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On the possible origin of the asteroid (1) Ceres
Abstract
The last three decades the asteroid (1) Ceres is an object of the intensive
ground-and space-based observations. A new unusual contributing to these
studies represents the recent detection of localized sources of water vapour
releasing from its surface at a rate about 6 kg s-1 (K\"uppers et al 2014). A
drastic distinction between asteroid (1) Ceres and nearest the large asteroid
(4) Vesta in terms of their composition and appearance emphasizes an urgent
state of a problem of the possible origin of Ceres in the main asteroid belt.
By analogy with the early assumptions of some well-known astronomers of Mercury
and Mars as the escaped satellites of their host planets we have put forward
and semi-empirically have justified a hypothesis for the plausible origin of
Ceres as the satellite of a disrupted planet in the past orbited the Sun of ~ 5
AU. The orbital location of this host of Ceres beyond the snow line of the
Solar System explains a formation the icy mantle of Ceres, which appears may be
a water vapour source.
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The presence of liquid water is a requirement of habitability on a planet. Possible indicators of liquid surface water on Mars include intermittent flow-like features observed on sloping terrains. These recurring slope lineae are narrow, dark markings on steep slopes that appear and incrementally lengthen during warm seasons on low-albedo surfaces. The lineae fade in cooler seasons and recur over multiple Mars years. Recurring slope lineae were initially reported to appear and lengthen at mid-latitudes in the late southern spring and summer and are more common on equator-facing slopes where and when the peak surface temperatures are higher. Here we report extensive activity of recurring slope lineae in equatorial regions of Mars, particularly in the deep canyons of Valles Marineris, from analysis of data acquired by the Mars Reconnaissance Orbiter. We observe the lineae to be most active in seasons when the slopes often face the sun. Expected peak temperatures suggest that activity may not depend solely on temperature. Although the origin of the recurring slope lineae remains an open question, our observations are consistent with intermittent flow of briny water. Such an origin suggests surprisingly abundant liquid water in some near-surface equatorial regions of Mars.
The 'snowline' conventionally divides Solar System objects into dry bodies, ranging out to the main asteroid belt, and icy bodies beyond the belt. Models suggest that some of the icy bodies may have migrated into the asteroid belt. Recent observations indicate the presence of water ice on the surface of some asteroids, with sublimation a potential reason for the dust activity observed on others. Hydrated minerals have been found on the surface of the largest object in the asteroid belt, the dwarf planet (1) Ceres, which is thought to be differentiated into a silicate core with an icy mantle. The presence of water vapour around Ceres was suggested by a marginal detection of the photodissociation product of water, hydroxyl (ref. 12), but could not be confirmed by later, more sensitive observations. Here we report the detection of water vapour around Ceres, with at least 10(26) molecules being produced per second, originating from localized sources that seem to be linked to mid-latitude regions on the surface. The water evaporation could be due to comet-like sublimation or to cryo-volcanism, in which volcanoes erupt volatiles such as water instead of molten rocks.
Since 1995, more than 500 exoplanets have been detected using different
techniques, of which 11 were detected with gravitational microlensing. Most of
these are gravitationally bound to their host stars. There is some evidence of
free-floating planetary mass objects in young star-forming regions, but these
objects are limited to massive objects of 3 to 15 Jupiter masses with large
uncertainties in photometric mass estimates and their abundance. Here, we
report the discovery of a population of unbound or distant Jupiter-mass
objects, which are almost twice (1.8_{-0.8}^{+1.7}) as common as main-sequence
stars, based on two years of gravitational microlensing survey observations
toward the Galactic Bulge. These planetary-mass objects have no host stars that
can be detected within about ten astronomical units by gravitational
microlensing. However a comparison with constraints from direct imaging
suggests that most of these planetary-mass objects are not bound to any host
star. An abrupt change in the mass function at about a Jupiter mass favours the
idea that their formation process is different from that of stars and brown
dwarfs. They may have formed in proto-planetary disks and subsequently
scattered into unbound or very distant orbits.
The accretion of bodies in the asteroid belt was halted nearly 4.6 billion years ago by the gravitational influence of the newly formed giant planet Jupiter. The asteroid belt therefore preserves a record of both this earliest epoch of Solar System formation and variation of conditions within the solar nebula. Spectral features in reflected sunlight indicate that some asteroids have experienced sufficient thermal evolution to differentiate into layered structures. The second most massive asteroid--4 Vesta--has differentiated to a crust, mantle and core. 1 Ceres, the largest and most massive asteroid, has in contrast been presumed to be homogeneous, in part because of its low density, low albedo and relatively featureless visible reflectance spectrum, similar to carbonaceous meteorites that have suffered minimal thermal processing. Here we show that Ceres has a shape and smoothness indicative of a gravitationally relaxed object. Its shape is significantly less flattened than that expected for a homogeneous object, but is consistent with a central mass concentration indicative of differentiation. Possible interior configurations include water-ice-rich mantles over a rocky core.
