HD 95086 is a young early-type star that hosts (1) a 5 MJ planet at the projected distance of 56 AU revealed by direct imaging, and (2) a prominent debris disk. Here we report the detection of 69 um crystalline olivine feature from the disk using the
Spitzer/MIPS-SED data covering 55-95 um. Due to the low resolution of MIPS-SED mode, this feature is not spectrally resolved, but is consistent with the emission from crystalline forsterite contributing 5% of the total dust mass. We also present detailed analysis of the disk SED and re-analysis of resolved images obtained by Herschel. Our results suggest that the debris structure around HD 95086 consists of a warm (175 K) belt, a cold (55 K) disk, and an extended disk halo (up to 800 AU), and is very similar to that of HR 8799. We compare the properties of the three debris components, and suggest that HD 95086 is a young analog of HR 8799. We further investigate and constrain single-planet, two-planet, three-planet and four-planet architectures that can account for the observed debris structure and are compatible with dynamical stability constraints. We find that equal-mass four-planet configurations of geometrically spaced orbits, with each planet of mass 5 MJ, could maintain the gap between the warm and cold debris belts, and also be just marginally stable for timescales comparable to the age of the system.
The Haumea family is currently the only identified collisional family in the Kuiper belt. We numerically simulate the long-term dynamical evolution of the family to estimate a lower limit of the familys age and to assess how the population of the fam
ily and its dynamical clustering are preserved over Gyr timescales. We find that the family is not younger than 100 Myr, and its age is at least 1 Gyr with 95% confidence. We find that for initial velocity dispersions of 50-400 m/s, approximately 20-45% of the family members are lost to close encounters with Neptune after 3.5 Gyr of orbital evolution. We apply these loss rates to two proposed models for the formation of the Haumea family, a graze-and-merge type collision between two similarly sized, differentiated KBOs or the collisional disruption of a satellite orbiting Haumea. For the graze-and-merge collision model, we calculate that >85% of the expected mass in surviving family members within 150 m/s of the collision has been identified, but that one to two times the mass of the known family members remains to be identified at larger velocities. For the satellite-break-up model, we estimate that the currently identified family members account for ~50% of the expected mass of the family. Taking observational incompleteness into account, the observed number of Haumea family members is consistent with either formation scenario at the 1 sigma level, however both models predict more objects at larger relative velocities (>150 m/s) than have been identified.
Recent lunar crater studies have revealed an asymmetric distribution of rayed craters on the lunar surface. The asymmetry is related to the synchronous rotation of the Moon: there is a higher density of rayed craters on the leading hemisphere compare
d with the trailing hemisphere. Rayed craters represent generally the youngest impacts. The purpose of this paper is to test the hypotheses that (i) the population of Near-Earth asteroids (NEAs) is the source of the impactors that have made the rayed craters, and (ii) that impacts by this projectile population account quantitatively for the observed asymmetry. We carried out numerical simulations of the orbital evolution of a large number of test particles representing NEAs in order to determine directly their impact flux on the Moon. The simulations were done in two stages. In the first stage we obtained encounter statistics of NEAs on the Earths activity sphere. In the second stage we calculated the direct impact flux of the encountering particles on the surface of the Moon; the latter calculations were confined within the activity sphere of the Earth. A steady-state synthetic population of NEAs was generated from a debiased orbital distribution of the known NEAs. We find that the near-Earth asteroids do have an asymmetry in their impact flux on the Moon: apex-to-antapex ratio of 1.32 +/- 0.01. However, the observed rayed crater distributions asymmetry is significantly more pronounced: apex-to-antapex ratio of 1.65 +/- 0.16. Our results suggest the existence of an undetected population of slower (low impact velocity) projectiles, such as a population of objects nearly coorbiting with Earth; more observational study of young lunar craters is needed to secure this conclusion.
HD 38529 is a post-main sequence G8III/IV star (3.5 Gyr old) with a planetary system consisting of at least two planets having Msin(i) of 0.8 MJup and 12.2 MJup, semimajor axes of 0.13 AU and 3.74 AU, and eccentricities of 0.25 and 0.35, respectively
. Spitzer observations show that HD 38529 has an excess emission above the stellar photosphere, with a signal-to-noise ratio (S/N) at 70 micron of 4.7, a small excess at 33 micron (S/N=2.6) and no excess <30 micron. We discuss the distribution of the potential dust-producing planetesimals from the study of the dynamical perturbations of the two known planets, considering in particular the effect of secular resonances. We identify three dynamically stable niches at 0.4-0.8 AU, 20-50 AU and beyond 60 AU. We model the spectral energy distribution of HD 38529 to find out which of these niches show signs of harboring dust-producing plantesimals. The secular analysis, together with the SED modeling resuls, suggest that the planetesimals responsible for most of the dust emission are likely located within 20-50 AU, a configuration that resembles that of the Jovian planets + Kuiper Belt in our Solar System. Finally, we place upper limits (8E-6 lunar masses of 10 micron particles) to the amount of dust that could be located in the dynamically stable region that exists between the two planets (0.25--0.75 AU).
