1. Habitability of Planets - George Hashimoto, Kobe University

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    from Kavli Frontiers of Science / Added

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    Habitability of Planets - Formation of Earth-like Planets George Hashimoto, Kobe University 1. Introduction The origin of life is one of the most attracting topic for mankind, but the question is still very open. It has been indicated that the first life appears on Earth at around 4.0 billion years ago. However, the surface environment around this important period of Earth’s history is uncertain because geologic evidence is very scarce. The surface environment of Earth must have a great influence on the origin of life. For example, results of the famous Miller-Urey experiment demonstrated that amino acids is synthesized by electric sparks in a hypothesized atmosphere. Subsequently, similar experiments established that the oxidation state of the atmosphere controls the yields of the synthesis of organic molecules greatly. The chemical composition of early Earth’s atmosphere would be a key for understanding the origin and early evolution of life. The composition of Earth’s early atmosphere has been considered rather oxidizing: CO2-rich mixtures with only trace amount of H2 and CH4 (e.g., Kasting, 1993). This prevailing view is based on the fact that modern volcanic gas composition is relatively oxidizing. However, origin of the oxidizing volcanic gas has not been examined. 2. Origin of the Earth and its Atmosphere Standard theories for the planetary formation predict that the planets grow via accretion of planetesimals. During the main accretionary phase, the atmosphere is probably reducing, since a large amount of metallic iron, which later becomes the core of the Earth, would be contained in the planetesimals. When the accretion of the Earth is almost completed, the accretional heat flux rapidly decreases and a hot proto-ocean would be formed as a result of the condensation of water vapor in the hot proto-atmosphere. Even after the formation of the first proto-ocean, proto-oceans would probably have been repeatedly vaporized by large impacts for several hundred million years. About 3.8 billion years ago, when the heavy bombardment of planetesimals is almost ended, the surface of the Earth probably started to harbor the life continuously since then. In the final stage of Earth’s accretion, an accretion of oxidizing material is inferred from the abundance of highly siderophile elements in the terrestrial mantle. Such late stage accretion of oxidizing material, so-called late veneer, is generally believed to generate an oxidizing atmosphere that is composed largely of H2O and CO2. However, whether H2O and CO2 were the main components of gas phase degassed from the late veneer is not examined yet. Recently, Hashimoto et al. (2007) examined the chemical composition of gas phase degassed from the late veneer. They demonstrated that the atmosphere generated by the late veneer is reducing, even if atmosphere is entirely generated by the accretion of CI chondrites that are the most oxidizing kind of meteorites. Although CI chondrites are one of the most oxidizing materials among the primitive materials in the solar system, it also contains reducing components such as organic matter. The gases formed through the decomposition of organic matter are intrinsically reducing. Even though some of the reducing gases are oxidized through the reaction with iron oxides, the abundance of oxygen stored in iron oxides is not enough to oxidize all the reducing gases released from organic matter. It is inevitable that an atmosphere generated by the late veneer contains a considerable amount of reducing gases. 3. Chemical Evolution of Atmosphere It is likely that the early reducing atmosphere is oxidized through hydrogen escape (e.g., Tian et al., 2005). When hydrogen is photodissociated from water vapor is lost, the remaining oxygen, a by-product of photodissociation, would oxidize the atmosphere. The timescale for hydrogen escape, which is the timescale for oxidation of the reducing atmosphere, is controlled by the energy available to drive the escape flow, since escape of hydrogen from a hydrogen-rich atmosphere is energy-limited. On the basis of the calculation made by Tian et al. (2005), it is likely that ancient terrestrial atmosphere had contained reducing species at least for a few hundred million years. 4. Conclusion The Earth’s early atmosphere is likely contain a significant amount of reducing species, such as H2, CO, and CH4, when the accretion is mostly completed. This conclusion is robust because reducing atmosphere is generated even if atmosphere is solely generated by accretion of CI chondrites. Since CI chondrites are the most oxidizing kind of meteorites, the atmosphere generated by CI chondrites will be the most oxidizing primitive atmosphere that is allowed in the currently accepted planetary formation theories. The most plausible process that changes the early reducing atmosphere into the present oxidizing one is hydrogen escape.

