1 Introduction

In recent studies, Mars-crossers and Near-Earth objects have been recognized as potential sources of the meteorites recovered on Earth. Near-Earth asteroids are divided into three classes, following their orbital parameters: the Atens have semimajor axes smaller than that of the Earth, the Apollos have orbits that cross the Earth's orbit (they are sometimes called Earth-crossers), and the Amors pass inside the Mars orbit but do not cross the Earth one. Nowadays, it is widely accepted that Near-Earth asteroids are fragments of larger objects of the main belt that, probably after a collision, were injected into a resonance. Later encounters with the terrestrial planets could then remove these bodies from the resonances and convert them into Near-Earth asteroids. On the other hand, an asteroid is a Mars-crosser when its current osculating perihelion distance is greater than 1.3 AU and its orbit intersects that of Mars. The Mars-crossing population has unstable orbits and can, through close encounters with the planet, evolve to Earth-crossing orbits. Recent dynamical works (Migliorini et al. 1998; Michel et al. 2000) suggested that the Mars-crosser population can account for an important fraction of the multikilometer Near-Earth asteroids. As the relationships among these classes of bodies are not at present completely understood, the study of these objects from a spectral reflectance point of view can help us to impose additional constraints on the origin of these populations.

  

Table 1: Observational circumstances for the Mars-crossers.

In order to increase our knowledge about the compositional distribution of these objects, we observed 22 Mars-crossers and 12 Near-Earth asteroids. We obtained fifty-seven reflectance spectra for the Mars-Crossers and twenty-seven for the Near-Earth objects, as part of our Small Solar System Objects Spectroscopic Survey (Lazzaro et al. 2001). We also present a spectrum obtained for the largest Near-Earth asteroid, 1036 Ganymed, whose rotational spectra have been published by Mothé-Diniz et al. (2000).

In Sect. 2 we describe the observing and reduction procedures and in Sect. 3 we present the obtained results. In Sect. 4 we make a brief discussion and present some conclusions.

  

Table 2: Observational circumstances for the NEAs.