73 research outputs found
Rotationally Resolved Spectroscopy of Asteroid Pairs: No Spectral Variation Suggests Fission is followed by Settling of Dust
We examine the spectral properties of asteroid pairs that were disrupted in
the last 2 Myrs to examine whether the site of the fission can be revealed. We
studied the possibility that the sub-surface material, perhaps on one
hemisphere, has spectral characteristics differing from the original weathered
surface, by performing rotationally-resolved spectroscopic observations to look
for local variations as the asteroid rotates. We observed 11 asteroids in pairs
in the near-IR and visible range. Photometry was also conducted to determine
the rotational phases of a spectrum on the asteroid lightcurves. We do not
detect any rotational spectral variations within the signal-to-noise, which
allow us to constrain the extent of any existing surface heterogeneity.
For each observed spectrum of a longitudinal segment of an asteroid, we
estimate the maximal size of an un-detected "spot" with a spectral signature
different than the average. For 5 asteroids the maximal diameter of such a spot
is smaller by a factor of two than the diameter of the secondary member.
Therefore, the site of the fission is larger than any area with a unique
spectral parameters and the site of the fission does not have a unique
spectrum. In the case of an S-complex asteroid, where the site of fission is
expected to present non-weathered spectra, a lack of a fission spot can be
explained if the rotational-fission process is followed by the spread of dust
that re-accumulates on the primary asteroid and covers it homogeneously. This
is demonstrated for the young asteroid 6070 that presents an Sq-type spectrum
while its inner material, that is presumably revealed on the surface of its
secondary member, 54827, has a fresher, Q-type spectrum. The spread of dust
observed in the disruption event of asteroid P/2013 R3, might be an example of
such a process and an indication that it was indeed formed in a
rotational-fission event.Comment: 16 pages, 15 figures, 6 Tables. Accepted for publication in Icaru
Observations of "Fresh" and Weathered Surfaces on Asteroid Pairs and Their Implications on the Rotational-Fission Mechanism
The rotational-fission of a rubble-pile asteroid can result in an "asteroid
pair", two un-bound asteroids sharing similar orbits. This mechanism might
exposes material that previously had never have been exposed to the weathering
conditions of space. Therefore, the surfaces of asteroid pairs offer the
opportunity to observe non-weathered fresh spectra. We report near-IR
spectroscopic observations of 31 asteroids in pairs. We analyze their spectral
slopes, 1 {\mu}m absorption band, taxonomy, and estimate the time elapsed since
their separation. Analyzing the 19 S-complex objects in our sample, we find two
fresh Q-type asteroids that are the first of their kind to be observed in the
main-belt over the full visible and near-IR range. This solidly demonstrates
that Q-type objects are not limited to the NEA population. The pairs in our
sample present a range of fresh and weathered surfaces with no clear evidence
for a correlation with the ages of the pairs. However, our sample includes old
pairs (1 to 2 My) that present low spectral slopes. This illustrates a
timescale of at least ~2 My before an object develops high spectral slope that
is typical for S-type asteroids.
We discuss mechanisms that explain the existence of weathered pairs with
young dynamical ages and find that the "secondary fission" model (Jacobson &
Scheeres 2011) is the most robust with our observations since: 1) the secondary
members in our sample present fresh parameters that tend to be fresher than
their weathered primaries; 2) most of the fresh pairs in our sample have low
size ratios between the secondary and the primary; 3) 33% of the primaries in
our sample are fresh, similar to the prediction set by this model; 4) known
satellites orbit two of the pairs in our sample with low size ratio and fresh
surface; 5) there is no correlation between the weathering state and the
primary shape as predicted by other models.Comment: 19 pages, 17 figures, 4 tables. Accepted to Icaru
Unexpected D-type Interlopers in the Inner Main Belt
Very red featureless asteroids (spectroscopic D-types) are expected to have
formed in the outer solar system far from the sun. They comprise the majority
of asteroids in the Jupiter Trojan population, and are also commonly found in
the outer main belt and among Hildas. The first evidence for D-types in the
inner and middle parts of the main belt was seen in the Sloan Digital Sky
Survey (SDSS). Here we report follow-up observations of SDSS D-type candidates
in the near-infrared. Based on follow up observations of 13 SDSS D-type
candidates, we find a ~20% positive confirmation rate. Known inner belt D-types
range in diameter from roughly 7 to 30 kilometers. Based on these detections we
estimate there are ~100 inner belt D-types with diameters between 2.5 and 20km.