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    • Nit d'astronomia al Taller Natural

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      from celdenit.com / Added

      163 Plays / / 0 Comments

      Nit de dissabte 11 de maig del 2013 al Taller Natural, a Sobrecastell, després de la sessió d'observació del curs d'iniciació a l'astronomia. L'equip és una càmera Canon EOS 60Da amb objectiu Samyang 8mm, tot muntat sobre la dolly Zewide amb moviment en dos eixos. Es van fer més de 450 imatges de 20 segons d'exposició, a ISO 1600 i disparant en raw per al posterior tractament. http://www.eltallernatural.com/ http://www.zewide.com/

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      • Local Group - Milky Way - Andromeda

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        from intelArt / Added

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        Created by intelArt - 2013

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        • A Hold / The Moon

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          from András Somogyi / Added

          186 Plays / / 0 Comments

          Egy tavcsore szerelt webkameraval vettuk fel.

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          • Isaac Newton's Testimony for God

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            from Lorentz Force / Added

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            Isaac Newton was the first to make a reflecting telescope, first to describe the law of gravity, first to describe the laws of motion, first to use a prism to show how sunlight is made of seven colors (same as the rainbow), invented Calculus. He also gave his testimony that there is a God, a Deity, a Creator, and Isaac Newton was a Christian (not Catholic). I show you my Linux Mint 12 desktop, used to order a book through eBay: Life of Sir Isaac Newton, published in 1831, written by David Brewster, perhaps previously owned by John Watson in 1834. Isaac Newton studied the prophecies in the Holy Bible, including the book of Revelation, also called the Apocalypse of St John. Jesus is Lord and God has raised him from the dead.

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            • Starmap PRO demo video

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              from Star Map / Added

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              Starmap PRO is our most expansive pocket planetarium app. This incredible technology lets you view and learn about the universe in infinite detail. Based on the iPhone Compass geo-location technology, Starmap Pro is an upgraded version of the Starmap app. Starmap PRO is the most informative handheld planetarium app available, and comes with a host of extra features that make it a professional astronomer’s tool.

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              • Past Earths - David Grinspoon, Southwest Research Institute

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                from Kavli Frontiers of Science / Added

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                Astrobiology and Planetary Exploration: Contextualizing Life on Earth David Grinspoon, Southwest Research Institute The scientific study of the possibility of extraterrestrial life has been reinvigorated in recent years, and re-named, from the "fringe"field of exobiology to the more acceptable and well-funded meta-field of astrobiology. Astrobiology is a highly interdisciplinary endeavour, involving planetary science, astronomy, evolutionary biology and all of the Earth sciences. I will briefly discuss the historical and scientific reasons for the re-emergence of astrobiology and how this "science without a subject" is given solidity by research programs on Earth and in space. Increased understanding of the origin and evolution of life on Earth, and the co-evolution of life and the terrestrial environment, help us to understand the range of extraterrestrial planetary properties which might be suitable for biological evolution. Exploration of the solar system helps us to know the range of possible environments for life in the universe. In particular, the characterization of "exotic" worlds like Titan, with very different conditions from those that have facilitated life on Earth, but with rich organic chemistry, liquid environments and abundant energy sources, challenge our assumptions about the "universal" requirements for life.

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                • Inspirational Astronomy Quote

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                  from Axolitl / Added

                  56 Plays / / 0 Comments

                  Blake Bullock: “I know sometime people feel insignificant or small when they think about astronomy and they think about the cosmos. And I think it’s amazing that we’re the people, we’re the species who are able to understand how we got here. And that’s not small, that’s pretty amazing” From BBC Horizon “Seeing Stars” (2011)

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                  • Planet / Star Formation - Andrew Youdin, JILA, University of Colorado, Boulder

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                    from Kavli Frontiers of Science / Added

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                    The Birth of Planets in the Solar System and Beyond Andrew Youdin, JILA, University of Colorado, Boulder The origin of the Earth and the Solar System is one of the greatest and longest-standing questions in science, and indeed for humanity. Recent breakthroughs in the discovery of extrasolar planets demonstrates that planet formation is ubiquitous, and also that planetary systems are diverse. I will review current progress towards a unified model of planet formation. This model starts with the disks of dust and gas around a young star, and ends with the often chaotic orbital evolution of interacting planets. The intermediate steps are understood to varying degrees of theoretical certainty and observational confirmation. Finally I will discuss some aspects of Solar System history that can be studied in more detail, including the delivery of the Earth's water and the cometary bombardment that likely exterminated the dinosaurs.

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