Little Green Microbes
By Kemi Ashing-Giwa
Humankind has long pondered life’s beginnings. Early investigations looked primarily to Earth for answers, but our gaze has since turned to the stars. The emerging, interdisciplinary field of astrobiology, now placed squarely at the forefront of science, promises to provide startling new discoveries about the nature of the cosmos, and how space too may hold the secrets of life.
Astrobiology, Defined
Astrobiology, simply put, is the study of life in the universe. But this relatively young field is a composite of other complex branches of study, including—but not limited to—chemistry, physics, oceanography, engineering, geology, and, unsurprisingly, astronomy and biology. An amalgamation of fields that is far more than the sum of its parts, astrobiology has the potential to answer some of humanity’s greatest questions. Although current astrobiology focuses on the interpretation of existing scientific data, speculation is required in order to provide context. Such predictions, in general, are still expected to adhere strictly to established knowledge about space and its capacity for life.
Astrobiologists study abiogenesis—or the inorganic origin of life—on Earth; detection of life using biosignatures; interactions between rock, water, and carbon; organic compounds in space; planetary habitability; and the potential for life to adapt to unique challenges in outer space, other planets, and Earth [1,2].
Biochemistry may have begun around 13.8 billion years ago, less than 17 million years after the birth of the Universe, during a certain “habitable epoch” [3]. A hypothesis known as panspermia states that microscopic life may thrive throughout the galaxy, dispersed by small bodies from ours and other solar systems, including asteroids, comets, [4] meteoroids, [5] planetoids, and space dust [6]. Recent research has revealed that the idiosyncratic conditions found within galaxies twice as large as ours may be even more conducive to fostering habitable planets, and by extension, life [7]. Yet Earth is still—unfortunately—the only location in the universe we know to function as a home.
Despite this, astrobiologists have uncovered countless fascinating theories to guide and further their field. These include estimates of the orbit range around other stars within which liquid water can exist under appropriate atmospheric pressure—such regions are known as circumstellar habitable (CHZ), or Goldilocks zones [8-10]. Further, the era-defining discoveries of liquid water on Mars and the existence of planets around the vast majority of stars, coupled with novel insights into extreme Earth habitats, intimate myriad life-supporting locales across the universe [11].
Other Worlds, Other Lives
Chemistry that lead to pre-life on Earth provides insights into the chemistry and geology of other planets. We know today that aqueous environments make the complex chemistry of life relatively straightforward because—put very simply—water mixes things. The popular primordial soup hypothesis intimates that life arose from a stew of organic compounds in Earth’s primitive oceans—oceans not vastly different from the ones Mars may still hide [21]. Further, extraterrestrial life does not have to originate from primordial soup, clay, or simple iron-sulfur complexes [21]. There are untold possible scenarios, each equally plausible.
In the planetary family formed by our solar system, Mars’s similarity and proximity make the Red Planet our sibling. No proof of life, past or present, has been uncovered on the Mars as of yet, but the probability it once existed has ignited the flames of astrobiological optimism. There has been no end to claims of evidence of aerobic bacterial life found on Martian meteorites—ALH84001 made an armada of headlines in 1996 when researchers suggested that the meteorite contained possible evidence of extraterrestrial life [12]. Decades of evidence illustrate time and time again that at least a third of Mars’s surface environment harbored oceans of liquid water, perhaps teeming with microorganisms [13-17]. A new study has also uncovered possible niches in the form of subglacial aquifers brimming with briny water whose high salinity might be beneficial to possible Martian life [18]. The Red Planet’s average surface temperature is around -63 °C, far below the freezing point of freshwater. However, saltwater, especially under pressure similar to that exerted on Mars from the ice above, freezes at lower temperatures than freshwater [18].
Thanks to a surface of ice-capped liquid water warmed by tidal flexing,19 Jupiter's moon Europa serves as another prime suspect for extraterrestrial life-harboring bodies in our solar system. Three million tons of fish-like creatures could call this watery world their home, according to provocative research that suggests Europa’s seas have all the necessary building blocks for life, and enough oxygen to sustain such animals [20]. Europa's various geological processes have slowly but surely increased the water’s oxidant levels; as seen on Earth, such a steady rise in oxygen may be beneficial for the evolution of life [20].
A lifeform can be defined as any autonomous agent that can reproduce and carry out at least one thermodynamic work cycle, a sequence of processes that transfer work and heat into and out of a system.[21] It is naive to assume that all life must be carbon-based with DNA heredity. The other crushing criteria we have created for the development of life are egocentric, as they assume Earth must be a universal standard, and, through the unimaginative constraints we decide upon, an all but impossible miracle. Humanity has been placing itself at the center of the cosmos for eons; we must overcome this deeply-entrenched inclination if we want to discover extraterrestrial life ourselves. If there are aliens—and there probably are—it’s possible they’ll be entirely beyond human contemplation. If we truly want to uncover the cosmos’s secrets, ours is the century in which we must sacrifice our fragile geocentric philosophy in favor of accepting galactic modesty.
