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IAA Transactions, No. 8, ``Celestial Mechanics'', 2002
The projects of IMCCE concerning the natural
planetary satellites
J. E. Arlot
Institut de mecanique celeste et de calcul des ephemerides­UMR 8028 du
CNRS, Observatoire de Paris, France
Astronomers of IMCCE are involved in the study of the natural planetary
satellites in constructing theoretical models as well as in producing observations
in order to validate and fit the theories. The goal of the present paper is to present
our current works and our plans for the next years.
Inner satellites of Jupiter
We are making numerical integration for Amalthea (J5), Thebe (J14), Metis (J15)
and Adrastea (J16) (Vachier et al., 2001) and also we are building an analytical
theory of their motions. We are continuing observations in the visible wavelengths
for J5 and J14 using a coronograph and in the infrared wavelengths for J15 and
J16 because of the brightness of Jupiter. We gathered observations from 1995
to 2001 made at Pic du Midi (France), Flagstaff (Arizona, USA) and Itajuba
(Brazil).
Galilean satellites of Jupiter
The present theory of the motion of the Galilean satellites is based upon the
Sampson­Lieske theory built in 1921 and revitalized in 1977. This theory appears
unable to be sufficiently accurate for the modern studies. So, we are building a
semi­analytical theory thanks to a frequency analysis of the results of a numer­
ical integration of the motion of the satellites. We continue to make and gather
observations for the fit of the initial conditions. At the present time, we have
about 2000 photographic observations for each satellite made from 1890 to 1991
and 1000 observations of mutual events made from 1973 to 1997 (see for example
the catalogue published by Arlot et al. in 1997). Observations of classical eclipses
and observations of positions made using a micrometer at the end of the XIXth
century are available but are not used. Our goal is to put into evidence the in­
fluence of the energy loss due to the tides created by Jupiter on the satellites
by measuring the acceleration in the motion of the satellites. The implication of
such a measure will help us to understand the interior of the satellites, Europa
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for example, which is suspected to have a deep ocean under an iced crust. On­
ly high precision observations may allow such a challenge. Aksnes and Franklin
(2001) published some values for these accelerations. That is why we will start a
campaign of observations of the mutual events of the Galilean satellites next Oc­
tober. Note that about 500 events will occur from October, 2002, to September,
2003. The list and some information concerning the observation of these events
are available at the web address: http://www.bdl.fr/phemu03 eng.html and have
been published (Arlot, 2002). Observers are encouraged to join this campaign
which will be only 6 months long. Afterwards, we will continue the observations
through classic CCD observations. In the past, observations of the occultations
of Io in the 3.8 micrometers infrared wavelength, allowed us to measure the flux
emitted by the volcanoes on this satellite (Arlot et al., 1997).
Outer satellites of Jupiter
The ephemerides of these objects are built using numerical integrations. Unfor­
tunately, the observations are rare and of poor accuracy, mainly because of the
use of unadapted star catalogues. We are observing these objects and performing
a new reduction procedure, attempting to avoid the zonal errors of the star cat­
alogues used. Our program concerns J6 to J13 and the newly discovered satellite
S/1999 J1. Note that these objects are not a goal for space probes and need
more ground based observations. At the present time, we are continuing CCD
observations using a 1.2 meter telescope at Observatoire de Haute Provence. We
made 244 observations of J6 to J13 in 1998, 406 in 1999, 186 observations in
2000 and 453 in 2001--2002. We made 53 observations of J17 in 2000 and 36 in
2001--2002. Some of these observations are available and we are interested to get
more observations.
Major satellites of Saturn
These objects have their motions modelized through a semi­analytical theory
TASS built a few years ago. This theory deals with the global system of the ma­
jor satellites of Saturn for the first time, but was fitted on several series of old
observations, the reduction of which requires to be done again with an improved
procedure. Our plans are to fit this theory on much more new and accurate ob­
servations such as new CCD observations and mutual events observations that
we made during the 1995 occurrence of (Thuillot et al., 2001). CCD direct ob­
servations were made together with these mutual events observations (Vienne et
al., 2001).
Outer satellites of Saturn
We are observing these objects and plan to build new ephemerides from numerical
integration for Phoebe (S9) and the newly discovered satellite S/2000 S3. We
made 135 observations of S9 in 1998, 39 in 1999, 78 in 2000 and 175 in 2001--
2002. We made 50 observations of S/2000 S3 in 2001--2002. These observations are
available (Fienga et al., 2002) and we also are interested to get the observations
made in other observatories.
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Satellites of Uranus and Neptune
We performed numerical integration for the satellites of Neptune (Veiga et al.,
1999). Tests were made by fitting the initial conditions on JPL ephemerides
and we plan now to fit it on new observations in order to get more accurate
ephemerides and to observe and modelize the motion of several small satellites
such as Puck (Descamps et al., 2002) thanks to the use of adaptive optics.
