Astronomers close in on Solar System's 'siblings'

An international team of astronomers using telescopes in Australia and the USA has discovered eight new planets orbiting nearby stars, bringing the number found to 74.

Most known extrasolar planets have elongated, non-circular orbits. But three of the new eight have nearly circular orbits like those of Earth and Mars.

"These discoveries suggest we could find a true counterpart of our solar system in only a few years," said team member Dr Chris Tinney of the Anglo-Australian Observatory in Sydney.

Last December the team announced the first extrasolar planet with a circular orbit, around the star epsilon Reticuli in the southern constellation of the Net. It later discovered another two around 47 Ursae Majoris in the northern constellation of the Big Dipper.

The two new circular-orbit planets lie near the stars HD23079, HD4208 and HD 114783. The planet orbiting HD23079 was found with the Anglo-Australian Telescope in New South Wales, Australia, and the other two with the Keck Telescope in Hawaii.

The minimum masses of the eight new planets range from 0.8 to 10 times the mass of Jupiter. Their distances from their stars range from less than a tenth of the EarthÂ’s distance from the Sun to more than three times that.

The further a planet lies from its star, the longer it takes to complete an orbit and the longer astronomers must observe to detect it.

"As our search continues we're finding planets in larger and larger orbits," said Dr Steve Vogt of the Lick Observatory, University of California at Santa Cruz. "Most of the planetary systems we've found have looked like very distant relatives of the Solar System — no family likeness at all. Now we're starting to see something like second cousins."

"In a few years' time we could be finding brothers and sisters."

The astronomers, from the United States, Australia, Belgium and the United Kingdom, are searching the nearest 1200 sun-like stars for planets similar to those in our Solar System, particularly Jupiter-like gas giants. Their findings will help astronomers assess whether planetary systems like ours are common or rare.

The team has made most of their discoveries with the Keck 10-m telescope on Mauna Kea, Hawaii; the Lick 3-m in Santa Cruz, California; and the 3.9-m Anglo-Australian Telescope in New South Wales, Australia.

To find evidence of planets, the astronomers use a high-precision technique developed by Dr Paul Butler of the Carnegie Institution of Washington and Dr Geoff Marcy of the University of California at Berkeley that measures how much a star "wobbles" in space as itÂ’s tugged on by a planet's gravity.

This research is supported by NASA, the US National Science Foundation, the Australian government (through DETYA) and the UK government (through PPARC).

Anglo-Australian Planet Search team

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

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

• 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).

Search team using the Keck telescope

• from the UK, Mr Kevin Apps (University of Sussex);

• from the US, Dr Steven S. Vogt (UCO/Lick Observatory), Dr R. Paul Butler (Carnegie Institution of Washington), Dr Geoffrey W, Marcy (University of California Berkeley and San Francisco State University), Dr Debra A. Fischer (University of California, Berkeley), Dr Gregory Laughlin (University of California,Berkeley); and

• from Belgium, Dr Dimitri Pourbaix (University of Brussels)


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

Dr Brad Carter, University of Southern Queensland
Tel: +61-7-4631-2801

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

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

Dr Hugh Jones, Liverpool John Moores University
Tel: +44-151-231-2909 / 2919
Mobile: +44-7956-945-276

Summary of new planets announced 16 October 2001

Star name Star mass (in solar masses) Orbital period of planet (days) Eccentricity of orbit (lower = more circular) Minimum mass (Msini), in Jupiter masses Semi-major axis (a measure of the distance of the planet from its star), in AU (the Earth-Sun distance) Telescope 
HD68988 1.20 6.28 0.14 1.90 0.071 Keck
HD142 1.10 338 0.37 1.36 0.980 AAT
HD4203 1.06 406 0.53 1.64 1.094 Keck
HD114783 0.92 501 0.10 0.99 1.201 Keck
HD23079 1.10 628 0.03 2.76 1.482 AAT
HD4208 0.93 829 0.04 0.81 1.686 Keck
HD33636 0.99 1553 0.39 7.71 2.616 Keck
HD39091 1.10 2280 0.67 9.94 3.500 AAT



Graphic of orbits of the three planets found by the Anglo-Australian Planet Search (around stars HD142, HD23079 and HD39091)

An artistÂ’s impression of the new planet H23079
Please credit as: "Illustration: David A. Hardy, Copyright (or ©) PPARC"

300dpi images of the Anglo-Australian Telescope dome (called misc001_300.jpg and misc001_300.tif) can be downloaded from
Please credit as "Copyright (or ©) David Malin".

Details and graphics of the new planets found with the Keck Telescope

Other links

Orbits and mass distributions for the planets found by the AAPS, Keck and Lick searches

The Extra-solar Planets Encyclopaedia

B-roll of Anglo-Australian Telescope available
Helen Sim +61-2-9372-4251 and +61-0419-635-905