The next logical step in this cosmic quandary is to ask what such developed life might look like. Reasonable answers can be found by utilizing the evolutionary diversification of life on our own planet as a starting point. Immediately evident are “universals”—structures that have evolved independently several times in the creatures we deem advanced, such as mechanisms for movement [21]. But Earth’s guidance must end here. There are necessary differences that must be taken into account when considering the possible chemicals, genetic information, and metabolic mechanisms that define alien life. Careless astrobiology asks what we would look like if we’d evolved on another planet, but the human form, of course, evolved because it works—to an acceptable degree—on Earth, and Earth alone. Suffice it to say that we will not be waging war against telepathic glowing bonobos anytime soon.
Future Forays
Astrobiological research plays a crucial role in how the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) arrange and design current and future missions. The hunt for organic molecules and other precursors of life on Mars and beyond is now one of the primary aims of NASA and ESA.
In 2020, the solar-powered rover Rosalind Franklin will launch [22]. Equipped with an extensive astrobiological laboratory, its seven-month Martian mission is to search for evidence of past life in the form of biosignatures and/or biomolecule [22]. Launching around the same time, the Mars 2020 rover will explore ancient environments of astrobiological pertinence. While studying the history and processes of Martian surface geology, the rover will assess the past habitability of the planet and investigate possible biosignature preservation [23]. Along its mission route, the rover will cache samples for a potential sample-return endeavor in the future [23, 24]. Three years later, the Europa Clipper mission will begin studying—unsurprisingly—Europa through a series of flybys while orbiting Jupiter. The Europa Clipper’s objectives are to survey the moon, explore its habitability, and collect data to appoint a future landing site for the planned Europa Lander [25]. The predominant foci of this investigation are life’s three great prerequisites: energy, chemistry, and liquid water [26].
In addition, significant investments into and advances in telescope technology have enabled astrobiologists to search for habitable planets outside our solar system, and to begin designing the missions necessary to confirm their findings.
We might never uncover extraterrestrial life. But the evolutionary and cosmic insights offered by astrobiology—not to mention the very interdisciplinarity that makes it such a fascinating field in the first place—make it highly probable that we’ll still have much to gain from it here on our miniscule blue marble.
Humankind has long pondered life’s beginnings. Early investigations looked primarily to Earth for answers, but our gaze has since turned to the stars. The emerging, interdisciplinary field of astrobiology, now placed squarely at the forefront of science, promises to provide startling new discoveries about the nature of the cosmos, and how space too may hold the secrets of life.
Astrobiology, Defined
Astrobiology, simply put, is the study of life in the universe. But this relatively young field is a composite of other complex branches of study, including—but not limited to—chemistry, physics, oceanography, engineering, geology, and, unsurprisingly, astronomy and biology. An amalgamation of fields that is far more than the sum of its parts, astrobiology has the potential to answer some of humanity’s greatest questions. Although current astrobiology focuses on the interpretation of existing scientific data, speculation is required in order to provide context. Such predictions, in general, are still expected to adhere strictly to established knowledge about space and its capacity for life.
Astrobiologists study abiogenesis—or the inorganic origin of life—on Earth; detection of life using biosignatures; interactions between rock, water, and carbon; organic compounds in space; planetary habitability; and the potential for life to adapt to unique challenges in outer space, other planets, and Earth [1,2].
Biochemistry may have begun around 13.8 billion years ago, less than 17 million years after the birth of the Universe, during a certain “habitable epoch” [3]. A hypothesis known as panspermia states that microscopic life may thrive throughout the galaxy, dispersed by small bodies from ours and other solar systems, including asteroids, comets, [4] meteoroids, [5] planetoids, and space dust [6]. Recent research has revealed that the idiosyncratic conditions found within galaxies twice as large as ours may be even more conducive to fostering habitable planets, and by extension, life [7]. Yet Earth is still—unfortunately—the only location in the universe we know to function as a home.
Despite this, astrobiologists have uncovered countless fascinating theories to guide and further their field. These include estimates of the orbit range around other stars within which liquid water can exist under appropriate atmospheric pressure—such regions are known as circumstellar habitable (CHZ), or Goldilocks zones [8-10]. Further, the era-defining discoveries of liquid water on Mars and the existence of planets around the vast majority of stars, coupled with novel insights into extreme Earth habitats, intimate myriad life-supporting locales across the universe [11].
Other Worlds, Other Lives
Chemistry that lead to pre-life on Earth provides insights into the chemistry and geology of other planets. We know today that aqueous environments make the complex chemistry of life relatively straightforward because—put very simply—water mixes things. The popular primordial soup hypothesis intimates that life arose from a stew of organic compounds in Earth’s primitive oceans—oceans not vastly different from the ones Mars may still hide [21]. Further, extraterrestrial life does not have to originate from primordial soup, clay, or simple iron-sulfur complexes [21]. There are untold possible scenarios, each equally plausible.
