220 research outputs found
Modelling the brightness increase signature due to asteroid collisions
We have developed a model to predict the post-collision brightness increase
of sub-catastrophic collisions between asteroids and to evaluate the likelihood
of a survey detecting these events. It is based on the cratering scaling laws
of Holsapple and Housen (2007) and models the ejecta expansion following an
impact as occurring in discrete shells each with their own velocity. We
estimate the magnitude change between a series of target/impactor pairs,
assuming it is given by the increase in reflecting surface area within a
photometric aperture due to the resulting ejecta. As expected the photometric
signal increases with impactor size, but we find also that the photometric
signature decreases rapidly as the target asteroid diameter increases, due to
gravitational fallback. We have used the model results to make an estimate of
the impactor diameter for the (596) Scheila collision of D=49-65m depending on
the impactor taxonomy, which is broadly consistent with previous estimates. We
varied both the strength regime (highly porous and sand/cohesive soil) and the
taxonomic type (S-, C- and D-type) to examine the effect on the magnitude
change, finding that it is significant at early stages but has only a small
effect on the overall lifetime of the photometric signal. Combining the results
of this model with the collision frequency estimates of Bottke et al. (2005),
we find that low-cadence surveys of approximately one visit per lunation will
be insensitive to impacts on asteroids with D<20km if relying on photometric
detections
Search for Dust Emission from (24) Themis Using the Gemini-North Telescope
We report the results of a search for a dust trail aligned with the orbit
plane of the large main-belt asteroid (24) Themis, which has been reported to
have water ice frost on its surface. Observations were obtained with the GMOS
instrument on the Gemini-North Observatory in imaging mode, where we used a
chip gap to block much of the light from the asteroid, allowing us to take long
exposures while avoiding saturation by the object. No dust trail is detected
within 2' of Themis to a 3-sigma limiting surface brightness magnitude of 29.7
mag/arcsec^2, as measured along the expected direction of the dust trail.
Detailed consideration of dust ejection physics indicates that particles large
enough to form a detectable dust trail were unlikely to be ejected as a result
of sublimation from an object as large as Themis. We nonetheless demonstrate
that our observations would have been capable of detecting faint dust emission
as close as 20" from the object, even in a crowded star field. This approach
could be used to conduct future searches for sublimation-generated dust
emission from Themis or other large asteroids closer to perihelion than was
done in this work. It would also be useful for deep imaging of collisionally
generated dust emission from large asteroids at times when the visibility of
dust features are expected to be maximized, such as during orbit plane
crossings, during close approaches to the Earth, or following detected impact
events.Comment: 11 pages, 4 figures, accepted for publication in PAS
Spectroscopy of D-type asteroids
We have performed a spectroscopic survey of 19 D-type asteroids. Comparison with previous photometry shows excellent agreement. Although the majority have similar colors to cometary nuclei, no cometary emission bands were present in any of the spectra. Absorption bands sporadically appearing were apparently due to stellar objects, and no features inherent to the asteroids were observed
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua
During the formation and evolution of the Solar System, significant numbers of cometary and asteroidal bodies were ejected into interstellar space. It is reasonable to expect that the same happened for planetary systems other than our own. Detection of such interstellar objects would allow us to probe the planetesimal formation processes around other stars, possibly together with the effects of long-term exposure to the interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known interstellar object, discovered by the Pan-STARRS1 telescope in October 2017. The discovery epoch photometry implies a highly elongated body with radii of ~ 200 × 20 m when a comet-like geometric albedo of 0.04 is assumed. The observable interstellar object population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity of 'Oumuamua implies a lack of surface ice. Here, we report spectroscopic characterization of ‘Oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer Solar System. We show that this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure. An internal icy composition cannot therefore be ruled out by the lack of activity, even though ‘Oumuamua passed within 0.25 au of the Sun
Extreme asteroids in the Pan-STARRS 1 Survey
Using the first 18 months of the Pan-STARRS 1 survey we have identified 33
candidate high-amplitude objects for follow-up observations and carried out
observations of 22 asteroids. 4 of the observed objects were found to have
observed amplitude mag. We find that these high amplitude
objects are most simply explained by single rubble pile objects with some
density-dependent internal strength, allowing them to resist mass shedding even
at their highly elongated shapes. 3 further objects although below the cut-off
for 'high-amplitude' had a combination of elongation and rotation period which
also may require internal cohesive strength, depending on the density of the
body. We find that none of the 'high-amplitude asteroids' identified here
require any unusual cohesive strengths to resist rotational fission. 3
asteroids were sufficiently observed to allow for shape and spin pole models to
be determined through light curve inversion. 45864 was determined to have
retrograde rotation with spin pole axes and asteroid 206167 was found to have best fit spin
pole axes , . An additional
object not initially measured with mag, 49257, was determined to
have a shape model which does suggest a high-amplitude object. Its spin pole
axes were best fit for values .
