We report the electron density in a plasma tail of Comet ISON (C/2012 S1) derived from interplanetary scintillation (IPS) observations during November 1--28, 2013. Comet ISON showed a well-developed plasma tail (longer than 2.98 x 10^{7} km) before i
ts perihelion passage on November 28. We identified a radio source whose line-of-sight approached the ISONs plasma tail in the above period and obtained its IPS data using the Solar Wind Imaging Facility at 327 MHz. We used the Heliospheric Imager onboard the Solar-Terrestrial Relation Observatory to distinguish between the cometary tail and solar eruption origins of their enhanced scintillation. From our examinations, we confirmed three IPS enhancements of a radio source 1148-00 on November 13, 16, and 17, which could be attributed to the disturbance in the cometary tail. Power spectra of 1148-00 had the steeper slope than normal ones during its occultation by the plasma tail. We estimated the electron density in the ISONs plasma tail and found 84 cm^{-3} around the tail axis at a distance of 3.74 x 10^{7} km from the cometary nucleus and an unexpected variation of the electron density in the vicinity of the tail boundary.
The Japanese Space Agencys Hayabusa II mission is scheduled to rendezvous with and return a sample from the near-Earth asteroid (162173) 1999 JU3. Previous visible-wavelength spectra of this object show significant variability across multiple epochs
which could be the result of a compositionally heterogeneous surface. We present new visible and near-infrared spectra to demonstrate that thermally altered carbonaceous chondrites are plausible compositional analogs, however this is a tentative association due to a lack of any prominent absorption features in our data. We have also conducted a series of high signal-to-noise visible-wavelength observations to investigate the reported surface heterogeneity. Our time series of visible spectra do not show evidence for variability at a precision level of a few percent. This result suggests two most likely possibilities. One, that the surface of 1999 JU3 is homogenous and that unaccounted for systematic effects are causing spectral variation across epochs. Or two, that the surface of 1999 JU3 is regionally heterogenous, in which case existing shape models suggest that any heterogeneity must be limited to terrains smaller than approximately 5% of the total surface area. These new observations represent the last opportunity before both the launch and return of the Hayabusa II spacecraft to perform ground-based characterization of this asteroid. Ultimately, these predictions for composition and surface properties will be tested upon completion of the mission.
We analyzed photographic observations of the re-entry of the Hayabusa spacecraft and capsule over Southern Australia on June 13, 2010, 13:52 UT. Radiometric measurements of the brightness of the associated fireball were obtained as well. We derived t
he trajectories and velocities of the spacecraft, its four fragments and the capsule. The capsule trajectory was within a few hundred meters of the trajectory predicted by JAXA prior the re-entry. The spacecraft trajectory was about 1 km higher than the capsule trajectory. Two major fragments separated from the spacecraft at a height of about 62 km with mutual lateral velocity of 250 m/s. The maximum absolute magnitude of the fireball of -12.6 was reached at a height of 67 km. The dynamic pressures acting on the spacecraft at the fragmentation points were only 1 - 50 kPa. No spacecraft fragment was seen to survive below the height of 47 km. The integral luminous efficiency of the event was 1.3%. As expected, the capsule had a very low luminous efficiency and very low ablation coefficient. The ablation coefficients and masses of the major spacecraft fragments are discussed.
