• 1950DA
• asteroid
• celestial mechanics
• Gaia mission
• impact monitoring
• near-earth asteroid
• near-earth object
• OrbFit
• orbit determination
• potentially hazardous asteroid

Gaia is one of the most important missions in the science programme of the
European Space Agency (ESA). The aim of the mission is to build the largest,
most precise three-dimensional space catalogue ever made by surveying nearly
two billion objects in the Milky Way.
The first ESA space mission entirely dedicated to precision astrometry, the
accurate measurement of the positions of celestial objects, was the Hipparcos
mission. It was launched in 1989 and operated until 1993. Hipparcos managed
to map the sky more accurately than ever before; its work is refined by Gaia,
which was launched on 19 December 2013 and operated in the
Sun-Earth Lagrange point L2 until 15 Janaury 2025.
Gaia spacecraft has two telescopes providing two observing directions (called
fields of view) and, during the five years of the nominal mission, Gaia is
expected to observe each object on average about 70 times; since the mission
has been extended to approximately ten years, we will expect to obtain twice
as many observations.
The first data release (Gaia Collaboration et al. 2016) was on 14 September 2016: it is based on 14 months
of observations. In the following years, there were four data releases: the
second on 25 April 2018, the third which was divided in two different parts
(the Early Data Release 3 on 3 December 2020 and the Data Release 3 on 13
June 2022) and the Focused Product Release (FPR, David et al. 2023) on 10 October 2023.
This thesis presents a new orbit determination process for the asteroids in
the Solar System; this method was introduced by Fuentes-Mu˜noz et al. 2024,
exploiting the new data of Gaia FPR. Moreover, they performed a statistical
analysis to test the accuracy of the reported positions and their associated
uncertainties.
The thesis is organized into four chapters, the content of which is described
below.
The first chapter is an introduction to the orbit determination problem; we
will give a brief description of the general setting, followed by the main
mathematical results concerning the computation of the orbits of celestial
bodies. In the end we will characterize the problem as a population orbit
determination case. The main reference is “Theory of Orbit Determination”
by Milani and Gronchi 2010.
In the second chapter we will give an overview of the Gaia mission; then we
will describe some properties of the dataset that are relevant to our study.
The core of this chapter is the new method for the orbit determination
which is based upon the so called photocenter correction, first introduced by
Fuentes-Mu˜noz et al. 2024. This method takes into account the displacement
of the object’s position due to the scattering of light by the asteroid’s surface.
In addition to this correction, the authors increase the astrometric
uncertainty due to the assumptions on the asteroid (i.e. the shape and light
reflection properties).
The third chapter will focus on the results of the experiments. The tests
are performed with the algorithm included in the software OrbFit (updated
according to the photocenter correction and the related uncertainty described
in Chapter 2) and the outcome will be compared with that of Fuentes-Mu˜noz
et al. 2024.
In the fourth chapter we will recall the main theoretical instruments concerning
the impact monitoring procedure, with special attention to Potentially
Hazardous Asteroids (PHA). We will study the asteroid 1950 DA, which is
a Near-Earth Object (NEO) and a PHA, currently in the risk list of the
on-line information system NEODyS-2. Given the new orbit determination
method implemented in OrbFit, we will determine the new orbit of 1950 DA
and update the Impact Probability (IP). The new IP will be compared with
that of Fuentes-Mu˜noz et al. 2024.
This work has been possible thanks to a long university internship at spin-off
company SpaceDyS, which provided the opportunity to study the code of
the OrbFit software.