Brett James Gladman

Pencil-Beam Surveys for Faint Trans-Neptunian Objects

Motivated by a desire to understand the size distribution of objects in the Edgeworth-Kuiper belt, an observing program has been conducted at the Palomar 5 m and Canada-France-Hawaii 3.6 m telescopes. We have conducted pencil-beam searches for outer solar system objects to a limiting magnitude of R ~ 26. The fields were searched using software recombinations of many short exposures shifted at different angular rates in order to detect objects at differing heliocentric distances. Five new trans-Neptunian objects were detected in these searches. Our combined data set provides an estimate of ~90 trans-Neptunian objects deg-2 brighter than 25.9. This estimate is a factor of 3 above the expected number of objects based on an extrapolation of previous surveys with brighter limits and appears consistent with the hypothesis of a single power-law luminosity function for the entire trans-Neptunian region. Maximum-likelihood fits to all self-consistent published surveys with published efficiency functions predicts a cumulative sky density Σ(

Discovery of five irregular moons of Neptune.

Each giant planet of the Solar System has two main types of moons. ‘Regular’ moons are typically larger satellites with prograde, nearly circular orbits in the equatorial plane of their host planets at distances of several to tens of planetary radii. The ‘irregular’ satellites (which are typically smaller) have larger orbits with significant eccentricities and inclinations. Despite these common features, Neptunes irregular satellite system, hitherto thought to consist of Triton and Nereid, has appeared unusual. Triton is as large as Pluto and is postulated to have been captured from heliocentric orbit; it traces a circular but retrograde orbit at 14 planetary radii from Neptune. Nereid, which exhibits one of the largest satellite eccentricities, is believed to have been scattered from a regular satellite orbit to its present orbit during Tritons capture. Here we report the discovery of five irregular moons of Neptune, two with prograde and three with retrograde orbits. These exceedingly faint (apparent red magnitude mR = 24.2–25.4) moons, with diameters of 30 to 50 km, were presumably captured by Neptune.