In the course of this project to date no large super-fast rotators ( h) have been identified.Comment: 31 pages; accepted by A
174P/Echeclus and its Blue Coma Observed Post-outburst
It has been suggested that centaurs may lose their red surfaces and become
bluer due to the onset of cometary activity, but the way in which cometary
outbursts affect the surface composition and albedo of active centaurs is
poorly understood. We obtained consistent visual-near-infrared (VNIR)
reflectance spectra of the sporadically active centaur 174P/Echeclus during a
period of inactivity in 2014 and six weeks after its outburst in 2016 to see if
activity had observably changed the surface properties of the nucleus. We
observed no change in the surface reflectance properties of Echeclus following
the outburst compared to before, indicating that, in this case, any surface
changes due to cometary activity were not sufficiently large to be observable
from Earth. Our spectra and post-outburst imaging have revealed, however, that
the remaining dust coma is not only blue compared to Echeclus, but also bluer
than solar, with a spectral gradient of -7.7+/-0.6% per 0.1 micron measured
through the 0.61-0.88 micron wavelength range that appears to continue up to a
wavelength of around 1.3 micron before becoming neutral. We conclude that the
blue visual color of the dust is likely not a scattering effect, and instead
may be indicative of the dust's carbon-rich composition. Deposition of such
blue, carbon-rich, comatic dust onto a red active centaur may be a mechanism by
which its surface color could be neutralized.Comment: 15 pages, 4 figures, 3 tables, AJ accepted, in pres
The Transient Jupiter Trojan-Like Orbit of P/2019 LD2 (ATLAS)
Comet P/2019 LD2 has orbital elements currently resembling those of a Jupiter
Trojan, and therefore superficially appears to represent a unique opportunity
to study the volatile content and active behavior of a member of this
population for the first time. However, numerical integrations show that it was
previously a Centaur before reaching its current Jupiter Trojan-like orbit in
2018 July, and is expected to return to being a Centaur in 2028 February,
before eventually becoming a Jupiter-family comet in 2063 February. The case of
P/2019 LD2 highlights the need for mechanisms to quickly and reliably
dynamically classify small solar system bodies discovered in current and
upcoming wide-field surveys.Comment: 7 pages, 3 figures. Accepted for publication in Icaru
The proposed Caroline ESA M3 mission to a Main Belt Comet
We describe Caroline, a mission proposal submitted to the European Space Agency in 2010 in response to the Cosmic Visions M3 call for medium-sized missions. Caroline would have travelled to a Main Belt Comet (MBC), characterizing the object during a flyby, and capturing dust from its tenuous coma for return to Earth. MBCs are suspected to be transition objects straddling the traditional boundary between volatile–poor rocky asteroids and volatile–rich comets. The weak cometary activity exhibited by these objects indicates the presence of water ice, and may represent the primary type of object that delivered water to the early Earth. The Caroline mission would have employed aerogel as a medium for the capture of dust grains, as successfully used by the NASA Stardust mission to Comet 81P/Wild 2. We describe the proposed mission design, primary elements of the spacecraft, and provide an overview of the science instruments and their measurement goals. Caroline was ultimately not selected by the European Space Agency during the M3 call; we briefly reflect on the pros and cons of the mission as proposed, and how current and future mission MBC mission proposals such as Castalia could best be approached
A laboratory study of water ice erosion by low-energy ions
Water ice covers the surface of various objects in the outer Solar system.
Within the heliopause, surface ice is constantly bombarded and sputtered by
energetic particles from the solar wind and magnetospheres. We report a
laboratory investigation of the sputtering yield of water ice when irradiated
at 10 K by 4 keV singly (13C+, N+, O+, Ar+) and doubly charged ions (13C2+,
N2+, O2+). The experimental values for the sputtering yields are in good
agreement with the prediction of a theoretical model. There is no significant
difference in the yield for singly and doubly charged ions. Using these yields,
we estimate the rate of water ice erosion in the outer Solar system objects due
to solar wind sputtering. Temperature-programmed desorption of the ice after
irradiation with 13C+ and 13C2+ demonstrated the formation of 13CO and 13CO2,
with 13CO being the dominant formed species.Comment: 10 pages, 7 figures, 3 tables, accepted for publication at MNRA
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