1-0-2 Life

0 Contents 1 Background 1-0 Overview 1-0-2 Life

Panspermia 1-0-2-1

1-0-2-0 * Astrobiology  

From Wikipedia, the free encyclopedia "Origin of life" redirects here. See also: Abiogenesis, Earliest known life forms, and Panspermia

 Introduction  

Introduction

Nucleic acids may not be the only biomolecules in the Universe capable of coding for life processes.[1]

Astrobiology is a branch of biology concerned with the origins, early evolution, distribution, and future of life in the universe. Astrobiology considers the question of whether extraterrestrial life exists, and how humans can detect it if it does.[2] The term exobiology is similar.[3]

Astrobiology makes use of molecular biology, biophysics, biochemistry, chemistry, astronomy, exoplanetology and geology to investigate the possibility of life on other worlds and help recognize biospheres that might be different from that on Earth.[4] The origin and early evolution of life is an inseparable part of the discipline of astrobiology.[5] Astrobiology concerns itself with interpretation of existing scientific data, and although speculation is entertained to give context, astrobiology concerns itself primarily with hypotheses that fit firmly into existing scientific theories.

This interdisciplinary field encompasses research on the origin of planetary systems, origins of organic compounds in space, rock-water-carbon interactions, abiogenesis on Earth, planetary habitability, research on biosignatures for life detection, and studies on the potential for life to adapt to challenges on Earth and in outer space.[6][7][8]

Biochemistry may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10–17 million years old.[9][10] According to the panspermia hypothesis, microscopic life—distributed by meteoroids, asteroids and other small Solar System bodies—may exist throughout the universe.[11] According to research published in August 2015, very large galaxies may be more favorable to the creation and development of habitable planets than such smaller galaxies as the Milky Way.[12] Nonetheless, Earth is the only place in the universe humans know to harbor life.[13][14] Estimates of habitable zones around other stars,[15][16] sometimes referred to as "Goldilocks zones,"[17][18] along with the discovery of hundreds of extrasolar planets and new insights into extreme habitats here on Earth, suggest that there may be many more habitable places in the universe than considered possible until very recently.[19][20][21]

Current studies on the planet Mars by the Curiosity and Opportunity rovers are searching for evidence of ancient life as well as plains related to ancient rivers or lakes that may have been habitable.[22][23][24][25] The search for evidence of habitability, taphonomy (related to fossils), and organic molecules on the planet Mars is now a primary NASA and ESA objective.

Overview

The term was first proposed by the Russian (Soviet) astronomer Gavriil Tikhov in 1953.[26] Astrobiology is etymologically derived from the Greek ἄστρον, astron, "constellation, star"; βίος, bios, "life"; and -λογία, -logia, study. The synonyms of astrobiology are diverse; however, the synonyms were structured in relation to the most important sciences implied in its development: astronomy and biology. A close synonym is exobiology from the Greek Έξω, "external"; Βίος, bios, "life"; and λογία, -logia, study. The term exobiology was coined by molecular biologist and Nobel Price winner Joshua Lederberg.[27] Exobiology is considered to have a narrow scope limited to search of life external to Earth, whereas subject area of astrobiology is wider and investigates the link between life and the universe, which includes the search for extraterrestrial life, but also includes the study of life on Earth, its origin, evolution and limits.

 

It is not known whether life elsewhere in the universe would utilize cell structures like those found on Earth. (Chloroplasts within plant cells shown here.)[28]

Another term used in the past is xenobiology, ("biology of the foreigners") a word used in 1954 by science fiction writer Robert Heinlein in his work The Star Beast.[29] The term xenobiology is now used in a more specialized sense, to mean "biology based on foreign chemistry", whether of extraterrestrial or terrestrial (possibly synthetic) origin. Since alternate chemistry analogs to some life-processes have been created in the laboratory, xenobiology is now considered as an extant subject.[30]

While it is an emerging and developing field, the question of whether life exists elsewhere in the universe is a verifiable hypothesis and thus a valid line of scientific inquiry.[31][32] Though once considered outside the mainstream of scientific inquiry, astrobiology has become a formalized field of study. Planetary scientist David Grinspoon calls astrobiology a field of natural philosophy, grounding speculation on the unknown, in known scientific theory.[33] NASA's interest in exobiology first began with the development of the U.S. Space Program. In 1959, NASA funded its first exobiology project, and in 1960, NASA founded an Exobiology Program, which is now one of four main elements of NASA's current Astrobiology Program.[2][34] In 1971, NASA funded the search for extraterrestrial intelligence (SETI) to search radio frequencies of the electromagnetic spectrum for interstellar communications transmitted by extraterrestrial life outside the Solar System. NASA's Viking missions to Mars, launched in 1976, included three biology experiments designed to look for metabolism of present life on Mars.

