Rare, but potentially devastating, asteroids have historically, and will in the future, hit the Earth. The Earth is continually being hit by dust and small meteoridal material. Slightly larger pieces can be seen as meteors which burn up (by frictional heating) within the atmosphere. Occasionally larger pieces, circa metres in size will survive the journey through the atmosphere and hit the ground to give us a meteorite. Larger objects still can lead to notable events such as the Chelyabinsk event where an object circa 17m in size entered the atmosphere and exploded. These rare events can lead to local destruction and human casualties.
What we will consider in this month’s blog is what happens when a much larger object, such as a small asteroid, circa km(s) in dimension, hits the Earth.
A lot has been written and broadcast on the threat of asteroids colliding with the Earth and several Hollywood films have painted scenarios and stories on such events. Much of the popular material is by its nature sensationalist. It is unlikely there will be a major asteroidal impact on Earth within the next 50 years. However, this is not completely certain, and we will look at the potential for such an event to occur. That an asteroid will, if not deflected, hit the Earth in the future is certain and in a future blog we will review current known threats, and when this may be.
What we will consider in this month’s blog is what happens when a much larger object, such as a small asteroid, circa km(s) in dimension, hits the Earth.
A lot has been written and broadcast on the threat of asteroids colliding with the Earth and several Hollywood films have painted scenarios and stories on such events. Much of the popular material is by its nature sensationalist. It is unlikely there will be a major asteroidal impact on Earth within the next 50 years. However, this is not completely certain, and we will look at the potential for such an event to occur. That an asteroid will, if not deflected, hit the Earth in the future is certain and in a future blog we will review current known threats, and when this may be.
Rare, mais potentiellement dévastateurs, des astéroïdes ont historiquement frappé la Terre, et il y aura plus de collisions à l’avenir. La Terre est toujours en train d’être frappée par de petits rochers et de la poussière. De plus grands morceaux de rocher peuvent être vus comme des méteors qui brûlent dans l’atmosphère. De temps en temps de plus grands morceaux (qui mesurent plusieurs mètres) survivent le voyage à travers l’atmosphère et frappent le sol pour nous donner un météorite. Des objets plus grands encore peuvent entraîner des événements importants comme à Tcheliabinsk où un objet mesurant environ 17m entré dans l'atmosphèreterrestre est a explosé est entre dans l’atmosphère et a explosé. Ces événement rares peuvent provoquer des dégâts, des blessés et des morts.
We have seen earlier that many objects cross the Earth’s orbit and a subset of the NEOs are designated potentially hazardous asteroids (PHAs). PHAs are defined by having a potential minimum separation from the Earth of less than 0.05 AUs (about 7.5 x 10**6 km). Of course, some PHAs can and do come much closer to the Earth than this, and the Earth is continually being impacted by small pieces of matter (meteoroids). We can see these as meteors and occasionally, a meteoroid will survive (i.e. not burn up completely to dust by heating due to friction) its passage through the atmosphere to become a meteorite.
Where the impacting object is large enough, greater than about 1km in dimension, frictional burn-up and velocity reduction (from orbital speed) due to the Earth’s atmosphere will not significantly slow the object, and it will hit the Earth’s surface at high velocity.
Depending upon the size of the impactor, this can cause massive destruction to the local area. Shock waves, or tsunamis if the impact is into the ocean, can have huge effects on both the local geology and in wider scope, life on Earth. Potentially huge amounts of dust will be thrown into the atmosphere by the impact. The atmosphere can become opaque to sunlight reaching the surface and thus plant photosynthesis cannot continue. This would result in vegetation loss and consequently loss of species dependent upon plant life. Marine life is also affected as phytoplankton, the lowest of the food chain in the oceans, is critically dependent on light for photosynthesis. This would affect all the food chain; no plankton leads to no larger fish, and of course marine mammals such as whales.
Where the impactor is large enough, species extinctions can occur and have done so. Throughout the geological record, periods of mass extinction* across the whole Earth have been detected. We will look more at these and the correlation to asteroid impact in next month’s blog.
(*) A mass extinction event is defined as the global decrease in diversity of life forms. It does not
happen immediately but occurs geologically abruptly, i.e. over a period of 10**5 to 10**6 years. It is
believed that at least 15 such events have occurred on Earth over the past 550 million years.
The Chicxulub crater and impact are well documented and occurred in close correlation to the geological record for the demise of the dinosaurs. Less well known and documented, and more accessible to European readers and visitors, is the Rochechouart impact in Limousin, France. This event also has a close temporal correlation to a mass species extinction event.
Our book on the Limousin impact provides an investigation into the likely progenitor and details the local and wider-scale effects this impact had. This is a highly recommended read.
Where the impacting object is large enough, greater than about 1km in dimension, frictional burn-up and velocity reduction (from orbital speed) due to the Earth’s atmosphere will not significantly slow the object, and it will hit the Earth’s surface at high velocity.
Depending upon the size of the impactor, this can cause massive destruction to the local area. Shock waves, or tsunamis if the impact is into the ocean, can have huge effects on both the local geology and in wider scope, life on Earth. Potentially huge amounts of dust will be thrown into the atmosphere by the impact. The atmosphere can become opaque to sunlight reaching the surface and thus plant photosynthesis cannot continue. This would result in vegetation loss and consequently loss of species dependent upon plant life. Marine life is also affected as phytoplankton, the lowest of the food chain in the oceans, is critically dependent on light for photosynthesis. This would affect all the food chain; no plankton leads to no larger fish, and of course marine mammals such as whales.
Where the impactor is large enough, species extinctions can occur and have done so. Throughout the geological record, periods of mass extinction* across the whole Earth have been detected. We will look more at these and the correlation to asteroid impact in next month’s blog.
(*) A mass extinction event is defined as the global decrease in diversity of life forms. It does not
happen immediately but occurs geologically abruptly, i.e. over a period of 10**5 to 10**6 years. It is
believed that at least 15 such events have occurred on Earth over the past 550 million years.
The Chicxulub crater and impact are well documented and occurred in close correlation to the geological record for the demise of the dinosaurs. Less well known and documented, and more accessible to European readers and visitors, is the Rochechouart impact in Limousin, France. This event also has a close temporal correlation to a mass species extinction event.
Our book on the Limousin impact provides an investigation into the likely progenitor and details the local and wider-scale effects this impact had. This is a highly recommended read.
An example of impact melt from Rochechouart evidencing the Limousin asteroid impact.
(notice the pumice-like air pockets)
(notice the pumice-like air pockets)
Further reading
The Limousin Asteroid impact of the Triassic Rhaetian age
N Taylor. Observatoire Solaire. 2017. ISBN 978-1-999-904-41-8
Next Month
We will look at mass species extinctions events and their correlation to asteroid and comet impacts. The topic list for future monthly blogs is now included in our blog index (alongside previous monthly topics)
The Limousin Asteroid impact of the Triassic Rhaetian age
N Taylor. Observatoire Solaire. 2017. ISBN 978-1-999-904-41-8
Next Month
We will look at mass species extinctions events and their correlation to asteroid and comet impacts. The topic list for future monthly blogs is now included in our blog index (alongside previous monthly topics)
