75 research outputs found
Asteroid Systems: Binaries, Triples, and Pairs
In the past decade, the number of known binary near-Earth asteroids has more
than quadrupled and the number of known large main belt asteroids with
satellites has doubled. Half a dozen triple asteroids have been discovered, and
the previously unrecognized populations of asteroid pairs and small main belt
binaries have been identified. The current observational evidence confirms that
small (<20 km) binaries form by rotational fission and establishes that the
YORP effect powers the spin-up process. A unifying paradigm based on rotational
fission and post-fission dynamics can explain the formation of small binaries,
triples, and pairs. Large (>20 km) binaries with small satellites are most
likely created during large collisions.Comment: 31 pages, 12 figures. Chapter in the book ASTEROIDS IV (in press
(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&
Libration-induced Orbit Period Variations Following the DART Impact
The Double Asteroid Redirection Test (DART) mission will be the first test of a kinetic impactor as a means of planetary defense. In late 2022, DART will collide with Dimorphos, the secondary in the Didymos binary asteroid system. The impact will cause a momentum transfer from the spacecraft to the binary asteroid, changing the orbit period of Dimorphos and forcing it to librate in its orbit. Owing to the coupled dynamics in binary asteroid systems, the orbit and libration state of Dimorphos are intertwined. Thus, as the secondary librates, it also experiences fluctuations in its orbit period. These variations in the orbit period are dependent on the magnitude of the impact perturbation, as well as the systemâs state at impact and the moments of inertia of the secondary. In general, any binary asteroid system whose secondary is librating will have a nonconstant orbit period on account of the secondaryâs fluctuating spin rate. The orbit period variations are typically driven by two modes: a long period and a short period, each with significant amplitudes on the order of tens of seconds to several minutes. The fluctuating orbit period offers both a challenge and an opportunity in the context of the DART mission. Orbit period oscillations will make determining the post-impact orbit period more difficult but can also provide information about the systemâs libration state and the DART impact
Spin vector and shape of (6070) Rheinland and their implications
Main belt asteroids (6070) Rheinland and (54827) 2001NQ8 belong to a small
population of couples of bodies which reside on very similar heliocentric
orbits. Vokrouhlicky & Nesvorny (2008, AJ 136, 280) promoted a term "asteroid
pairs", pointing out their common origin within the past tens to hundreds of
ky. Previous attempts to reconstruct the initial configuration of Rheinland and
2001NQ8 at the time of their separation have led to the prediction that
Rheinland's rotation should be retrograde. Here we report extensive photometric
observations of this asteroid and use the lightcurve inversion technique to
directly determine its rotation state and shape. We confirm the retrograde
sense of rotation of Rheinland, with obliquity value constrained to be >= 140
deg. The ecliptic longitude of the pole position is not well constrained as
yet. The asymmetric behavior of Rheinland's lightcurve reflects a sharp,
near-planar edge in our convex shape representation of this asteroid. Our
calibrated observations in the red filter also allow us to determine and values of the H-G system. With the
characteristic color index for the S-type asteroids, we
thus obtain for the absolute magnitude of (6070) Rheinland.
This a significantly larger value than previously obtained from analysis of the
astrometric survey observations. We next use the obliquity constraint for
Rheinland to eliminate some degree of uncertainty in the past propagation of
its orbit. This is because the sign of the past secular change of its semimajor
axis due to the Yarkovsky effect is now constrained. Determination of the
rotation state of the secondary component, asteroid (54827) 2001NQ8, is the key
element in further constraining the age of the pair and its formation process.Comment: Published in AJ, 28 pages, 4 figures, 2 table
Dimorphos's Orbit Period Change and Attitude Perturbation due to Its Reshaping after the DART Impact
On 2022 September 26 (UTC), NASA's Double Asteroid Redirection Test (DART) mission achieved a successful impact on Dimorphos, the secondary component of the near-Earth binary asteroid system (65803) Didymos. Subsequent ground-based observations suggest a significant reshaping of Dimorphos, with its equatorial axis ratio changing from 1.06 to âŒ1.3. Here we report the effects of this reshaping event on Dimorphos's orbit and attitude. Given the reported reshaping magnitude, our mutual dynamics simulations show that approximately 125 s of the observed 33 minute orbit period change after the DART impact may have resulted from reshaping. This value, however, is sensitive to the precise values of Dimorphos's post-impact axis ratios and may vary by up to 2 times that amount, reaching approximately 250 s within the current uncertainty range. While the rotational state of the body is stable at the currently estimated axis ratios, even minor changes in these ratios or the introduction of shape asymmetry can render its attitude unstable. The perturbation to Dimorphos's orbital and rotational state delivered by the impact directly, combined with any reshaping, leads to a strong possibility for a tumbling rotation state. To accurately determine the momentum enhancement factor (ÎČ) through measurements by the European Space Agency's Hera spacecraft and to evaluate the effectiveness of the kinetic deflection technique for future planetary defense initiatives, the effects of reshaping should not be overlooked.This work was supported in part by the DART mission, NASA contract 80MSFC20D0004 to JHU/APL. R.N. acknowledges support from NASA/FINESST (NNH20ZDA001N). S.D.R. and M.J. acknowledge support from the Swiss National Science Foundation (project number 200021_207359). P.M. acknowledges funding support from the French Space Agency CNES and The University of Tokyo. P.P. acknowledges support from the grant Agency of the Czech Republic, grant 23-04946S. S.R.S. acknowledges support from the DART Participating Scientist Program, grant No. 80NSSC22K0318. A.C.B. and P.Y.L. acknowledge funding by the NEO-MAPP project 717 GA 870377, EC H2020-SPACE-718 2018-2020/H2020-SPACE-2019, and by MICINN (Spain) PGC2021, PID2021-125883NB-C21. P.Y.L. acknowledges funding from the European Space Agency OSIP contract N.4000136043/21/NL/GLC/my. A portion of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (No. 80NM0018D0004)
In-Space Utilisation of Asteroids::âAnswers to Questions from the Asteroid Minersâ
The aim of the Asteroid Science Intersections with In-ÂSpace Mine Engineering (ASIME) 2016 conference on September 21-Ââ22, 2016 in Luxembourg City wasto provide an environment for the detailed discussion of the specific properties of asteroids, with the engineering needs of space missions that utilize asteroids.The ASIME 2016 Conference produced a layered record of discussions from theasteroid scientists and the asteroid miners to understand each otherâs key concerns and to address key scientific questions from the asteroid mining companies: Planetary Resources, Deep Space Industries and TransAstra. These Questions were the focus of the two day conference, were addressed byscientists inside and outside of the ASIME Conference and are the focus ofthis White Paper.The Questions from the asteroid mining companies have been sorted into the three asteroid science themes: 1) survey, 2) surface and 3) subsurface and 4)Other. The answers to those Questions have been provided by the scientists with their conference presentations or edited directly into an early open-Ââaccess collaborative Google document (August 2016-ÂâOctober 2016), or inserted byA. Graps using additional reference materials. During the ASIME 2016 last two-Ââhours, the scientists turned the Questions from the Asteroid Miners around by presenting their own key concerns: Questions from the Asteroid Scientists. These answers in this White Paper will point to the Science Knowledge Gaps (SKGs) for advancing the asteroid in-Ââspace resource utilisation domain
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