Meteors
Meteors
What are meteors?
A meteoroid is a small celestial body, typically a rock or metal fragment, that travels through space with velocities ranging from ∼ 11 to ∼ 72 km/s. Meteoroids vary in size, ranging from tiny particles of ∼ 10 μm to larger objects of up to 1 m. They can originate from various sources, such as asteroids, comets, or even lunar ejecta.
As these meteoroids enter the Earth’s atmosphere, they encounter immense friction, causing them to heat up and emit a bright streak of light, typically between altitudes of ~ 80 to ~ 120 km. This luminous display is what we perceive as a meteor, commonly known as shooting star. While the majority of meteoroids disintegrate completely during their descent, some larger ones reach the Earth's surface, becoming meteorites.
Most meteors occur at any time and in any direction. They belong to what is called the sporadic background. They constitute the bulk of meteors falling into the Earth’s atmosphere. However, there is a second population of meteors, often associated with dust released by a comet when it approaches the sun. If Earth is crossing the orbit of this comet, it experiences an increased meteor activity every year at the same time, called a meteor shower.
Due to a geometrical effect, all meteors belonging to a meteor shower seem to come from one point in the sky called the radiant. Each meteor shower is named after the constellation from which the meteors appear to originate. For example, the radiant of the Perseids is located in the Perseus constellation. Its maximum activity is in the night of the 12-13 August, where we can observe up to 100 meteors per hour under ideal circumstances.
Why should we study meteors?
The difference between meteroid, meteor (shooting star) and meteorite. The Perseids meteor shower in August 2009. Credits: NASA/JPL
Studying meteors is crucial for a range of scientific purposes. One significant aspect is the detection of new meteor showers. By observing meteor activity and noting distinctive patterns in the timing and direction of meteors, astronomers can pinpoint the existence of previously unknown meteor showers. Additionally, meteors offer vital clues about their parent bodies - comets and asteroids. Analyzing the chemical composition and isotopic ratios of meteoroids can help trace their origins, which is crucial for understanding the formation and evolution of our Solar System.
Meteors also play a pivotal role in spacecraft protection, which are constantly exposed to the risks posed by meteoroids. Although less abundant than space debris in low-earth orbits, the speed of meteoroids is often much higher, and is therefore a significant source of potential damage to spacecraft. This risk is even more critical for interplanetary travel. As a result, the determination of meteor fluxes, speeds and directions are important for space agencies and private space companies.
Since meteors ablate around ~ 100 km altitude, they provide a continuous sampling of the mesosphere lower thermosphere (MLT) region. Due its position, MLT is too high for balloons, which can only fly up to a few tens of km, and too low for satellites. By observing meteors, scientists can gain insights into MLT wind speeds and other atmospheric parameters, such as water vapour, ozone, and temperature distribution. This research is essential for global circulation models of the atmosphere and is therefore useful for climatologists.
How can we observe meteors?
The meteors can be detected and examined visually or by radio observations. The COMETA group hosts various projects to observe meteors: BRAMS, CAMS and FRIPON.
The BRAMS (Belgian RAdio Meteor Stations) network is a research infrastructure developed by the Belgian Institute for Space Aeronomy (BIRA) since 2010, in the frame of the Solar-terrestrial Centre of Excellence (STCE). It uses forward scatter of very high frequency (VHF) radio waves on ionized meteor trails to detect and characterize meteoroids falling into the Earth’s atmosphere. In October 2023, the network comprises a transmitter, 46 receiving stations (most in Belgium, a few in France, Luxembourg, the Netherlands) and an interferometer. Contrary to optical observations, radio detection can be performed during daylight, independently of the weather conditions. Radio systems such as BRAMS are also sensitive to fainter meteors and thus to meteoroids of smaller masses.
Forward scattering of a radio wave on a meteor trail
The ULiège BRAMS receiving station
The CAMS (Cameras for Allsky Meteor Surveillance) network is a global system of meteor cameras designed to monitor and record meteors in the night sky. It consists of a network of high-resolution, low-light video cameras that continuously monitor the sky for meteors. The data collected from these cameras is used to track and analyze the trajectories of meteors, determine their orbits, and study their characteristics. The information gathered from CAMS allows for a better understanding of meteor showers and the origins of meteoroids. In October 2023, the CAMS network in the Benelux consists of about 100 cameras that cover the sky above Belgium, the Netherlands, Luxembourg and part of Germany.
The ULiège hosted CAMS camera at the la Silla Observatory
FRIPON (Fireball Recovery and InterPlanetary Observation Network) is a network of cameras that continuously monitors the sky to detect fireballs, which are meteors with a magnitude lower than -4, equivalent to that of the planet Venus. FRIPON reconstructs the orbit of each object to identify its potential parent body. Additionally, it automatically determines the trajectory of the fireball in the atmosphere to identify the impact zone on the ground, which allows to organize meteorite search. The network consists of more than 100 connected cameras covering the entirety of France. FRIPON also includes dozens of cameras abroad thanks to partners such as PRISMA (Italy) and SCAMP (United Kingdom).
The ULiège FRIPON camera at Sart Tilman
