J/A+A/650/A64 Mars moon ephemerides for 14yrs Mars Express data (Lainey+, 2021)
Mars moon ephemerides after 14 years of Mars Express data.
Lainey V., Pasewaldt A., Robert V., Rosenblatt P., Jaumann R., Oberst J.,
Roatsch T., Willner K., Ziese R., Thuillot W.
<Astron. Astrophys. 650, A64 (2021)>
=2021A&A...650A..64L 2021A&A...650A..64L (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Planets ; Ephemerides
Keywords: ephemerides - astrometry - celestial mechanics
Abstract:
The Mars Express (MEX) mission has been successfully operated around
Mars since 2004. Among many results, MEX has provided some of the most
accurate astrometric data of the two Mars moons, Phobos and Deimos. We
present new ephemerides of the Mars moons benefitting from all
previously published astrometric data to the most recent MEX SRC data.
Observations from 1877 until 2018 and including spacecraft
measurements from Mariner 9 to MEX were included. Assuming a
homogeneous interior, we fitted the forced libration amplitude of
Phobos simultaneously with the Martian tidal k2/Q ratio and the
initial state of the moons. Our solution of the physical libration
1.09±0.01 degrees deviates notably from the homogeneous solution.
Considering the very low error bar, however, this may essentially
suggest the necessity to consider higher order harmonics with an
improved rotation model in the future. While most data could be
successfully fitted, we found a disagreement between the Mars
Reconnaissance Orbiter and the Mars Express astrometric data at the
kilometer level, probably associated with a biased phase correction.
The current solution precision is expected at the level of a few
hundred meters for Phobos and several hundred meters for Deimos for
the coming years. The real accuracy of our new ephemerides will have
to be confirmed by comparison with independent observational means.
Description:
Table 2: Mean (ν) and standard deviation (σ) on separation
s and position angle p (multiplied by the separation) in seconds
of degrees for each satellite. N is the number of observations by
satellite (one number per coordinate). The year appearing next to each
observatory name corresponds to the observed Mars opposition.
Table 3: Mean (ν) and standard deviation (σ) on right
ascension and declination in seconds of degrees for each satellite.
N is the number of observations by satellite.
Table 4: Mean (ν) and standard deviation (σ) on right
ascension and declination for each satellite. Both angles are
multiplied by the distance spacecraft-moon to obtain kilometers. N
is the number of observations by satellite. In the Pasewaldt et al.
(2015) publication positions of Phobos have been determined using
control point (CP) and/or limb point (LF) measurements. The former are
based on the satellite's control network, a set of identifiable
surface features well-distributed over the body's surface and defining
its reference system. Recent MEX SRC measurements have been
distinguished into observations made during linear and non-linear
pointing variations. If the observations' pre-fit residuals deviated
by more than three sigma from the mean value, they have been
additionally categorised as an outlier. In case of only a few outliers
it could not be clarified whether they have been related to non-linear
variations in pointing or not. Some measurements are based on fits of
the shape model-derived limb to only very short limb point arcs in the
image (see also subsection 3.2.1).
Table 5: Mean (ν) and standard deviation (σ) on sample and
line in pixel and kilometer for each satellite. N is the number of
observations by satellite. MRO (single) gathers data where only one
moon was observable at a time.
Table 6: Initial conditions and related uncertainties of Phobos and
Deimos in the ICRF after fit at initial epoch J2000 (Julian day
2451545.0). Units are km and km/sec. All digits have been kept for
reproducibility of our results.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 129 18 Mean and standard deviation on separation
and position angle
table3.dat 131 36 Mean and standard deviation on right ascension
and declination for each satellite
table4.dat 131 36 *Mean and standard deviation on right ascension
and declination for each satellite
table5.dat 87 4 Mean and standard deviation on sample and line
in pixel and kilometer for each satellite
table6.dat 160 2 *Initial conditions and related uncertainties of
Phobos and Deimos in the ICRF after fit at
initial epoch J2000 (Julian day 2451545.0)
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Note on table4.dat: In the Pasewaldt et al. (2015, Cat. J/A+A/580/A28)
publication positions of Phobos have been determined using control point (CP)
and/or limb point (LF) measurements. The former are based on the satellite's
control network, a set of identifiable surface features well-distributed over
the body's surface and defining its reference system. Recent MEX SRC
measurements have been distinguished into observations made during linear and
non-linear pointing variations. If the observations' pre-fit residuals
deviated by more than three sigma from the mean value, they have been
additionally categorised as an outlier. In case of only a few outliers it
could not be clarified whether they have been related to non-linear
variations in pointing or not. Some measurements are based on fits of the
shape model-derived limb to only very short limb point arcs in the image
(see also subsection 3.2.1).
