Haumea, an intriguing Water Ice Surface in the transNeptunian Belt

Discovered in 2005 by Santos-Sanz in 2005, (136108) Haumea is one of the four Dwarf Planets in the trans-Neptunian belt and the only one that shows water ice on its surface (Pinilla-Alonso et al. 2006, Brown et al. 2006). Its spectrum in the visible and near-infrared is dominated by absorptions of water ice and does not show any feature due to other constituents previously suggested (Trujillo et al. 2007). These (e.g HCN, CH4, pyroxenes, hydrated ammonia) are completely discarded by modeling of the reflectance (Pinilla-Alonso et al. 2009) in the visible and near-infrared range. Other characteristic of it spectrum is the absence of color in the visible wavelengths (S'(vis) = 0.0±2 [%/1000 Å]) which is indicative of the lack of complex organics. Rotationally resolved models of its reflectance at 5 different phases covering an 80% of the surface (Pinilla-Alonso et al. 2009) reveal a fairly homogeneous surface covered with water ice up to a 92%, with a upper limit of 8% for all the other studied materials. This composition is in agreement with the high albedo estimated for this object ( ~70%, Rabinowitz et al. 2007) Surprisingly, this characteristic is shared by a small group of TNOs, Haumea's cohort, that shows very similar orbital parameters (Brown et al. 2007, Pinilla-Alonso et al. 2007) A signature around 1.65 microns, in the spectrum of Haumea, indicates the presence of crystalline water ice. This was first interpreted by Rabinowitz et al. (2008) as a proof of the youth of its surface. But later, it was showed that this band is compatible with the presence of a 50% of amorphous ice indicative of a moderately old surface (> 100 Myr) (Pinilla-Alonso et al. 2009) I will present here simulations of how the irradiation and collisional resurfacing affect the surface of this TNO. As Gil-Hutton (2009) explains, a collisional event releases energy that could be partially converted into heat that would produce the crystallization of water ice, but the eroded material would also be sublimated and distributed homogeneously over the surface of the TNO while condensing. After the collisional event, the irradiation process starts to transform crystalline into amorphous water ice again. Through modeling of these two processes we find that the object must be covered by a thin crust of ~0.12 cm, while the original composition of the object is still present at 1.61 cm or more below the surface. In addition, these models show how crystalline water ice can presist on the surface of this TNO for more than 1 billion years. Why this object does not have any other material on the surface but pure water ice, is still a mystery that makes this object and its budies so interesting. Brown et al. Nature, 2007, 446, 294. Brown et al. 2006, AAS,DPS meeting, 38,37.1.AAS Bulletin, 38, 550. Gil-Hutton et al. 2009, A&A, 500, 909. Pinilla-Alonso et al. 2006 AAS, DPS meeting, 38, 40.3. AAS Bulletin 38, 556. Pinilla-Alonso et al. 2007, A&A, 468, L25. Pinilla-Alonso et al. 2009, A&A, 496,547. Rabinowitz et al. 2007, ApJ, 639, 1238. Rabinowitz et al. 2008, ApJ, 136,1502. Santos-Sanz et al. 2005. IAU Circular 8577,2. Trujillo et al. 2007. ApJ, 655, 1172.