a huge region
surrounding the solar system that contains billions of bits of
cosmic rubble left over from the formation of planets.
Of the millions of rocks it throws out of orbit at each visit,
some hurtle Earthwards - and have several times nearly wiped out
life on Earth.
Astronomers have long wondered if the Sun has a smaller partner.
Recently, two independent groups of researchers have found
evidence of one.
One group, led by John Matese, professor of physics at
the University of Louisiana at Lafayette, confirms the notion
that it is most likely to be a brown dwarf, a star that never
accumulated enough mass to ignite and which has simply sat in
space smoldering for billions of years.
Matese studied 82 comets from the Oort Cloud and found common
elements in the shape of their orbits that could only be
explained if they had been influenced by the gravitational pull
of an object several times the size of Jupiter and existing
about 25,000 times farther from the Sun than the Earth.
"A companion to the Sun orbiting
at these distances would have little effect on the planets.
But it would play a big role in the way comets 'made their
way' from their birth places in the planetary disc out to
the Oort Cloud and on how they can return to the inner solar
Further research was published last
week by Richard Muller, professor of physics at the
University of California, Berkeley, following analyses of moon
rock samples brought back to Earth by Apollo 14.
The absence of a protective atmosphere means the moon has been
subjected to intense bombardment in its 4.5 billion- year
Muller's breakthrough was to find a way to date how long ago any
particle was melted - meaning he could build up a picture of
whether the moon gets a constant barrage or suffers spells of
"The evidence clearly shows that
the moon has gone through spells of relatively frequent
impacts and others of reduced intensity. I believe it is
likely that this is because the Oort Cloud is being
disturbed by a massive body that is throwing comets out of
stable orbits, a small fraction of which could reach the
Muller and others believe that the
dark star probably takes about 26m years to complete an orbit
around the sun.
Other scientists have already noted that mass extinctions of
life on Earth seem to occur in a pattern with gaps equivalent to
multiples of 26m, suggesting some regular event is causing the
comets to come Earth's way.
The best-known such event was the one that wiped out the
dinosaurs 65m years ago, but that was not the worst; the planet
has suffered several such large mass extinctions.
Astronomers have found the first Earth-sized planet orbiting
another star. The discovery raises the chances of finding
planets that could support life as we know it.