اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEvidence for longitudinal variability of ethane ice on the surface of Pluto
164
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We present the results of an investigation using near-infrared spectra of Pluto taken on 72 separate nights using SpeX/IRTF. These data were obtained between 2001 and 2013 at various sub-observer longitudes. The aim of this work was to confirm the presence of ethane ice and to determine any longitudinal trends on the surface of Pluto. We computed models of the continuum near the 2.405 {mu}m band using Hapke theory and calculated an equivalent width of the ethane absorption feature for six evenly-spaced longitude bins and a grand average spectrum. The 2.405 {mu}m band on Pluto was detected at the 7.5-{sigma} level from the grand average spectrum. Additionally, the band was found to vary longitudinally with the highest absorption occurring in the N$_2$-rich region and the lowest absorption occurring in the visibly dark region. The longitudinal variability of $^{12}$CO does not match that of the 2.405 {mu}m band, suggesting a minimal contribution to the band by $^{13}$CO. We argue for ethane production in the atmosphere and present a theory of volatile transport to explain the observed longitudinal trend.
قيم البحث
اقرأ أيضاً
Context: The dwarf planet (1) Ceres - next target of the NASA Dawn mission - is the largest body in the asteroid main belt; although several observations of this body have been performed so far, the presence of surface water ice is still questioned.
Aims: Our goal is to better understand the surface composition of Ceres, and to constrain the presence of exposed water ice. Methods: We acquired new visible and near-infrared spectra at the Telescopio Nazionale Galileo (TNG, La Palma, Spain), and reanalyzed literature spectra in the 3-$mu$m region. Results: We obtained the first rotationally-resolved spectroscopic observations of Ceres at visible wavelengths. Visible spectra taken one month apart at almost the same planetocentric coordinates show a significant slope variation (up to 3 %/10$^3AA$). A faint absorption centered at 0.67 $mu$m, possibly due to aqueous alteration, is detected in a subset of our spectra. The various explanations in the literature for the 3.06-$mu$m feature can be interpreted as due to a variable amount of surface water ice at different epochs. Conclusions: The remarkable short-term temporal variability of the visible spectral slope, and the changing shape of the 3.06-$mu$m band, can be hints of different amounts of water ice exposed on the surface of Ceres. This would be in agreement with the recent detection by the Herschel Space Observatory of localized and transient sources of water vapour over this dwarf planet.
The origin of the interstellar object 1I/Oumuamua, has defied explanation. In a companion paper (Jackson & Desch, 2021), we show that a body of N2 ice with axes 45 m x 44 m x 7.5 m at the time of observation would be consistent with its albedo, non-g
ravitational acceleration, and lack of observed CO or CO2 or dust. Here we demonstrate that impacts on the surfaces of Pluto-like Kuiper belt objects (KBOs) would have generated and ejected ~10^14 collisional fragments--roughly half of them H2O ice fragments and half of them N2 ice fragments--due to the dynamical instability that depleted the primordial Kuiper belt. We show consistency between these numbers and the frequency with which we would observe interstellar objects like 1I/Oumuamua, and more comet-like objects like 2I/Borisov, if other stellar systems eject such objects with efficiency like that of the Sun; we infer that differentiated KBOs and dynamical instabilities that eject impact-generated fragments may be near-universal among extrasolar systems. Galactic cosmic rays would erode such fragments over 4.5 Gyr, so that fragments are a small fraction (~0.1%) of long-period Oort comets, but C/2016 R2 may be an example. We estimate Oumuamua was ejected about 0.4-0.5 Gyr ago, from a young (~10^8 yr) stellar system, which we speculate was in the Perseus arm. Objects like Oumuamua may directly probe the surface compositions of a hitherto-unobserved type of exoplanet: exo-plutos. Oumuamua may be the first sample of an exoplanet brought to us.
Sputnik Planitia, Plutos gigantic ice glacier, hosts numerous scientific mysteries, including the presence of thousands of elongated pit structures. We examine various attributes of these pit structures in New Horizons data sets, revealing their leng
th, aspect ratios, and orientation properties; we also study their interior reflectivities, colors, and compositions, and compare these attributes to some other relevant regions on Pluto. We then comment on origin mechanisms of the pits and also the fate of the missing volatiles represented by the pits on Sputnik Planitia.
Acetylene (C$_2$H$_2$) and ethane (C$_2$H$_6$) are both produced in the stratosphere of Jupiter via photolysis of methane (CH$_4$). Despite this common source, the latitudinal distribution of the two species is radically different, with acetylene dec
reasing in abundance towards the pole, and ethane increasing towards the pole. We present six years of NASA IRTF TEXES mid-infrared observations of the zonally-averaged emission of methane, acetylene and ethane. We confirm that the latitudinal distributions of ethane and acetylene are decoupled, and that this is a persistent feature over multiple years. The acetylene distribution falls off towards the pole, peaking at $sim$30$^{circ}$N with a volume mixing ratio (VMR) of $sim$0.8 parts per million (ppm) at 1 mbar and still falling off at $pm70^circ$ with a VMR of $sim$0.3 ppm. The acetylene distributions are asymmetric on average, but as we move from 2013 to 2017, the zonally-averaged abundance becomes more symmetric about the equator. We suggest that both the short term changes in acetylene and its latitudinal asymmetry is driven by changes to the vertical stratospheric mixing, potentially related to propagating wave phenomena. Unlike acetylene, ethane has a symmetric distribution about the equator that increases toward the pole, with a peak mole fraction of $sim$18 ppm at about $pm50^{circ}$ latitude, with a minimum at the equator of $sim$10 ppm at 1 mbar. [...] The equator-to-pole distributions of acetylene and ethane are consistent with acetylene having a shorter lifetime than ethane that is not sensitive to longer advective timescales, but is augmented by short-term dynamics, such as vertical mixing. Conversely, the long lifetime of ethane allows it to be transported to higher latitudes faster than it can be chemically depleted.
The origin of the interstellar object 1I/Oumuamua has defied explanation. We perform calculations of the non-gravitational acceleration that would be experienced by bodies composed of a range of different ices and demonstrate that a body composed of
N2 ice would satisfy the available constraints on the non-gravitational acceleration, size and albedo, and lack of detectable emission of CO or CO2 or dust. We find that Oumuamua was small, with dimensions 45 m x 44 m x 7.5 m at the time of observation at 1.42 au from the Sun, with a high albedo of 0.64. This albedo is consistent with the N2 surfaces of bodies like Pluto and Triton. We estimate Oumuamua was ejected about 0.4-0.5 Gyr ago from a young stellar system, possibly in the Perseus arm. Objects like Oumuamua may directly probe the surface compositions of a hitherto-unobserved type of exoplanet: exo-plutos. In a companion paper (Desch & Jackson, 2021) we demonstrate that dynamical instabilities like the one experienced by the Kuiper belt, in other stellar systems, plausibly could generate and eject large numbers of N2 ice fragments. Oumuamua may be the first sample of an exoplanet brought to us.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
