nebular hypothesis
The advent of Earth traces back to a star forming nursery called a planetary nebula. This is referred to as the nebular hypothesis. Planetary nebula are expansive regions in space, typically one light year (5.88 trillion miles) in diameter, or larger, composed of gas and dust (typically 90% Hydrogen, 9% Helium, and oxygen, carbon, nitrogen, and other elements rounding out the remaining 1%). Planetary nebula condense to form stars, like our Sun, the star of our Solar System. This condensing, triggered by a supernova, or exploding star, begins a process known as accretion. Accretion is the process by which planetary nebula form protostars, or the beginning stage of a star's evolutionary cycle. Gravity and other forces are in full effect, driving the accretion process, which can ultimately yield a solar system like our own, with the local star (Sun) taking hold as the center, occupying 99.8% of the mass of the entire Solar System. The remaining 0.2% includes all of the planets, dwarf planets, moons, asteroids, etc., which are gravitationally bound to the Sun, as is the case for our solar system. The images shown below are of the Orion Nebula, which is located 1,500 light-years away, making it the closest large star-forming region to Earth. The Orion Nebula may resemble the nebula that our Sun was born from, 4.5 billion years ago. Alpha Centauri is the closest star system and closest planetary system to Earth's Solar System at 4.37 light-years from the Sun, or 25.7 trillion miles.
NASA Spitzer and Hubble Space Telescopes have teamed up to expose the chaos that baby stars are creating 1,500 light-years away in a cosmic cloud called the Orion nebula. (IC: NASA)
This image composite outlines the region near Orion sword that was surveyed by NASA Spitzer Space Telescope white box. The Orion nebula, our closest massive star-making factory, is the brightest spot near the hunter sword. (IC:NASA)
NASA Spitzer Space Telescope and ESA Herschel mission combined to show this view of the Orion nebula, found below the three belt stars in the famous constellation of Orion the Hunter, highlights fledgling stars hidden in the gas and clouds. (IC:NASA)
Astronomers using NASA Hubble Space Telescope have found a bow shock around a very young star in the nearby Orion nebula, an intense star-forming region of gas and dust. (IC:NASA)
NASA's Hubble Space Telescope has helped astronomers find the final piece of a celestial puzzle by nabbing a third runaway star. The stars were battling each other in a gravitational tussle, which ended with the system breaking apart and at least three stars being ejected in different directions. (IC:NASA)
The parts that are easily observed in visible light, known alternatively as the Orion Nebula or Messier 42, correspond to the light blue regions. This is the glow from the warmest dust, illuminated by clusters of hot stars that have only recently been born in this chaotic region. The red spine of material running from corner to corner reveals colder, denser filaments of dust and gas that are scattered throughout the Orion nebula. In visible light this would be a dark, opaque feature, hiding the reservoir of material from which stars have recently formed and will continue to form in the future. (IC:NASA)
The advent of Earth descends from the advent of our Sun. The advent of our Sun was an unremarkable, undeniably common event in the Universe, with regards to the stellar evolution cycle. The Milky Way galaxy contains billions of stars. And there are many billions of galaxies in the observable Universe.
The advent of Earth was an unremarkable event set against the size of the Universe, and the vast quantity of planets yielding from the development of stars and solar systems, past, present, & future.
Yet, the advent of Earth may have been the most remarkable event to occur in the Universe.
Life on Earth, life being a system, a self-sustaining chemical system capable of Darwinian evolution--is the only known life in the Universe.
Scientific instruments of incredible capacity on Earth, and in space, are in fact looking, frantically and passionately. We want to find it. And if it is there, humanity will find it.
But for now, it is only us. Only Earth. And we have so much understanding and work to accomplish.
Advent Earth is part of a penta-website network dedicated to the story of Earth and the future of humanity. Earth is likely to have four main phases over the course of its existence. Phase one is "Advent Earth", or the beginning. Phase two or the "How did Earth" emerge and develop conditions favorable to life. Phase three is present day, or generally speaking the ages of "A Living Earth". Phase four is the final act, "Farewell, Earth", as Earth as a defined planet will have an end point of its existence.
As for life, and in particular, human life, whether our existence extends beyond Earth and is sustained beyond Earth, or beyond our Solar System, those remain open, profound questions.
"Space Hazard" is a study and presentation of the many hazards and hardships of sustaining life off Earth.
(IC:NASA/JPL)
