Detection of large terrestrial planets around M and K dwarf stars in orion by transit photometry

A ground based transit survey of M and K-dwarf stars near the galactic plane should be able to determine the abundance of the lower end of the planetary radius function, i.e., extrasolar planets smaller than Neptune. We have shown (Doyle et al. 2000, ApJ 535, 338), that the ground-based detection of planets as small as 2.5 Earth-radii within the M-star circumstellar habitable zone (CHZ) is possible by applying signal detection techniques to differential stellar photometry. Telescopes of 4-meter size with wide-field imaging cameras (greater than one-half degree field of view) are capable of surveying about 35 000 stars in the galactic plane near Orion, with about 8000 stars being G, 12 500 being K, and another 8000 stars being M-dwarf systems, at the magnitude range of 18 to 22. Observations of about 1000 hours, accumulated over a 5-year program, would cover both the full orbital phase of transit-aligned planetary orbits with periods less than 30 days, as well as provide a sufficient number of transit signals for reliable statistical detection confidence. An extrapolation of the mass function of known extrasolar planets predicts that a couple of hundred of these sub-Neptune/large-terrestrial planets might be detected in this way, some within the CHZs of the M2 to M5 stars.