Why the meteor that crossed Spain and Portugal is a bolide

A mateora lit up the night between the two villages green-blue

by Lorenzo Ciotti
Why the meteor that crossed Spain and Portugal is a bolide
© Dan Kitwood / Staff Getty Images Sport

Spain and Portugal saw a blinding blue-green shine on the night of Saturday 18 May 2024. A meteorite has fallen in northern Portugal, lighting up midnight. Several people filmed the event and then shared the videos on their social media. The meteor (or bolide) crossed Castro Daire, Lisbon and some cities in Spain.

The event therefore took everyone by surprise, as the local Civil Protection had issued an alert for a possible meteorite arrival but it was then withdrawn. The blue color of the trail is probably due to the presence of calcium in the meteorite fragment that incinerated in the atmosphere. At the moment, several teams are searching for the meteorite in the impact area.

But why is this meteor called a bolide? And what is a bolide? A bolide is a meteor of high brightness, of negative magnitude, which corresponds to the maximum magnitude reached by the planet Venus (−4.6a), therefore a magnitude higher than that of any star and planet and lower only than the brightness of the Sun, the Moon and of a part of the galactic supernovae and novae. There is no maximum brightness limit, bolides with magnitudes higher than that of the Sun (−26.3a) have been observed.

The bolides can also take on other clearly visible colours. The main ones are emerald green, red, electric blue and orange.
During their appearance, which can last up to over 10 s, with documented cases up to 101 s, they can present flares, fragmentations and have non-rectilinear trajectories. The variation in brightness during the appearance is linked to the composition and structure of the cosmic body, called meteoroid, which gives rise to the bolide.

Bolides can make noises, usually similar to distant thunder. They are generally perceived 1 to 3 minutes after the appearance of the fireball, as sound travels at a speed of about 0.3 km/s and takes longer than light to reach the observer. Furthermore, only sounds generated at a height of no more than 50 km are perceptible, because at higher heights they are reflected upwards and disappear into the upper atmosphere. The sounds are due to the often explosive disintegration of the meteoroid.
A bolide as bright as the full Moon usually has a pre-atmospheric mass of 100 kg. Only one out of every 100 fireballs with a magnitude like that of the full Moon gives rise to meteorites.