Excalibur: Sword in the Stone
It is perhaps the most famous example of metal-meets-rock in the entire mythological multiverse. Excalibur, the sword in the stone. The first recorded account of this mythical sword shows it appearing on Christmas Eve, when it was embedded within an anvil poised on a rock. In a more famous version, dating to the 15th century, next to the sword, anvil and stone was found the inscription, "Whoso pulleth out this sword of this stone and anvil, is rightwise king born" Merlin, himself, was responsible for both the inscription and the embedded sword. As every noble aspired to the throne, each one of them attempted to extract the sword, but to no avail. Their lack of success was hardly surprising. Merlin made sure that the greater the exertion applied to its attempted withdrawal, the stranger its resistance to removal became. Even the mightiest noble couldn't so much as lift the sword a micrometer out of place. Finally, a humble squire in the service of Sir Kay, who knew nothing of the challenge but saw a sword within reach, effortlessly removed it from the anvil to everyone's amazement. When challenged to repeat the deed, he yet again did so with only the slightest effort. That simple squire, Arthur, then realized that he was not the son of Sir Ector, but of Uther Pendragon,himself and, consequently, the rightful heir to the throne.
It is perhaps the most famous example of metal-meets-rock in the entire mythological multiverse. Excalibur, the sword in the stone. The first recorded account of this mythical sword shows it appearing on Christmas Eve, when it was embedded within an anvil poised on a rock. In a more famous version, dating to the 15th century, next to the sword, anvil and stone was found the inscription, "Whoso pulleth out this sword of this stone and anvil, is rightwise king born" Merlin, himself, was responsible for both the inscription and the embedded sword. As every noble aspired to the throne, each one of them attempted to extract the sword, but to no avail. Their lack of success was hardly surprising. Merlin made sure that the greater the exertion applied to its attempted withdrawal, the stranger its resistance to removal became. Even the mightiest noble couldn't so much as lift the sword a micrometer out of place. Finally, a humble squire in the service of Sir Kay, who knew nothing of the challenge but saw a sword within reach, effortlessly removed it from the anvil to everyone's amazement. When challenged to repeat the deed, he yet again did so with only the slightest effort. That simple squire, Arthur, then realized that he was not the son of Sir Ector, but of Uther Pendragon,himself and, consequently, the rightful heir to the throne.
THE SOUTHWORTH PLANETARIUM
207-780-4249 www.usm.maine.edu/planet
70 Falmouth Street Portland, Maine 04103
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Altitude: 10 feet below sea level
Founded January 1970
Julian Date: 2459242.18
2020-2021: LXXVIII
THE DAILY ASTRONOMER
Wednesday, January 27, 2021
Wednesday, January 27, 2021
Exploratorium XIII: A Long Time Ago, a Hundred Light Years Away
Location
100 light years (or so) from Earth
Time
3 million years ago
In today's exploratorium, we venture into the distant past to watch a supernova explode. The time is 3 million years before modern day. The location is about 100 light years from Earth. Astronomers believe that a supernova exploded around this time and place. Today's topic pertains to how astronomers could possibly know this occurrence. And, how that knowledge relates to, of all things, ocean crust.
In today's exploratorium, we venture into the distant past to watch a supernova explode. The time is 3 million years before modern day. The location is about 100 light years from Earth. Astronomers believe that a supernova exploded around this time and place. Today's topic pertains to how astronomers could possibly know this occurrence. And, how that knowledge relates to, of all things, ocean crust.
Supernovae happen at the end of a highly massive star's life cycle. A star generates energy and sustains its structure by core thermonuclear fusion reactions. These reactions transform light elements into heavier ones (such as hydrogen into helium or carbon into oxygen, to cite two common examples.) The fusion transmutes some of the initial material into energy, the pressure from which balances the relentless gravitational compression. If a star is sufficiently massive, its core pressures are high enough to permit fusion of heavier elements, such as silicon and even iron. However, no star can produce the temperatures necessary for iron fusion. The exhaustion of the core iron reserves disrupts the balance between the contracting gravity and expanding energy. The outer layers collapse onto the core, precipitating an explosion.
Not only does the supernova destroy the star, it also imparts enough energy to facilitate the high-powered fusion reactions needed to create all the elements heavier than iron. The resultant heavy-element nebula expands through space, conveying the heavy elements to other star systems. So, if a supernova is close enough to a star/planetary system, its nebula will sprinkle particles onto the bodies within it.
Now, one might think that if we can identify these particles, we could conclude that a supernova happened nearby, right? Well, unfortunately, the issue is not quite that simple. You see, our solar system (including us) formed from a nebula that, itself, was rife with supernova elements. We're all composed of exploded star bits. How could we distinguish between recent supernova fragments and those that have been around awhile?
It's time to examine that ocean crust.
Scientists extracted pieces of what's known as "deep ocean ferromanganese crust" from the Pacific bottom. These iron rich-metallic crusts serve as handy geological repositories because they grow at the painfully slow rate of 2.5 millimeters per million years. By studying the different layers, scientists can identify the sediments that settled onto the crust at various epochs. Well, at the layer corresponding to the era about three million years ago, they discovered a sharp increase of iron-60: a radioactive iron isotope with a half life of 2.6 million years.* (Follow that asterisk if you'd like more information related to that last sentence.)
