Impact winter

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Artistic impression of an asteroid slamming into tropical, shallow seas of the sulfur-rich Yucatan Peninsula in what is today Southeast Mexico. The aftermath of this immense asteroid collision, which occurred approximately 66 million years ago, is believed to have caused the mass extinction of non-avian dinosaurs and many other species on Earth. The impact spewed hundreds of billions of tons of sulfur into the atmosphere, producing a worldwide blackout and freezing temperatures which persisted for at least a decade. Chicxulub impact - artist impression.jpg
Artistic impression of an asteroid slamming into tropical, shallow seas of the sulfur-rich Yucatán Peninsula in what is today Southeast Mexico. The aftermath of this immense asteroid collision, which occurred approximately 66 million years ago, is believed to have caused the mass extinction of non-avian dinosaurs and many other species on Earth. The impact spewed hundreds of billions of tons of sulfur into the atmosphere, producing a worldwide blackout and freezing temperatures which persisted for at least a decade.

An impact winter is a hypothesized period of prolonged cold weather due to the impact of a large asteroid or comet on the Earth's surface. If an asteroid were to strike land or a shallow body of water, it would eject an enormous amount of dust, ash, and other material into the atmosphere, blocking the radiation from the Sun. This would cause the global temperature to decrease drastically.[ quantify ] [2] [3] If an asteroid or comet with the diameter of about 5 km (3.1 mi) or more were to hit in a large deep body of water or explode before hitting the surface, there would still be an enormous amount of debris ejected into the atmosphere. [2] [3] [4] It has been proposed that an impact winter could lead to mass extinction, wiping out many of the world's existing species. The Cretaceous–Paleogene extinction event probably involved an impact winter, and led to mass extinction of most tetrapods weighing more than 25 kilograms (55 pounds). [5]

Contents

Possibility of impact

Each year, the Earth is hit by 5 m (16 ft) diameter meteoroids that deliver an explosion 50 km (31 mi) above the surface with the power equivalent of one kiloton of TNT. [6] The Earth is hit every day by a meteor less than 5 m (16 ft) in diameter that disintegrates before reaching the surface. The meteors that do make it to the surface tend to strike unpopulated areas and cause no harm. A human is more likely to die in a fire, flood, or other natural disaster than to die because of an asteroid or comet impact. [2] Another study in 1994 found a 1-in-10,000 chance that the Earth will be hit by a large asteroid or comet with a diameter of about 2 km (1.2 mi) during the next century. This object would be capable of disrupting the ecosphere and would kill a large fraction of the world's population. [2] One such object, Asteroid 1950 DA, currently has a 0.005% chance of colliding with Earth in the year 2880, [7] though when first discovered the probability was 0.3%. [6] The probability goes down as orbits are refined with additional measurements.

Over 300 short-period comets pass near larger planets, such as Saturn and Jupiter, which can change the comets' trajectories and could potentially put them into an Earth-crossing orbit. This could happen for long-period comets also but the chance is highest for short-period comets. The chance of these directly impacting Earth is far lower than a near-Earth object (NEO) impact. Victor Clube and Bill Napier support a controversial theory that a short-period comet in an Earth-crossing orbit does not need to impact to be hazardous, as it could disintegrate and cause a dust veil with possibilities of a "nuclear winter" scenario with long-term global cooling lasting for thousands of years (which they consider to be similar in probability to a 1 km impact). [8] [9] [10] [11]

Necessary impact factors

The Earth experiences a never-ending barrage of cosmic debris. Small particles burn up as they enter the atmosphere and are visible as meteors. Many of them go unnoticed by the average person even though not all of them burn up before they hit the Earth's surface. Those that strike the surface are known as meteorites. [4] Thus, not every object that hits the Earth will cause an extinction-level event or even cause any real harm. Objects release most of their kinetic energy in the atmosphere and will explode if they experience a column of atmosphere greater than or equal to their mass. [2] Extinction-level impacts on the Earth occur about every 100 million years. [3] [4] [12] Although extinction events happen very rarely, large projectiles can do severe damage. [2] [12] This section will discuss the nature of the hazards posed by projectiles as a function of their size and composition.

