Though the star Tau Ceti is similar to the Sun, any planets it has are
unlikely to be havens for life, say a team of UK astronomers. Using
submillimetre images of the disk of material surrounding Tau Ceti, they
found that it must contain more than ten times as many comets and
asteroids than there are in the Solar System. With so many more space
rocks hurtling around the star, devastating collisions of the sort that
could lead to the destruction of life would be much more likely in the
Tau Ceti system than in our own planetary system.

Publication of the result in Monthly Notices of the Royal Astronomical
Society coincides with an exhibit ‘Hunting for Planets in Stardust’ at
the Royal Society Summer Exhibition by the same science team from the
UK Astronomy Technology Centre in Edinburgh and the University of St.
Andrews. (Details of the media preview are given in the notes.)

Tau Ceti, only 12 light years away, is the nearest sun-like star and is
easily visible without a telescope. It is the first star to be found to
have a disk of dust and comets around it similar in size and shape to
the disk of comets and asteroids that orbits the Sun. But the
similarity
ends there explains Jane Greaves, Royal Astronomical Society Norman
Lockyer Fellow and lead scientist: ‘Tau Ceti has more than ten times
the
number of comets and asteroids that there are in our Solar System. We
don’t yet know whether there are any planets orbiting Tau Ceti, but if
there are, it is likely that they will experience constant bombardment
from asteroids of the kind that is believed to have wiped out the
dinosaurs. It is likely that with so many large impacts life would not
have the opportunity to evolve.’

The discovery means that scientists are going to have to rethink where
they look for civilisations outside our Solar System. Jane Greaves
continues, ‘We will have to look for stars which are even more like the
Sun, in other words, ones which have only a small number of comets and
asteroids. It may be that hostile systems like Tau Ceti are just as
common as suitable ones like the Sun.’

The reason for the larger number of comets is not fully understood
explains Mark Wyatt, another member of the team: ‘It could be that the
Sun passed relatively close to another star at some point in its
history
and that the close encounter stripped most of the comets and asteroids
from around the Sun.’

The new results are based on observations taken with the world’s most
sensitive submillimetre camera, SCUBA. The camera, built by the Royal
Observatory, Edinburgh, is operated on the James Clerk Maxwell
Telescope
in Hawaii. The SCUBA image shows a disk of very cold dust (-210 degrees
C) in orbit around the star. The dust is produced by collisions between
larger comets and asteroids that break them down into smaller and
smaller pieces.

IMAGES

Images are available from http://www.pparc.ac.uk/Nw/tc_images.asp and can be accessed using
username tcMedia and password ngc247.
(The password will be taken off once the embargo expires.)

1. Artist’s impression: For any planets orbiting Tau Ceti, the skies
will be criss-crossed with comets and meteors will frequently strike
the surface.
Credit: David Hardy.

2. SCUBA Image: Image of the disc of dust particles around the star Tau
Ceti, taken with the submillimetre-wavelength camera SCUBA. The false
colours show the brightness of the disc. Its diameter is slightly
larger than the Solar System. Credit: James Clerk Maxwell Telescope.

3. The James Clerk Maxwell Telescope (JCMT) was used to take the image
of the Tau Ceti dust disk. It is the world’s largest single-dish
submillimetre telescope. It collects faint submillimetre signals with
its 15 metre diameter dish. It is situated near the summit of Mauna Kea
on the Big Island of Hawaii, at an altitude of approximately 4000
metres (14000 feet) above sea level.
Credit: Nik Szymanek.

CONTACTS

Dr Jane Greaves, Astronomer, University of St Andrew
Phone: (+44) (0)7745 127391
e-mail: jsg5@st-andrews.ac.uk

Peter Barratt, Head of Communications, PPARC
Phone (+44) (0)1793 442025
e-mail: peter.barratt@pparc.ac.uk

Eleanor Gilchrist, Public Relations Officer,
Royal Observatory Edinburgh
Phone (mobile): (+44) (0)771 873 6971
Phone (office): (+44) (0)131 668 8379
e-mail: efg@roe.ac.uk

Douglas Pierce Price, James Clerk Maxwell Telescope
Phone: (+1) 808 969 6524
e-mail: outreach@jach.hawaii.edu

NOTES

1. Royal Society Summer Exhibition
The Royal Society Summer Exhibition runs from 5 to 8 July and is
open to the general public on
Monday 5 July 6 p.m. – 9 p.m.; Tuesday 6 July 11a.m. – 4.30 p.m.;=20
Wednesday 7 and Thursday 8 July 10 a.m. – 4.30 p.m.

There is a media preview on Tuesday 5 July 10 a.m. – 11 a.m. To
pre-register please email press@royalsoc.ac.uk.

2. Observing Tau Ceti

Tau Ceti is in the constellation Cetus. Although it is visible without
a telescope, at this time of year it rises in the South East at about
3 a.m. – just before the Sun, so is very hard to spot.

3. The James Clerk Maxwell Telescope (JCMT)

The JCMT is the world’s largest single-dish submillimetre telescope. It
is situated near the summit of Mauna Kea on the Big Island of Hawaii,
at
an altitude of approximately 4000 metres (14000 feet) above sea level.
It is operated by the Joint Astronomy Centre, on behalf of the UK
Particle Physics and Astronomy Research Council, the Canadian National
Research Council, and the Netherlands Organisation for Scientific
Research.

4. SCUBA

SCUBA (the Submillimetre Common-User Bolometer Array) is the world’s
most powerful submillimetre camera. It is attached to the James Clerk
Maxwell Telescope, and contains sensitive detectors called bolometers,
which are cooled to 60 milliKelvin, 0.06 degrees above absolute zero
(60 milliKelvin is about -273.1 degrees Celsius or -459.6 degrees
Fahrenheit). SCUBA was built in the UK by the Royal Observatory,
Edinburgh, at what is now the UK Astronomy Technology Centre.

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