The lower and upper limits for total mass of inner belt D-types is 2x
kg to 2x kg which represents 0.01% to 0.1% of the mass of the inner
belt. The inner belt D-types have albedos at or above the upper end typical for
D-types which raises the question as to whether these inner belt bodies
represent only a subset of D-types, they have been altered by external factors
such as weathering processes, or if they are compositionally distinct from
other D-types. All D-types and candidates have diameters less than 30km, yet
there is no obvious parent body in the inner belt. Dynamical models have yet to
show how D-types originating from the outer solar system could penetrate into
the inner reaches of the Main Belt under current scenarios of planet formation
and subsequent Yarkovsky drift.Comment: 16 pages, 3 figures, 4 tables -- accepted for publication in Icaru
Astrometric detection of binary asteroids
Binary asteroids probe thermal-radiation effects on the main-belt asteroids'
evolution. We discuss the possibility of detecting binary minor planet systems
by the astrometric wobble of the center-of-light around the center-of-mass.
This method enables the exploration of the phase-space of binary asteroids,
which is difficult to explore using common detection techniques. We describe a
forward model that projects the center-of-light position with respect to the
center-of-mass, as it is seen by the observer. We study the performance of this
method using simulated Gaia-like data. We apply the astrometric method to a
subset of the Gaia DR2 Solar System catalog and find no significant evidence of
binary asteroids. This is likely because the Gaia DR2 removed astrometric
outliers, which in our case may be due to astrophysical signals. Applying this
method to binary asteroid (4337) Arecibo, for which Gaia DR3 reported a
possible astrometric signal with a period of P = 32.85+/-0.38 hr, reveals a
possible 2.2-sigma solution with a period of 16.26 hr (about half the reported
period). We find a small, marginally significant, excess of astrometric noise
in the known binary asteroid population from Pravec et al. relative to the
entire asteroid population in the Gaia DR2 Solar System catalog. We also
discuss some caveats like precession and asteroid rotation.Comment: Submitted to MNRA
(3200) Phaethon: Bulk density from Yarkovsky drift detection
The recent close approach of the NEA (3200) Phaethon offered a rare
opportunity to obtain high-quality observational data. We used the newly
obtained optical light curves to improve the spin and shape model of Phaethon
and to determine its surface physical properties derived by thermophysical
modeling. We also used the available astrometric observations of Phaethon,
including those obtained by the Arecibo radar and the Gaia spacecraft, to
constrain the secular drift of the orbital semimajor axis. This constraint
allowed us to estimate the bulk density by assuming that the drift is dominated
by the Yarkovsky effect. We used the convex inversion model to derive the 3D
shape model of Phaethon, and a detailed numerical approach for an accurate
analysis of the Yarkovsky effect. We obtained a unique solution for Phaethon's
pole orientation at ecliptic longitude and latitude
(uncertainty of ), and confirm the previously reported
thermophysical properties ( km, SI). Phaethon
has a top-like shape with possible north-south asymmetry. The characteristic
size of the regolith grains is 1-2 cm. The orbit analysis reveals a secular
drift of the semimajor axis of au Myr. With
the derived volume-equivalent size of 5.1~km, the bulk density is
g cm. If the size is slightly larger km, as
suggested by radar data, would decrease to g cm. We
further investigated the suggestion that Phaethon may be in a cluster with
asteroids (155140) 2005 UD and (225416) 1999 YC that was formed by rotational
fission of a critically spinning parent body. Phaethon's is consistent
with typical values for large ( km) C-complex asteroids and supports its
association with asteroid (2) Pallas. These findings render a cometary origin
unlikely for Phaethon.Comment: Accepted for publication in A&
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