Surface heterogeneity of 2005 UD from photometric observations

2010

Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example. We conducted a focused, infrared spectroscopic survey of B-type asteroids to search for waterrelated features in these objects. Our results show that the negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 μm. The 1 μm band can be matched in position and shape using magnetite (Fe 3 O 4 ), which is an important indicator of past aqueous alteration in the parent body. Furthermore, our observations of B-type asteroid (335) Roberta in the 3 μm region reveal an absorption feature centered at 2.9 μm, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. The new observations suggest that at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration.

Section: Introductionsupporting

confidence: 78%

Identification of Magnetite in B-Type Asteroids

Yang

2010

“…They identified asteroid 2005 UD, classified as an Apollo type, as having a common origin with 3200 Phaethon (Ohtsuka et al 2006). Subsequent photometry of 2005 UD revealed that it has unusual blue optical colors like those of Phaethon, consistent with the idea that these two bodies have a common origin Kinoshita et al 2007).…”

Section: Introductionmentioning

confidence: 80%

Observations of 1999 Yc and the Breakup of the Geminid Stream Parent

Kasuga

2008

The Apollo asteroid 1999 YC may share a dynamical association with the Phaethon-Geminid Stream Complex (PGC) (Ohtsuka et al. 2008). Here, we present photometric observations taken to determine the physical properties of 1999 YC. The object shows a nearly neutral reflection spectrum, similar to but slightly redder than the related objects 3200 Phaethon and 2005 UD. Assuming an albedo equal to that of 3200 Phaethon, we find that the diameter is 1.4 ± 0.1 km. Time-resolved broadband photometry yields a double-peaked rotational period of 4.4950 ± 0.0010 h, while the range of the light curve indicates an elongated shape having a projected axis ratio of ∼1.9. Surface brightness models provide no evidence of lasting mass loss of the kind seen in active short-period cometary nuclei. An upper limit to the mass loss is set at ∼10 −3 kg s −1 , corresponding to an upper limit on the fraction of the surface that could be sublimating water ice of <10 −3 . If sustained over the 1000 yr age of the Geminid stream, the total mass loss from 1999 YC (3 × 10 7 kg) would be small compared to the reported stream mass (∼10 12 -10 13 kg), suggesting that the stream is the product of catastrophic, rather than steady-state, breakup of the parent object.

“…This object is dynamically associated with the Geminid meteor stream (e.g., Williams & Wu 1993) and with several other small asteroids including 2005 UD (Ohtsuka et al 2006;Konoshita et al 2007) and 1999 YC (Ohtsuka et al 2008;Kasuga & Jewitt 2008). All these objects may be related to a precursor body that disintegrated ∼10 3 yr ago (Ohtsuka et al 2006).…”

Section: Observations Of Active Asteroidsmentioning

confidence: 92%

The Active Asteroids

2012

297

244

Some asteroids eject dust, unexpectedly producing transient, comet-like comae and tails. First ascribed to the sublimation of near-surface water ice, mass-losing asteroids (also called "main-belt comets") can in fact be driven by a surprising diversity of mechanisms. In this paper, we consider 11 dynamical asteroids losing mass, in nine of which the ejected material is spatially resolved. We address mechanisms for producing mass loss including rotational instability, impact ejection, electrostatic repulsion, radiation pressure sweeping, dehydration stresses, and thermal fracture, in addition to the sublimation of ice. In two objects (133P and 238P) the repetitive nature of the observed activity leaves ice sublimation as the only reasonable explanation, while in a third ((596) Scheila), a recent impact is the cause. Another impact may account for activity in P/2010 A2, but this tiny object can also be explained as having shed mass after reaching rotational instability. Mass loss from (3200) Phaethon is probably due to cracking or dehydration at extreme (∼1000 K) perihelion temperatures, perhaps aided by radiation pressure sweeping. For the other bodies, the mass-loss mechanisms remain unidentified, pending the acquisition of more and better data. While the active asteroid sample size remains small, the evidence for an astonishing diversity of mass-loss processes in these bodies is clear.