Astrobiology
What Is Astrobiology?
Astrobiology is the study of life in the Universe. The search for life beyond the Earth requires an understanding of life, and the nature of the environments that support it, as well as planetary, planetary system and stellar interactions and processes. To provide this understanding, Astrobiology combines the knowledge and techniques from many fields, including Astronomy, Biology, Chemistry, Geology, Atmospheric Science, Oceanography and Aeronautical Engineering. Astrobiologists can work alone on particular scientific questions, but often Astrobiologists from different scientific disciplines work together to examine complex questions that no one field can answer alone.
These questions cover topics such as:
1. How does life originate?
2. How does life evolve?
3. What kind of environment is necessary for life to survive?
4. What are the environmental limits or “extremes” under which life can survive?
5. What might life look like on another world?
6. Is there or has there been life elsewhere in our solar system?
7. How can we observe and identify a habitable – or even inhabited – world?
8. What is humanity’s future on Earth and beyond?
The World of Astrobiology
While the United States of America (USA) and NASA have pioneered many lines of Astrobiological study, we are hardly alone – as is only proper for an effort to address such enormous and universal questions. Few Astrobiology missions launch without significant international partnership, and the trend is for ever greater interdependence. The much-anticipated mission to bring to Earth the rock and grain being now being cached by the Perseverance rover in Jezero Crater will feature major roles for both NASA and European Space Agency (ESA).
The Chinese Space Agency now has a rover on Mars as well, and is planning for the Tianwen-3 mission to collect Mars samples for transport back to Earth. Another high-profile example is the ExoMars mission headed by the European Space Agency (ESA), which includes a series of missions, the first phase of which was the Trace Gas Orbiter that launched in 2016. One of the major efforts of the Trace Gas Orbiter is to look for methane on Mars, a key question for NASA as well. Astrobiology cooperation is often intellectual as well as operational.
The next step for ExoMars is the delivery of the Rosalind Franklin rover to the Martian surface, which initially included input from the Russian Space Agency (Roscosmos) and NASA. The ExoMars rover cooperation was suspended in March 2022, but efforts are underway to find alternatives.
Astrobiology may sometimes seem most defined by high-profile missions, but often those missions represent years of prior theoretical and laboratory work. And once data from missions have been obtained, more lab analysis and testing are necessary. The data is then challenged and critiqued by colleagues before the results can be released as a significant finding. For instance, it took almost two years of intensive lab work and data analysis before members of the Curiosity science team could announce that they had teased out from Mars drill samples the presence of long-sought organic compounds, the building blocks of life as we know it.
Astrobiology, a multidisciplinary field dealing with the nature, existence, and search for extraterrestrial life (life beyond Earth). Astrobiology encompasses areas of biology, astronomy, and geology.
Although no compelling evidence of extraterrestrial life has yet been found, the possibility that Biota might be a common feature of the universe has been strengthened by the discovery of Extrasolar Planets (planets around other stars), by the strong suspicion that several moons of Jupiter and Saturn might have vast reserves of liquid water, and by the existence of microorganisms called Extremophiles that are tolerant of environmental extremes. The first development indicates that habitats for life may be numerous. The second suggests that even in the solar system there may be other worlds on which life evolved. The third suggests that life can arise under a wide range of conditions. The principal areas of astrobiology research can be classified as (1) understanding the conditions under which life can arise, (2) looking for habitable worlds, and (3) searching for evidence of life.
For life like that on Earth (based on complex carbon compounds) to exist, a world must have liquid water. Because planets either too close to or too far from their host stars will be at temperatures that cause water either to boil or to freeze, Astrobiologists define a “habitable zone,” a range of orbital distances within which planets can support liquid water on their surfaces. In the solar system, only Earth is inside the Sun’s habitable zone. However, photographs and other data from spacecraft orbiting Mars indicate that water once flowed on the surface of the red planet and is still present in large quantities underground. Consequently, there is a sustained international effort to use robotic probes to examine Mars for evidence of past, and even present, life that could have retreated to subsurface, liquid aquifers.
Also, discoveries primarily due to the Galileo space probe (launched in 1989) suggest that some of the moons of Jupiter—principally Europa but also Ganymede and Callisto—as well as Saturn’s moon Enceladus, might have long-lived liquid oceans under their icy outer skins. These oceans can be kept warm despite their great distance from the Sun because of gravitational interactions between the moons and their host planet, and they might support the kind of life found in deep sea vents on Earth.
