Have you ever wished upon a shooting star and wondered what caused the streak of light hurtling through the sky? Astronomers call this phenomenon a meteor, and it can be a wondrous sight, especially if you are fortunate enough to view an event such as a meteor shower.
So, why do things burn up in the atmosphere? When an object hits the atmosphere, the air in front of it compresses incredibly fast. As a gas compresses, its temperature rises. The collision with the gas molecules also converts some of the object’s energy of motion, also known as kinetic energy, into heat. This causes objects to heat up to temperatures as high as 3000 degrees Fahrenheit (1650 degrees Celsius)!
And the air will keep the object burning until it vaporizes or strikes the Earth.
Objects are able to pass through the furthest layers of the atmosphere with no issue, known as the exosphere and the thermosphere, as these layers don’t contain any significant amount of air.
Most of the heating occurs between 100 and 50 kilometers from the Earth’s surface, in the outer fringes of our atmosphere called the mesosphere.
The mesosphere, which is approximately 35 kilometers thick, is the first layer where there is enough gas to collide with the object and create heat.
What Burns Up In The Earths Atmosphere?
Anything that travels at a significant enough speed can burn in the atmosphere. Predominantly these are objects called meteors. On rare occasions, space debris from man-made objects will enter the atmosphere. On even rarer occasions, an asteroid or comet can come into contact.
A solid body, while in the vacuum of space and before reaching the atmosphere, is called a meteoroid.
Upon entry into the atmosphere, it is referred to as a meteor.
Collisions with air molecules are extremely violent and begin to tear atoms off the body of the meteor, vaporizing its surface layers.
The rock is quickly stripped away by the intense heat.
The trail of hot, evaporated matter burned from the meteor, along with the meteor’s collision with the various gases of the atmosphere, emits energy in the form of light.
This is the glow we see as a falling star.
Most meteoroids that enter the atmosphere are the size of a raisin or smaller and completely vaporize.
Larger pieces, after being slowed down by air resistance, could survive the plummet and reach the ground.
The fragments that hit the Earth are then referred to as meteorites.
If the meteoroid is larger than a few centimeters when entering the atmosphere, it will create a ball of incandescent gas around it and sometimes leave a luminous or smoky trail.
These meteors, which are sometimes visible during daylight, are referred to as “fireballs.”
Rare cases of people being hit by meteorites have been recorded.
In a well-documented case in 1954, in Oak Grove, Alabama, a woman by the name of Ann Elizabeth Fowler Hodges was struck by a grapefruit-sized meteorite after it crashed through the roof of her house.
She was badly bruised but otherwise unharmed.
There is a common misconception that comets are the same as meteors.
A common theory is that a comet or asteroid struck the Earth about 65 million years ago, thus ending the reign of the dinosaurs.
However, lucky for us, a comet has never entered our atmosphere since. Comets are balls of ice and gas rather than rock.
They are visible as they near the sun and the ice melts, creating a trail of gas and dust particles behind it.
Can The Earth Be Destroyed By A Meteor?
Potentially, yes. If the meteor, or any celestial object for that matter, is large enough when it enters the atmosphere, it will not burn away completely and can cause catastrophic destruction when it strikes the Earth.
About 100 tons of meteoroids strike the Earth every day!
Fortunately for us, the atmosphere significantly slows down or burns up the majority of these.
However, the atmosphere can do very little to slow down meteoroids that are more than a few feet across.
Meteors of this size can potentially cause serious damage.
Every few thousand years, the Earth is struck by a large meteoroid, with a body many tens of meters or more in size.
These meteors can create an enormous blast on impact, as its remaining kinetic energy is released.
An impact by a meteoroid the size of a football stadium would have the explosive power of the largest thermonuclear bombs ever built.
When an object this size strikes the Earth at orbital speeds, the kinetic energy released travels away from the impact site in a shock wave that blasts out a deep crater.
Were this to occur in a heavily populated area, the results would be catastrophic.
Though we have been spared such a disaster recently, there have been some explosive impacts in the distant past.
