Bibcode
Licandro, J.; Hargrove, K.; Kelley, M.; Campins, H.; Ziffer, J.; Alí-Lagoa, V.; Fernández, Y.; Rivkin, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 537, id.A73
Advertised on:
1
2012
Journal
Citations
27
Refereed citations
25
Description
Context. The Themis collisional family is one of the largest and best
established families in the main belt. Composed of primitive asteroids,
there is evidence that water is likely present in a large fraction of
its members, either in aqueously altered silicates or in water ice
reservoirs. The study of the abundance of water in the outer asteroid
belt is important as it may be linked to the origin of Earth's water.
Studying the Themis family can also help to constrain the compositional
and thermal environment in the region of the solar nebula where these
asteroids formed. Aims: Our aim is to constrain the composition
and thermal properties of the surfaces of several Themis family
asteroids. Methods: We present 5-14 μm spectra of 8 Themis
family asteroids observed with Spitzer: (222) Lucia, (223) Rosa, (316)
Goberta, (383) Janina, (468) Lina, (492) Gismonda, (515) Athalia, and
(526) Jena. We determine their diameters, geometric albedos and beaming
parameters using the near-Earth asteroid thermal model. Their emissivity
spectra are studied in order to determine if they exhibit an emission
plateau from 9 to 12 μm which has been observed in other primitive
asteroids and attributed to fine-grained silicates (the Si-O stretch
fundamental). Results: The derived mean albedo of our sample of
Themis family asteroids is bar pV = 0.07 ± 0.02 = 0.07
± 0.02, and the mean beaming parameter is bar η = 1.05
± 0.10. The derived bar η value is close to unity, which
implies that the infrared beaming is not significant, there is likely
little night-side emission from the asteroids, and the thermal inertia
is probably low. The emissivity spectra of at least 5 of our 8 asteroids
show a 9-12 μm emission plateau with spectral contrast of 2-4%,
similar but smaller than that observed in the spectra of Trojan
asteroids and cometary dust. The plateau may be due to the surfaces
having either small silicate grains embedded in a relatively transparent
matrix, or from a very under-dense (fairy-castle) surface structure. Conclusions: The surfaces of a large fraction of Themis family
asteroids with D 50 km are covered by a fine grained silicate mantle
as observed on Trojan asteroids of similar or larger size. The lower
amplitude of the silicate emission in Themis family asteroids spectra
(2-4%) with respect to that of Trojan asteroids (10-15%) could be
attributed to larger dust particles, a slightly denser structure, or a
lower silicate dust fraction.
Related projects
Minor Bodies of the Solar System
This project studies the physical and compositional properties of the so-called minor bodies of the Solar System, that includes asteroids, icy objects, and comets. Of special interest are the trans-neptunian objects (TNOs), including those considered the most distant objects detected so far (Extreme-TNOs or ETNOs); the comets and the comet-asteroid
Julia de
León Cruz