Meteorite myths, checked against the evidence

Only the outer skin melts during the few seconds of fiery entry, and that melted layer is blown away. The inside stays at the cold temperature of space, and the stone cools in the last minutes of its fall. Fresh falls are usually warm, cool or even frosty to the touch.

The air brakes them to their terminal velocity, roughly 300 to 600 km/h for a typical stone. Only very large masses, many tonnes or more, keep part of their cosmic speed and blast out craters.

Most land with a thud and make a small pit no bigger than themselves. Only large objects that keep their cosmic speed make true impact craters.

There are almost no reliable reports of a meteorite setting anything alight. The stones are not hot enough by the time they land.

A shooting star is a meteor: the glow of air and vapour around a speck of dust burning up 70 to 120 km high. Most are smaller than a grain of sand and never reach the ground.

Shower meteors are fragile comet dust and burn up completely. No meteorite has ever been linked to a meteor shower. Meteorites come from asteroids, and they arrive at random times.

A meteoroid is the rock in space, a meteor is the streak of light in the sky, and a meteorite is any piece that survives to reach the ground.

Fireballs brighter than the planet Venus happen thousands of times a day over the whole Earth, but most occur over oceans, in daylight or over empty land, so few people see them.

Sound from a fireball usually arrives minutes later, like thunder, because it travels slowly. But some witnesses report hissing or crackling at the same moment, called electrophonic sound, probably caused by radio waves from the fireball making nearby objects vibrate.

Nothing burns in the usual sense, because there is little oxygen at those heights. The air in front of the object is squeezed and heated to thousands of degrees, and the surface melts and vaporises. The light comes from that superheated gas and vapour.

The rate of falls is about the same day and night, but more afternoon and evening falls are seen and recovered simply because more people are awake and outside.

The pieces fall in an oval called a strewn field, often several kilometres long. The heaviest pieces carry furthest along the flight path, and the smallest land first.

The fusion crust is usually less than a millimetre thick, like an eggshell. Under it, the rock looks just as it did in space.

Most meteorites attract a magnet because of their iron-nickel metal, but some rare kinds, including many from the Moon and Mars and some achondrites, barely react.

Magnetite, many iron ores, slag and man-made iron all attract a magnet. A magnet is a useful first check, never proof.

A fresh fusion crust is black or dark brown and usually matt. Older finds rust to brown, and some rare types, such as aubrites, have pale crusts.

Gas bubbles and holes usually mean slag or volcanic rock. Meteorites are dense and almost never full of holes. The smooth thumbprint dents on irons, called regmaglypts, are shallow and rounded.

Only about 1,300 meteorites have been seen to fall. The tens of thousands of others are finds, most of them picked up in Antarctica and hot deserts like the Sahara.

Weathered stony meteorites can look very ordinary, which is why most go unnoticed. But a fresh crust, metal flecks on a broken face and unusual weight are strong clues.

Photos help experts rule out obvious look-alikes, but only laboratory tests can confirm a meteorite. Even professionals are fooled by pictures.

A positive nickel test on bright metal is a strong hint, because Earth rocks and man-made iron rarely contain several per cent nickel. But some stony meteorites have little exposed metal, and a lab analysis is still needed.

Detectors pick up the metal in most ordinary chondrites and all irons, and they are widely used in strewn fields. Metal-poor types, like many achondrites, are hard to detect.

Micrometeorites, tiny space grains under a millimetre across, have been found on city rooftops. But most magnetic grains in gutters are industrial dust, and real ones need a microscope and experience to recognise.

Water speeds up rusting and can ruin a meteorite for science. Keep a find dry, handle it as little as possible and store it in a clean bag.

Only about 5% of meteorites seen to fall are irons. Most are stony. Irons are over-represented in old collections because they survive longer and are easier to recognise.

They are iron-nickel alloys, usually 5% to 25% nickel, with cobalt and other trace metals. Etched with acid, most reveal a crystal pattern that forms only by cooling over millions of years.

Meteorites are made of the same chemical elements as Earth. Some contain minerals rarely or never found naturally on Earth's surface, but no new elements.

No living organism or fossil has ever been confirmed in a meteorite. Claims, such as a 2013 report of fossils in stones from Polonnaruwa in Sri Lanka, did not stand up; those rocks were from Earth.

They contain tiny natural amounts of radioactive elements, like ordinary rocks. Freshly fallen meteorites are very faintly radioactive from cosmic rays, but far below any health concern.

The oldest are the white calcium-aluminium-rich inclusions, about 4,567 million years old. Chondrules formed over the next few million years.

Most formed about 4.56 billion years ago, but some Martian meteorites crystallised only 150 to 600 million years ago, and lunar basalts range from about 2.5 to 4 billion years.

Under the dark crust, most stony meteorites are pale grey with metal flecks and chondrules; eucrites are light grey; irons are bright metal.

In damp climates the crust weathers away in decades to centuries. In dry deserts and Antarctica it can survive for many thousands of years.

