Extreme AO Observations of Two Triple Asteroid Systems with SPHERE

We present the discovery of a new satellite of asteroid (130) Elektra - S/2014 (130) 1 - in differential imaging and in integral field spectroscopy data over multiple epochs obtained with SPHERE/VLT. This new (second) moonlet of Elektra is about 2 km across, on an eccentric orbit and about 500 km away from the primary. For a comparative study, we also observed another triple asteroid system (93) Minerva. For both systems, component-resolved reflectance spectra of the satellites and primary were obtained simultaneously. No significant spectral difference was observed between the satellites and the primary for either triple system. We find that the moonlets in both systems are more likely to have been created by sub-disruptive impacts as opposed to having been captured.Comment: 8 pages, 4 figures, 1 table, accepted to be published in the Astrophysical Journal Letter

Constraining multiple systems with GAIA

GAIA will provide observations of some multiple asteroid and dwarf systems. These observations are a way to determine and improve the quantification of dynamical parameters, such as the masses and the gravity fields, in these multiple systems. Here we investigate this problem in the cases of Pluto's and Eugenia's system. We simulate observations reproducing an approximate planning of the GAIA observations for both systems, as well as the New Horizons observations of Pluto. We have developed a numerical model reproducing the specific behavior of multiple asteroid system around the Sun and fit it to the simulated observations using least-square method, giving the uncertainties on the fitted parameters. We found that GAIA will improve significantly the precision of Pluto's and Charon's mass, as well as Petit Prince's orbital elements and Eugenia's polar oblateness.Comment: 5 pages, accepted by Planetary and Space Science, Gaia GREAT-SSO-Pis

739 observed NEAs and new 2-4m survey statistics within the EURONEAR network

We report follow-up observations of 477 program Near-Earth Asteroids (NEAs) using nine telescopes of the EURONEAR network having apertures between 0.3 and 4.2 m. Adding these NEAs to our previous results we now count 739 program NEAs followed-up by the EURONEAR network since 2006. The targets were selected using EURONEAR planning tools focusing on high priority objects. Analyzing the resulting orbital improvements suggests astrometric follow-up is most important days to weeks after discovery, with recovery at a new opposition also valuable. Additionally we observed 40 survey fields spanning three nights covering 11 sq. degrees near opposition, using the Wide Field Camera on the 2.5m Isaac Newton Telescope (INT), resulting in 104 discovered main belt asteroids (MBAs) and another 626 unknown one-night objects. These fields, plus program NEA fields from the INT and from the wide field MOSAIC II camera on the Blanco 4m telescope, generated around 12,000 observations of 2,000 minor planets (mostly MBAs) observed in 34 square degrees. We identify Near Earth Object (NEO) candidates among the unknown (single night) objects using three selection criteria. Testing these criteria on the (known) program NEAs shows the best selection methods are our epsilon-miu model which checks solar elongation and sky motion and the MPC's NEO rating tool. Our new data show that on average 0.5 NEO candidates per square degree should be observable in a 2m-class survey (in agreement with past results), while an average of 2.7 NEO candidates per square degree should be observable in a 4m-class survey (although our Blanco statistics were affected by clouds). At opposition just over 100 MBAs (1.6 unknown to every 1 known) per square degree are detectable to R=22 in a 2m survey based on the INT data, while our two best ecliptic Blanco fields away from opposition lead to 135 MBAs (2 unknown to every 1 known) to R=23.Comment: Published in Planetary and Space Sciences (Sep 2013

Interest of old data for the determination of the heliocentric distance of Pluto

Pluto was discovered in 1930. It is also the multiple system which has been known for the longest time with the discovery of its first satellite Charon in 1978. Because of Pluto’s distance to the Sun, the system still has not completed a revolution since its discovery, hence an uncertain heliocentric distance. The difference between the different ephemeris available far exceeds the uncertainty needed for the mission New Horizons, that is 1,000 km. A new astrometric reduction of old photographic plates may be an efficient way to constrain it.

Multiple asteroid systems (45) Eugenia and (87) Sylvia: Sensitivity to external and internal perturbations

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VizieR Online Data Catalog: Pluto's observations between 1997 and 2010 (Beauvalet+, 2013)

plutoohp.dat 242x43 Astrometric data of Pluto observed at; Haute-Provence Observatory (tablea2)Astrometric data from Pluto's observations at Observatoire de Haute-Provence between 1997 and 2010. Topocentric observations obtained with the 120cm telescope (f=7.2m). The field of view is 11.8'x11.8' and the camera resolution is 0.69 arcsec/pixel. (1 data file)

VizieR Online Data Catalog: Pluto's observations between 1997 and 2010 (Beauvalet+, 2013)

plutoohp.dat 242x43 Astrometric data of Pluto observed at; Haute-Provence Observatory (tablea2)Astrometric data from Pluto's observations at Observatoire de Haute-Provence between 1997 and 2010. Topocentric observations obtained with the 120cm telescope (f=7.2m). The field of view is 11.8'x11.8' and the camera resolution is 0.69 arcsec/pixel. (1 data file)

Astronomy Astrophysics ODIN: a new model and ephemeris for the Pluto system ⋆,⋆⋆

Because of Pluto’s distance from the Sun, the Pluto system has not yet completed a revolution since its discovery, hence an uncertain heliocentric distance. In this paper, we present the fitting of our dynamical model ODIN (Orbite, Dynamique et Intégration Numérique) to observations. The small satellites P4 and P5 are not taken into account. We fitted our model to the measured absolute coordinates (RA, DEC) of Pluto, and to the measured positions of the satellites relative to Pluto. The masses we found for the bodies of the system are consistent with those of previous studies. Yet the masses of the small satellites Nix and Hydra are artificially constrained by the number of observations of Charon. The best way to improve the determination of their masses would be to use observations of P4 and P5, but there are still not enough published observations. Concerning the heliocentric distance of the system, we compared the value we obtained using ODIN and those of other models. The difference between the models far exceeds the uncertainty needed (about 1000 km) for the mission New Horizons. A new astrometric reduction of old photographic plates may be an efficient way to constrain this distance. The ephemeris for Pluto’s satellites is available on the web page of the IMCC

New orbits of irregular satellites designed for the predictions of stellar occultations up to 2020, based on thousands of new observations

International audienc

Dynamical parameter determinations in Pluto’s system

Pluto is the multiple system that has been observed the longest. Yet, the masses of its smallest satellites, Nix and Hydra, which were discovered in 2005, are still imprecisely known, because of the short time span and number of available observations. We present a numerical model that takes into account the second order gravity fields and Pluto’s orbital motion in the solar system. We investigated the dynamical parameters that may be reliably determined today. We also assessed the possible improvements on the parameter uncertainties with the future increase of observations, including the New Horizons mission. Fitting our model to simulated data, we show that the precision of observations prevents the quantification of the polar oblateness J2 and equatorial bulge c22 of Pluto and Charon. Similarly, we show that the masses are on the detection limit. In particular, unless 25 observations are made every year, the mass of Nix may be constrained with confidence only with New Horizons data. Hydra’s mass will only be constrained by the probe. The recent discovery of P4 might change this situation, but our knowledge of this object is still too vague to draw any conclusion.United States. National Aeronautics and Space Administration (New Horizons Mission science team