Practice English Speaking&Listening with: The Dangerous Nature of Near Earth Asteroids

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This is the asteroid Toutatis.

Its just a rock like countless others in the solar system, except that its a dangerous

one.

It is 2.5 kilometers wide, is loosely composed, essentially a conglomeration of rubble and

due to frequent planetary approaches, it has a very chaotic orbit.

And, it could someday hit earth.

If it did, it could destroy human civilization.

In 1992, 1996, 2000, 2004, 2008, 12 and 16, this object made very close passes of earth

and will do so again in the coming decades.

There is a chance it could eventually hit us.

While its not likely to ever impact earth, its expected to be ejected at some point

from the inner solar system before it likely has a chance of impacting, it does illustrate

one of the spooky realities of the solar system.

That at any time Earth could be hit by an asteroid or comet.

This happens routinely on a small scale, meteorites fall on earth constantly, and each year several

detections of larger airbursting meteorites are picked up, typically over the oceans.

Sometimes though, they do occur over land, such as the Chelyabinsk meteorite over Russia,

which cause significant damage including broken windows over a large area, and even caused

the collapse of a brick building.

On a larger, crater forming scale, impacts are less common, but moderate sized crater

forming events have happened within the scope of human prehistory, including a recently

discovered crater in Greenland that was buried under a glacier.

We obviously survived it.

But very large events that threaten extinction are much rarer, but as the impact that ended

the Cretaceous period shows, they do indeed happen, and while rare, nothing currently

stops them from happening again.

But there are efforts to detect near earth asteroids underway and many objects have been

found that have some chance of eventually colliding with earth.

These are termed PHOs, for potentially hazardous objects.

They further break down into two groups, potentially hazardous asteroids, and potentially hazardous

comets.

There are currently thousands of potentially hazardous asteroids known, and at least 8

short-period comets that come close enough to earth to be considered dangerous.

While none are currently slated to actually impact earth, if one did the damage would

be beyond catastrophic.

Even small events, such as Chelyabinsk, which was about 20 meters in diameter, produced

an airburst detonation 30 times greater than the Hiroshima bomb.

An asteroid the size of Toutatis impacting would be utterly catastrophic for life on

earth.

We can get some idea of what this might be like by looking at the end Cretaceous or K-T

impact.

There are a number of surviving indicators that this impact occurred.

The first clue was the discovery of a layer in the geologic record from about 66 million

years ago that bears high levels of iridium.

Iridium is a rare element on earths surface, due to it sinking down to the core early in

the planets history.

But it remains very common in asteroids.

Also found were spherules of formerly molten rock that were created in the impact, along

with shocked quartz.

Then came the discovery of evidence of gigantic tsunamis around the modern Caribbean, and

it was found that the beds get thicker in areas of North and Central America.

Finally was the discovery of the crater itself, which has been identified to underlie part

of Mexicos Yucatan peninsula.

This impact would have presented a truly apocalyptic vision.

While the exact size of the impactor is not known, it was somewhere between 11 and 81

kilometers in diameter -- much larger than Toutatis -- and would have unleashed the energy

of conceivably hundreds of billions hiroshima bombs.

The impact instantly vaporized the gypsum ocean floor digging directly into the underlying

granite, excavating the crater.

From there a megatsunami, estimated at over 100 meters tall, would have devastated nearby

coastlines.

Oddly, however, the tsunami could have been much, much worse.

It was limited by what are believed to have been shallow waters in the area.

Had the impact occurred in deep ocean, it could have conceivably been several miles

tall.

At this time, there would also have been massive amounts of steam and excavated material being

released as the object penetrated the ground.

Some of that material would have been ejected out of the atmosphere, only to fall again

and possibly cause widespread wildfires.

Subject to the massive shock waves generated by the even, planet earth would have then

unleashed volcanism and earthquakes and the atmosphere would have been filled with particulate

matter that would hang around for years, all of which may have had secondary roles in the

mass extinction of life that followed the impact.

Indeed, there is fossil evidence of an immediate mass die off of animal life in the wake of

the impact thousands of miles away from it.

The aftermath of the impact however would see far more death.

For over a decade, dust particles from the impact hung in the atmosphere, causing dramatic

surface cooling, a kind of impact winter.

