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Approach images taken by the LORRI imaging system during the New Horizons spacecraft encounter have been used to determine the mean radii and shapes of Pluto and Charon. The primary observations are limb locations derived using three independent approaches. The resulting mean radii of Pluto and Charon are 1188.3±1.6km and 606.0±1.0km, respectively (2-σ). The corresponding densities are 1854±11kg/m...
We give an explanatory description of the unusual “climate zones” on Pluto that arise from its high obliquity (mean 115°) and high amplitude (±12°) of obliquity oscillation over a 2.8 million year period. The zones we describe have astronomically defined boundaries and do not incorporate atmospheric circulation. For such a high mean obliquity, the lines of tropics (greatest latitudes where the Sun...
Carbon dioxide is one of the most abundant ices present in comets and is therefore important for understanding cometary composition and activity. We present analysis of observations of CO2 and [OI] emission in three comets to measure the CO2 abundance and evaluate the possibility of employing observations of [OI] emission in comets as a proxy for CO2. We obtained NIR imaging sensitive to CO2 of comets...
The science payload on the Deep Impact mission includes a 1.05–4.8µm infrared spectrometer with a spectral resolution ranging from R ∼ 200–900. The Deep Impact IR spectrometer was designed to optimize, within engineering and cost constraints, observations of the dust, gas, and nucleus of 9P/Tempel 1. The wavelength range includes absorption and emission features from ices, silicates, organics, and...
We analyze the first color and polarization images of Comet ISON (C/2012 S1) taken during two measurement campaigns of the Hubble Space Telescope (HST) on UTC 2013 April 10 and May 8, when the phase angles of Comet ISON were α≈13.7° and 12.2°, respectively. We model the particles in the coma using highly irregular agglomerated debris particles. Even though the observations were made over a small range...
We present a new analysis of Spitzer observations of Comet 29P/Schwassmann–Wachmann 1 taken on UT 2003 November 21, 23, and 24, similar to a previous investigation of the observations (Stansberry et al., 2004), but using the most recent Spitzer data pipeline products and intensive image processing techniques. Analysis of images from the IRAC 5.8 and 8.0μm bands and the MIPS 24.0 and 70.0μm bands resulted...
Previously proposed mechanisms have difficulty explaining the disruption of Comet C/2012 S1 (ISON) as it approached the Sun. We describe a novel cometary disruption mechanism whereby comet nuclei fragment and disperse through dynamic sublimation pressure, which induces differential stresses within the interior of the nucleus. When these differential stresses exceed its material strength, the nucleus...
In order to link infrared observations of dust formed during planet formation in debris disks to mid-infrared spectroscopic data of planetary materials from differentiated terrestrial and asteroidal bodies, we obtained absorption spectra of a representative suite of terrestrial crustal and mantle materials, and of typical martian meteorites.A series of debris disk spectra characterized by a strong...
Comet C/1995 O1 (Hale–Bopp) has provided an unprecedented opportunity to observe a bright comet over a wide range of heliocentric distances. We present here Spitzer Space Telescope observations of Hale–Bopp from 2005 to 2008 that show a distinct coma and tail, the presence of which is uncommon given its large heliocentric distance (21.6AU and 27.2AU, respectively). The morphology of the dust is compared...
We present an analysis of comet activity based on the Spitzer Space Telescope component of the Survey of the Ensemble Physical Properties of Cometary Nuclei. We show that the survey is well suited to measuring the activity of Jupiter-family comets at 3–7AU from the Sun. Dust was detected in 33 of 89 targets (37±6%), and we conclude that 21 comets (24±5%) have morphologies that suggest ongoing or recent...
We derive the spin state of the nucleus of Comet 103P/Hartley 2, its orientation in space, and its short-term temporal evolution from a mixture of observations taken from the DIXI (Deep Impact Extended Investigation) spacecraft and radar observations. The nucleus is found to spin in an excited long-axis mode (LAM) with its rotational angular momentum per unit mass, M, and rotational energy per unit...
We obtained high-resolution (λ/Δλ∼28,000) infrared spectra of Comet 103P/Hartley 2 on UT 2010 November 4.6 using the NIRSPEC spectrometer at the W.M. Keck Observatory. Here we present spectra of Hartley 2 between 2.832 and 3.639μm (3531–2748cm −1 ), representing the most complete high-resolution infrared survey of a Jupiter-family comet to date in this wavelength region. We have tabulated...
We have studied the photometric properties of the nucleus of a hyperactive comet, 103P/Hartley 2, at visible wavelengths using the DIXI flyby images with both disk-integrated and disk-resolved analyses. The disk-integrated phase function of the nucleus has a linear slope of 0.046±0.002mag/deg and an absolute magnitude of 18.4±0.1 at V-band. The nucleus displays an overall linear, featureless spectrum...
The coma of Comet 103P/Hartley 2 has a significant population of large particles observed as point sources in images taken by the Deep Impact spacecraft. We measure their spatial and flux distributions, and attempt to constrain their composition. The flux distribution of these particles implies a very steep size distribution with power-law slopes ranging from −6.6 to −4.7. The radii of the particles...
We conducted high-dispersion spectroscopic observations of Comet 103P/Hartley 2 in the near-infrared wavelength region using the Keck II telescope with NIRSPEC. We obtained observations on four dates, with the last observations performed during the EPOXI closest approach. For this work we focus on the observations performed on UT 2010 October 17 and 21, while observations carried out on UT 2010 September...
Data from the Extrasolar Planet Observation and Deep Impact Extended Investigation (EPOXI) mission show Comet 103P/Hartley 2 is a bi-lobed, elongated, nearly axially symmetric comet 2.33km in length. Surface features are primarily small mounds <40m across, irregularly-shaped smooth areas on the two lobes, and a smooth but variegated region forming a “waist” between the two lobes. Assuming parts...
The evolution of the spin rate of Comet 9P/Tempel 1 through two perihelion passages (in 2000 and 2005) is determined from 1922 Earth-based observations taken over a period of 13year as part of a World-Wide observing campaign and from 2888 observations taken over a period of 50 days from the Deep Impact spacecraft. We determine the following sidereal spin rates (periods): 209.023±0.025°/dy (41.335±0...
An explosion on Comet 17P/Holmes occurred on 2007 October 23, projecting particulate debris of a wide range of sizes into the interplanetary medium. We observed the comet using the mid-Infrared Spectrograph (5–40μm), on 2007 November 10 and 2008 February 27, and the imaging photometer (24 and 70μm), on 2008 March 13, on board the Spitzer Space Telescope. The 2007 November 10 spectral mapping revealed...
During 2006 March–2007 January, we used the IRAC and MIPS instruments on the Spitzer Space Telescope to study the infrared emission from the ensemble of fragments, meteoroids, and dust tails in the more than 3° wide 73P/Schwassmann-Wachmann 3 debris field. We also investigated contemporaneous ground-based and HST observations. In 2006 May, 55 fragments were detected in the Spitzer image. The wide...
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