Detection of Extrasolar Planets

Recent reports of extrasolar planets have revolutionized the field of planetary formation because of the Jupiter-mass planets that appear to exist in close proximity to their stars (e.g Mayor and Queloz, 1995). Such planet-star configurations may be common. Unfortunately, no extrasolar candidate has yet to be confirmed with independent techniques. Most such candidates have been uncovered with the radial velocity technique. However, given the high angular resolution of the SKA such systems are ideal for astrometric detection.

As noted in section 2.4.4, the SKA will detect the non-flaring Sun out to $\sim$50 pc. The binary motion of the Sun due to the orbit of Jupiter would be measurable by the SKA out to several 10's of pc. The ability of the SKA to detect normal radio emission from solar-type stars would therefore allow the detection of Jovian planets by astrometric observations of the parent stars. Such studies would yield a census of Jovian planets in the Solar neighbourhood and statistical constraints on the range of orbital separations and masses.Independent confirmation of extrasolar planets will be a high priority for future Optical-IR arrays. The SKA will complement those efforts using radio selected stars.

  

Figure 4.1: The angular motion of a one solar-mass star due to the presence of Jupiter as a function of distance. The astrometric accuracies of the SKA at $\lambda$21 cm, $\lambda$6 cm and $\lambda$1.5 cm are shown by the horizontal lines. At $\lambda$1.5 cm the presence of Jovian planets would be detectable up to several tens of pc distance.

Jupiter emits intense, coherent bursts of radiation at decameter wavelengths (Carr and Wang 1990). It has often been suggested that Jupiter-like planets orbiting other stars might be detectable by decametric observations of similar emission. At a distance of 10 pc, Jupiter's bursts would be at the 10 $\mu$Jy level. A further consequence of the much smaller orbits in the systems detected to date is the high probability of strong interactions of stellar winds with the magnetospheres of the Jupiter-mass planets. The proximity of the planets to their stars should make low-frequency radio emission from the planets much stronger than what is currently observed from Jupiter. A search for steep-spectrum cyclotron masers from extra-solar planets is planned for the 74 MHz VLA. The SKA would increase the detectable volume by a factor of 1000.