Abstract
Abstract Dust emission was detected on main-belt asteroid 596 Scheila in 2010 December and was attributed to the collision of a few-tens-of-meters projectile on the surface of the asteroid. In such an impact, the ejected material from the collided body is expected to mainly come from its fresh, unweathered subsurface. Therefore, it is expected that the surface of 596 was partially or entirely refreshed during the 2010 impact. By combining spectra of 596 from the literature and our own observations, we show that the 2010 impact event resulted in a significant slope change in the near-infrared (0.8–2.5 μm) spectrum of the asteroid, from moderately red (T type) before the impact to red (D type) after the impact. This provides evidence that red carbonaceous asteroids become less red with time due to space weathering, in agreement with predictions derived from laboratory experiments on the primitive Tagish Lake meteorite, which is spectrally similar to 596. This discovery provides the very first telescopic confirmation of the expected weathering trend of asteroids spectrally analog to Tagish Lake and/or anhydrous chondritic porous interplanetary dust particles. Our results also suggest that the population of implanted objects from the outer solar system is much larger than previously estimated in the main belt, but many of these objects are hidden below their space-weathered surfaces.
Highlights
596 Scheila, a dark outer main-belt asteroid with a diameter of 114 km (mean value obtained fromIRAS (Tedesco et al 2002), AKARI (Usui et al 2011), and WISE (Masiero et al 2011)) discovered in 1906, was found to exhibit a comet-like appearance on 2010 December 11, about 100 years after its discovery (Larson et al 2010). 596 is rather unique in that it is one of the only two main-belt asteroids larger than 100 km in diameter for which cometary-like activity was ever detected, and the second one being the dwarfplanet 1 Ceres (Kuppers et al 2014)
This provides evidence that red carbonaceous asteroids become less red with time due to space weathering, in agreement with predictions derived from laboratory experiments on the primitive Tagish Lake meteorite, which is spectrally similar to 596
Spectra obtained by Yang & Hsieh (2011) after the impact event, which are not from MITHNEOS observations, and the one obtained in this study, which is from MITHNEOS observations, are consistent within that uncertainty range (Figure 1)
Summary
596 Scheila, a dark outer main-belt asteroid with a diameter of 114 km (mean value obtained fromIRAS (Tedesco et al 2002), AKARI (Usui et al 2011), and WISE (Masiero et al 2011)) discovered in 1906, was found to exhibit a comet-like appearance on 2010 December 11, about 100 years after its discovery (Larson et al 2010). 596 is rather unique in that it is one of the only two main-belt asteroids larger than 100 km in diameter for which cometary-like activity was ever detected, and the second one being the dwarfplanet 1 Ceres (Kuppers et al 2014). 596 is rather unique in that it is one of the only two main-belt asteroids larger than 100 km in diameter for which cometary-like activity was ever detected, and the second one being the dwarfplanet 1 Ceres (Kuppers et al 2014). From spectroscopy in the 3 μm region, the surface of 596 was found to have no more than a few percent of water ice (Yang & Hsieh 2011) These observational results suggested that the cometary activity of 596 is not due to ice sublimation, they do not themselves establish that the activity of 596 was not due to ice sublimation considering that the production rates of sublimation products could have been below the detection limits of the observations
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