This would have directly affected much of life on earth, but most damaging was the drop

in photosynthesis, which in turn seriously affected the food chain on earth, though increases

in levels of carbon dioxide released from the event may have helped the recovery of

what survived of the plants after the dust settled.

Following this would be a period of mass extinction of animal life, where the world would see

three quarters of its plant and animal species go extinct, opening the way for the

evolution and dominion of mammals which would ultimately lead to us and our civilization.

In a way, we owe our existence to an asteroid impact.

But, our own extinction could easily come at the hands of an asteroid.

And, even small ones could do serious, if not fatal damage to our civilization, if one

of the regularly occurring larger meteorite falls were to happen directly over a major

city.

Perhaps the most famous of these kinds of airbursts was the 1908 Tunguska Event, where

an object from space entered the earths atmosphere and detonated relatively close

to the ground.

The explosion felled 2000 square kilometers of forest, but luckily the event occured over

an unpopulated area in Siberia, and there are no known officially recorded deaths of

any humans, though it may have killed two people according to unofficial accounts.

The reindeer in the area are a different story, charred corpses of hundreds of them were reported.

Tunguskas yield was roughly equivalent to a large nuclear detonation, something similar

in yield to the USs largest ever nuclear test, Castle Bravo, though considerably smaller

than Russias biggest test, the tsar bomba.

If Tunguska had detonated over a city, the devastation would have been similar to that

of a nuclear war, essentially obliterating anything under it.

While evidence of a meteoric nature for Tunguska has been advanced, its not totally settled

if it it was, in fact an asteroid, but instead a comet.

But another incident is certain because it went off like a bomb and shot iron meteorite

shrapnel all over a mountainside.

In 1947 over, once again, over the huge landmass of Russia, an iron asteroid entered the atmosphere

and broke apart.

Due to it happening during daylight hours, it was widely witnessed.

The impacting fragments and shrapnel from the meteorites did form small craters, but

fundamentally the original object effectively blew into more or less tiny pieces.

No one is known to have been injured by the fall, but its not hard to imagine the damage

that could be done to a city if tens of thousands of kilograms of iron fell out of the sky on

it.

But, this very thing may actually have happened in the past.

Perhaps the most disturbing incident involving falling rocks from space happened in the year

1490 in China.

The information on this one is scant, but there are accounts, generally considered by

historians as reliable, of rocks falling from the skies and killing apparently up to ten

thousand people.

Thats a lot, especially for an airburst meteorite fall that didnt form a known

crater, or leave a ton of meteorites around that wed still be able to find in weathered

condition today.

And, one wonders about things like ridiculously sized hail that can occasionally fall on earth.

But one particular account sounds very much like a meteorite fall.

It describes stones that fell that were the size of goose eggs and smaller ones the size

of water chestnuts.

It then goes on to say that more than ten thousand people were killed, and that everyone

else in the city fled.

Until actual meteorites from this event are found, its difficult to say for sure exactly

what happened in 1490 in China.

But it does stand as a warning sign that even moderate to small meteorite falls can be seriously

dangerous locally.

Its unlikely that, for the foreseeable future, we will be able to detect and mitigate

these types of occurences.

But with larger impacts, we do have hope.

While smaller objects like Tunguska would be more difficult to detect, large potentially

very dangerous asteroids like that which impacted at the end of the cretaceous are more easily

detected and tracked.

While the odds are low, one prediction is that there is a 1 in 10,000 chance of earth

being impacted within the next century, on longer time scales it is a certainty that

an impact will occurif we dont mitigate the threat through detection and deflection

of the asteroid before hand.

We are only just recently technologically able to start tracking potentially dangerous

near earth asteroids.

But, if an immediate threat presented itself to us, were probably not quite yet to the

level where we could do much about it, if we had only a few months or years to try.

We would simply have to hope for the best, and those that might have survived the impact

would need to trudge on, if possible, through the resultant impact winter and massive global

disruption that would occur.

Effectively, well either survive, or we wont and its anyones guess if civilization

itself would continue.

Science fiction has taken on this trope many times, dystopian worlds where civilization

falls and a new dark ages falls upon humanity.

This has happened before in human history, where a level of civilization is achieved,

but then conditions change, as it did with the western Roman Empire, the Mayan city states

of Central America, Cahokia in North America, et cetera where that civilization can no longer

be maintained at its previous level.