One of the most famous is located in northern Arizona.
Approximately 50,000 years ago, a meteoroid estimated to have been around 50 meters in diameter struck the Earth about 40 miles east of what is now Flagstaff.
The result was a crater approximately 1.2 kilometers across and 200 meters deep.
In 2013, there were a number of recorded observations of a large meteor explosion over Russia.
The shock wave of the blast blew in windows and injured more than a thousand people.
The explosion was estimated to have been the equivalent of approximately 500 kilotons of TNT.
At What Speed Do Objects Burn Up In The Atmosphere?
An object traveling at speeds of approximately 10 to 40 kilometers per second will produce enough air pressure to begin burning.
The large range of speeds is caused by the fact that the Earth itself is traveling at approximately 30 km/sec as it orbits the sun.
On the evening side of the Earth, meteoroids must catch up to the Earth’s atmosphere and tend to be slower.
On the morning side of the Earth, meteoroids enter the atmosphere head-on and tend to be faster. This is similar to why you get wetter when you run through the rain.
Because of this difference in speeds, you are more likely to spot meteors between midnight and dawn rather than the evening hours.
So, if you want to make that wish on a shooting star, be prepared to stay awake until the early morning.
Can You Enter The Atmosphere Without Burning Up?
For a spacecraft to enter the atmosphere safely, it must approach the atmosphere at a precise angle so as not to skip off it and bounce back into space or, worse yet, meet a fiery end. Shielding is required to protect a rocket from the intense heat caused by friction with the air molecules.
Heat shields were originally developed during the Cold War to protect long-range ballistic missiles so they wouldn’t explode before reaching their targets.
Ablative heat shields, meaning they were designed to be damaged or destroyed in use, were made from a layer of heavy plastic resin.
With enough heat, the material on the shield burns up and causes a chemical reaction that pushes the hot gas away from the spacecraft.
These early models were designed for single use.
When reusable heat shields were required, they were designed using silica tiles that reradiated the heat outwards from the craft, while insulation between the tiles and the spacecraft was protected at the point of attachment.
Once properly shielded, the two remaining factors that need to be taken into consideration are the shape of the spacecraft and the angle of re-entry.
It was found that rockets with a blunt shape created a lower heat load.
This is due to the fact that air molecules can’t move out of the way quickly and actually serve as a cushion, slowing the vehicle down and keeping the hot gas away from the vehicle’s surface.
The angle that the spacecraft re-enters is also an important factor. If the angle is too steep, there is more friction and heat.
If it is too shallow, the spacecraft can skip out of orbit, similar to how a stone skips across a pond. A typical re-entry angle would be around 40 degrees.
Do Things Burn Up When Leaving The Atmosphere?
For the most part, things do not burn up when leaving the atmosphere. But that doesn’t mean they can’t.
There is always a point when a space shuttle reaches its maximum aerodynamic stress before leaving the atmosphere.
This is the threshold when it could potentially start burning up. During a normal shuttle launch, this altitude is reached at approximately 11 kilometers above the Earth’s surface.
At this point, the main engines of the shuttle are throttled back to about 70 percent of the thrust, minimizing the speed and avoiding the negative effects of the ascent that could cause burning.
Why Don’t Things Burn Up When Leaving The Atmosphere?
Shuttles do not burn up when leaving the atmosphere as they are going their slowest at low altitudes, where the air is the densest, and only reach high enough speeds to cause the friction needed for burning when the atmosphere is very thin.
The acceleration would be the smallest at lift-off, when the rocket’s mass, including all fuel, would be at maximum.
As fuel is consumed, the acceleration of the rocket increases. This also increases the friction between the rocket and the atmosphere.
The friction between the air and the rocket will slow the rocket down, causing it to burn more fuel to increase momentum.
Eventually, the shuttle will reach the point where the speed and friction could result in burning. This was discussed in the previous section.
Once the rocket clears the atmosphere, there are no gas particles to interact with the rocket, and the danger of burning would be clear.