Size

A large asteroid or comet could collide with the Earth's surface with the force of hundreds to thousands of times the force of all the nuclear bombs on the Earth. [4] For example, the Cretaceous–Paleogene extinction event has been proposed to have caused extinction of all non-avian dinosaurs 66 million years ago. Early estimates of this asteroid's size put it at about 10 km (6.2 mi) in diameter. This means it hit with nearly a force of 100,000,000 MT (418 ZJ). [13] That is over six billion times larger than the atomic bomb yield (16 kilotons, 67 TJ) that was dropped on Hiroshima during WW2. This impactor excavated the Chicxulub crater that is 180 km (110 mi) in diameter. With an object this size, dust and debris would still be ejected into the atmosphere even if it hit the ocean, which is only 4 km (2.5 mi) deep. [3] An asteroid, meteor, or comet would remain intact through the atmosphere by virtue of its sheer mass. However, an object smaller than 3 km (1.9 mi) would have to have a strong iron composition to breach the lower atmosphere - the troposphere or the lower levels of the stratosphere. [2]

Composition

There are three different composition types for an asteroid or comet: metallic, stony and icy. The composition of the object determines whether or not it will make it to the Earth's surface in one piece, disintegrate before breaching the atmosphere, or break up and explode just before reaching the surface. [2] [4] A metallic object tends to be made up of iron and nickel alloys. [2] These metallic objects are the most likely to impact the surface because they stand up better to the stresses of ram pressure induced flattening and fragmentation during deceleration in the atmosphere. [2] The stony objects, like chondritic meteorites, tend to burn, break up, or explode before leaving the upper atmosphere. Those that do make it to the surface need a minimum energy of about 10  Mt (4×1016  J ) or about 50 m (160 ft) diameter to breach the lower atmosphere (this is for a stony object hitting at 20 kilometres per second (40,000 mph)). The porous comet-like objects are made up of low-density silicates, organics, ice, volatile and often burn up in the upper atmosphere because of their low bulk density (≤1 g/cm3 (60 lb/cu ft)). [2]

Possible mechanisms

Although the asteroids and comets that impact the Earth hit with many times the explosive force of a volcano, the mechanisms of an impact winter are similar to those that occur after a mega-volcanic eruption-induced volcanic winter. In this scenario massive amounts of debris injected into the atmosphere would block some of the Sun's radiation for an extended period of time and lower the mean global temperature by as much as 20 °C after a year. [3] The two main mechanisms that could lead to an impact winter are mass ejection of regolith and multiple firestorms.

Mass ejection of regolith

This diagram shows the size distribution in micrometres of various types of atmospheric particulate matter. Airborne-particulate-size-chart.svg
This diagram shows the size distribution in micrometres of various types of atmospheric particulate matter.

In a study conducted by Curt Covey et al., it was found that an asteroid about 10 km (6.2 mi) in diameter with the explosive force of about 108 MT could send upward of about 2.5x1015 kg of 1  μm sized aerosol particles into the atmosphere. Anything larger would fall quickly back to the surface. [3] These particles would then be spread throughout the atmosphere and absorb or refract the sunlight before it is able to reach the surface, cooling the planet in a similar fashion as the sulfurous aerosol rising from a megavolcano, producing deep global dimming. [3] [14] This is controversially purported to have occurred following the Toba eruption.

These pulverized rock particles would remain in the atmosphere until dry deposition and due to their size, they would also act as cloud condensation nuclei and would be washed out by wet deposition/precipitation, but even then, about 15% of the sun's radiation might not reach the surface.[ why? ] After the first 20 days, the land temperature might drop quickly, by about 13 °C. After about a year, the temperature could rebound by about 6 °C, but by this time about one-third of the Northern Hemisphere might be covered in ice. [3]

However, this effect could be largely mitigated, even reversed, by a release of enormous quantities of water vapor and carbon dioxide caused by the initial global heat pulse after the impact. If the asteroid hit an ocean (which would be the case with the majority of impact events), water vapor would form the majority of any ejected matter, and would likely result in a major greenhouse effect and a net increase in temperature.[ citation needed ]

If the impact event is sufficiently energetic it might cause mantle plume (volcanism) at the antipodal point (the opposite side of the world). [15] This volcanism could alone therefore create a volcanic winter, irrespective of the other impact effects.

