Are we alone? The scientific quest to find life on worlds beyond our Earth seeks to answer this profound question, and its ultimate answer will certainly go to the very heart of humanity's true place in the cosmic scheme of things. Extremophiles are bizarre forms of life on Earth that have managed to survive in environments that were once believed incapable of sustaining living organisms. These inhospitable environments include extreme heat, extreme cold, extreme pressure, and highly acidic surroundings. In their ceaseless search for extraterrestrial life, scientists have studied the other planets in our Solar System, their moons, and also extrasolar worlds that belong to the distant families of stars beyond our Sun. However, Venus, our Earth's nearest so-called "twin" planet, has traditionally been ruled out because it is a sizzling, inhospitable Earth-size ball of hell. But even though the surface of Venus itself would smash and fry delicate living organisms, some astronomers are now taking a second look at an old theory that offers a new "vista" in their hunt for life beyond Earth: the Venusian clouds.
In our own Solar System, Mars has been the traditional theoretical abode of alien life. And, indeed, it does sport geological features that suggest that it had--and still has--life-sustaining subsurface liquid water. The presence of liquid water is necessary for the emergence of life as we know it. In addition, astronomers have more recently seen promise in some of our Solar System's many moons: Titan and Enceladus of Saturn, for example, as well as Jupiter's moons Europa, Ganymede and Callisto. These intriguing icy moons, located in the outer Solar System, are considered to be possible abodes for precious life swimming around in their subsurface liquid water oceans well-hidden beneath their icy crustal shells.
In a paper published online in the March 30, 2018 issue of the journal Astrobiology, an international team of researchers led by planetary scientist Dr. Sanjay Limaye of the University of Wisconsin-Madison's Science and Engineering Center, present an intriguing argument suggesting that the atmosphere of Venus is a possible niche for the emergence of extraterrestrial microbial life.
"Venus has had plenty of time to evolve life on its own," Dr. Limaye noted in a March 30, 2018 University of Wisconsin-Madison Press Release. He added that some models indicate Venus once had a habitable climate with life-sustaining liquid water pooling on its surface--and this comfortable climate could have existed for as long as 2 billion years. "That's much longer than is believed to have occurred on Mars," Dr. Limaye continued to comment.
On our own planet, microorganisms living on Earth's surface--primarily bacteria--are known to float up into the atmosphere. These living tidbits have been found alive at altitudes of as much as 25 miles by scientists using balloons that have been specially equipped for this purpose, according to study co-author Dr. David J. Smith of NASA's Ames Research Center in Mountain View, California.
There is also a growing list of microbes known to thrive in incredibly inhospitable environments on our own planet, including deep ocean hydrothermal vents, the hot springs of Wyoming's Yellowstone National Park, toxic sludge present in polluted areas, and in acidic lakes all over Earth.
"On Earth, we know that life can thrive in very acidic conditions, can feed on carbon dioxide, and produce sulfuric acid," noted Dr. Rakesh Mogul, a professor of biological chemistry at California State Polytechnic University, Pomona. Dr. Mogul, a co-author on the new paper, said in the March 30, 2018 University of Wisconsin-Madison Press Release that the cloudy, highly reflective and acidic atmosphere of Venus is composed mostly of carbon dioxide and droplets of water that contain sulfuric acid.
Even though Earth is the only planet that we know of that hosts life, that doesn't mean it doesn't exist elsewhere. In fact, life may very well be dispersed abundantly throughout the Universe. However, because astronomers have not found extraterrestrial life, and extraterrestrial life has not found us, from a scientific perspective Earth is the only planet that is actually known to harbor life. The presence of life elsewhere in the Universe is still only a statistical probability--albeit a great statistical probability.
Extremophiles are life-forms that flourish on Earth under hostile conditions that would kill other creatures. It was not until the 1970s that these bizarre creatures were first detected, but as more and more scientists began to look into the matter, they found more and more of these bizarre creatures. Scientists have found that most archaea, bacteria, and a few protists are able to flourish in some of the most bizarre and inhospitable environments on Earth. But even though most of the known extremophiles are microbes, this is not always the case. Indeed, some strange organisms that flourish in harsh environments, such as Antarctic krill, are not microbes.
As scientists learn more about these bizarre organisms, they may also gain a new understanding about the possibility of life beyond Earth. Astrobiology is a new field that develops theories about the distribution, nature, and future of life-forms that may dwell elsewhere in the Universe. Astrobiologists are especially interested in extremophiles because these organisms are able to flourish in environments that are similar to those already known to exist on other planets and their mysterious moons.
