August hails the end of sweltering summer days as well as the height of the year’s largest meteor shower. Each August, the Earth passes through the trail left by the giant Swift-Tuttle comet, a 16-mile-wide hunk of ice and dust. In its wake, the comet leaves debris — the intergalactic fodder for the annual Perseids meteor shower which peaks on the night of August 11th this year. The debris incinerates as it enters the Earth’s atmosphere, decorating the night sky with glowing, celestial streaks.
But those shooting stars are more than a beautiful spectacle to wish upon – in fact, they are not stars at all. Each of these flashes is a flaming space rock hurtling towards the planet at high speeds. These rocks are meteors, and most burn up into dust before crashing on Earth’s surface. The ones that reach the ground are called meteorites, and many are too small to notice unless you know what you’re looking for.
Meteorites can tell us a lot about our own planet and the universe around us, making them vital scientific resources. The Smithsonian National Museum of Natural History boasts one of the largest museum collections of meteorites in the world, with over 45,000 specimens.
As we take a break from watching the Perseids light up the night sky, let’s turn our attention to some things you may not know about the cosmic rocks streaking across the sky.
From a galaxy not too far away
Have you ever looked at a falling meteor and wondered where it came from? Meteors all originate from debris within our planetary system: whether it be from fragments of planets or moons, shards of space rocks called asteroids or pieces of compacted dirt and ice called comets that paid our system a visit once upon a time.
It is usually difficult to know from where a meteorite originates unless it is analyzed in a lab, but meteors from showers are more straightforward. Meteor showers, like the Perseids, happen during our planet’s yearly pass through the residual dust left by a comet’s tail.
How far is the shooting star?
For a meteor to be visible to the naked eye, its surface must ignite in Earth’s atmosphere. This process occurs quickly after the rock enters the atmosphere because of the intense friction caused by the surrounding air.
But that begs the question: where in the atmosphere do we begin to see the meteor’s glow? Scientists have estimated that the meteor ignites at between 50 to 75 miles above the Earth’s surface. That may seem far but considering that Earth’s atmosphere extends more than 6,000 miles from the ground, it’s relatively an arm’s length away.
The colors of the rainbow
Meteors are more than just white flashes in the sky – each meteor shines in a specific color. Through a telescope lens, flaming meteors can glow in colors from red to violet.
What determines the meteor’s color is its chemical composition, because different elements burn in different shades. For instance, meteors composed primarily of magnesium glow a light blue, and those composed primarily of sodium glow orange.
The dust must add up
About 25 million meteors enter Earth’s atmosphere every day, but thankfully not all of them are noticeable or disastrous like the Lorton meteorite in the museum’s collection that fell through a doctor’s office in Virginia in 2010.
“The Lorton meteorite was one of the rare times that a meteorite hit a human-made structure,” said Cari Corrigan, a research geologist at the museum who examined the rogue rock. “When it was brought to us for identification, there were still marks on it from the roof and ceiling tile that it passed through!” According to Corrigan, the unsuspecting doctors narrowly missed being just the second person ever struck by a meteorite. Thankfully they caught a lucky break when one of their patients cancelled an appointment that afternoon. Otherwise, “one of them would have been in the exam room with the patient when the meteorite fell,” Corrigan said.
However, most meteorites burn up into dust before they reach Earth’s surface. Still, that ash and dust floats down eventually and makes for a lot of extra weight that the Earth must carry.
It’s estimated that meteors add roughly 50 tons or 100,000 pounds of weight to Earth’s mass every day – which may sound like a lot, but that’s only a fraction of a percent of Earth’s total mass. Also, Earth is actually losing more mass to space than it is gaining, so no need to fear being buried in space dust.
A shooting boulder
Meteorites have a wide range of size: from specks of dust to hard-to-miss. The fact is that most meteorites aren’t big enough to be noticeable when they land. Meteorites must be massive to cause a calamitous crash (as the dinosaurs unfortunately found out the hard way). But somehow, the largest meteorite found on Earth didn’t even leave a crater. Measuring nine feet across and weighing in at around 60 tons, this is a bit of a headscratcher.Hoba is the nickname of this behemoth meteorite, and it was found in 1920 by a farmer in Namibia. The reason for the absent crater isn’t confirmed, but scientists believe its shape may play a role. Hoba is fairly flat for a meteorite – three feet tall versus its nine-foot length – meaning that it may have fallen slower and thus hit softer than other meteorites that punch holes in the ground.
If you catch a glimpse of one of the Perseids glint across the sky or a rogue flash on any other night, just remember that meteors and meteorites have a lot more to them than meets the eye. Whether it’s a flash in the sky or a lump of space on the ground, meteors totally rock.