In the planetary family formed by our solar system, Mars’s similarity and proximity make the Red Planet our sibling. No proof of life, past or present, has been uncovered on the Mars as of yet, but the probability it once existed has ignited the flames of astrobiological optimism. There has been no end to claims of evidence of aerobic bacterial life found on Martian meteorites—ALH84001 made an armada of headlines in 1996 when researchers suggested that the meteorite contained possible evidence of extraterrestrial life [12]. Decades of evidence illustrate time and time again that at least a third of Mars’s surface environment harbored oceans of liquid water, perhaps teeming with microorganisms [13-17]. A new study has also uncovered possible niches in the form of subglacial aquifers brimming with briny water whose high salinity might be beneficial to possible Martian life [18]. The Red Planet’s average surface temperature is around -63 °C, far below the freezing point of freshwater. However, saltwater, especially under pressure similar to that exerted on Mars from the ice above, freezes at lower temperatures than freshwater [18].
Thanks to a surface of ice-capped liquid water warmed by tidal flexing,19 Jupiter's moon Europa serves as another prime suspect for extraterrestrial life-harboring bodies in our solar system. Three million tons of fish-like creatures could call this watery world their home, according to provocative research that suggests Europa’s seas have all the necessary building blocks for life, and enough oxygen to sustain such animals [20]. Europa's various geological processes have slowly but surely increased the water’s oxidant levels; as seen on Earth, such a steady rise in oxygen may be beneficial for the evolution of life [20].
A lifeform can be defined as any autonomous agent that can reproduce and carry out at least one thermodynamic work cycle, a sequence of processes that transfer work and heat into and out of a system.[21] It is naive to assume that all life must be carbon-based with DNA heredity. The other crushing criteria we have created for the development of life are egocentric, as they assume Earth must be a universal standard, and, through the unimaginative constraints we decide upon, an all but impossible miracle. Humanity has been placing itself at the center of the cosmos for eons; we must overcome this deeply-entrenched inclination if we want to discover extraterrestrial life ourselves. If there are aliens—and there probably are—it’s possible they’ll be entirely beyond human contemplation. If we truly want to uncover the cosmos’s secrets, ours is the century in which we must sacrifice our fragile geocentric philosophy in favor of accepting galactic modesty.
The next logical step in this cosmic quandary is to ask what such developed life might look like. Reasonable answers can be found by utilizing the evolutionary diversification of life on our own planet as a starting point. Immediately evident are “universals”—structures that have evolved independently several times in the creatures we deem advanced, such as mechanisms for movement [21]. But Earth’s guidance must end here. There are necessary differences that must be taken into account when considering the possible chemicals, genetic information, and metabolic mechanisms that define alien life. Careless astrobiology asks what we would look like if we’d evolved on another planet, but the human form, of course, evolved because it works—to an acceptable degree—on Earth, and Earth alone. Suffice it to say that we will not be waging war against telepathic glowing bonobos anytime soon.
Future Forays
Astrobiological research plays a crucial role in how the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) arrange and design current and future missions. The hunt for organic molecules and other precursors of life on Mars and beyond is now one of the primary aims of NASA and ESA.
In 2020, the solar-powered rover Rosalind Franklin will launch [22]. Equipped with an extensive astrobiological laboratory, its seven-month Martian mission is to search for evidence of past life in the form of biosignatures and/or biomolecule [22]. Launching around the same time, the Mars 2020 rover will explore ancient environments of astrobiological pertinence. While studying the history and processes of Martian surface geology, the rover will assess the past habitability of the planet and investigate possible biosignature preservation [23]. Along its mission route, the rover will cache samples for a potential sample-return endeavor in the future [23, 24]. Three years later, the Europa Clipper mission will begin studying—unsurprisingly—Europa through a series of flybys while orbiting Jupiter. The Europa Clipper’s objectives are to survey the moon, explore its habitability, and collect data to appoint a future landing site for the planned Europa Lander [25]. The predominant foci of this investigation are life’s three great prerequisites: energy, chemistry, and liquid water [26].
In addition, significant investments into and advances in telescope technology have enabled astrobiologists to search for habitable planets outside our solar system, and to begin designing the missions necessary to confirm their findings.
We might never uncover extraterrestrial life. But the evolutionary and cosmic insights offered by astrobiology—not to mention the very interdisciplinarity that makes it such a fascinating field in the first place—make it highly probable that we’ll still have much to gain from it here on our miniscule blue marble.
Our solar system’s estimated circumstellar habitable zone (Figure 1)
Model of Europa, Jupiter’s snazziest moon (Figure 2)
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