The surface of (136108) Haumea (2003 EL₆₁), the largest carbon-depleted object in the trans-Neptunian belt

Abstract

Context. Previously known as 2003 EL 61 , (136108) Haumea, is the largest member of a group of trans-Neptunian objects (TNOs) with similar orbits and "unique" spectral characteristics in the form of a neutral slope in the visible and the deepest water ice absorption bands observed in the trans-Neptunian belt (TNb). Studying the surface of 2003 EL 61 provides useful constraints of the origin of this particular group of TNOs and about the outer Solar System's history. Aims. We attempt to study the composition of the surface of 2003 EL 61 . Methods. We present visible and near-infrared spectra of 2003 EL 61 obtained with the 4.2 m WHT and the 3.6 m TNG telescopes at the "Roque de los Muchachos" Observatory (Canary Islands, Spain). Near-infrared spectra were obtained at different rotational phases covering almost one complete rotational period. Spectra are fitted using scattering models based on Hapke theory and constraints on the surface composition are derived. Results. The observations confirm previous results that the 2003 EL 61 spectrum is neutral in color and exhibits deep water-ice absorption bands. They also provide new facts about the surface of this object: the lack of significant variations in the spectral slope (in the near-infrared) and the depth of the water-ice absorption bands at different rotational phases clearly evident in the data, suggest that the surface of 2003 EL 61 is homogeneous. The scattering models indicate that a 1:1 intimate mixture of crystalline and amorphous water ice is the most probable surface composition of this big TNO, and constrain the presence of other minor constituents to a maximum traction of 8%. Conclusions. The derived composition suggests that: a) cryovolcanism is unlikely to be the resurfacing process that retains the surface of this TNO, and the other members of this population, covered mainly by water ice; b) the surface is older than 10 8 yr which constrains the timescale of any catastrophic event. such as the collision suggested to be the origin of this population, to at least 10 8 yr; c) the surface of 2003 EL 61 is depleted of carbon-bearing species. According to the orbital parameters of the population, this implies that is a possible source of carbon-depleted, Jupiter-Family comets.

Methane, ammonia, and their irradiation products at the surface of an intermediate-size KBO?

“…(136108) Haumea is a 2000 km-class fast-rotating elongated dwarf planet from the classical Kuiper belt with the highest water ice surface content currently known among KBOs and a neutral visible spectrum (see Pinilla-Alonso et al 2009;Merlin et al 2007, and references therein). Brown et al (2007b) identified several objects with similar spectral properties in a dynamical area that is close to Haumea.…”

“…Haumea itself has a much higher albedo (0.6-0.84 Rabinowitz et al 2006;Stansberry et al 2008), and density (2600-3340 kg m −3 Rabinowitz et al 2006) and much deeper water ice absorption bands. Pinilla-Alonso et al (2009) showed that it has a spectrally homogeneous surface best described by a simple intimate mixture of amorphous and crystalline water ice and that it is probably depleted of any other ices. As a consequence, cryovolcanism cannot be invoked as possible a re-surfacing process, whereas it might play a role in Orcus' evolution.…”

The Size and Shape of the Oblong Dwarf Planet Haumea

“…Its rapid rotation rate, multiple satellites, and dynamically-related family members all suggest an early giant impact ). Its surface spectrum reveals a nearly pure water ice surface Trujillo et al 2007;Merlin et al 2007;Dumas et al 2011), with constraints on other organic compounds with upper bounds < 8% (Pinilla-Alonso et al 2009). Lacerda et al (2008) also find evidence for a dark spot on one side of the rotating body, make the surface albedo -3 -non-uniform.…”

Characterisation of candidate members of (136108) Haumea’s family

“…is surprisingly small (Schlichting & Sari 2009;Leinhardt et al 2010); 5. its surface composition is dominated by water ice (Tegler et al 2007;Trujillo et al 2007;Merlin et al 2007;Pinilla-Alonso et al 2009;Dumas et al 2011), yet it has a high density of 2.5-3.3 g cm −3 ); 6. it surface has a hemispherical colour heterogeneity, with a dark red "spot" on one side (Lacerda et al 2008;Lacerda 2009). Brown et al (2007) proposed that Haumea suffered a giant collision that ejected a large fraction of its ice mantle, which formed both the two satellites and the dynamical family and left Haumea with rapid rotation.…”