Multiple firestorms

In combination with the initial debris ejected into the atmosphere, if the impactor is extremely large (3 km (1.9 mi) or more), like at the Cretaceous–Paleogene extinction event (estimated 10 km (6.2 mi)), there might be the ignition of multiple fire storms, possibly with a global reach into every dense and therefore firestorm-prone forest. These wood fires might release enough amounts of water vapor, ash, soot, tar and carbon dioxide into the atmosphere to perturb the climate on their own and cause the pulverized rock dust cloud blocking the sun to last longer. Alternatively it could cause it to last for a much shorter time, as there would be more water vapor for the rocky aerosol particles to form cloud condensation nuclei. If it causes the dust cloud to last longer, it would prolong the Earth's cooling time, possibly causing thicker ice sheets to form. [3] [14]

Past events

In 2016, a scientific drilling project drilled deep into the peak ring of the Chicxulub impact crater to obtain rock core samples from the impact itself. This crater is one of the best known impact craters and was the impact responsible for the extinction of the non-avian dinosaurs.

The discoveries were widely seen as confirming current theories related to both the crater impact and its effects. They confirmed that the rock comprising the peak ring had been subjected to immense pressures and forces, and had been melted by immense heat and shocked by immense pressure from its usual state into its present form in just minutes. The fact that the peak ring was made of granite was also significant, since granite is not a rock found in sea-floor deposits – it originates much deeper in the earth and had been ejected to the surface by the immense pressures of impact. Gypsum, a sulfate-containing rock that is usually present in the shallow seabed of the region, had been almost entirely removed and must therefore have been almost entirely vaporized and entered the atmosphere, and that the event was immediately followed by a huge megatsunami (a massive movement of sea waters) sufficient to lay down the largest known layer of sand separated by grain size directly above the peak ring.

These strongly support the hypothesis that the impactor was large enough to create a 120-mile peak ring, eject molten granite from deep within the earth, create colossal water movements, and eject an immense quantity of vaporized rock and sulfates into the atmosphere, where they would have persisted for a long time. This global dispersion of dust and sulfates would have led to a sudden and catastrophic effect on the climate worldwide by causing large temperature drops, devastating the food chain. [16] [17]

Impact on humans

Artist's impression of the Toba eruption, circa 74,000 years ago. Some scientists believe this eruption led to a population collapse and subsequent genetic bottleneck in humans. Tobaeruption.png
Artist's impression of the Toba eruption, circa 74,000 years ago. Some scientists believe this eruption led to a population collapse and subsequent genetic bottleneck in humans.

An impact winter would have a devastating effect on humans, as well as the other species on Earth. With the sun's radiation being severely diminished, the first species to die would be plants and animals who survive through the process of photosynthesis. This lack of food would ultimately lead to other mass extinctions of other animals that are higher up on the food chain and possibly kill up to 25% of the human population. [6] Depending on location and size of the initial impact, the cost of clean-up efforts could be so high as to cause an economic crisis for the survivors. [19] These factors would make life on Earth, for humans, extremely difficult.