Ceres appears likely to be differentiated and to have experienced planetary evolution processes. This conclusion is based on current geophysical observations and thermodynamic modeling of Ceres' evolution. This makes Ceres similar to a small planet, and in fact it is thought to represent a class of objects from which the inner planets formed. Verification of Ceres' state and understanding of the many steps in achieving it remains a major goal. The Dawn spacecraft and its instrument package are on a mission to observe Ceres from orbit. Observations and potential results are suggested here, based on number of science questions. © 2012 Springer Science+Business Media New York. All rights are reserved.
The asteroid Ceres has been thought to contain abundant water. Observations acquired with the Herschel Space Observatory now show that this Solar System object is spewing water vapour from its surface. See Letter p.525
In this review paper I address the current knowledge of the formation of Mars, focusing on its primary constituents, its formation time scale and its small mass compared to Earth and Venus. I argue that the small mass of Mars requires the terrestrial planets to have formed from a narrow annulus of material, rather than a disc extending to Jupiter. The truncation of the outer edge of the disc was most likely the result of giant planet migration, which kept Mars’ mass small. From cosmochemical constraints it is argued that Mars formed in a couple of million years and is essentially a planetary embryo that never grew to a full-fledged planet. This is in agreement with the latest dynamical models. Most of Mars’ building blocks consists of material that formed in the 2 AU to 3 AU region, and is thus more water-rich than that accreted by Earth and Venus. The putative Mars could have consisted of 0.1 % to 0.2 % by mass of water.
The Dawn mission journeys to the center of the main asteroid belt to orbit and explore the two most massive main belt asteroids, Vesta and Ceres. Dawn aims to increase our understanding not just of the present state of these two bodies, but also of the conditions during the time of their formation. It attempts this through achieving a set of measurement objectives in which the physical properties of these asteroids such as mass, slopes, size, density, and spin state are accurately determined, and in which the mineralogical and elemental composition of the surface and near-surface material are probed. Dawn employs ion propulsion technology to enable a modestly-sized launcher to start a moderately-sized spacecraft on its journey, to not only reach the two massive asteroids but also to orbit them, descending to near the surface. Unlike most orbital missions, the initial (Vesta) phase must be completed with sufficient reserves and within a time window that later allows Dawn to explore Ceres. Dawn carries a redundant framing camera, a visible and near-IR spectrometer, a gamma ray and neutron spectrometer, and achieves high-accuracy radiometric and optical navigation to enable gravity field determination. The spacecraft was developed by Orbital Sciences Corporation under the management of the Jet Propulsion Laboratory for the National Aeronautics and Space Administration. Dawn is a Principal Investigator-led mission of the Discovery Program. The PI institution, the University of California, Los Angeles, manages directly the science team, the Dawn Science Center, and the Education and Public Outreach program.
A true (genetic) asteroid family is the fragments of a disrupted parent
body which follow similar orbits around the Sun (dynamical association).
The Ceres asteroid family is a dynamical association of 7 asteroids at
approximately 2.8 AU from the Sun. Asteroid collisional evolution models
[4] suggest that 1 Ceres is an intact object and is unlikely to have
suffered impacts capable of producing the other family members. Based on
the taxonomic mix of these family members, it has been suggested that
Ceres may be an interloper in its own family, or that this may not be a
true (genetic) family. However, the most recent work shows that a
genetic relationship probably exists between 3 family members (39
Laetitia, 264 Libussa, and 446 Aeternitas). Prior to the present study,
asteroid family work had been limited to dynamical or taxonomic
evaluations of family memberships. Dynamical studies are required to
identify statistically significant clusters of asteroids. Taxonomic
studies are suggestive and often point out intriguing puzzles to work
on. However, only a careful analysis of the family member geology and
mineralogy allows a genetic family membership to be established and
interlopers to be identified. Using the compositions of the genetic
family members it is possible to determine the degree of differentiation
and stratigraphy of the parent body of the family. This, in turn, allows
us to accurately determine the size, thermal history and original
composition of the parent body. Recently, spectrophotometric data were
obtained for the remaining members (374 Burgundia, 403 Cyane, and 441
Bathilde) of the Ceres family which permits the genetic study of this
family. This is the first detailed compositional study of an asteroid
family. ACKNOWLEDGEMENTS: Various portions of this work were supported
by NSF Solar System Astronomy grant AST-9012180 and by NASA Planetary
Geology and Geophysics grant NAGW-642. M.J. Gaffey and M.S. Kelley are
Visiting Astronomers at the IRTF which is operated by the Univ. of
Hawai'i under contract to the National Aeronautics and Space
Administration.
