Since 1995, Paul Butler and his team have discovered over half of the planets found orbiting nearby stars. Unlike the situation in our own solar system, most of these extrasolar planets have elongated, eccentric orbits. However, some are very close to their parent stars in circular orbits with periods of as little as three days. Because the detection technique is limited to large planets, most of these newly found objects have masses on a par with those of Jupiter or Saturn.
Butler and colleagues have developed the most precise method to date for finding these remote bodies: the precision Doppler velocity technique. After further refinements to their method, in 2002 Butler and team announced the smallest planetary at that time, with a mass just 40 times that of Earth. They also announced the discovery of the first true analogue to our own Solar System, three planets in mostly circular orbits around the star 55 Cancri. The outermost planet in the system, at between 3.5 and 5 times Jupiter’s mass and at a distance of 5.9 AU from its star, is analogous to Jupiter, which is 5.2 AU from our Sun (1 AU is the distance from the Earth to the Sun).
Butler’s work is part of a multiyear project to carry out the first reconnaissance of all 2,000 nearby Sun-like stars within 150 light-years of the solar system (1 lightyear is about 9.4 trillion kilometres). His team is currently monitoring about 1,700 stars, including 1,000 Northern Hemisphere stars with the Keck telescope in Hawaii and the UCO Lick Observatory telescope in California, and 300 Southern Hemisphere stars with the Anglo-Australian telescope in New South Wales, Australia. The remaining Southern Hemisphere stars are being surveyed with Carnegie’s Magellan telescopes in Chile. The ultimate goal is to find planets that resemble the Earth.
- Supergiants and Cepheid Variable Stars
- Precision Doppler Instrumentation
- Observational Astrophysics
- Stellar Spectroscopy
- Extrasolar Planets
- Sun-like Stars
Prof Butler’s publications can be viewed here