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Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life
Estimates of these sources for plausible end-member oxidation states of the early terrestrial atmosphere suggest that the heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources.
Earth and Mars: Evolution of Atmospheres and Surface Temperatures
Solar evolution implies, for contemporary albedos and atmospheric composition, global mean temperatures below the freezing point of seawater less than 2.3 aeons ago, contrary to geologic and
A search for life on Earth from the Galileo spacecraft
In its December 1990 fly-by of Earth, the Galileo spacecraft found evidence of abundant gaseous oxygen, a widely distributed surface pigment with a sharp absorption edge in the red part of the
Cometary delivery of organic molecules to the early Earth.
A comprehensive treatment of comet-asteroid interaction with the atmosphere, surface impact, and resulting organic pyrolysis demonstrates that organics will not survive impacts at velocities greater than about 10 kilometers per second and that even comets and asteroids as small as 100 meters in radius cannot be aerobraked to below this velocity in 1-bar atmospheres.
Voyager 2 at Neptune: Imaging Science Results
Voyager 2 images of Neptune reveal a windy planet characterized by bright clouds of methane ice suspended in an exceptionally clear atmosphere above a lower deck of hydrogen sulfide or ammonia ices.
The early faint sun paradox: organic shielding of ultraviolet-labile greenhouse gases
It is shown that ultraviolet absorption by steady-state amounts of high-altitude organic solids produced from methane photolysis may have shielded ammonia sufficiently that ammonia resupply rates were able to maintain surface temperatures above freezing.
Encounter with saturn: voyager 1 imaging science results.
As Voyager 1 flew through the Saturn system it returned photographs revealing many new and surprising characteristics of this complicated community of bodies, including small inner satellites that interact gravitationally with one another and with the ring particles in ways not observed elsewhere in the solar system.
Ultraviolet selection pressure on the earliest organisms.
  • C. Sagan
  • Physics
    Journal of theoretical biology
  • 1 April 1973