The presence of this radioactive iron compels us to ask: "how could it be there?" We know that nothing in the solar system could have smothered the planet with Iron-60. The only mechanism with which we're familiar is a supernova explosion: the event that creates heavy elements, including the radioactive Iron-60, and sends them in all directions around it. (Note: the radioactive Iron-60 within the supernova cloud that formed the solar system would have vanished long before.)
Based on the detected Iron-60 amounts, scientists estimate that the supernova exploded about 100 light years from Earth. (Had it been closer, the Iron-60 abundance would have been greater.) So, examination of the ferromanganese crust led to the Iron-60 discovery, that, itself, led to the supernova's "discovery." This "discovery" is not a direct sight discovery, but instead, a theory based on chemical analysis of the crust. The crust is acting like a telescope: enabling us to learn about a star that might have exploded within our vicinity.
Some worry that such proximate supernovae could destroy Earth life. Not only did this event not diminish life, but, as mentioned previously, it could have led to Earth's rapid human migration from its African origin. The idea is that the supernova energized cosmic rays. These enhanced rays might have precipitated more cloud particle condensation, resulting in increased cloud cover. Such cover would have reduced the solar heating and cooled the planet. Such cooling might have made the African region drier, prompting the inhabitants to migrate away to more favorable climes.
Now, that last paragraph is stuffed with assumptions!
The notion that this supernova indirectly led to human migration is a fascinating idea, but we cannot categorically state that this correlation existed. Again, it is a theory. However, it is intriguing to think that not only could a supernova have created the solar system, but that another one might have driven humans to populate the world.
*One can think of an "isotope" as being a type of element. Within a nucleus one finds protons and neutrons. The proton number defines the element; for instance, an Iron nucleus contains 26 protons. The Iron-60 nucleus also contains 34 neutrons: the sum of protons and neutrons defining the number 60. Iron-60 is radioactive, meaning that it spontaneously emits radiation as it transmutes to Cobalt-60. Half-life pertains to the transmutation rate. If we had an Iron-60 sample in front of us, half of it would change into Cobalt-60 in 2.5 million years. Another 2.5 million years would elapse before half of that sample transmuted.
Not only does the supernova destroy the star, it also imparts enough energy to facilitate the high-powered fusion reactions needed to create all the elements heavier than iron. The resultant heavy-element nebula expands through space, conveying the heavy elements to other star systems. So, if a supernova is close enough to a star/planetary system, its nebula will sprinkle particles onto the bodies within it.
Now, one might think that if we can identify these particles, we could conclude that a supernova happened nearby, right? Well, unfortunately, the issue is not quite that simple. You see, our solar system (including us) formed from a nebula that, itself, was rife with supernova elements. We're all composed of exploded star bits. How could we distinguish between recent supernova fragments and those that have been around awhile?
It's time to examine that ocean crust.
Scientists extracted pieces of what's known as "deep ocean ferromanganese crust" from the Pacific bottom. These iron rich-metallic crusts serve as handy geological repositories because they grow at the painfully slow rate of 2.5 millimeters per million years. By studying the different layers, scientists can identify the sediments that settled onto the crust at various epochs. Well, at the layer corresponding to the era about three million years ago, they discovered a sharp increase of iron-60: a radioactive iron isotope with a half life of 2.6 million years.* (Follow that asterisk if you'd like more information related to that last sentence.)
The presence of this radioactive iron compels us to ask: "how could it be there?" We know that nothing in the solar system could have smothered the planet with Iron-60. The only mechanism with which we're familiar is a supernova explosion: the event that creates heavy elements, including the radioactive Iron-60, and sends them in all directions around it. (Note: the radioactive Iron-60 within the supernova cloud that formed the solar system would have vanished long before.)
Based on the detected Iron-60 amounts, scientists estimate that the supernova exploded about 100 light years from Earth. (Had it been closer, the Iron-60 abundance would have been greater.) So, examination of the ferromanganese crust led to the Iron-60 discovery, that, itself, led to the supernova's "discovery." This "discovery" is not a direct sight discovery, but instead, a theory based on chemical analysis of the crust. The crust is acting like a telescope: enabling us to learn about a star that might have exploded within our vicinity.
Some worry that such proximate supernovae could destroy Earth life. Not only did this event not diminish life, but, as mentioned previously, it could have led to Earth's rapid human migration from its African origin. The idea is that the supernova energized cosmic rays. These enhanced rays might have precipitated more cloud particle condensation, resulting in increased cloud cover. Such cover would have reduced the solar heating and cooled the planet. Such cooling might have made the African region drier, prompting the inhabitants to migrate away to more favorable climes.
Now, that last paragraph is stuffed with assumptions!
The notion that this supernova indirectly led to human migration is a fascinating idea, but we cannot categorically state that this correlation existed. Again, it is a theory. However, it is intriguing to think that not only could a supernova have created the solar system, but that another one might have driven humans to populate the world.
*One can think of an "isotope" as being a type of element. Within a nucleus one finds protons and neutrons. The proton number defines the element; for instance, an Iron nucleus contains 26 protons. The Iron-60 nucleus also contains 34 neutrons: the sum of protons and neutrons defining the number 60. Iron-60 is radioactive, meaning that it spontaneously emits radiation as it transmutes to Cobalt-60. Half-life pertains to the transmutation rate. If we had an Iron-60 sample in front of us, half of it would change into Cobalt-60 in 2.5 million years. Another 2.5 million years would elapse before half of that sample transmuted.
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