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Monday, January 30, 2017
Maybe we are the first
I've said several times that it is possible that the human species is the first species in the Milky Way galaxy to evolve to our level of intelligence and technology. This opinion is based on information about just how much needs to happen to allow for the spark of life in conjunction with the apparent rarity of our own solar system. The recent study Relative likelihood for life as a function of cosmic time seems to confirm this idea.
A basic premise is that life requires stars for two different purposes. The study states,
Life is very unlikely to have occurred until Population I stars formed and supported terrestrial planets. Terrestrial planets in the Goldilocks Zone around their star then had to have the necessary events and composition to allow for the spark of life to occur, and subsequently support life until species of higher intelligence evolve.
This could explain why we've not seen evidence of extraterrestrial intelligent life in our galaxy. Maybe we are among the very first. Others like us are so rare, we will not be able to contact each other.
Maybe a billion years from now, a future intelligent species will evolve on some future (yet to exist) world, and when they point radio telescopes into their night sky, they receive a song of hundreds of thousands radio signals from just as many other civilizations. Maybe, if our species is able to continue evolving, our long-from-now-posterity becomes the evil invaders of other worlds, rather than our world being the one constantly invaded, as Hollywood would have us imagine. Maybe we are the monsters in waiting.
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A basic premise is that life requires stars for two different purposes. The study states,
Life requires stars for two reasons. Stars are needed to produce the heavy elements (carbon, oxygen and so on, up to iron) out of which rocky planets and the molecules of life are made. Stars also provide a heat source for powering the chemistry of life on the surface of their planets.[001]This means that rogue planets aren't likely to spark or support life. This also means that Population III and most Population II stars systems will not have life either, because they are unlikely to have the elements necessary to form terrestrial planets. That pretty much leaves us with Population I stars.
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| Rogue planet, artist concept |
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| Population III or II stars, artist concept |
What's all this about "Population"? It's a name for stars at various stages of galaxy development.
- Population III stars are the stars that likely formed right after the Big Bang. They have not been directly observed, so their existed is estimated. They were made up of mostly Hydrogen and Helium. As such, they are unlikely to have any planets.
- Population II stars are stars that are still made up of mostly Hydrogen and Helium, but have higher concentrations of elements such as Oxygen, Silicon, Neon, etc. Typically, such star systems are still unlikely to contain terrestrial planets. Many Population II stars still exist in our galaxy, though in regions without access to many heavier elements.
- Population I stars are stars that are yet again still made up of mostly Hydrogen and Helium, but have much higher concentrations of the more stable element Iron and other heavy elements. Population I star systems are much more likely to contain terrestrial planets. The Sun (Sol) is a Population I star.
Life is very unlikely to have occurred until Population I stars formed and supported terrestrial planets. Terrestrial planets in the Goldilocks Zone around their star then had to have the necessary events and composition to allow for the spark of life to occur, and subsequently support life until species of higher intelligence evolve.
Is Earth ahead of the curve for the development of life?
The previously mentioned study suggests that Earth may have developed life to the human-level a bit earlier than average. The study concludes that, "life around low mass stars in the distant future is much more likely than terrestrial life around the Sun today."[001] Life throughout the galaxy may be far more common billions of years from now than it is today. That also means that there may not be any/many other alien species with which we can contact and interact right now. The study puts our odds at 0.1%.[001]This could explain why we've not seen evidence of extraterrestrial intelligent life in our galaxy. Maybe we are among the very first. Others like us are so rare, we will not be able to contact each other.
Maybe a billion years from now, a future intelligent species will evolve on some future (yet to exist) world, and when they point radio telescopes into their night sky, they receive a song of hundreds of thousands radio signals from just as many other civilizations. Maybe, if our species is able to continue evolving, our long-from-now-posterity becomes the evil invaders of other worlds, rather than our world being the one constantly invaded, as Hollywood would have us imagine. Maybe we are the monsters in waiting.
Response:
Facebook1 and Facebook2
Article Series:
- Limited lifespan of Habitable Zones around other stars [and a loosely held secret finally revealed about me]
- Small stars may have stable Habitable Zones, but habitable planets might not be common there
- Habitable Planets around White Dwarfs
- Habitable Worlds Around Binary Star Systems might not match Sci-fi
- How many Earth-like planets are orbiting Sun-like stars?
- First round of life in the Universe might have been possible extremely early
- Factors a planet needs for suitability of life; perhaps
- "Goldilocks zone of metallicity" on a galactic scale
- Maybe we are the first
Saturday, January 28, 2017
Monday, January 23, 2017
"Goldilocks zone of metallicity" on a galactic scale
What does the night sky look like to a planet within the Galactic Bulge? Cool Cosmos describes it as,
The concept of Habitable Zones around stars has been studied for a couple of decades. Life similar to ours can only exist on planets that are a certain distance from their sun. This is due to the amount of energy from the sun that is received by the planet. Too much energy, the planet is too hot. Too little energy, the planet is too cold, hence the Goldilocks reference.
