A single sub-kilometre Kuiper belt object from a stellar occultation in archival data.

The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects. Small, sub-kilometre-sized, Kuiper belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Observations at both optical and X-ray wavelengths claim to have detected such occultations, but their implied abundances are inconsistent with each other and far exceed theoretical expectations. Here we report an analysis of archival data that reveals an occultation by a body with an approximately 500-metre radius at a distance of 45 astronomical units. The probability of this event arising from random statistical fluctuations within our data set is about two per cent. Our survey yields a surface density of Kuiper belt objects with radii exceeding 250 metres of 2.1(-1.7)(+4.8) x 10(7) deg(-2), ruling out inferred surface densities from previous claimed detections by more than 5sigma. The detection of only one event reveals a deficit of sub-kilometre-sized Kuiper belt objects compared to a population extrapolated from objects with radii exceeding 50 kilometres. This implies that sub-kilometre-sized objects are undergoing collisional erosion, just like debris disks observed around other stars.

IOM finds scientific merit to medical marijuana. Institute of Medicine.

AIDS: The Institute of Medicine (IOM) has issued a report on the medical uses of marijuana, coming in the aftermath of voter referenda supporting its medical use. For the purposes of the study, marijuana was defined as unpurified plant substances ingested by eating or smoking. The IOM panel looked at the effects of cannabinoids, health risks associated with medical marijuana use, and the efficacy of medical marijuana. Cannabinoids offer broad-spectrum relief for a variety of conditions, but the health risks associated with smoking remain. Medical marijuana can help patients with nausea, vomiting, anorexia, headache, and pain. There are concerns expressed that the drug diminishes psychomotor performance, and patients using marijuana should not drive a car. There are also short-term immunosuppressive effects that warrant further study.^ieng

Hubble Space Telescope fine-guidance-sensor transfer function and its impact on telescope alignment and guidance.

We describe the use of Hubble Space Telescope Fine Guidance Sensor transfer scans to characterize telescope alignment. To accomplish this we developed a software system to extract the aberration content from the observed transfer scans. The transfer scans show large aberration levels that do not originate in the telescope. The appearance of significant coma in the transfer scans has been identified as resulting from the shearing of spherical aberration caused by a beam misalignment within the Fine Guidance Sensors themselves.