Agriculture

With the Earth's atmosphere full of dust and other material, radiation from the sun would be refracted and scattered back into space and absorbed by this debris. The first effect on the Earth, after the blast wave and potential multiple fire storms, would be the death of most, if not all, of the photosynthetic life forms on Earth. Those in the ocean that survive would possibly become dormant until the sun came out again. [3] [6] Those on land could possibly be kept alive in underground microclimates, with one such example being the Zbrašov aragonite caves. Greenhouses in underground complexes with fossil or nuclear energy power stations could conceivably keep artificial sunlight growing lamps on until the atmosphere began to clear. Meanwhile, those outside that were not killed by the lack of sunlight would most likely be killed or kept dormant by the extreme cold of the impact winter. This death of plants might lead to a long period of famine if enough people survived the initial blast wave and would result in increased food costs in undeveloped countries only a few months after the first crop failures. Developed countries wouldn't encounter famine unless the cooling event was to last longer than a year, due to larger canned food and grain stockpiles in these countries. However, if the impactor was similar in size to the K/T boundary impactor, agricultural losses might not be compensated with imports to the northern hemisphere from the southern hemisphere or vice versa. [6] [19] The only way to keep from starving would be for each country to amass at least a year's worth of food for their people. Not many countries have this; the world's average cereal stock levels are only about 30% of the yearly production. [6] [20]

Economics

The cost to clean up after an asteroid or comet impact would cost billions to trillions of dollars, depending on the location impacted. [19] [20] An impact in New York City (the 16th most populated city in the world) could cost billions of dollars in financial losses and it could take years for the financial sector (i.e. stock market) to recover. [19] However, the probability of such a naturally specifically aimed impact would be exceedingly low.

Survivability

As of February 20,2018, there are 17,841 near-Earth objects known. 8,059 potentially hazardous objects are known; they are larger than 140 m (460 ft) and may approach the Earth closer than 20 times the distance to the Moon. [6] 888 NEAs larger than 1 km have been discovered, [21] or 96.5% of an estimated total of about 920. [22]

See also

Related Research Articles

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An impact crater is a depression in the surface of a solid astronomical body formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters are typically circular, though they can be elliptical in shape or even irregular due to events such as landslides. Impact craters range in size from microscopic craters seen on lunar rocks returned by the Apollo Program to simple bowl-shaped depressions and vast, complex, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth.

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<span class="mw-page-title-main">Near-Earth object</span> Small Solar System body with an orbit that can bring it close to Earth

A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun (perihelion) is less than 1.3 times the Earth–Sun distance. This definition applies to the object's orbit around the Sun, rather than its current position, thus an object with such an orbit is considered an NEO even at times when it is far from making a close approach of Earth. If an NEO's orbit crosses the Earth's orbit, and the object is larger than 140 meters (460 ft) across, it is considered a potentially hazardous object (PHO). Most known PHOs and NEOs are asteroids, but about 0.35% are comets.

<span class="mw-page-title-main">Tunguska event</span> 1908 meteor air burst explosion in Siberia

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<span class="mw-page-title-main">433 Eros</span> Near-Earth asteroid

433Eros is a stony asteroid of the Amor group, and the first discovered, and second-largest near-Earth object. It has an elongated shape and a volume-equivalent diameter of approximately 16.8 kilometers. Visited by the NEAR Shoemaker space probe in 1998, it became the first asteroid ever studied from its own orbit.

<span class="mw-page-title-main">Meteoroid</span> Sand- to boulder-sized particle of debris in the Solar System

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<span class="mw-page-title-main">Impact event</span> Collision of two astronomical objects

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<span class="mw-page-title-main">Asteroid impact avoidance</span> Methods to prevent destructive asteroid hits

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<span class="mw-page-title-main">Chicxulub crater</span> Prehistoric impact crater in Mexico

The Chicxulub crater is an impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is offshore, but the crater is named after the onshore community of Chicxulub Pueblo. It was formed slightly over 66 million years ago when an asteroid, about ten kilometers in diameter, struck Earth. The crater is estimated to be 200 kilometers in diameter and 1 kilometer in depth. It is believed to be the second largest impact structure on Earth, and the only one whose peak ring is intact and directly accessible for scientific research.

