My last post was about meteoroids. Prior to that, I wrote about comets. I must now fill the third apex of this triangle of space nomads and write something about asteroids. The bulk of my post will feature one asteroid that probably changed the course of evolution on planet Earth but I will also cover a couple more in less detail. They need to be mentioned as they are interesting in their own right. First, some stamps about asteroids.
The stamp above: This stamp is issued by Luxembourg on 30th June 2018 in commemoration of "Asteroid Day"
The stamp below: This is an unusual stamp, issued by the nation of Bhutan. When studied, it shows a space ship traveling through a field of asteroids. It is unusual because, when observed, there is a 3 dimensional effect that has been included in the stamp.
Timelines
Before I get into the details about asteroids, it is important to be apprised of some basic facts.
It is estimated that the age of our planet is 4.5 billion years. There is credible historical evidence in the form of fossils found in Western Australia which demonstrate that forms of life have existed on Earth since at least 3.7 billion years ago. Furthermore, there are cohorts of researchers who believe that life may have existed on Earth even earlier, say 4.3 billion years ago.
In this timeline of events, the dinosaurs dominated most parts of the planet about 200 million years ago whilst human beings (homo sapiens) only appeared approximately 250,000 years ago. These are certainly unfathomable lengths of time when compared to the lifespan of an average human being.
To fully appreciate some of the points I present in this post, it is also important to have a 30 second primer in geologic time scales.
Here goes.....In order to describe the timing and relationship of events that have occurred over a long period of time (such as the Earth’s history), geologists, paleontologists and other Earth scientists have developed a geologic time scale (GTS). This is a system of chronological dating that relates strata in the geology of the Earth (stratigraphy) to time. For the purpose of this post, we only need to know that within the GTS, the Cretaceous is a geological period that lasted from about 145 to 66 million years ago whilst the Tertiary is a geologic period from 66 million to 2.6 million years ago.
The Alvarez Theory
Now, let's apply some of this knowledge and understand the basis of Alvarez's Theory. In a previous post I had written briefly on how a comet could "die" by plunging onto a planet and I highlighted the devastating example of the comet Shoemaker Levy impact into Jupiter which occurred in July 1994. If a comet could plunge into a planet, then surely, also could an asteroid with an equally catastrophic effect.
The Alvarez hypothesis, attributed to Nobel laureate Luis Alvarez and his son Walter, held that an asteroid, the size of San Francisco, traveling so fast that it compressed the air beneath it so violently that the air temperature was briefly several times hotter than the surface of the Sun, plunged through the atmosphere of Earth and crashed into the planet approximately 65 million years ago. The asteroid itself was so large (estimated at between 10.6 km and 80.9km in diameter) that even at the instant of contact with the surface of the shallow water of the sea, the top of the asteroid would have towered nearly two kilometres above the notional flying altitude of a passenger aircraft. The impact set off earthquakes greater than 11 in magnitude, widespread tsunamis and the shrouding of the globe in a thick cocoon of sky-blackening dust and debris for many years. This cataclysmic event not only claimed nearly 75 percent of all the species of life on our planet, including the dinosaurs (leaving only birds to carry their legacy), but also most varieties of flora and fauna and many types of microscopic organisms. It effectively ended the reign of the domination of the dinosaurs and opened the door for the ascension of mammals.
The Coverscape below: This coverscape, with a relevant stamp captures this life extinction event.
The Alvarez hypothesis was accepted as theory by an international panel of 41 experts in geology, paleontology, and other related fields after an exhaustive review of the relevant data in March 2010. Seminal evidence substantiating the theory was initially obtained in 1977 from Gubbio, Italy where a thin layer of red clay, found (by Walter Alvarez, a geologist) between the limestone, marking the end of the Cretaceous period and the beginning of the Tertiary period, was about 600 times richer in iridium than the surrounding limestone. Iridium, a silvery-white metal is virtually absent from the Earth’s crust, but high concentrations are common in extra-terrestrial objects, such as asteroids.The evidence became more convincing when this same “iridium anomaly” was subsequently discovered in clay layers at locations in Denmark and New Zealand, and later, more than a dozen other sites around the world. The iridium-spiked layers of clay also contained an abundance of soot. Comparisons of ratios between iridium and several other key elements in the clay layers indicated that the widely scattered iridium anomalies all came from the same source – one that was not of this earth.