Note on table6.dat: All digits have been kept for reproducibility of our
results.
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See also:
J/A+A/488/361 : Phobos Mars Express astrometric observations (Willner+, 2008)
J/A+A/545/A144 : Astrometric observations of Deimos (Pasewaldt+, 2012)
J/A+A/572/A104 : Astrometric obs. of Phobos and Deimos in 1971 (Robert+, 2014)
J/A+A/580/A28 : Astrometric observations of Phobos (Pasewaldt+, 2015)
J/A+A/582/A36 : USNO Martian observations (Robert+, 2015)
J/A+A/614/A15 : Mars Express astrometric obs. of Martian moons (Ziese+, 2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 84 A84 --- Obs Observations (1)
86- 92 F7.4 arcsec Sep [] Mean separation
94- 99 F6.4 arcsec s_Sep Standard deviation on separation
101-107 F7.4 arcsec PA [] Mean position angle
(multiplied by the separation)
109-114 F6.4 arcsec s_PA Standard deviation on position angle
116-118 I3 --- o_Sep Number of observations by satellite
for separation
120-122 I3 --- o_PA Number of observations by satellite
for position angle
124-129 A6 --- Sat Satellite, Phobos or Deimos
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Note (1): The year appearing next to each observatory name corresponds to the
observed Mars opposition.
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Byte-by-byte Description of file: table3.dat table4.dat
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Bytes Format Units Label Explanations
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1- 84 A84 --- Obs Observations
86- 92 F7.4 arcsec RAcosDE Mean right ascension, RA*cosDE
94-100 F7.4 arcsec s_RAcosDE Standard deviation on right ascension
(RA*cosDE)
102-108 F7.4 arcsec DE Mean declination
110-116 F7.4 arcsec s_DE Standard deviation on declination
118-120 I3 --- o_RAcosDE Number of observations by satellite
for RAcosDE
122-124 I3 --- o_DE Number of observations by satellite for DE
126-131 A6 --- Sat Satellite, Phobos or Deimos
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Obs Observations (1)
14- 20 F7.4 pix samplep Mean on sample in pixel
22- 28 F7.4 km samplek Mean on sample in kilometer
30- 35 F6.4 pix s_samplep Standard deviation on sample in pixel
37- 42 F6.4 km s_samplek Standard deviation on sample in kilometer
44- 50 F7.4 pix linep Mean line in pixel
52- 58 F7.4 km linek Mean line in kilometer
60- 65 F6.4 pix s_linep Standard deviation on line in pixel
67- 72 F6.4 km s_linek Standard deviation on line in kilometer
74- 76 I3 --- o_sample Number of observation for sample
78- 80 I3 --- o_line Number of observation for line
82- 87 A6 --- Sat Satellite, Phobos or Deimos
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Note (1): MRO (single) gathers data where only one moon was observable at a
time.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Sat Satellite, Phobos or Deimos
8- 24 F17.11 km x X position
26- 30 F5.3 km e_x Error on X position
32- 49 F18.11 km y Y position
51- 55 F5.3 km e_y Error on Y position
56- 73 F18.11 km z Z position
75- 79 F5.3 km e_z Error on Z position
81- 96 F16.14 km/s vx Velocity along X axis
98-104 E7.3 km/s e_vx Error on velocity along X axis
106-125 F20.17 km/s vy Velocity along Y axis
127-133 E7.3 km/s e_vy Error on velocity along Y axis
135-152 F18.15 km/s vz Velocity along Z axis
154-160 E7.3 km/s e_vz Error on velocity along Z axis
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Acknowledgements:
Valery Lainey, lainey(at)imcce.fr
(End) Patricia Vannier [CDS] 07-Jan-2021