Because of the objectively existing causes, such as an irregular shape of a
celestial body, the lack of the satellites, the low values of albedo at
moderate sizes, and a large remoteness from the Sun, creating a more exact the
physical properties database of trans-Neptunian dwarf planets in comparison
with existing that continues to remain a problem. We offer a new calculation
procedure of the physical properties of these objects involving earlier unknown
the relationships harmonizing these properties. It allows us to conjecture of
they are a group of uniform celestial bodies by their origin beyond the Kuiper
belt. The calculated physical properties of these dwarf planets are in a good
agreement with the estimates received from observational data and can form the
basis for support the validity of this improved physical properties database.
Ceres appears likely to be differentiated and to have experienced planetary evolution processes. This conclusion is based
on current geophysical observations and thermodynamic modeling of Ceres’ evolution. This makes Ceres similar to a small planet,
and in fact it is thought to represent a class of objects from which the inner planets formed. Verification of Ceres’ state
and understanding of the many steps in achieving it remains a major goal. The Dawn spacecraft and its instrument package are
on a mission to observe Ceres from orbit. Observations and potential results are suggested here, based on number of science
questions.
KeywordsDawn–Ceres–Evolution of ice-silicate bodies
To date, no accretion model has succeeded in reproducing all observed
constraints in the inner Solar System. These constraints include 1) the orbits,
in particular the small eccentricities, and 2) the masses of the terrestrial
planets -- Mars' relatively small mass in particular has not been adequately
reproduced in previous simulations; 3) the formation timescales of Earth and
Mars, as interpreted from Hf/W isotopes; 4) the bulk structure of the asteroid
belt, in particular the lack of an imprint of planetary embryo-sized objects;
and 5) Earth's relatively large water content, assuming that it was delivered
in the form of water-rich primitive asteroidal material. Here we present
results of 40 high-resolution (N=1000-2000) dynamical simulations of late-stage
planetary accretion with the goal of reproducing these constraints, although
neglecting the planet Mercury. We assume that Jupiter and Saturn are
fully-formed at the start of each simulation, and test orbital configurations
that are both consistent with and contrary to the "Nice model." We find that a
configuration with Jupiter and Saturn on circular orbits forms low-eccentricity
terrestrial planets and a water-rich Earth on the correct timescale, but Mars'
mass is too large by a factor of 5-10 and embryos are often stranded in the
asteroid belt. A configuration with Jupiter and Saturn in their current
locations but with slightly higher initial eccentricities (e = 0.07-0.1)
produces a small Mars, an embryo-free asteroid belt, and a reasonable Earth
analog but rarely allows water delivery to Earth. None of the configurations we
tested reproduced all the observed constraints. (abridged)
The possibility that Mercury might once have been satellite of a Venus, suggested by a number of anomalies, is investigated by a series of numerical computer experiments. Tidal interaction between Mercury and Venus would result in the escape of Mercury into a solar orbit. Only two escape orbits are possible, one exterior and one interior to the Venus orbit. For the interior orbit, subsequent encounters are sufficiently distant to avoid recapture or large perturbations. The perihelion distance of Mercury tends to decrease, while the orientation of perihelion librates for the first few thousand revolutions. If dynamical evolution or nonconservative forces were large enough in the early solar system, the present semimajor axes could have resulted. The theoretical minimum quadrupole moment of the inclined rotating Sun would rotate the orbital planes out of coplanarity. Secular perturbations by the other planets would evolve the eccentricity and inclination of Mercury's orbit through a range of possible configurations, including the present orbit. Thus the conjecture that Mercury is an escaped satellite of Venus remains viable, and is rendered more attractive by our failure to disprove it dynamically.
A genetic study of the Ceres asteroid family
- M S Kelly
- M J Gaffey
Kelly, M. S., Gaffey, M. J., 1996. A genetic study of the Ceres asteroid family. Bull. Am.
Astron. Soc. 28, 1097.