ABSTRACT We present new optical colors for 28 Kuiper Belt objects (KBOs) and 35 Centaur objects measured with the 1.8 m Vatican Advanced Technology Telescope and the 4.3 m Discovery Channel ...Telescope. By combining these new colors with our previously published colors, we increase the sample size of our survey to 154 objects. Our survey is unique in that the uncertainties in our color measurements are less than half the uncertainties in the color measurements reported by other researchers in the literature. Small uncertainties are essential for discerning between a unimodal and a bimodal distribution of colors for these objects as well as detecting correlations between colors and orbital elements. From our survey, it appears red Centaurs have a broader color distribution than gray Centaurs. We find red Centaurs have a smaller orbital inclination angle distribution than gray Centaurs at the 99.3% confidence level. Furthermore, we find that our entire sample of KBOs and Centaurs exhibits bimodal colors at the confidence level. KBOs and Centaurs with HV > 7.0 have bimodal colors at the 99.96% confidence level and KBOs with HV < 6.0 have bimodal colors at the 96% confidence level.
Methane and Nitrogen Abundances on Pluto and Eris Tegler, S. C; Cornelison, D. M; Grundy, W. M ...
Astrophysical journal/The Astrophysical journal,
12/2010, Letnik:
725, Številka:
1
Journal Article
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ABSTRACT
We present spectra of Eris from the MMT 6.5 m Telescope and Red Channel Spectrograph (5700–9800 Å, 5 Å pixel
−1
) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 m ...Telescope and Boller and Chivens Spectrograph (7100–9400 Å, 2 Å pixel
−1
) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane–nitrogen and methane–argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov & Yantsevich, and comparing methane bands in our Eris and Pluto spectra and methane bands in our laboratory spectra of methane and nitrogen ice mixtures, we find Eris' bulk methane and nitrogen abundances are ∼10% and ∼90% and Pluto's bulk methane and nitrogen abundances are ∼3% and ∼97%. Such abundances for Pluto are consistent with values reported in the literature. It appears that the bulk volatile composition of Eris is similar to the bulk volatile composition of Pluto. Both objects appear to be dominated by nitrogen ice. Our analysis also suggests, unlike previous work reported in the literature, that the methane and nitrogen stoichiometry is constant with depth into the surface of Eris. Finally, we point out that our Eris spectrum is also consistent with a laboratory ice mixture consisting of 40% methane and 60% argon. Although we cannot rule out an argon-rich surface, it seems more likely that nitrogen is the dominant species on Eris because the nitrogen ice 2.15 μm band is seen in spectra of Pluto and Triton.
We present three near-infrared spectra of Pluto taken with the Infrared Telescope Facility and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously ...published spectra of Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases-one highly diluted by nitrogen and the other rich in methane. Application of the Wilcoxon rank sum test to our measurements finds these small differences are statistically significant. This result is contrary to the expectation that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth.
•We present new optical constants of methane–nitrogen ice mixtures.•We study the mixtures spectral behavior at different temperatures and mixing ratios.•These data enable us to account for ...thermodynamic equilibrium on Pluto’s surface.
The methane–nitrogen phase diagram of Prokhvatilov and Yantsevich (1983. Sov. J. Low Temp. Phys. 9, 94–98) indicates that at temperatures relevant to the surfaces of icy dwarf planets like Pluto, two phases contribute to the methane absorptions: nitrogen saturated with methane N2‾:CH4 and methane saturated with nitrogen CH4‾:N2. No optical constants are available so far for the latter component limiting construction of a proper model, in compliance with thermodynamic equilibrium considerations. New optical constants for solid solutions of methane diluted in nitrogen (N2:CH4) and nitrogen diluted in methane (CH4:N2) are presented at temperatures between 40 and 90K, in the wavelength range 1.1–2.7μm at different mixing ratios. These optical constants are derived from transmission measurements of crystals grown from the liquid phase in closed cells. A systematic study of the changes of methane and nitrogen solid mixtures spectral behavior with mixing ratio and temperature is presented.
Kuiper-belt objects (KBOs) are an ancient reservoir of comets beyond Neptune's
orbit. Some of these objects were recently found to have
the reddest optical colours in the Solar System, but the number
...of objects for which accurate colours were available was too small for any
correlation to be discerned between colour and physical or dynamical properties,
which might shed light on the origin of these objects. Here we report that
all nine of the KBOs in our survey on near-circular (low-eccentricity) orbits
with perihelion distances larger than 40 AU have extremely
red surfaces, thereby connecting an observable property with a dynamical class.