Water Bears
Tardigrades--also known as water bears--are particularly interesting extremophiles. Indeed, tiny water bears are impressive organisms that scientists often consider to be Earth's toughest animal. Because of their appearance, water bears have two plans to ensure their survival in the extreme environments they find themselves in. In case of flooding, these microscopic animals can blow themselves up into a balloon-like form and float up to the surface of the water in order to get oxygen. In addition, in case of cold or drought, these tiny animals can replace most of the water in their bodies with a sugar called trehalose. This type of sugar solution does not create destructive ice crystals when frozen, and so many of these little tardigrades have managed to survive for more than a century in museum samples, as well as a 12 day excursion into the frigid vacuum of interplanetary space onboard the Russian FOTON M3, launched aboard a Soyuz-U rocket on September 14, 2007. Most of the water bears survived their trip into space because they were well-protected by a UV filter. Alas, the ones without the filter did not.
According to Las Cumbres Observatory's Global Spacebook there are several inhospitable environments that host known extremophiles on Earth:
--Extreme Heat: One type of extremophiles on Earth are called thermophiles. These strange creatures can survive at very high temperatures. Back in the 1960s, heat resistant bacteria were found in hot springs in Yellowstone National Park. This form of bacteria, that goes by the technical name of thermus aquaticus, can survive temperatures of a very toasty 120 to 175 degrees Fahrenheit! A few years after these organisms were discovered, other bacteria were detected flourishing in an even more inhospitable environment within hydrothermal vents on the ocean floor. These extremophiles were found deep in the ocean under such great pressure that the water boils at 340 degrees Centigrade. The hydrothermal vent extremophiles surprised scientists when they discovered the bacteria flourishing and dwelling in the vents at such extreme temperatures and pressures. However, the bacteria had company in this uncomfortable environment. Only centimeters away from the vents--where the water was cooler--a complete ecosystem was living off the bacteria. There were clams and tubeworms, among other bizarre species. All of these organisms survived not from photosynthesis, but from the carbon dioxide and energy from the hydrothermal vents. Indeed, some scientists propose that these vents on the sea floor may have been the cradle where life first formed on Earth.
Extreme Cold--Other extremophiles have evolved in ways that enable them to survive in frigid temperatures. Deep ocean water maintains a reasonably constant temperature of 2 degrees C. However, because of its salt content, in colder regions, ocean water can plummet to temperatures as low as -12 degrees C without freezing. Extremophiles, dubbed psychorophiles have been found thriving at these incredibly low temperatures. But different species have developed different methods of survival in these frigid conditions. For example, some psychorophiles have managed to form substances, such as glycerol or antifreeze proteins, which lower the freezing point of water by several degrees.
The greatest danger to organisms inhabiting these frigid environments is the damage resulting from ice crystals as water freezes and expands. Some species of turtles and frogs have developed proteins which actually facilitate the freezing of body liquids. If the animal's body liquids start to freeze, it trips off a chain reaction that causes all of the body's liquids to freeze very quickly. This prevents the formation of ice crystals that are large enough to do damage. Numerous forms of microorganisms are able to survive freezing and thawing--just as long as the problem of ice crystal formation is avoided. This can be performed in a laboratory by flash freezing the organisms very quickly in liquid nitrogen.
Extreme Pressure--Many organisms survive on the ocean floor, even at great depths. Indeed, life has been discovered 11 kilometers deep in the Mariana Trench. At this extreme depth, organisms are under a smashing pressure of 1,100 atmospheres. Unfortunately, scientists have found these organisms difficult to study because creating such a high pressure environment in a laboratory is difficult--to put it mildly.
Isolated Ecosystems--There are still certain ecosystems on Earth have not yet been explored. Some very fascinating ones are high pressure subsurface lakes beneath the ice cap in Antarctica. These lakes are kept warm by geothermal energy--and they are also insulated by miles of ice above them. These lakes have been separated from the rest of our planet's biosphere for millions of years, if not considerably longer--perhaps even for their entire existence. Scientists have drilled into one of these lakes, Lake Vostok, and are making plans to dispatch a robot to gather water samples. This environment is thought to be similar to some of Jupiter's moons, such as Europa. Europa is thought to harbor a global ocean of liquid water beneath a cracked crustal surface of ice that resembles a shattered egg shell. For this reason, this type of environment and others similar to it are of special interest to astrobiologists.
Life Beneath Earth's Surface--The late Cornell University astrophysicist Thomas Gold (1920-2004) proposed that the oil and coal that exist beneath the surface of our planet are not the remains of algae and plants that perished very long ago--as most scientists believe. Instead, Gold suggested that subsurface oil and coal were incorporated into Earth's crust about 4.5 billion years ago when our primordial Solar System was in the process of forming during the period of accretion. He theorized that these hydrocarbons provide the carbon for a subsurface ecosystem that, perhaps, is totally separate from our biosphere.