 

In June 2014, the John W. Kluge Center of the Library of Congress held a seminar focusing on astrobiology. Panel members (L to R) Robin Lovin, Derek Malone-France, and Steven J. Dick

Advancements in the fields of astrobiology, observational astronomy and discovery of large varieties of extremophiles with extraordinary capability to thrive in the harshest environments on Earth, have led to speculation that life may possibly be thriving on many of the extraterrestrial bodies in the universe. A particular focus of current astrobiology research is the search for life on Mars due to this planet's proximity to Earth and geological history. There is a growing body of evidence to suggest that Mars has previously had a considerable amount of water on its surface,[35][36] water being considered an essential precursor to the development of carbon-based life.[37]

Missions specifically designed to search for current life on Mars were the Viking program and Beagle 2 probes. The Viking results were inconclusive,[38] and Beagle 2 failed minutes after landing.[39] A future mission with a strong astrobiology role would have been the Jupiter Icy Moons Orbiter, designed to study the frozen moons of Jupiter—some of which may have liquid water—had it not been cancelled. In late 2008, the Phoenix lander probed the environment for past and present planetary habitability of microbial life on Mars, and researched the history of water there.

The European Space Agency's astrobiology roadmap from 2016, identified five main research topics, and specifies several key scientific objectives for each topic. The five research topic are:[40] 1) Origin and evolution of planetary systems; 2) Origins of organic compounds in space; 3) Rock-water-carbon interactions, organic synthesis on Earth, and steps to life; 4) Life and habitability; 5) Biosignatures as facilitating life detection.

In November 2011, NASA launched the Mars Science Laboratory mission carrying the Curiosity rover, which landed on Mars at Gale Crater in August 2012.[41][42][43] The Curiosity rover is currently probing the environment for past and present planetary habitability of microbial life on Mars. On 9 December 2013, NASA reported that, based on evidence from Curiosity studying Aeolis Palus, Gale Crater contained an ancient freshwater lake which could have been a hospitable environment for microbial life.[44][45]

The European Space Agency is currently collaborating with the Russian Federal Space Agency (Roscosmos) and developing the ExoMars astrobiology rover, which is to be launched in July 2020.[46] Meanwhile, NASA is developing the Mars 2020 astrobiology rover and sample cacher for a later return to Earth.

Methodology

Planetary habitability

When looking for life on other planets like Earth, some simplifying assumptions are useful to reduce the size of the task of the astrobiologist. One is the informed assumption that the vast majority of life forms in our galaxy are based on carbon chemistries, as are all life forms on Earth.[47] Carbon is well known for the unusually wide variety of molecules that can be formed around it. Carbon is the fourth most abundant element in the universe and the energy required to make or break a bond is at just the appropriate level for building molecules which are not only stable, but also reactive. The fact that carbon atoms bond readily to other carbon atoms allows for the building of extremely long and complex molecules.

The presence of liquid water is an assumed requirement, as it is a common molecule and provides an excellent environment for the formation of complicated carbon-based molecules that could eventually lead to the emergence of life.[48] Some researchers posit environments of water-ammonia mixtures as possible solvents for hypothetical types of biochemistry.[49]

A third assumption is to focus on planets orbiting Sun-like stars for increased probabilities of planetary habitability.[50] Very large stars have relatively short lifetimes, meaning that life might not have time to emerge on planets orbiting them. Very small stars provide so little heat and warmth that only planets in very close orbits around them would not be frozen solid, and in such close orbits these planets would be tidally "locked" to the star.[51] The long lifetimes of red dwarfs could allow the development of habitable environments on planets with thick atmospheres. This is significant, as red dwarfs are extremely common. (See Habitability of red dwarf systems).

Since Earth is the only planet known to harbor life, there is no evident way to know if any of these simplifying assumptions are correct.

Communication attempts