The people adapt and survive, but the civilization as it was does not, and only parts of it make

it through to the new paradigm.

That might be the case with an impact event, where a handful of people survive, presumably

on canned food stockpiles, but the paradigm change is so great that many things that once

made sense, no longer do.

Theres not much point to manufacturing much of what we currently use as a civilization

if electricity can no longer be generated, for example.

Indeed, technologies that no longer work can become a liability in such a case, such as

being stuck in a building with electronic locks.

At that point, the lock is no longer useful.

Then formerly obsolete techniques and technologies must be relearned, such as subsistence farming

with manual tools and labor.

In such case, this favors groups that still remember those skills.

Same with manual methods of irrigation, building shelters, and so on.

Even what was formerly trash to be discarded can be become situationally useful, such as

plastic bottles for holding and storing clean water.

Or even keeping seeds over winter from the mice ... if they hadnt gone extinctwhen

enough dust settles for agriculture to become possible again.

But eventually, technology might return, useful things are useful things after all, and humans

are on the whole resilient and intelligent, but in the short term the only carry overs

to the new civilization might be things like religions, folk tales that can be told from

memory about how the world once was, perhaps some literature, and so on.

And, quite a bit of archeological evidence of what happened.

Or, say we dont survive, post-apocalyptic earth would be left to its own devices.

Its unlikely that an impact event can eradicate all life on earth.

The KT event didnt, there are animals still around whose ancestors once walked with the

dinosaurs, such as the alligators and crocodiles.

Or were dinosaurs in the case of the birds.

Its uncertain why these animals survived, but a clue may lie in that the crocodiles

and alligators at least havent changed that much from what they were like at the

time of the impact.

That may mean that these animals are just simply extremely well adapted to living on

this planet, even when things arent so nice.

Even more resilient are the insects.

Even during major past mass extinctions, they tended to weather them relatively unscathed.

Only during the particularly awful end Permian extinction were they seriously affected.

That extinction, which ironically allowed for the rise of the dinosaurs, makes the end

cretaceous extinction look like an amusement park fun ride, yet its linked to massive

volcanism rather than any single impact event.

That was, however, before we came along with our environmental changes and pesticides,

there is currently a mass extinction of insects occuring right now.

Look around, this is what a typical day in what a technological mass extinction looks

like.

But even if the insects were wiped out, there is still one form of life on this planet that

would almost certainly survive.

The microbes.

Its thought that they are impervious to most forms of mass extinction likely to happen

to earthexcept that from the sun as it ages.

Nothing can survive the baking of the earth.

As a result, even after a major impact event whatever is left of life on earth would continue

to evolve and would result in a changed, but still living world.

Perhaps in the far future another civilization might arise, this time based on something

other than a primate.

Perhaps not even a mammal.

But all is not lost, we are fast gaining enhanced ability to detect threatening objects.

The more we look and catalog these objects, the better chance well have in detecting

a problem years before the impact, allowing us come up with a strategy to avoid disaster.

This is possible, there are several hypothetical ways to deflect an asteroid, and the more

time you have, the easier it would generally be to deflect the asteroid.

In the future though, well have a full command of the asteroids of the solar system,

and here the the potential threat they present to us yields to asteroids and their movements

being extremely useful.

The first will be to mine them for materials, which we will no doubt do as they stand as

a ready source of valuable materials that we can use when colonizing space.

Even today, asteroids are being looked at as a possibility for profitable ventures mining

precious metals from them.

But in the far future, asteroids may provide us with a means of saving earth.

Over very long periods of time, asteroids can be used to gravitationally tug planets

into different orbits, including earth.

As the sun ages, it may be advantageous for us to simply migrate earth outward, if were

still around.

Hopefully we are, but one last thing about asteroid impacts, its recently been found

that the frequency of asteroid impacts on earth has doubled over the last few hundred

million years.

Thanks for listening!

I am science fiction author and futurist John Michael Godier currently plugging Astrotours.com.

This coming June, I will be joining Fraser Cain, Paul Sutter and quite a few others for

the all stars star party tour at Joshua Tree National Park.

See the astrotours website, link below, for details and check out my books at your favorite

online book retailer and subscribe to my channel for regular, in-depth explorations into the

interesting, weird and unknown aspects of this amazing universe in which we live.

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