series ring 
Helium is a chemical element with symbol He and atomic number ___MASK78___ . It is a colorless , odorless , tasteless , non - toxic , inert , monatomic gas , the first in the noble gas group in the periodic table . Its boiling point is the lowest among all the elements . ___MASK60___ ( often shortened to SF , sci - fi or scifi ) is a genre of speculative fiction , typically dealing with imaginative concepts such as futuristic science and technology , space travel , time travel , faster than light travel , parallel universes , and extraterrestrial life . ___MASK60___ often explores the potential consequences of scientific and other innovations , and has been called a " literature of ideas ." It usually avoids the supernatural , and unlike the related genre of ___MASK18___ , historically science fiction stories were intended to have a grounding in science - based fact or theory at the time the story was created , but this connection is now limited to hard science fiction . ___MASK61___ is a characteristic distinguishing physical entities having biological processes , such as signaling and self - sustaining processes , from those that do not , either because such functions have ceased , or because they never had such functions and are classified as inanimate . Various forms of ___MASK61___ exist , such as plants , animals , fungi , protists , archaea , and bacteria . The criteria can at times be ambiguous and may or may not define viruses , viroids , or potential artificial ___MASK61___ as " living ". Biology is the primary science concerned with the study of ___MASK61___ , although many other sciences are involved . A generation ship , or generation starship , is a hypothetical type of interstellar ark starship that travels at sub - light speed . Ring is a 1994 ___MASK60___ ___MASK91___ by author Stephen Baxter . Ring tells the story of the end of the universe and the saving of mankind from its destruction . Two parallel plots are followed throughout the ___MASK91___ : that of Lieserl , an AI exploring the interior of the sun , and that of the Great Northern , a generation ship on a five - million - year journey . A starship , ___MASK49___ or interstellar spacecraft is a theoretical spacecraft designed for traveling between planetary systems , as opposed to a vehicle designed for orbital spaceflight or interplanetary travel . An interstellar ark or Generation ship is a conceptual space vehicle designed for interstellar travel . Interstellar arks may be the most economically feasible method of traveling such distances . The ark has also been proposed as a potential habitat to preserve ___MASK36___ and knowledge in the event of a global catastrophe . Carbon ( from " coal ") is a chemical element with symbol C and atomic number 6 . It is nonmetallic and tetravalent  making four electrons available to form covalent chemical bonds . Three isotopes occur naturally , C and C being stable , while C is a radioactive isotope , decaying with a half - ___MASK61___ of about 5 , 730 years . Carbon is one of the few elements known since antiquity . A star is a luminous sphere of plasma held together by its own gravity . The nearest star to ___MASK46___ is the Sun . Many other stars are visible to the naked eye from ___MASK46___ during the night , appearing as a multitude of fixed luminous points in the sky due to their immense distance from ___MASK46___ . Historically , the most prominent stars were grouped into constellations and asterisms , the brightest of which gained proper names . Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations . However , most of the stars in the ___MASK99___ , including all stars outside our galaxy , the Milky Way , are invisible to the naked eye from ___MASK46___ . Indeed , most are invisible from ___MASK46___ even through the most powerful telescopes . Lieserl is the title of the fifth story in Stephen Baxter ' s ___MASK60___ anthology " Vacuum Diagrams ". It was originally published in " Interzone " in 1993 and represents a small , but integral part of the ___MASK91___ , Ring . ___MASK46___ , otherwise known as the world , is the third planet from the Sun and the only object in the ___MASK99___ known to harbor life . It is the densest planet in the Solar System and the largest of the four terrestrial planets . Vacuum Diagrams is a collection of ___MASK60___ short stories written by Stephen Baxter . The collection connects the novels of the ___MASK14___ and also shows the history of mankind in the Xeelee universe , and ultimately the universe . While each short story in the collection is self - contained , the stories are presented as being contained in the context of the first story , " Eve ", about a man who is forced to witness the events in the short stories by a god - like being . " Eve " acts as a structure for the short stories , with an introduction at the beginning of " Vacuum Diagrams ", short scenes occurring between each " era " ( with " Eve " character explaining and introducing the next section ), and an ending that wraps up the plot for the " Eve " story itself . " Vacuum Diagrams " won the Philip K . Dick Award in 1999 . The Sun is the star at the center of the Solar System . It is a nearly perfect sphere of hot plasma , with internal convective motion that generates a magnetic field via a dynamo process .< ref name =" doi10 . 1146 / annurev - astro - 081913 - 040012 "></ ref > It is by far the most important source of energy for ___MASK61___ on Earth . Its diameter is about 109 times that of Earth , and its mass is about 330 , 000 times that of Earth , accounting for about 99 . 86 % of the total mass of the Solar System . About three quarters of the Sun ' s mass consists of hydrogen (~ 73 %); the rest is mostly helium (~ 25 %), with much smaller quantities of heavier elements , including oxygen , carbon , neon , and iron . The Solar System is the gravitationally bound system comprising the Sun and the objects that ___MASK25___ it , either directly or indirectly . Of those objects that ___MASK25___ the Sun directly , the largest eight are the planets , with the remainder being significantly smaller objects , such as dwarf planets and small Solar System bodies . Of the objects that ___MASK25___ the Sun indirectly , the moons , two are larger than the smallest planet , Mercury . Iron is a chemical element with symbol Fe ( from ) and atomic number 26 . It is a metal in the first transition series . It is by mass the most common element on ___MASK46___ , forming much of ___MASK46___ ' s outer and inner core . It is the fourth most common element in the ___MASK46___ ' s crust . Its abundance in ___MASK6___ planets like ___MASK46___ is due to its abundant production by fusion in high - mass stars , where it is the last element to be produced with release of energy before the violent collapse of a supernova , which scatters the iron into space . Hydrogen is a chemical element with chemical symbol H and atomic number 1 . With an atomic weight of , hydrogen is the lightest element on the periodic table . Its monatomic form ( H ) is the most abundant chemical substance in the ___MASK99___ , constituting roughly 75 % of all baryonic mass . Non - remnant stars are mainly composed of hydrogen in the plasma state . The most common isotope of hydrogen , termed " protium " ( name rarely used , symbol H ), has one proton and no neutrons . Oxygen is a chemical element with symbol O and atomic number 8 . It is a member of the chalcogen group on the periodic table and is a highly reactive nonmetal and oxidizing agent that readily forms oxides with most elements as well as other compounds . By mass , oxygen is the third - most abundant element in the ___MASK99___ , after hydrogen and helium . At standard temperature and pressure , two atoms of the element bind to form dioxygen , a colorless and odorless diatomic gas with the formula . This is an important part of the atmosphere and diatomic oxygen gas constitutes 20 . 8 % of the Earth ' s atmosphere . Additionally , as oxides the element makes up almost half of the Earth ' s crust .