The latter will be aimed at looking for O 2 and CH 4 both of which are products of life and life alone. They are much too reactive to exist without replenishment by life. B. Indirect observations of extrasolar planets. Latham et al. Proper motion wobbles.
Period gives orbital motion.
Amplitude gives mass ratio. Measurement error now is about 0.05 arcsec. Hubble Space Telescope now has 1-2 millisec resolution. There are not enough of them, but that is another story and not particularly relevant to life. T Tauri stars.