Shooting stars: what are they, how are meteors formed, can they hit Earth, are they radioactive or magnetic?

As the Perseid meteor shower reaches its peak this weekend, many of us will gaze skyward, hopeful of witnessing the spectacular dance of "shooting stars".

It's only natural to wonder about the science behind these celestial phenomena. What separates a meteor from a meteoroid or a meteorite? Why do some burn up in our atmosphere while others survive to reach the Earth's surface?

Here is everything you've ever wanted to ask about meteors... but were maybe too embarrassed to.

What's the difference between a meteor, a meteorite and a meteoroid?

"Shooting star" is a colloquial term for a meteor, a bright streak of light that occurs when a meteoroid enters Earth's atmosphere and burns up due to friction with the atmosphere.

A meteoroid is a small rocky or metallic body in outer space. It's significantly smaller than an asteroid, typically ranging in size from a grain of sand to a few metres in diameter.

When a meteoroid enters Earth's atmosphere and begins to burn up due to friction with the air, it creates a streak of light in the sky, which is commonly known as a meteor or a "shooting star." Most meteors are relatively small and burn up completely before reaching the Earth's surface.

If a meteoroid survives its journey through the Earth's atmosphere and lands on the surface of the Earth, it's then referred to as a meteorite. Meteorites can vary in size from tiny fragments to large masses.

How are they formed?

Meteoroids are remnants of comets or asteroids that have broken off due to collisions or other processes in space. They are made of various materials, including rock, metal and sometimes even ice.

Comets are icy bodies that often originate from the outer regions of the solar system. As they approach the Sun, their ices can vaporise, releasing dust and rocky material. This debris can form meteoroids, and it's this process which most commonly gives us some of the more spectacular meteor showers here on Earth.

When larger asteroids collide or undergo disruptive events, they can break apart into smaller fragments which become meteoroids. Additionally, the surfaces of asteroids and other celestial bodies can be weathered by the harsh conditions of space over time, creating small particles that become meteoroids.

Meteoroids, meteors and meteorites can contain various elements and minerals, some of which might be radioactive, and can contain trace amounts of radioactive isotopes like uranium. However, the radioactivity levels in most meteorites are usually quite low and not a significant concern.

Similarly, some meteorites - such as those that contain metallic iron-nickel alloys - do exhibit magnetic properties. It's worth remembering that the presence of both radioactivity or magnetism depends on the type and origin of the meteorite.

Why do they burn up in the Earth's atmosphere?

Meteors burn up in the atmosphere due to the extreme heat generated by the process of "ablation", which causes the meteoroid's outer layers to vaporise and glow, creating the luminous trail we see as a shooting star.

As a meteoroid enters Earth's atmosphere, it collides with the air molecules at extremely high speeds. These collisions cause the air molecules to compress and heat up, creating a shock wave in front of the meteoroid.

The intense compression and heating of the air in front of the meteoroid result in its outer layers rapidly vaporising and disintegrating. The meteoroid's surface material is stripped away in a series of interactions with the heated air.

As the meteoroid continues to penetrate deeper into the atmosphere, it heats up to such high temperatures that its atoms become ionised, forming a glowing trail of plasma behind it. This is what we perceive as a meteor or shooting star streaking across the night sky.

Most meteoroids are relatively small, which means that even a small amount of ablation can cause significant material loss. In most cases, the entire meteoroid disintegrates and vaporises before it reaches the Earth's surface.

Can they hit Earth?

Though the vast majority of meteoroids that enter Earth's atmosphere are small and burn up, meteors and meteoroids can indeed hit Earth. In fact, Earth is constantly bombarded by small meteoroids.

But most of these are harmless due to their small size, and when larger meteoroids survive the journey through Earth's atmosphere and reach the surface (becoming meteorites), they serve as valuable scientific specimens that provide insights into the composition of asteroids, comets and other celestial bodies.

Larger impacts that could have more significant effects are much less frequent, and efforts are made to track and monitor near-Earth objects (NEOs), including potentially hazardous ones, to assess any potential impact risk and take appropriate measures to mitigate the threat if necessary.

The vast majority of meteors are not dangerous to people on the surface of the Earth. They pose no threat and are a natural and beautiful phenomenon that can be observed in the night sky.

In fact, most go unnoticed, as they can occur at any time of day; it's only at night when the sky is dark that meteors are more easily visible against the backdrop of a dark sky.