J/A+A/562/A48 Light curves of asteroid (25143) Itokawa (Lowry+, 2014)
The internal structure of asteroid (25143) Itokawa as revealed by detection
of YORP spin-up.
Lowry S.C., Weissman P.R., Duddy S.R., Rozitis B., Fitzsimmons A.,
Green S.F., Hicks M.D., Snodgrass C., Wolters S.D., Chesley S.R.,
Pittichova J., van Oers. P.
<Astron. Astrophys. 562, A48 (2014)>
=2014A&A...562A..48L 2014A&A...562A..48L
ADC_Keywords: Minor planets ; Photometry
Keywords: methods: observational -
minor planets, asteroids: individual: (25143) Itokawa -
techniques: photometric - radiation mechanisms: thermal
Abstract:
Near-Earth asteroid (25143) Itokawa was visited by the Hayabusa
spacecraft in 2005, resulting in a highly detailed shape and surface
topography model. This model has led to several predictions for the
expected radiative torques on this asteroid, suggesting that its spin
rate should be decelerating.
To detect changes in rotation rate that may be due to YORP-induced
radiative torques, which in turn may be used to investigate the
interior structure of the asteroid.
Through an observational survey spanning 2001 to 2013 we obtained
rotational lightcurve data at various times over the last five close
Earth-approaches of the asteroid. We applied a
polyhedron-shape-modelling technique to assess the spin-state of the
asteroid and its long term evolution. We also applied a detailed
thermophysical analysis to the shape model determined from the
Hayabusa spacecraft.
We have successfully measured an acceleration in Itokawa's spin rate
of dw/dt=(3.54±0.38)*10-8rad/day2, equivalent to a decrease of
its rotation period of ∼45ms/yr. From the thermophysical analysis we
find that the center-of-mass for Itokawa must be shifted by ∼21m
along the long-axis of the asteroid to reconcile the observed YORP
strength with theory.
This can be explained if Itokawa is composed of two separate bodies
with very different bulk densities of 1750±110kg/m3 and
2850±500kg/m3, and was formed from the merger of two separate
bodies, either in the aftermath of a catastrophic disruption of a
larger differentiated body, or from the collapse of a binary system.
We therefore demonstrate that an observational measurement of
radiative torques, when combined with a detailed shape model, can
provide insight into the interior structure of an asteroid.
Futhermore, this is the first measurement of density inhomogeneity
within an asteroidal body, that reveals significant internal structure
variation. A specialised spacecraft is normally required for this.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 55 10 *Observational log and geometry for all optical
photometry
table2.dat 29 923 Photometry
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Note on table1.dat: All images were taken in either the broadband V- or R-filter
(λc(V)=550nm, λc(R)=657nm).
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See also:
J/A+A/509/A94 : Lightcurves of 14 NEAs (Kwiatkowski+, 2010)
J/A+A/511/A49 : Lightcurves of 12 NEAs (Kwiatkowski+, 2010)
J/A+A/550/L11 : Near-Earth Asteroid 162173 (1999 JU3) lightcurves (Kim+ 2013)
J/A+A/561/A45 : Asteroid (341843) 2008 EV5 WISE light curves (Ali-Lagoa+, 2014)
object.dat :
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Code Name H i e a
mag deg AU
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25143 Itokawa 19.20 1.621593 0.28020346 1.32404946
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Tel Telescope (1)
8- 9 I2 --- LC [1/10] Light curve segment number
11- 18 A8 "YY/MM/DD" Date Date (first day of the observation)
19 A1 --- --- [-]
20- 21 I2 d end ? Last day of the observation
23- 26 F4.2 AU Rh Distance from object to the Sun
28- 31 F4.2 AU delta Distance from object to the Earth δ
33- 36 F4.1 deg alpha Solar phase angle α
38- 41 F4.1 deg Aspect Aspect angle (angle between observer
line-of-sight and the known rotation axis
of the asteroid)
43- 45 I3 --- o_LC Number of data points
47- 50 F4.1 deg oPhase Phase offset (φYORP)
52 A1 --- l_oPhase Limit flag on e_oPhase
53- 55 F3.1 deg e_oPhase 1 sigma error on oPhase
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Note (1): Telescope key as follows:
PAL60 = Palomar Observatory 60-inch Telescope (California, USA)
TMO = Table Mountain Observatory (California, USA)
S60 = Steward Observatory 60-inch Telescope (Arizona, USA)
S90 = Steward Observatory 90-inch Bok Telescope (Arizona, USA)
LT = 2m Liverpool Telescope (La Palma, Spain),
NTT = European Southern Observatory 3.5m New Technology Telescope (Chile)
INT = 2.5m Isaac Newton Telescope (La Palma, Spain)
PAL200 = Palomar Observatory 5m Hale Telescope (California, USA)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- LC [1/10] Lightcurve segment number (1)
4- 16 F13.5 d JD Julian Date
18- 23 F6.3 mag Rmag Relative magnitude
25- 29 F5.3 mag e_Rmag 1-σ uncertainty in relative magnitude
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Note (1): There are 10 lightcurve segments included in the file (see Table 1).
Also note that there may be several nights of data in any given lightcurve
segment.
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Acknowledgements:
Stephen Lowry, S.C.Lowry(at)kent.ac.uk
(End) Patricia Vannier [CDS] 09-Jan-2014