Context. The recently discovered Apollo asteroid 2005 UD is the most likely candidate for being a large member of the Phaethon-Geminid stream Complex (PGC). Aims. Detecting more complex members like this should clarify the formation and evolution of the PGC. Methods. Our backward and forward (±10 000-yr) integration of the Kustaanheimo-Stiefel regularized equation of motion revealed that the orbital evolutions of Apollo asteroids (3200) Phaethon and 2005 UD show a similar profile, time-shifting by ∼4600 yr. Results. Within the PGC, this time shift is rather large against the time-lag of 220 yr for Phaethon-Geminids and ∼3900 yr between PhaethonSextantids, although much smaller than that of ∼19 000 yr between Phaethon-Canis Minorids.Conclusions. This is a km-order object, hence may be a split nucleus of Phaethon. Besides, the orbital parameters of 2005 UD and the Sextantids are in good agreement along with the time-lag of 100 yr. Therefore, the Sextantid meteor shower seems to be associated more closely with 2005 UD than Phaethon.

Apollo-type near-Earth asteroid 3200 Phaethon, having a small perihelion distance of $q$$\sim$ 0.14 AU, is classified as F- or B-type, one of subclasses among the C-complex (C-, G-, B-, and F-types) asteroids. The F/B-type asteroids and dehydrated CI and CM carbonaceous chondrites, which are regarded as being linked to each other, underwent a thermal history of high-temperature heatings at more than hundreds of degrees and dehydration for a certain period of time after aqueous alteration in their parent bodies. However, their primary heating mechanism and its timing are less certain and still controversial. We have investigated solar-radiation heating effects on Phaethon at the present planetary-epoch. As a consequence, we have found that the effects on Phaethon, if it is still hydrated, might indeed be a likely candidate for the primary metamorphic heat source. We also found that solar-radiation heating on Phaethon is a function of the latitude, since Phaethon has a highly tilted polar axis. Thus, the northern hemisphere would be selectively more heated than the southern hemisphere. Therefore, we hypothesized that the northern hemisphere, especially the north pole–northern midlatitude region, would be more thermally metamorphosed and dehydrated, if solar-radiation heating is the primary metamorphic heat source of Phaethon. This may provide the latitude-dependent color variations on Phaethon’s surface, although this has not been proven by the existing Phaethon’s spectral data.

Context. The recently discovered Apollo-type near-Earth asteroid 2005 UD has been suggested to be a fragment of (3200) Phaethon. Aims. To test this hypothesis, we carried out photometric observations of 2005 UD using the 1-m telescope at Lulin Observatory. Methods. Multi-color photometry was used to compare the surface properties of (3200) Phaethon and 2005 UD. Surface-color variation due to the rotation was also examined. Conclusions. The similarity of surface colors between (3200) Phaethon and 2005 UD observationally supports the hypothesis that 2005 UD is likely to be a fragment of (3200) Phaethon. A simple explanation for the inhomogeneity of the surface is that we see the surface and subsurface of the precursor object. Another explanation is the topographical structure that such as a large crater causes on this heterogeneous surface.

We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles α= 57 • -141 • around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are P max =7.32±0.25 % at phase angles of α max =124 • ±8 • in the V -band and P max =7.04±0.21 % at α max =124 • ±6 • in the R C -band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of p V =0.25±0.02, which is in agreement with that of Q-type taxonomic asteroids. α max is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance q=0.187 au and a short rotational period of T rot =2.27 hours) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.

Context. The quasi-Hilda comets (QHCs), being in unstable 3:2 Jovian mean motion resonance, are considered a major cause of temporary satellite capture (TSC) by Jupiter. Although the QHCs may be escaped Hilda asteroids, their origin and nature have not yet been studied in sufficient detail. Of particular interest are long TSCs/orbiters. Orbiters -in which at least one full revolution about the planet is completed -are rare astronomical events, because only four have been known to occur in the last several decades. Every case has been associated with a QHC: 82P/Gehrels 3, 111P/Helin-Roman-Crockett, P/1996 R2 (Lagerkvist), and the possibly QHC-derived D/1993 F2 (Shoemaker-Levy 9, SL9). Aims. We focus on long TSC/orbiter events involving QHCs and Jupiter. Thus we survey the known QHCs, searching for other long TSCs/orbiters over the past century. Methods. First, we confirmed the long TSC/orbiter events of 82P, 111P, and 1996 R2 in order to test our method against previous work, applying a general N-body Newtonian code. We then used the same procedure to survey the remaining known QHCs and search for long TSC/orbiter events. Results. We newly identified another long TSC/orbiter: 147P/Kushida-Muramatsu from 1949 May 14 +97days −106days −1961 July 15. Our result is verified by integrations of 243 cloned orbits that take account of the present orbital uncertainty of this comet. The event involves an L 2 → L 1 transition as with 82P and 1996 R2. This may represent a distinct subtype of TSCs from QHC-derived (L 1 →) longer captures exemplified by 111P and (probably) SL9, though this classification is still only based on a small database of TSCs. Conclusions. This is the third long TSC and the fifth orbiter to be found, thus long TSC/orbiter events involving Jupiter have occurred once per decade. Two full revolutions about Jupiter were completed and the capture duration was 12.17 +0.29 −0.27 years. Both these numbers rank 147P as third among long TSC/orbiter events, behind SL9 and 111P. This study also confirms the importance of the QHC region as a dynamical route into and out of Jovian TSC, via the Hill's sphere.