There's another type of Habitable Zone at the galactic scale which uses a somewhat different set of criteria. Solar systems which have planets that can support life must themselves be made from material that has a lot of elements that are heavier than Helium. In astronomy, elements heavier than Helium are often referred to as metals. Metal content of a star is called its metallicity. The danger is that is if a solar system is made from material that is too rich in metallicity, Earth-sized planets may not be able to exist due to the likelihood of much larger (heavier) worlds displacing those Earth-size planets. Hence, "Goldilock zone of metallicity" is the idea that certain regions of a galaxy may be too metal-rich and other regions may be metal-poor in order to allow for the presence of Earth-like worlds.[002]
Where can solar systems with habitable planets reside within the Milky Way? According to the study The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way, the inner bulge component, diffuse halo component, and a thick disk component of our Milky Way Galaxy would not likely allow for Earth-size planets to exist within the right timeframe.[002] So, the Habitable Zone of our Milky Way Galaxy isn't even really based on distance from the galactic core. It's a somewhat washer-shape region in between all the places that Earth-sized planets cannot exist within solar systems.
Knowing our Milky Way's Habitable Zone helps us in the search for life on other worlds. We can focus more efforts on this space. This isn't to say that this is the only space where life can and does reside. The Galactic Habitable Zone is just our safest bet for finding evidence of life.
Primary reference:
C. H. Lineweaver,Y. Fenner, B. K. Gibson, Science 303:59–62, DOI: 10.1126/science.1092322, The galactic habitable zone and the age distribution of complex life in the Milky Way
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Stars in the Galactic Center are so concentrated that they typically are only a few light weeks away from each other. In contrast, our local neighborhood of stars are separated from one another by light years. If we found ourselves on a planet near the Galactic Center, our nighttime sky would light up in a blazing display every night, filled with stars as bright as the planet Venus looks to us.[001]However, would there be a habitable planet from which to see this sight? Is it possible to have life-supporting planets near the Galaxy's center?
The concept of Habitable Zones around stars has been studied for a couple of decades. Life similar to ours can only exist on planets that are a certain distance from their sun. This is due to the amount of energy from the sun that is received by the planet. Too much energy, the planet is too hot. Too little energy, the planet is too cold, hence the Goldilocks reference.
There's another type of Habitable Zone at the galactic scale which uses a somewhat different set of criteria. Solar systems which have planets that can support life must themselves be made from material that has a lot of elements that are heavier than Helium. In astronomy, elements heavier than Helium are often referred to as metals. Metal content of a star is called its metallicity. The danger is that is if a solar system is made from material that is too rich in metallicity, Earth-sized planets may not be able to exist due to the likelihood of much larger (heavier) worlds displacing those Earth-size planets. Hence, "Goldilock zone of metallicity" is the idea that certain regions of a galaxy may be too metal-rich and other regions may be metal-poor in order to allow for the presence of Earth-like worlds.[002]
It's not just the metals
Metallicity is not the only factor, however.Early intense star formation toward the inner Galaxy provided the heavy elements necessary for life, but the supernova frequency remained dangerously high there for several billion years.[002]If a solar system is too close to the galactic core, the intense supernova frequency in a young galaxy might've keep many worlds from supporting life. This is because they would have experienced numerous blast waves, cosmic rays, gamma rays and x-rays that are fatal to lifeforms.[002] As the collective of solar systems age and die, they would have contributed to increasing metallicity. This means, the right conditions for life on Earth-like planets may have never happened near the galactic core. Stars that are too close to the galactic core never had and never will have the right conditions to support Earth-like worlds with Earth-like life.
Where can solar systems with habitable planets reside within the Milky Way? According to the study The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way, the inner bulge component, diffuse halo component, and a thick disk component of our Milky Way Galaxy would not likely allow for Earth-size planets to exist within the right timeframe.[002] So, the Habitable Zone of our Milky Way Galaxy isn't even really based on distance from the galactic core. It's a somewhat washer-shape region in between all the places that Earth-sized planets cannot exist within solar systems.
Current Habitable Zone of Milky Way
Given all of these factors, the authors of the study The Galactic Habitable Zone and the Age Distribution of Complex Life in the Milky Way state,We identified the Galactic habitable zone (GHZ) as an annular region between 7 and 9 kiloparsecs from the Galactic center that widens with time and is composed of stars that formed between 8 and 4 billion years ago.[002]
Primary reference:
C. H. Lineweaver,Y. Fenner, B. K. Gibson, Science 303:59–62, DOI: 10.1126/science.1092322, The galactic habitable zone and the age distribution of complex life in the Milky Way
Response:
Facebook 1
Facebook 2
meneame
Article Series:
- Limited lifespan of Habitable Zones around other stars [and a loosely held secret finally revealed about me]
- Small stars may have stable Habitable Zones, but habitable planets might not be common there
- Habitable Planets around White Dwarfs
- Habitable Worlds Around Binary Star Systems might not match Sci-fi
- How many Earth-like planets are orbiting Sun-like stars?
- First round of life in the Universe might have been possible extremely early
- Factors a planet needs for suitability of life; perhaps
- "Goldilocks zone of metallicity" on a galactic scale
- Maybe we are the first
Sunday, January 22, 2017
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