It is well accepted that asteroids have brought water on the surface of the Earth. This has also been possible because of the key role of the giant planets, mainly Jupiter and Saturn. As most of the known extra-solar systems host at least a giant planet, it is important to highlight the influence of the gravitational perturbations from the secondary star and the giant planet (a Jupiter-like) on a ring of asteroids and therefore on the water transport to the circumprimary HZ. In , I give a statistical overview about the efficiency of the water transport in double star systems. Indeed, I show that small bodies also participate in bearing a non-negligible amount of water to the HZ. The proximity of a companion moving on an eccentric orbit increases the flux of asteroids to the HZ, which could result in a more efficient water transport on a short timescale, causing a heavy bombardment. In contrast to asteroids moving under the gravitational perturbations of one G-type star and a gas giant, we show that the presence of a companion star not only favours a faster depletion of our disk of planetesimals, but can also bring 4-5 times more water into the whole HZ.
In , I give a dynamical explanation to justify the statistical results obtained: a secular resonance with location and width varying according to the secondary star's characteristics can exist in the icy asteroid belt region and overlap with MMRs, which have an impact on the dynamical lifetime of the disk. In addition, we point out that, in any case, the 2:1 MMR, the 5:3 MMR, and the secular resonance are powerful perturbations for the flux of icy asteroids towards the HZ and the transport of water therein.
Because of these orbital resonances, increasing the orbital eccentricity, the impact velocity on the surface of planetary embryos (Moon-to-Mars-sized objects) or planets (Earth-sized objects) can go from one to several times the escape velocity of the target. In , we treat for the first time, realistic collisions using a GPU 3D-SPH code to assess the water loss in the projectile. Compared to a purely merging approach, realistic collisions could reduce up to 50% the amount of water reaching the target.
The Potentially Hazardous Asteroid (PHA) Apophis, previously designated 2004 MN4, is emblematic of the situation of studies of PHAs, and is one of the closest approaching asteroids to the Earth presently known. Observations gathered since its discovery in 2004 have ruled out any possibility of collision with the Earth in 2029. However, Apophis will pass at about 33 500 km from the Earth surface, that is, below the position of a geosynchronous orbit, and should be visible to the naked eye. Apophis will remain a companion of the Earth for decades and will show subsequent close approaches. The high sensitivity of the orbit to small effects, caused by the close encounter with the Earth and the gravitational pull together with the current uncertainty on the orbit and dynamical modeling, prevent any accurate prediction for the far future. On the one hand, a small change of the orbit well in advance in time can avoid any collision trajectory, on the other hand, the orbit is not sufficiently accurate to enable to predict the trajectory with high confidence. Observational data, and in particular astrometric positions, are therefore mandatory to monitor the orbit of a PHA.
In , I analyze new astrometric data of Apophis acquired at the Pic du Midi one-meter telescope (T1m) during March 2011. Indeed, this asteroid was again visible from ground-based stations after a period of several years of unfavorable conjunction with the Sun. I show that these additional observations shift the center of the ellipse uncertainty in the 2029-b-plane, therefore moving away or coming closer from some primary or secondary keyholes. In addition, I address the influence of the Yarkovsky effect (a non gravitational effect) on the results and I point out that it can significantly influence the location of the nominal solution in the b-plane in 2029.
In the context of Gaia, and mainly the Gaia Follow-up Network of Solar System Objects (Gaia-FUN-SSO), ensuring that moving objects first detected by ESA’s Gaia mission remain recoverable after their discovery, we analyse in 2732 high quality astrometric observations (published and unpublished) acquired during the Gaia-FUN-SSO campaign and reduced with the Platform for Reduction of Astronomical Images Automatically (PRAIA), using the USNO CCD Astrograph Catalogue 4 (UCAC4) as a reference. We show that our reduction of this astrometric campaign with a reliable stellar catalog substantially improves the quality of the astrometric results. We present evidence that the new data will help to reduce the orbit uncertainty of Apophis during its close approach in 2029. We show that uncertainties due to geolocations of observing stations, as well as rounding of astrometric data can introduce an unnecessary degradation in the quality of the resulting astrometric positions.
Gaia is an astrometric mission launched in spring 2013. There are many scientific outcomes from this mission and as far as our Solar System is concerned, the satellite will be able to map thousands of main belt asteroids (MBAs) and near-Earth objects (NEOs) down to magnitude < 20. The high precision astrometry (0.3-5 mas of accuracy) will allow orbital improvement, mass determination, and a better accuracy in the prediction and ephemerides of potentially hazardous asteroids (PHAs). In , we give some simulation tests to analyse the impact of Gaia data on known asteroids’s orbit, and their value for the analysis of NEOs through the example of asteroid (99942) Apophis. I show that one single Gaia observations with a 5 mas accuracy, can bring the propagated position uncertainty in 2029 down to 1 km of uncertainty.
As the satellite won't follow any observed objects, I present in the same article and in proceedings of several the need for a follow-up network for newly discovered asteroids by Gaia, insisting on the synergy of ground and space data for the orbital improvement. The strategy developed is based on a statistical ranging using a Monte Carlo method and gaussian distributions in order to create a sample of millions of observations compatible with the two Gaia observations. The sample is then propagated from one to several days after the discovery and thanks to the maximum likelyhood of the distribution, observers can focus their telescope where the asteroid is "likely" to be re-observed. This strategy is also useful to optimize the Gaia-FUN-SSO as shown in my Ph.D Thesis
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The integration of the equations of motion in gravitational dynamical systems, either in our Solar System or for extra-solar planetary system, being non integrable in the global case, is usually performed by means of numerical integration. Among the different numerical techniques available for solving ordinary differential equations, the numerical integration using Lie series has shown some advantages. In its original form, it was limited to the N-body problem where only gravitational interactions are taken into account. In , we consider two cases involving position and position-velocity dependent perturbations: relativistic acceleration in the framework of General Relativity and a simplified force for the Yarkovsky effect. A general iteration procedure is applied to derive the Lie series to any order and precision. We then give an application to the integration of the equation of motions for typical Near-Earth objects and planet Mercury.