<span class="mw-page-title-main">Sudbury Basin</span> Third largest verified astrobleme on earth, remains of an Paleoproterozoic Era impact

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<span class="mw-page-title-main">Woodleigh impact structure</span> Impact structure in Western Australia

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<span class="mw-page-title-main">Alvarez hypothesis</span> Asteroid impact hypothesis as cause of the Cretaceous–Paleogene extinction

The Alvarez hypothesis posits that the mass extinction of the non-avian dinosaurs and many other living things during the Cretaceous–Paleogene extinction event was caused by the impact of a large asteroid on the Earth. Prior to 2013, it was commonly cited as having happened about 65 million years ago, but Renne and colleagues (2013) gave an updated value of 66 million years. Evidence indicates that the asteroid fell in the Yucatán Peninsula, at Chicxulub, Mexico. The hypothesis is named after the father-and-son team of scientists Luis and Walter Alvarez, who first suggested it in 1980. Shortly afterwards, and independently, the same was suggested by Dutch paleontologist Jan Smit.

<span class="mw-page-title-main">Geology of solar terrestrial planets</span> Geology of Mercury, Venus, Earth, Mars and Ceres

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<span class="mw-page-title-main">Cretaceous–Paleogene boundary</span> Geological boundary between time periods

The Cretaceous–Paleogene (K–Pg) boundary, formerly known as the Cretaceous–Tertiary (K–T) boundary, is a geological signature, usually a thin band of rock containing much more iridium than other bands. The K–Pg boundary marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. Its age is usually estimated at 66 million years, with radiometric dating yielding a more precise age of 66.043 ± 0.043 Ma.

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The climate across the Cretaceous–Paleogene boundary is very important to geologic time as it marks a catastrophic global extinction event. Numerous theories have been proposed as to why this extinction event happened including an asteroid known as the Chicxulub asteroid, volcanism, or sea level changes. While the mass extinction is well documented, there is much debate about the immediate and long-term climatic and environmental changes caused by the event. The terrestrial climates at this time are poorly known, which limits the understanding of environmentally driven changes in biodiversity that occurred before the Chicxulub crater impact. Oxygen isotopes across the K–T boundary suggest that oceanic temperatures fluctuated in the Late Cretaceous and through the boundary itself. Carbon isotope measurements of benthic foraminifera at the K–T boundary suggest rapid, repeated fluctuations in oceanic productivity in the 3 million years before the final extinction, and that productivity and ocean circulation ended abruptly for at least tens of thousands of years just after the boundary, indicating devastation of terrestrial and marine ecosystems. Some researchers suggest that climate change is the main connection between the impact and the extinction. The impact perturbed the climate system with long-term effects that were much worse than the immediate, direct consequences of the impact.

<span class="mw-page-title-main">Cretaceous–Paleogene extinction event</span> Mass extinction event about 66 million years ago

The Cretaceous–Paleogene (K–Pg) extinction event, also known as the K–T extinction, was the mass extinction of three-quarters of the plant and animal species on Earth approximately 66 million years ago. The event caused the extinction of all non-avian dinosaurs. Most other tetrapods weighing more than 25 kg (55 lb) also became extinct, with the exception of some ectothermic species such as sea turtles and crocodilians. It marked the end of the Cretaceous period, and with it the Mesozoic era, while heralding the beginning of the current era, the Cenozoic. In the geologic record, the K–Pg event is marked by a thin layer of sediment called the K–Pg boundary, Fatkito boundary or K–T boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium, which is more common in asteroids than in the Earth's crust.

<span class="mw-page-title-main">Timeline of Cretaceous–Paleogene extinction event research</span> Research timeline

Since the 19th century, a significant amount of research has been conducted on the Cretaceous–Paleogene extinction event, the mass extinction that ended the dinosaur-dominated Mesozoic Era and set the stage for the Age of Mammals, or Cenozoic Era. A chronology of this research is presented here.

<span class="mw-page-title-main">Impact events on Jupiter</span> Modern observed impacts on Jupiter

In modern times, numerous impact events on Jupiter have been observed, the most significant of which was the collision of Comet Shoemaker–Levy 9 in 1994. Jupiter is the most massive planet in the Solar System and thus has a vast sphere of gravitational influence, the region of space where an asteroid capture can take place under favorable conditions.

References

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