Ceres is one of the major objects of the main belt. Using a cometary-like model, we study the water sublimation and the surface temperature

Ammannito, E.

Bockelee-Morvan, D.

CAPACCIONI, FABRIZIO

CAPRIA, MARIA TERESA

DE SANCTIS, MARIA CRISTINA

FORMISANO, Michelangelo

Magni, G.

Raymond, C. A.

Russell, C.

OA@INAF - Istituto Nazionale di Astrofisica

2015Publication Year2020-05-22T15:05:29ZAcceptance in OA@INAFWater Sublimation and Surface Temperature Simulations of CeresTitleFORMISANO, Michelangelo; DE SANCTIS, MARIA CRISTINA; CAPRIA, MARIA TERESA; Ammannito, E.; CAPACCIONI, FABRIZIO; et al.Authorshttp://hdl.handle.net/20.500.12386/25097HandleWater sublimation and surface temperature simulations of Ceres.  M.Formisano(1,*), M.C.De Sanctis(1), M.T. Capria(1), E.Ammannito(1,2), F.Capaccioni(1), G.Magni(1), D.Bockelee-Morvan(3), C.A.Raymond(4), and C.Russell(2),(1) INAF-IAPS, Roma, Italy,(2) IGPP, UCLA, CA, USA,(3) LESIA, Observatoire de Paris, France (4) JPL, Pasadena, CA, USA. *michelangelo.formisano@iaps.inaf.it    Introduction:  Ceres  is  the  biggest  body of the main belt and it represents a peculiar object. In fact, it  is the link between the rocky and icy asteroids of the belt and possibly one the key to understand the main  phases  of the  evolution  of the  solar  system.  NASA mission  DAWN scheduled  to  arrive  at  Ceres  in  the spring 2015 [1]. Theoretical models suggest that Ceres has a differ-entiated interior,  consisting in  a silicate core (with a weak presence of metals),  an  icy mantle  [2,3,4]  and hydrated minerals at surface [5]. Water  vapor presence has  been recently observed by Herschel [6]: the observations give a flux of at least of 1026 molecules for second from mid-latitude local-ized sources.  Water  emission was also suggested for the first time by [7]. Thermo-physical Model: In the literature we can find several works dedicated to the study of Ceres, in particular  to  the  formation  and  internal  evolution [2,3,4]. These models consider Ceres like an icy satel-lite and deal with its geophysical evolution.Our model, conversely, derives from the the study of the thermal evolution of cometary nuclei [8,9,10].The model contemporary solves the 1-D heat diffu-sion equation,  taking  into account the energy gained or lost by the solid matrix due to sublimation and re-condensation  of H2O ice,  and  the  mass conservation equation that  controls the gas flow through the pore system. The model is a “quasi-3D” model, since the illu-mination for each facets (which cover the entire sur-face of the body), is calculated by the insulation on the body. Surface temperature derives from the balance of solar  input  and  the energy re-emitted in  space,  con-ducted in the interior and used the sublimate surface ices.We assume Ceres as a  spherical  body, composed by water ice, dust and organics in well-defined propor-tions.  Dust  grains  are  distributed  in  different  size classes having different physical and thermal features. The physical and orbital parameters used in the model are reported in the following Table. Results:  We developed several  scenarios in  order to study the  effects of the different physical parame-ters on the sublimation. First, we explored the depen-dence  of the  water  emission  (and,  generally,  of the thermal evolution) on the initial internal temperature:we examined the cases of 163 K, i.e. equilibrium sur-face temperature assuming a solar constant of 1330 W m−2 and an emissivity of 0.9, and the case of a lower temperature, i.e. 80 K. The water ice has been consid-ered on the surface or at  different  distance from the surface:  0.25  m  (comparable  with  the  diurnal  skin depth of 0.15 m) and 100 m (below the annual  skin  depth  of about  9  m).  A typical  surface  temperature map, in case of silicatic crust (no ice on the surface),  is shown in Fig.1.Fig.1: Typical surface temperature.2405.pdf46th Lunar and Planetary Science Conference (2015)The maximum temperatures achieved with the differ-ent models is about 235 K at 2.72 AU, consistent with  measured temperature of the warmest area (235 ± 4)K [11]. In Fig.2 we show a flux profile vs time, in case of porosity of 0.6, at top with initial temperature of 80 K and on the bottom with initial  temperature of 163 K. Conclusions:  We  applied  a  cometary-like  model [8,9,10] in order to study the surface temperature and water sublimation of Ceres, one of the targets of the DAWN NASA mission. We have seen that ice on sur-face at the equator is stable for very few orbits. Thus if the water emission comes from the equatorial surface we should have a continuos replinishment of water on the surface. In this case, relatively small active area is necessary to fit the Herschel observations. Conversely, water  ice is quite stable for very long time if buried below few tens of centimeters of dust. In this case, the water flux is small. Our  simulations  will  be  an  useful  support  for Dawn to better understand the phyiscal conditions for water sublimation and ice stability.References: [1]Russell,  C.T.  And  Raymond,  C.A,  SSR, do10.1007/s11214-011-9836-2, 2011[2]McCord,  T.B.,  and  Sotin,  C.,  JGR,  110, E05009, 2005[3]Thomas,  P.C.,  et  al.,  Nature,  437,  224-226, 2005[4]Castillo-Rogez, J.C., and McCord, T.B., Icarus, 2005, 443-459, 2010.[5]McCord,  T.B.,  Castillo-Rogez,  J.,  and  Rivkin, A., SSR, 163, 63, 2011.[6]Kuppers,  M.,  et  al.,  Nature,  505,  525-527, 2014.[7]A'Hearn,  M.F., and Feldman,  P.D.,  Icarus,  98, 54-60, 1992.[8]De  Sanctis,  M.C.,  et  al.,  Icarus,  207, 341,2010(a)[9]De Sanctis, M.C., et al., AJ, 140, 1, 2010(b)[10] Lasue, J., et al., PSS, 56, 1977, 2008.[11] Saint-Pe, O., Combes, M., Rigaut, F., Icarus, 105, 2, pp 271-281.Additional Information:  This work is supported by an  ASI  grant.  The  computational  resources  used  in this  research  have  been  supplied  by  INAF-IAPS through the DataWell project.Fig.2: Water flux vs time at the equator for initial temperature of 80 K (on the top) and 163 K (on the bottom) for porosity of 0.6. 2405.pdf46th Lunar and Planetary Science Conference (2015)

Water Sublimation and Surface Temperature Simulations of Ceres

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Water Sublimation and Surface Temperature Simulations of Ceres

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