  In 1980, Alvarez and colleagues proposed that, in the transition from the
Cretaceous to Paleogene, a large impactor collided with Earth being the cause
of the mass extinction occurred at the limit K / Pg. In 1980 there was no known
impact structure, which could be responsible for this extinction. It was not
until 1991 that an international group of researchers proposed that a circular
structure between 180 and 200 km, buried under Tertiary deposits in the Yucatan
Peninsula in Mexico, was the crater formed by the impact proposed by the group
of Alvarez (Hildebrand et al., 1991). It is very probable that an impact of
this magnitude have had large effects on the surface and in the environment. To
study these effects, it is necessary to estimate the characteristics that the
impactor had. The literature often mentions the nature of the impactor, and has
been proposed both an asteroid and a comet, and even a comet shower that
produced periodic extinctions. However, the physical parameters of the impactor
are not limited, so the aim of this study is to estimate the most relevant
features of this one such as the size, mass and kinetic energy. We found that
the kinetic energy of the impactor is in the range from 1.3e24 J to 5.8e25 J.
The mass is in the range of 1.0e15 kg to 4.6e17 kg. Finally, the diameter of
the object is in the range of 10.6 km to 80.9 km. Based on the mass of the
impactor and iridium abundance in different types of meteorites, we calculate
the concentration of iridium, which should be observed in the K/Pg layer. When
compared with the measurements, we concluded that the best estimation is that
the impactor was a comet.