This asteroid that caused this life extinction event is called the the Chicxulub Impactor.
A Few Seconds More ...
Our planet rotates on its axis every 24 hours. It is this rotation that gives us day and night. If the Chicxulub Impactor had arrived a few moments earlier, it would have plunged into the deep sea of the Atlantic Ocean, somewhere between Africa and the Americas. Alternatively, if it had arrived a little later, it would have plunged into the waters of the Pacific Ocean (to the left of the Americas on the map below). The depth of the water would have absorbed some of the force of the impact and limited the expulsion of much of the associated toxic fumes that choked the atmosphere for many of the subsequent months and years. Large dinosaurs may have survived such an impact and homo sapiens may not have had a chance to evolve, many eons later. It must be recalled that 65 million years ago, the relative positions of the continents, due to plate tectonics movement were different as shown in the map below. It is the simplest, relevant map I could retrieve that explains the position.
ApophisNow let's fast forward to present day.......
Apophis is an asteroid with an estimated diameter of 370 metres. It caused a brief period of concern in December 2004 as initial observations indicated a probability of up to 2.7% that it would hit our planet on 13th April 2029.
Apophis was discovered on 19th June 2004 by R. Tucker, D. Tholen and F. Bernardi. Additional observations provided improved predictions that eliminated the possibility of an Earth or Moon impact in 2029. However, until 2006, a possibility remained that during its 2029 close encounter with Earth, Apophis would pass through a gravitational keyhole that would set up a future impact exactly seven years later on 13th April, 2036. It was only in August 2006 that Apophis's rating on the Torino scale was lowered to zero (a rating of 0 indicates an object has a negligibly small chance of collision with the Earth whilst a rating of 10 indicates that a collision is certain, and the impacting object is large enough to precipitate a global disaster).
As things stand today, the closest known approach of Apophis will occur on 13th April 2029, when the asteroid comes within a distance of approximately 31,000 kilometres from Earth's surface. That distance is ten times closer than the Moon, and even closer than some man-made satellites. It will be the closest asteroid of its size in recorded history. It will be quite an event for the those interested in astronomy (and probably for many who are not!).
Hayabusa & Itokawa
The word "Hayabusa" translated in the Japanese language refers to a Peregrine falcon, a bird renowned for its speed in flight, having been recorded diving at more that 320 km/hr. Then in 1999, the Japanese motorcycle manufacturer, Suzuki, launched the Hayabusa (or GSX 1300R), which immediately won global acclaim as the world's fastest production sport motorcycle.
On 9th May 2003, the "Mu Space Engineering Spacecraft C", a robotic spacecraft developed by the Japan Aerospace Exploration Agency (which also adopted the "Hayabusa" name), was launched with the objective of making a complex rendezvous with a small near-Earth asteroid named Itokawa (discovered on 26th September 1998). Hayabusa was also to land on the asteroid, collect a sample of asteroidal material and return the collected sample back to Earth. The asteroid itself was named after rocket scientist Hideo Itokawa (1912 -1999), who is regarded as the father of Japanese rocketry. In mid September 2005, the Hayabusa spacecraft arrived at the rendezvous point. It then landed on the asteroid in November 2005, performed its sampling objectives and lifted-off from the asteroid. It returned the collected samples to Earth on 13th June 2010. Hayabusa is legendary because it was the first robotic spacecraft to land on an asteroid, collect a sample, lift off, and then, successfully return the sample to Earth.
The stamps below: These are issued by the nations of The Gambia (African continent) and again, also by Guyana (Latin America) commemorate the achievements of the Japanese Hayabusa mission. The series of stamps from Guyana are particularly instructive as they depict major milestones being achieved.
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It is worthwhile to mention a few words about Guyana. There is a trend that some small countries issue beautiful stamps to commemorate a variety of international achievements and events as a means of raising national income. It was a relatively poor country but in 2015, ExxonMobil discovered vast quantities of oil in its offshore areas. The capital of Guyana is Georgetown.
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