No meteorite has been proved to come from a comet. Comets are too fragile for pieces to survive the fall, though some carbonaceous chondrites may come from comet-like bodies.

Apollo astronauts brought back Moon rock, but lunar and Martian meteorites arrived by themselves. No sample has yet been returned from Mars.

In 1996 scientists suggested that features in Allan Hills 84001 might be traces of microbes. Most researchers now think they formed without life, though the debate launched modern astrobiology.

Every meteorite studied so far comes from our own Solar System. A couple of interstellar objects have passed through, but none has been shown to have dropped a meteorite.

Many small asteroids are 'rubble piles': loose heaps of boulders and gravel held together by weak gravity, as missions to Itokawa, Ryugu and Bennu showed.

Earth gains thousands of tonnes of space dust and rock each year, but it loses more than that as hydrogen and helium leak away from the top of the atmosphere.

The asteroid belt is not the wreck of a planet. But iron meteorites are cores of small melted worlds, up to hundreds of kilometres across, that were broken apart early on.

No death has been fully confirmed. Ann Hodges of Sylacauga, Alabama, was badly bruised in 1954, the best-documented injury. Historical reports of deaths cannot be verified.

The Valera meteorite in Venezuela was reported to have killed a cow in 1972, and the owners kept the stone. A story that a dog was killed by the Nakhla meteorite in 1911 has never been confirmed.

They were killed by the effects of an asteroid about 10 km across that hit Mexico 66 million years ago, making the Chicxulub crater. The asteroid was almost entirely vaporised, so no meteorite from it is known.

Small fireballs happen daily, but objects big enough to cause damage, like the 20-metre Chelyabinsk asteroid of 2013, arrive only every few decades. Global catastrophes are tens of millions of years apart.

Sky surveys scan for near-Earth asteroids every night and have found over 95% of those bigger than a kilometre. In 2022 NASA's DART spacecraft changed the orbit of the asteroid Dimorphos, the first test of planetary defence.

The 1908 Tunguska event in Siberia was far bigger, flattening about 2,000 km² of forest. Chelyabinsk in 2013 was the biggest since then and injured about 1,500 people, mostly with broken glass.

The object exploded several kilometres above the ground. No crater and no meteorite pieces have ever been confirmed.

It was once thought volcanic, but Daniel Barringer argued for an impact and, in 1960, Eugene Shoemaker found shocked minerals that proved it. It was made by an iron meteorite about 50,000 years ago.

Only around 200 confirmed impact structures are known, because erosion, plate tectonics and plants hide most of them. The Moon, without weather, keeps its craters.

Meteorites are harmless. After the 2007 Carancas fall in Peru, villagers felt unwell, probably from gas released from the groundwater the stone struck, not from the meteorite itself.

Reports in 2013 described Russian plans for a warning and tracking system, but there is no physical shield over any country.

Some European collections did discard a few specimens to avoid embarrassment, but there is little evidence of whole collections being thrown out.

It has often been suggested, but the stone has never been studied scientifically, and other explanations such as impact glass or ordinary rock are also proposed. Its nature is unknown.

The quote, about the 1807 Weston fall in Connecticut, is widely repeated but no record shows Jefferson said it.

It is the oldest in Europe with material still preserved. The Japanese Nogata meteorite, said to have fallen in AD 861 and kept at a shrine, is older.

A 2012 study found the 'Iron Man' statue is carved from the Chinga meteorite, but its claimed 11th-century age is disputed; others think it is a 20th-century carving.

A popular internet story, because the plant grows wild only near Wilmington, North Carolina. It is a normal Earth plant with relatives worldwide.

Common stony meteorites can sell for less than a pound per gram. Fresh falls, rare types, and Moon and Mars rocks are far more valuable. Most finds won't make anyone rich.

A few rare Martian and lunar specimens have sold for more per gram than gold, but the great majority of meteorites are worth far less.

It depends where. In many countries it belongs to the landowner. In some places, such as Denmark and the Australian states, meteorites must be reported or belong to the state, and export is often controlled.

In most countries a meteorite belongs to the owner of the land where it lands. Always ask permission before searching.

Collection is reserved for scientific programmes under the Antarctic Treaty system, and finds go to national research collections.

Fakes and meteor-wrongs are common online. Buy from reputable dealers who give the official name and classification, ideally members of the International Meteorite Collectors Association (IMCA).

Slices show off the inside for collectors, but cutting is also how scientists study meteorites. Thin sections ground to 0.03 mm are examined under polarising microscopes.

Some irons rust badly, especially if they contain chlorine. Collectors store them dry, sometimes with a light protective coating, and away from damp.

Genuine pieces often use Gibeon or Muonionalusta iron, or pallasite olivine. Cheap 'meteorite' jewellery is sometimes made from etched steel or imitation material.

Space rock and dust reach Earth all the time, and tens of thousands of meteorites are catalogued. They just go unnoticed: most fall into the sea, into forests or onto empty land.