Detecting extrasolar planet. Computer artwork of the transit method of detecting an extrasolar planet. The planet (dark spot) is seen transiting (passing in front of) its parent star. This can be detected by the regular (periodic) dimming of the star as the planet passes in front of it. This is known as the photometric transit method, and only works if the planet passes directly between its star and Earth. Although the probability of this alignment is below 1 percent, several extrasolar planets orbiting other stars have been detected by this method.