British astronomers, together with Australian and American colleagues, have
used the 3.9m Anglo-Australian Telescope [AAT] in New South Wales, Australia
to discover a new planet outside our Solar System – the 100th to be
detected. The discovery, which is part of a search for solar systems that
resemble our own, will be announced today (Tuesday) at a conference on “The
origin of life” in Graz, Austria. This takes the total number of planets
found outside our solar system to 100, and scientists are now seeing a
pattern in the orbits, giving clues to how they form.

The new planet, which has a mass about that of Jupiter, circles its star
Tau1 Gruis about every four years. Tau1 Gruis can be found in the
constellation Grus (the crane) and is about 100 light years away from Earth.
The planet is three times as far from its star as the Earth is from the Sun.

‘Now our searches have become precise enough to find many planets in orbits
like those in our Solar System, we are seeing clues which may help us
understand how planets are formed.’ said UK team leader Hugh Jones of
Liverpool John Moores University. ‘We are seeing a pattern for these planets
to be of two types, those very close-in and another set with orbits further
out. This Tau1 Gruis planet builds this second group. Why are there these
two groups? We hope the theorists will be able to explain this.’

The long-term goal of this programme is the detection of true analogues to
the Solar System. This discovery of a companion planet to the Tau1 Gruis
star with a relatively long-period orbit and mass similar to that of Jupiter
is a step toward this goal. The discovery of other such planets and
planetary satellites within the next decade will help astronomers assess the
Solar System’s place in the galaxy and whether planetary systems like our
own are common or rare.

‘The Anglo-Australian Telescope is providing the most accurate planet-search
observations in the Southern Hemisphere’, said Dr Alan Penny, the other UK
team member from the Rutherford Appleton Laboratory.

The researchers have found that as they probe for planets in larger orbits,
the distribution of planets around stars is quite different from that of
binary stars orbiting one another, where there is a smooth distribution of
orbits. In contrast to the early discoveries of exoplanets, we now find that
less than 1 in 5 exoplanets are to be found very close to their stars, a few
orbiting with a period of 5 to 50 days but most giant planets are orbiting
at large distances from their host stars. This supports the idea that they
are formed at Jupiter-like distances from their host star. Dependent on the
details of the early solar system, most giant planets probably spiral
inwards towards their star until they reach a point where a lack of
frictional forces stops their further migration.

To find evidence of planets, the astronomers use a high-precision technique
developed by Paul Butler of the Carnegie Institute of Washington and Geoff
Marcy of the University of California at Berkeley to measure how much a star
“wobbles” in space as it is affected by a planet’s gravity. As an unseen
planet orbits a distant star, the gravitational pull causes the star to move
back and forth in space. That wobble can be detected by the ‘Doppler
shifting’ it causes in the star’s light. The AAT team measure the Doppler
shift of stars to an accuracy of 3 metres per second – bicycling speed. This
very high precision allows the team to find planets.

Notes for Editors:

The team are supported by the UK Particle Physics and Astronomy Research
Council, the Australian government, the US National Science Foundation and

Dr Alan Penny will be giving a presentation at the second European Workshop
on Astrobiology in Graz, Austria. The paper describing the new planet has
been submitted for publication the Monthly Notices of the Royal Astronomical

The members of the Anglo-Australian Planet Search team are:

From the UK; Dr Hugh R. A. Jones (Liverpool John Moores University) and Dr Alan J. Penny (Rutherford Appleton Laboratory).

From Australia; Dr Chris G. Tinney (Anglo-Australian Observatory) and Dr Brad Carter (University of Southern Queensland).

From the US; Dr R. Paul Butler (Carnegie Institution of Washington), Dr Geoffrey W. Marcy (University of California Berkeley and San Francisco State University) and Dr Chris McCarthy (Carnegie Institution of Washington).

For more information please contact:

Liverpool John Moores University
Dr Hugh Jones
Tel: 0151 231 2909 / 2919
Mobile: 07956 945276 (Friday)

Rutherford Appleton Laboratory
Dr Alan Penny

Julia Maddock
PPARC Press Office
Tel: 01793 442094

Anglo Australian Observatory
Dr Chris Tinney
Tel: +61 2 9372 4849
Mobile: +61 0416 092 117

Anglo Australian Observatory
Helen Sim
Communications Manager
Tel: +61 2 9372 4251
University of Southern Queensland
Brad Carter
Mobile +61 0401 337 319

Carnegie Institution of Washington
Dr R. Paul Butler
Tel: +1 202 478 8866

University of California, Berkeley
Dr Geoff Marcy
Tel: +1 510 642 1952


The Anglo-Australian Planet Search Home Page –

Exoplanets Home Page –

The Extra-solar Planets Encyclopaedia –

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