Albedo and atmospheric constraints of dwarf planet Makemake from a stellar occultation

Abstract

Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies 1,2 . Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos 3 . Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto 4 , and is currently at a distance to the Sun intermediate between the two. Although Makemake's size (1,420 6 60 km) and albedo are roughly known 5,6 , there has been no constraint on its density and there were expectations that it could have a Plutolike atmosphere 4,7,8 . Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 6 9 km (1s) and 1,502 6 45 km, implying a V-band geometric albedo p V 5 0.77 6 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4-12 nanobar (1s) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 6 0.3 g cm 23 is inferred from the data. Stellar occultations allow detection of very tenuous atmospheres and can provide accurate sizes and albedos 9,10,11,3,12 , so we embarked on a programme of predicting and observing occultations by (136472) Makemake, also known as 2005 FY 9 . The occultation of the faint star NOMAD 1181-0235723 (with magnitude m R 5 18.22, where NOMAD is the Naval Observatory Merged Astronomic Dataset) was predicted in 2010 by methods similar to those used to predict occultations by several large bodies 13 , but refined as shown in Supplementary Information section 1. We arranged a campaign involving 16 telescopes, listed in Supplementary Table 1. The occultation was successfully recorded from seven telescopes, listed in Table 1, at five sites. From the images obtained, we made photometric measurements as a function of time (light curves).The light curves of the occultation are shown in Fig. 1. Fitting synthetic square-well models to the light curves yielded the disappearance and reappearance times of the star (Table 1), from which we calculate one chord in the plane of the sky for each site (see Supplementary Information section 3). On the basis of analyses of the light curves, taking into account the cycle time between the images and the dispersion of the data, we deduce that there were no secondary occultations, so we can reject the existence of a satellite larger than about 200 km in diameter in the areas sampled by the chords. The result is consistent with a deep-image survey that did not find any satellites 16 . The chords can be fitted with two shape models (Fig. 2). Our preferred shape, which is compatible with our own and other observations (see Supplementary Information section 8), corresponds to an elliptical object ...

“TNOs are Cool”: A survey of the trans-Neptunian region

“…lightcurve period P and amplitude Δm) is available for 44 objects of the sample, as summarized in Table 5. Density (ρ) estimates are also available for 14 objects, mostly binary systems (Sicardy et al 2011;Santos-Sanz et al 2012;Vilenius et al 2012;Mommert et al 2012;Ortiz et al 2012;Fornasier et al 2013). Figure 3 shows plots of η vs. Δm, P and ρ, none of which shows trends beyond the 1.3σ confidence level.…”

“…Based on Mendis & Brin (1977) equations for atmospheric-assisted thermal conductivity (proportional to atmospheric pressure), Lellouch et al (2000) estimated that this process may contribute to the thermal inertia of Pluto, where the pressure is ∼20 μbar. In the case of Makemake, however, stellar occultation observations provide an upper limit to any global atmosphere at the level of 4-12 nbar (Ortiz et al 2012). This probably rules out the explanation, especially because the measured thermal inertia refers to Makemake's bright terrains, where an atmosphere is not likely to exist.…”

“…The case for Makemake is peculiar, as its 24-500 μm SED cannot be fit with a NEATM (nor a thermophysical model) assuming a homogeneous surface; it is suspected that the SED includes a contribution from a dark and warmer component that dominates at the shortest wavelengths (Lim et al 2010). For this reason, we considered only the SPIRE measurements at 250-500 μm from Lim et al (2010), and those were modeled with D = 1430 ± 9 km and p V = 0.77 ± 0.02 (Ortiz et al 2012). The resulting η value (2.29 +0.46 −0.40 , see Table 3) is similar to that found by Lim et al (2010) for Makemake "bright terrain" (nominally, 1.9).…”

Rotational properties of the binary and non-binary populations in the trans-Neptunian belt

“…On the other hand, stellar occultations allow us to derive the size of the object with a high precision, but the system density can only be derived if the system mass is known (Sicardy et al 2011). If the system mass is unknown (or if the object is not a binary), the lower limit of the density can only be estimated from the light curve (Ortiz et al 2012a). …”

Orbit determination of trans-Neptunian objects and Centaurs for the prediction of stellar occultations

“…We provide ephemerides of TNO/Centaurs usable with SPICE library and available at http://www.imcce.fr/~desmars/ research/tno/ The offset observations of the selected TNOs are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A96 Affiliated researcher at Observatoire de Paris/IMCCE, 77 avenue Denfert Rochereau 75014 Paris, France accuracy (Elliot et al 2010;Sicardy et al 2011;Ortiz et al 2012;Braga-Ribas et al 2013) from the resulting light curves of ground-based observers located inside the shadow path or just outside it. This level of accuracy in dimensions can only be rivaled by space missions.…”