PDO is the acronym of ESA’s Planetary Defence Office within its Space Safety programme (S2P). The goals of the Office are to: 1) be aware of the current and future position of near-Earth objects relative to our planet, 2) estimate the likelihood of Earth impacts, 3) assess the consequences of any possible impact, 4) inform relevant parties, e.g. national emergency response agencies and 5) develop methods to deflect any risky asteroids. More info at: https://www.esa.int/Safety_Security/Risky_asteroids.

S2P is the acronym for ESA's "Space Safety Programme”. Its aim is "the protection of our planet, humanity and assets in space and on Earth from dangers originating in space". More info at: https://www.esa.int/Safety_Security/Plans_for_the_future.

The Torino scale is a function of the impact energy and probability of the event, with no reference to the time of impact. In the Palermo scale, the risk posed by a possible impactor is compared to the 'background risk' between now and the time of impact. In addition, the Torino scale is discrete (from 0 to 10), whereas the Palermo scale is a continuous scientific scale.

SSA is the acronym of ESA's "Space Situational Awareness" programme, which was the precursor to the current Space Safety Programme. SSA ran between 2009 and 2019. More info at: https://www.esa.int/Safety_Security/The_story_so_far

The first NEA, (433) Eros, was discovered by Gustav Witt from the Urania Sternwarte Berlin and independently by Auguste Charlois from the Observatoire de Nice, on 13 August 1898. The discovery circumstances, and the orbit of Eros, turned out to be rather unusual.

Even if an asteroid misses the Earth, it can come back and hit our planet in a subsequent "return". Whether this happens or not, depends on whether the object passes through well-defined regions in space called "keyholes". There, the gravitational deflection imparted on the object is exactly the right amount to put it onto a future collision course.

The word NEO stands for near-Earth object, indicating a small body of the Solar System which can come into the Earth’s neighbourhood. A broad classification of NEOs distinguishes NECs (near-Earth comets) from NEAs (near-Earth asteroids), which constitute the vast majority of NEOs.