25 research outputs found
Survival of water ice in Jupiter Trojans
Jupiter Trojans appear to be a key population of small bodies to study and
test the models of the Solar System formation and evolution. Because
understanding the evolution of Trojans can bring strong and unique constraints
on the origins of our planetary system, a significant observational effort has
been undertaken to unveil their physical characteristics. The data gathered so
far are consistent with Trojans having volatile-rich interiors (possibly water
ice) and volatile-poor surfaces (fine grained silicates). Since water ice is
not thermodynamically stable against sublimation at the surface of an object
located at ~5 AU, such layering seems consistent with past outgassing. In this
work, we study the thermal history of Trojans after the formation of a dust
mantle by possible past outgassing, so as to constrain the depth at which water
ice could be stable. We find that it could have survived 100 m below the
surface, even if Trojans orbited close to the Sun for ~10,000 years, as
suggested by the most recent dynamical models. Water ice should be found ~10 m
below the surface in most cases, and below 10 cm in the polar regions in some
cases
Thermal processing of Jupiter Family Comets during their chaotic orbital evolution
Evidence for cometary activity beyond Jupiter and Saturn's orbits -- such as
that observed for Centaurs and long period comets -- suggests that the thermal
processing of comet nuclei starts long before they enter the inner Solar
System, where they are typically observed and monitored. Such observations
raise questions as to the depth of unprocessed material, and whether the
activity of JFCs can be representative of any primitive material. Here we model
the coupled thermal and dynamical evolution of Jupiter Family Comets (JFCs),
from the moment they leave their outer Solar System reservoirs until their
ejection into interstellar space. We apply a thermal evolution model to a
sample of simulated JFCs obtained from dynamical simulations (arXiv:1706.07447)
that successfully reproduce the orbital distribution of observed JFCs. We show
that due to the stochastic nature of comet trajectories toward the inner solar
system, all simulated JFCs undergo multiple heating episodes resulting in
significant modifications of their initial volatile contents. A statistical
analysis constrains the extent of such processing. We suggest that primordial
condensed hypervolatile ices should be entirely lost from the layers that
contribute to cometary activity observed today. Our results demonstrate that
understanding the orbital (and thus, heating) history of JFCs is essential when
putting observations in a broader context.Comment: 30 pages, 10 figures, to be published in Ap
Thermal Shadows and Compositional Structure in Comet Nuclei
We use a fully 3-dimensional thermal evolution model to examine the effects
of a non-uniform surface albedo on the subsurface thermal structure of comets.
Surface albedo markings cast "thermal shadows", with strong lateral thermal
gradients. Corresponding compositional gradients can be strong, especially if
the crystallization of amorphous water ice is triggered in the hottest regions.
We show that the spatial extent of the structure depends mainly on the
obliquity, ther- mal conductivity and heliocentric distance. In some
circumstances, subsurface structure caused by the thermal shadows of surface
features can be maintained for more than 10 Myr, the median transport time from
the Kuiper Belt to the inner solar system. Non-uniform compositional structure
can be an evolutionary product and does not necessarily imply that comets
consist of building blocks accumulated in different regions of the
protoplanetary disk.Comment: Accepted in Ap
The Sources of HCN and CH3OH and the Rotational Temperature in Comet 103P/Hartley 2 from Time-Resolved Millimeter Spectroscopy
One of the least understood properties of comets is the compositional
structure of their nuclei, which can either be homogeneous or heterogeneous.
The nucleus structure can be conveniently studied at millimeter wavelengths,
using velocity-resolved spectral time series of the emission lines, obtained
simultaneously for multiple molecules as the body rotates. Using this
technique, we investigated the sources of CH3OH and HCN in comet 103P/Hartley
2, the target of NASA's EPOXI mission, which had an exceptionally favorable
apparition in late 2010. Our monitoring with the IRAM 30 m telescope shows
short-term variability of the spectral lines caused by nucleus rotation. The
varying production rates generate changes in brightness by a factor of 4 for
HCN and by a factor of 2 for CH3OH, and they are remarkably well correlated in
time. With the addition of the velocity information from the line profiles, we
identify the main sources of outgassing: two jets, oppositely directed in a
radial sense, and icy grains, injected into the coma primarily through one of
the jets. The mixing ratio of CH3OH and HCN is dramatically different in the
two jets, which evidently shows large-scale chemical heterogeneity of the
nucleus. We propose a network of identities linking the two jets with
morphological features reported elsewhere, and postulate that the chemical
heterogeneity may result from thermal evolution. The model-dependent average
production rates are 3.5x10**26 molec/s for CH3OH and 1.25x10**25 molec/s for
HCN, and their ratio of 28 is rather high but not abnormal. The rotational
temperature from CH3OH varied strongly, presumably due to nucleus rotation,
with the average value being 47 K.Comment: Published in ApJ 756, 80 (2012). Supplementary materials available at
http://www.its.caltech.edu/~mdrahus/103p_paperII.htm
Distant activity of 67P/Churyumov-Gerasimenko in 2014: Ground-based results during the Rosetta pre-landing phase
Context. As the ESA Rosetta mission approached, orbited, and sent a lander to comet 67P/Churyumov-Gerasimenko in 2014, a large campaign of ground-based observations also followed the comet.
Aims. We constrain the total activity level of the comet by photometry and spectroscopy to place Rosetta results in context and to understand the large-scale structure of the comet’s coma pre-perihelion.
Methods. We performed observations using a number of telescopes, but concentrate on results from the 8 m VLT and Gemini South telescopes in Chile. We use R-band imaging to measure the dust coma contribution to the comet’s brightness and UV-visible spectroscopy to search for gas emissions, primarily using VLT/FORS. In addition we imaged the comet in near-infrared wavelengths (JHK) in late 2014 with Gemini-S/Flamingos-2.
Results. We find that the comet was already active in early 2014 at heliocentric distances beyond 4 au. The evolution of the total activity (measured by dust) followed previous predictions. No gas emissions were detected despite sensitive searches.
Conclusions. The comet maintains a similar level of activity from orbit to orbit, and is in that sense predictable, meaning that Rosetta results correspond to typical behaviour for this comet. The gas production (for CN at least) is highly asymmetric with respect to perihelion, as our upper limits are below the measured production rates for similar distances post-perihelion in previous orbits
The Comet Interceptor Mission
Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule
Internal structure and cryovolcanism on Trans-Neptunian objects
International audienc