Thursday, July 25th 2019, 4:59 pm - Think you may have stumbled upon a meteorite? This expert guide will help you know for sure!
A blaze of light flashed through the early morning darkness on Wednesday, July 24, flaring so brightly that, for just a few moments, night became like day.
Finding the object behind this brilliant display could reveal answers to mysteries about the birth of our solar system, or could provide us with even deeper questions to be answered.
Here's your guide to meteorites, and everything you need to know to identify them.
- Rocks in space are known meteoroids (larger ones are usually called asteroids)
- When a meteoroid enters the atmosphere, it produces a streak of light across the sky, called a meteor
- Larger meteoroids produce a bright fireball, or can even explode as a bolide
- Any piece of a meteoroid or asteroid that hits the ground is called a meteorite
- There are three basic kinds of meteorites - iron, stony, and stony-iron
- Most meteorites contain some of the earliest minerals to form in our solar system, over 4.5 billion years ago
- Some meteorites are even from Mars or the Moon!
In general, the relationship between Earth and Space appears fairly tranquil.
We have a few prominent meteor showers each year, as well as several minor ones that may or may not be noticed, depending on the phase of the Moon and the local light pollution. Occasionally, there's an exceptionally bright meteor that flashes through our sky, and perhaps once a century, we witness something much bigger - such as the object that exploded over Chelyabinsk, Russia in February 2013.
The dawn sky over Chelyabinsk, Russia was lit up like full daylight on February 15, 2013, as this massive asteroid plunged into the atmosphere. The event was recorded by dashcam. Credit: Aleksandr Ivanov/Wikimedia Commons (CC BY 3.0)
In between these events, though, it doesn't seem like much happens.
Appearances can be deceiving, though.
Based on careful surveys, it is now estimated that, on any particular day, anywhere from 5 to 300 metric tons of cosmic rock and ice (aka meteoroids) plunge into Earth's atmosphere, all travelling at anywhere from 40,000 to 256,000 kilometres per hour when they hit the top of the atmosphere.
If we were able to capture a day's worth of accumulated meteoroids, before they flashed through the sky, we would find that most are microscopic dust grains and ice crystals. Mixed in with all of that microscopic matter would be some larger bits, and the larger the size, the fewer samples there'd be, with ones that get up over a metre in size being quite rare.
A primer on meteoroids, meteors and meteorites. Credits: Scott Sutherland/NASA JPL (Asteroids Ida & Dactyl)/NASA Earth Observatory (Blue Marble)
The smallest meteoroids go unnoticed as they enter the atmosphere. Although they're moving very fast, they are so small that they are either stopped immediately, or they vapourize without a trace. Some of the surviving dust can collect water vapour at very high altitudes, producing noctilucent clouds!
Larger grains survive longer, and produce streaks of light across the sky (aka meteors). This occurs as the bit of rock or ice compresses the air in its path, causing the air to heat up to the point where it glows. Many of these do not survive, as the intense heat of the air surrounding them eventually vapourizes them, as well.
Even larger meteoroids produce very bright meteors, which are called fireballs, or bolides if the meteoroid explodes, and these are the ones where pieces are likely to survive all the way to the ground, to become meteorites.
Watch below as Dr. Kim Tait, Curator of Mineralogy at the Royal Ontario Museum, talks about the three basic types of meteorites.
Here are some examples:
PIECES OF SOLAR SYSTEM HISTORY
Meteorites can tell us a lot about what went on in the early stages of our solar system, and even throughout its development, until the present day, and it's the stony ones that can tell us the most.
This is simply based on the crystals, granules and other components that make up each of these rocks, since many of them are virtually untouched since they were formed, over 4.5 billion years ago.
Royal Ontario Museum technician Ian Nicklin, below, relates just how much we can learn from one of these stony meteorites.
According to Nicklin, this large stony meteorite is a chondrite meteorite, named for the tiny, rounded mineral granules - known as chondrules - that surround the ancient calcium aluminum inclusions (CAI) he talks about here.
Nicklin says that there are likely many different processes that formed these chondrules, but invariably it involved the CAI crystals being flash heated to their melting point. In the zero-g environment of space, these molten minerals settled into rounded spheroid shapes and then quickly froze into that shape.
The meteoroid itself most likely formed over time as the chondrules and CAIs stuck together due to a combination of accumulated space dust, the gases in the space environment and the heat of these objects brushing up against one another as they jostled around in the inner solar system.
As simple conglomerations of these earliest minerals, chondrites are some of the most primitive objects in our solar system, and these represent the majority of meteorites found on Earth.
Less than 10 per cent of meteorites found are more evolved objects, known as achondrites. These were meteoroids that went through some kind of processing at an early point in their history - collisions, heating, melting - which melded all the chondrules together into a more uniform consistency, long before they came crashing down to Earth.
CHUNKS OF KNOWN OBJECTS
So, chondrites and achondrites represent some very primitive chunks of our solar system, but not all meteorites are.
Some were once part of much more evolved bodies, before they were were blasted into space, and eventually found their way to Earth's surface.