Even Titan, a large moon of Saturn with a thick atmosphere, might conceivably have some unusual biology on its cold surface, where lakes of liquid methane and ethane may exist. The European space probe Huygens landed on Titan on January 14, 2005, and saw signs of liquid flow on its surface. Such discoveries as these have strongly promoted the emergence of astrobiology as a field of study by broadening the range of possible extraterrestrial habitats far beyond the conventional notion of a “habitable zone.”
An additional impetus has been the discovery since 1995 of hundreds of Extrasolar Planets around other normal stars. Most of these are giant worlds, similar to Jupiter and therefore unlikely to be suitable for life themselves, although they could have moons on which life might arise. However, this work has shown that at least 5 to 10 percent (and possibly as much as 50 percent or more) of all Sun-like stars have planets, implying many billions of solar systems in the Milky Way Galaxy. The discovery of these planets has encouraged astrobiology and in particular has motivated proposals for several space-based telescopes designed:
1. to search for smaller, Earth-size worlds and
2. if such worlds are found, to analyze spectrally the light reflected by the planets’ atmospheres in the hope of detecting oxygen, methane, or other substances that would indicate the presence of Biota.
While no one can say with certainty what sort of life might be turned up by these experiments, the usual assumption is that it will be microbial, as single-celled life is adaptable to a wide range of environments and requires less energy. However, telescopic searches for extraterrestrial intelligence (SETI) are also part of astrobiology’s extensive research palette.
Looking for Life
At the heart of Astrobiology is yet another basic and unanswered question: What actually is life? One might think after centuries of study that issue would be resolved, for life on Earth at least. Actually, it’s getting increasingly complicated to come up with an answer that takes in all the “lifeforms” discovered and that might have once existed on our planet. One frequently used definition of life is “a self-sustaining system capable of Darwinian evolution.” But there are literally several hundred more.
Ironically, some Astrobiologists argue that we really won’t know what life is until we find an alternative to the basic structure found on Earth – the same DNA, metabolism and carbon-based blueprint shared by all known life. In other words, ET life could tell us what life really is.
A corollary to this line of thinking is the ever-present concern that a rover or lander has, or will, come across an example or signature of life present or past and not know it. This reality helps explain the emphasis that astrobiology puts on understanding the origins and logic of early life on Earth. In addition to its inherent importance, origin-of-life research guides the search for extraterrestrial life.
That NASA is very much in the business of the search for life beyond Earth is by now well known to the public, while the agency’s mission to make progress in understanding the origins of life on Earth is less well understood. Some, however, no doubt wonder why NASA investigates biological questions at all. Isn’t the primary focus of the agency to use robots and astronauts in space capsules to travel in space and explore destination such as the moon and Mars?
Actually, today’s NASA has a much broader portfolio, one that includes the study of classic astronomical topics such as the very early universe and the formation of galaxies, stars and solar systems – all of which will be explored with greatly expanded precision by the James Webb Space Telescope. The JWST was also adapted to allow for newly possible explorations of exoplanets and their atmospheres, which are of paramount interest to Astrobiologists.
The search for life beyond Earth is so intertwined with other NASA goals (and is so interdisciplinary by nature and design), it can never really be separated or isolated from them. The Cassini mission to Saturn discovered plumes spitting out of the moon Enceladus, and the Hubble Space Telescope did the same for Europa. Both plumes tell of an inner water world, and so are important to planetary science as well as astrobiology. The Kepler mission identified thousands of exoplanets in a small segment of the constellation Cygnus, 500 light years away, adding enormously to our understanding of the inventory and nature of distant planets. Included in those discoveries are the detection of rocky planets within the habitable zones of their central stars. TESS has also substantially added to the count of exoplanets, with more than 5,000 new exoplanet candidates.
The central goal of astrobiology is to find evidence of past or present life beyond Earth, if it ever existed. But there are countless mysteries about planets and moons, about solar systems, about galaxies and about the makeup of the space between them that inevitably will be confronted and hopefully unraveled along the way. Ultimately, the search for extraterrestrial life is possible only as part of an exploration of the makeup, the dynamics, the history and the many as yet unknown wonders of the cosmos.
Space Biology and Astrobiology: What’s the difference?
From chemistry to physics, NASA researchers from various disciplines conduct groundbreaking work studying life every day.