Of the objects with orbital eccentricities greater than 0.1, about half are
also very red, while the rest have colours similar to the Sun, meaning that
reflected sunlight is not strongly modified by the objects' surface properties.
In addition, of the 13 'classical' KBOs (those with semimajor
axis a 45 AU and eccentricity
e < 0.15), the ten that are very red are in orbits with small angles
of inclination to the ecliptic, whereas the three with solar colours are all
in high-inclination orbits. We suggest that these three 'grey'
classical KBOs may be part of a dynamical group that is separate from the
'red' classical KBOs.
Accurate absolute optical magnitude values (
H
V
and
H
R
) for Kuiper belt objects (KBOs) and Centaurs are becoming increasingly important as observations in other wavelengths, particularly SIRTF ...thermal infrared measurements, become available for large samples of objects. We present accurate
H
V
and
H
R
values for 90 KBOs and Centaurs, based on our published optical photometry. We find that our
H
V
values are in good agreement with those available from the European photometric survey of minor bodies in the outer Solar System. Comparison with
H
V
values from the JPL Horizons database and the Minor Planet Center database shows that these sources are systematically brighter than ours by about 0.3 mag.
A combination band due to a mechanism whereby a photon excites two or more vibrational modes (e.g., a bend and a stretch) of an individual molecule is commonly seen in laboratory and astronomical ...spectroscopy. Here, we present evidence of a much less commonly seen combination band-one where a photon simultaneously excites two adjacent molecules in an ice. In particular, we present near-infrared spectra of laboratory CO/N2 ice samples where we identify a band at 4467.5 cm−1 (2.239 m) that results from single photons exciting adjacent pairs of CO and N2 molecules. We also present a near-infrared spectrum of Neptune's largest satellite Triton taken with the Gemini-South 8.1 m telescope and the Immersion Grating Infrared Spectrograph that shows this 4467.5 cm−1 (2.239 m) CO-N2 combination band. The existence of the band in a spectrum of Triton indicates that CO and N2 molecules are intimately mixed in the ice rather than existing as separate regions of pure CO and pure N2 deposits. Our finding is important because CO and N2 are the most volatile species on Triton and so dominate seasonal volatile transport across its surface. Our result will place constraints on the interaction between the surface and atmosphere of Triton.
•We confirmed the fast spin of (455213) 2001OE84 is 0.486542 h with no change since first measured.•Current estimations of asteroid cohesion are insufficient to maintain an intact rubble pile.•We ...argue that a monolithic asteroid is the most plausible model.•Constraints applied from collision probabilities and spin evolution, set an age for OE84 between 2-10 Myrs.
At a mean diameter of ∼650 m, the near-Earth asteroid (455213) 2001 OE84 (OE84 for short) has a rapid rotation period of 0.486542 ± 0.000002 h, which is uncommon for asteroids larger than ∼200 m. We revisited OE84 14 years after it was first, and last, observed by Pravec et al. (2002) in order to measure again its spin rate and to search for changes. We have confirmed the rapid rotation and, by fitting the photometric data from 2001 and 2016 using the lightcurve inversion technique, we determined a retrograde sense of rotation, with the spin axis close to the ecliptic south pole; an oblate shape model of a/b=1.32±0.04 and b/c=1.8±0.2; and no change in spin rate between 2001 and 2016. Using these parameters we constrained the body’s internal strength, and found that current estimations of asteroid cohesion (up to ∼80 Pa) are insufficient to maintain an intact rubble pile at the measured spin rate of OE84. Therefore, we argue that a monolithic asteroid, that can rotate at the rate of OE84 without shedding mass and without slowing down its spin rate, is the most plausible for OE84, and we give constraints on its age, since the time it was liberated from its parent body, between 2−10 million years.
The discovery of the first member of the Kuiper belt-a formerly hypothetical ancient reservoir of objects located beyond Neptune's orbit-started a revolution in our understanding of the outer Solar ...System: there is no longer a sharp edge at Pluto's orbit. About 60 Kuiper-belt objects, intermediate in size between comets and planets, are now known to exist on stable circular orbits around the Sun, and no doubt many more objects await discovery. But owing to the recent discovery and intrinsic faintness of these objects, little has been done to explore their physical and chemical properties. Here we report the results of a two-year survey of the broad-band optical colours of about one-quarter of the known Kuiper-belt objects. We find that their colours indicate the presence of two distinct populations: one consists of objects whose surface colours are only slightly redder than the colour of the Sun, while the other consists of the reddest objects known in the Solar System.
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