All_About_Space_-_Issue_94_2020

hurtling towards our Sun, smashing into whatever

they encountered.

That in itself would have been rather eye-

catching, but here is where things became even

more interesting. Muller's theory postulated that

this star was the Sun's undetected companion – the

‘evil twin’ that we alluded to at the start. He also

reckoned the reason why there may have been

this notable cycle of mass extinction events was

because the red dwarf star was regularly putting

itself among the set of icy rocks that make up the

equally theoretical Oort Cloud in the outermost

reaches of the Solar System.

It would do so every 26 million years, he says,

neatly accounting for the calculated apocalyptic

timeframe on Earth. But in order to do this the red

dwarf star needed to be in a 1.5 light year elliptical

orbit, periodically bringing it closer to the Oort

Cloud and sending comets hurtling our way. What's

more, the theory continued, there was enough of a

gravitational pull on the ‘death star’ by the Sun to

prevent it from drifting away.

When Muller presented his hypothesis in 1984, it

caused international controversy. The scientist was

suggesting that the companion star was born at the

same time as the Sun, and so was part of a binary

star system – that is, one gravitationally bound and

orbiting a common centre of mass. Yet in the last

35 years there has never been any sighting, even

though it's not been for a lack of trying.

In many ways this is rather odd. Muller said

Nemesis was likely to have a magnitude between

seven and 12 and that it should be possible to view

it through a small or medium telescope. But the

Infrared Astronomical Satellite – the first space

telescope to perform a survey of the night sky at

infrared wavelengths – did not see any signs of it

during the 1980s, while the Two Micron All-Sky

Survey, or 2MASS, which surveyed the sky between

1997 and 2001, couldn't detect an additional star in

the Solar System either.

The best shot was thought to be NASA's Wide-

field Infrared Survey Explorer (WISE), which

spotted a brown dwarf 7.2 light years away in 2014.

But it wasn't Nemesis. In actual fact, when Kevin

Luhman, an astronomer at Pennsylvania State

University's Center for Exoplanets and Habitable

Worlds, analysed images from WISE a year earlier in

the outer Solar System, there was simply no sign of

the companion star that Muller had proposed.

Instead, evidence kept stacking up against it. For

starters, some astronomers questioned the inherent

“ Stars generally do not form in isolation but

are born together in groups within clouds

of gas and dust or nebulae” Pavel Kroupa

Where is Nemesis located?

Nemesis has never been seen, but some astronomers have theorised

its potential orbit in relation to the Solar System

Ellipticalorbit

TheNemesistheory says

a hypotheticalred dwarf

takes a highly ellipticalorbit

around our Sun some1.5

light years away.

OortCloud

Every 26 millionyears,

Nemesisapproaches

andpassesthough

thehypothetical

OortCloudwhereicy

planetesimalsreside

inthefarreachesof

thetrans-Neptunian

region.

PastPluto

Toputthisintoperspective,theOort

CloudiswaypasttheKuiperBelt

wherePlutoorbitsandalsobeyond

thescattereddisc,hometoEris.

Sun

Disrupting

influence

When Nemesis passes

through the Oort Cloud, it

is said to have a disruptive

effect on the bodies there,

sending comets – which are

ordinarily a light year away –

hurtling towards the Sun.

Boundaryofthe

SolarSystem

Ifproventobetrue,

Nemesiswouldbe

closerthanAlpha

Centauri,which

isacceptedas

theSun'snearest

neighbour.

2 light years

© Jcpag2012

4 light years

Oort Cloud

MYSTERIES

UNIVER SE

OF

THE