Two of these disciplines are Astrobiology and Space Biology. While they may sound similar, they are quite different in what they do. What they do have in common is their ability to help us understand how life functions on Earth and in the Universe.
Astrobiology
Astrobiology is the study of the origin, evolution, and distribution of life in the Universe1. The hunt for extraterrestrial life might sound like something out of the science-fiction genre, but scientific logic guides this search.
For NASA scientists, the search to understand life in the Universe starts on Earth. Understanding how life evolved on Earth and what steps made it possible are key to understanding what life might exist outside of it.
To guide us in our search for life beyond Earth, scientists are studying how life on Earth exists in extreme environments like the scorching hot desert or the freezing Arctic tundra. In our solar system, environments like these can be found on Mars or the icy moons2 around Saturn and Jupiter. Future Astrobiology missions will study if these environments in space harbor life.
In space, tools like robotic science rovers can help scientists search for some of the biosignatures — or signs of life. During the Mars 2020 mission, the rover Perseverance collected data that could be used to look for signs of ancient microbial life3. The rover also collected a suite of samples that a future Mars Sample Return mission will be able to bring back to Earth for study, with all the sophistication and thoroughness of Earth-based instrumentation.
Understanding both how life emerged and evolved on Earth and what the limits are to life as we know it guides NASA in its mission to search for life elsewhere in the Universe. Astrobiology strives to answer the question: “Are we alone?”
Space Biology
Space Biology is the study of how the space flight environment — such as ionizing radiation, microgravity, isolation, and altered atmosphere — affects life. Studying how living things respond at a fundamental level to these extreme conditions can inform what’s needed to ensure crew health on deep space missions and contribute to biomedical and agricultural advancements on Earth.
The main objective of NASA’s Space Biology research is to better understand how spaceflight affects living systems in spacecraft, such as the International Space Station, as well as in deep space, on planetary surfaces, or in ground-based experiments that mimic aspects of spaceflight.
The experiments NASA conducts on these platforms examine how plants, microbes, and model organisms (such as fruit flies, worms, and rodents) adjust or adapt to living in space. Researchers examine metabolism, growth, stress responses, physiology, and developmental processes.
They study how organisms repair cellular damage and protect themselves from infection and disease in microgravity conditions while also exposed to space radiation. And they do it across the spectrum of biological organization, from molecules to cells, tissues, organs and systems to whole organisms, communities, and ecosystems.
Another focus of Space Biology is plant biology. Since space is limited aboard spacecraft, astronauts will need access to sustainable, nutritious sources of food for long-term stays in space.
Limited water supplies, microgravity, and different atmospheric and light conditions can affect plant health. Understanding how plants grow in the harsh conditions of space can help scientists determine which ones are most suitable for becoming “space crops.” Research in this field has already contributed to agricultural advancements on Earth, including hydroponic, aeroponic, and vertical farming.
Astrobiology focuses on the origins, evolution, and the limits to life on Earth to understand where and how to search for life in space. Space Biology studies how Earthly life responds to space environmental conditions to further our understanding of how life operates in built environments for space exploration.
NASA’s research in both fields has contributed to scientific knowledge, biomedical and technological innovations, and agricultural advancements that benefit both space exploration and terrestrial life.
What is happening in the field of Astrobiology in this 1st Quarter (25 years) of the 21st Century?
While Astrobiology is a relatively young field, it has a secure and promising future. Astrobiology research has a significant impact on how agencies such as the National Aeronautics and Space Administration (NASA) and the European Space Agency (ESA) plan for current and future space missions. For example, many recent missions have focused on exploring worlds in our own Solar System for signs of past, present or the precursors of life, including Mars (Phoenix , Pathfinder , Global Surveyor, and others) and Titan (Cassini-Huygens). At the same time, significant advances and investments in telescope technology (Kepler, James Webb Space Telescope) have allowed researchers to begin planning and searching for habitable planets outside our solar system.
In the United States of America (USA), NASA and the NASA Astrobiology Institute (NAI) are leading policy makers and funders in Astrobiology. An overview of the research goals and objectives they have articulated can be found in the NASA Astrobiology Roadmap. Internationally, Astrobiology networks and institutes have been established in Europe, Australia, Canada, Mexico and South America, including the Centro de Astrobiologia in Spain, the Nordic Network of Astrobiology Graduate Schools, and the Australian Center for Astrobiology.