As a conclusion, I would like to present the data base of astrometric obser­
vations of the natural planetary satellites which is available on the Web site of
IMCCE, the NSDB/NSDC providing raw data as published by the observers, bib­
liographic data on observations and theoretical works on natural satellites and an
interactive software allowing to know what data are included as standard data
in the data base. The data base is available at http://www.bdl.fr/nsdc.html on
Internet and has been made thanks to the collaboration of the Sternberg Insti­
tute in Moscow. We thank in advance the observers for sending their data to the
NSDC data base. The observations of natural planetary satellites demand only
small telescopes as it was shown in (Arlot et Colas, 1997).
References
1. Vachier F., Thuillot W., Arlot J. E., Colas F., Fienga A. Dynamical be­
haviour of the faint inner jovian satellites, CELMEC III Workshop, Roma,
Italy, 2001.
2. Arlot J.­E., Ruatti C., Thuillot W., Arsenijevic J., Baptista R., Barroso Jr.,
J., Bauer C., Berthier J., Blanco C., Bouchet P., Bourgeois J., Bulder H. J. J.,
Burchi R., Cano J. A., Casas R., Chauvet F., Chis D., Colas F., Colin J.,
DAmbrosio V., De Angelis G., De Benedetto G., Denzau H., Desbats J. M.,
Descamps P., Dipaolantonio A., Dumitrescu A., Farcas L., Federspiel M.,
Flatres T., Froeschle M., Gherega O., Gomez­Forrellad J. M., Guarro J.,
Hainaut O., Horvat A., Helmer G., Hube D., Ito Y., Kidger M., Lecacheux J.,
Le Campion J. F., Le Floch J. C., Mallama A., Martin B. E., Mellilo J. F.,
Meyer C., Molau S., Montignac G., Morando B., Nicolet B., Nitschelm B.,
Oprescu G., Piersimoni A., Przewozny D., Protitch­Benishek V., Rapa­
port M., Riou R., Sacre J. J., Sevre F., Shkodrov V., Souchay J., Takami H.,
Taylor R., Tholen D. J., Turcu V., Vasundhara R., Vidal J. L., Vu D. T.,
White G., Wilds R. P. A catalog of the observations of the mutual phenom­
ena of the Galilean satellites made in 1991 during the PHEMU91 campaign,
Astron. Astrophys. Suppl., 1997, 125, 399.
3. Aksnes K., Franklin F. A. Secular acceleration of Io derived from mutual
satellite events. Astronomical Journal, 2001, 122, 2734--2739.
4. Arlot J. E. Predictions of the mutual events of the Galilean satellites of
Jupiter occurring in 2002--2003, Astron. Astrophys., 2002, 383, 719.
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5. Arlot J.­E., Descamps P., Thuillot W. Occultations of Io in 1997--1998: pre­
dictions for the observations of hot spots, Icarus, 1997, 125, 465.
6. Thuillot W., Arlot J.­E., Ruatti Ch. , Berthier J., Blanco C., Co­
las F., Czech W., Damani M., DAmbrosio V., Descamps P., Dourneau G.,
Emelianov N., Foglia S., Helmer G., Irsmambetova T. R., James N.,
Laques P., Lecacheux J., Le Campion J.­F., Ledoux C., Le Floch J.­C.,
Oprescu G., Rapaport M., Riccioli R., Starosta B., Tejfel V. G., Trunk­
ovsky E. M., Viateau B., Veiga C. H., Vu D. T. The PHESAT95 catalogue
of observations of the mutual events of the Saturnian satellites , Astron.
Astrophys., 2001, 371, 343.
7. Vienne A., Thuillot W., Veiga C. H., Arlot J.­E., Vieira Martins R. Saturnian
satellites observations made in Brazil during the 1995 opposition with an
astrometric analyzis, Astron. Astrophys., 2001, 380, 727--733.
8. Fienga A., Arlot J.­E., Bec­Borsenberger A., Baron N., Crochot A. CCD
observations of the 9th satellite of Saturn, Phoebe, made in 1998 and 1999,
Astron. Astrophys., 2002 (submitted).
9. Veiga C., Vieira­Martins R., Le Guyader C. CCD observations of Nereid and
a new orbital determination, Astron. Astrophys. Supp. Series, 1999, 136, 44.
10. Descamps P., Marchis F., Berthier J., Prang R., Fusco T., Le Guyader C.
First ground­based astrometric observations of Puck, CRAS, 2002, 3,1, 121--
128.
11. Arlot J.­E., Colas F. CCD astrometry of the Solar system, Celest. Mech.
Dyn. Astron., 1997, 66, 123.
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