More recently, several teams of scientists discovered microbes by excavating many miles into Earth's crust and mantle. Some of these tidbits of life were then tested in laboratories in order to determine if they could thrive in those strange underground conditions. This would prove that they were not the product of contamination during the actual drilling process. Some of these microbes were then placed in a sealed flask with carbon dioxide, basalt, and hot water for a year. The scientists found that not only did these microbes manage to survive, they actually flourished under these conditions.
Whatever the origin of petroleum may be, there seems to be at least some life forms living and thriving in it. However, most geologists still think that it was produced by the remains of long-dead plant material.
Scientists have found that it is not always easy to define what "life" is--and determining how some ambiguous entities should be classified is difficult. Viruses are microscopic infectious tidbits that can replicate only inside a cell belonging to an unambiguously living host--and victim. Viruses are intracellular parasites that can only reproduce their own kind by invading an unlucky organism's cells.
Viruses are made up of genetic material encased within a protective shell termed a capsid. They are completely unable to reproduce themselves outside of the unfortunate living host cell that they have taken over and destroyed. However, unlike some other parasites--such as bacteria, some fungi, and an assortment of other unappealing organisms--viruses are often considered to be nonliving. Because scientists have such a hard time determining what is alive and what is not on Earth, it's logical to conclude that they will have an even worse time determining whether certain entities are alive or not on distant worlds beyond our own. Any life that very well may exist on faraway worlds would have followed an entirely different line of evolution than living creatures on Earth.
Living In The Clouds
The potential habitability of the clouds of Venus was first proposed in 1967 by the biophysicist Dr. Harold Morowitz (1927-2016) and the famous astronomer Dr. Carl Sagan (1934-1996). Several decades later, the planetary scientists Dr. David Grinspoon (Planetary Science Institute), Dr. Mark Bullock (Southwest Research Institute) and their colleagues further expanded on this theory.
To investigate the idea that the Venusian atmosphere could host living tidbits, a series of space probes were dispatched to the planet between 1962 and 1978. The probes revealed that the temperature and pressure conditions in the lower and middle regions of the Venusian atmosphere--at altitudes between 40 and 60 kilometers--would not be hospitable to microbial life. The surface conditions on Venus itself are completely hostile to the evolution of life--with temperatures skyrocketing to more than 860 degrees Fahrenheit. Indeed, this hottest planet in our Sun's family was the ancient victim of a greenhouse effect gone completely mad, and the rocks of Venus are so hot that they actually emit an eerie reddish glow akin to the coils of a toaster.
Dr. Limaye, who performs his research as a NASA participating scientist in the Japan Aerospace Exploration Agency's Akatsuki mission to explore the planet Venus, became interested in reexamining the planet's atmosphere following a discussion with the research paper's co-author Dr. Grzegorz Slowik of Poland's University of Zielona Gora. Dr. Slowik told him about bacteria on our own planet that possess light-absorbing properties that appear to closely resemble those of certain unidentified particles that compose some mysterious dark patches observed in the Venusian clouds. Spectroscopic observations, that were mostly performed in the ultraviolet, reveal that the dark patches seen in the clouds of Venus are made up of concentrated sulfuric acid--as well as some other unknown light-absorbing particles.
Those mysterious dark patches have presented an intriguing puzzle to astronomers ever since they were first spotted by ground-based telescopes almost 100 years ago, Dr. Limaye noted in the March 30, 2018 University of Wisconsin-Madison Press Release. Eventually, they were observed in more detail when space probes were launched to study Venus.
"Venus shows some episodic dark, sulfuric rich patches, with contrasts up to 30-40 percent in the ultraviolet, and muted in longer wavelengths. These patches persist for days, changing their shape and contrasts continually and appear to be scale dependent," Dr. Limaye continued to explain.
The particles that compose the strange dark patches proved to have almost the same dimensions as some bacteria on Earth. However, the instruments that have obtained samples of Venus's atmosphere to date have been incapable of observing the difference between inorganic and organic materials in the Venusian clouds.
These very intriguing patches could be composed of something similar to the algae blooms that occur in the oceans and lakes of our own planet, according to Dr. Limaye and Dr. Mogul--only these would have to inhabit the clouds of Venus.
Dr. Limaye, who specializes in the study of planetary atmospheres, became even more intrigued with the idea during a visit to Tso Kar. Tso Kar is a high-altitude salt lake in northern India. It was here that Dr. Lymaye observed powdery residue left by sulfur-fixing bacteria collecting on decaying grass beside the lake. He noted that this residue gently floated up into Earth's atmosphere.
However, according to Dr. Limaye, there is one very important missing piece to this puzzle--it isn't known when Venus' liquid water evaporated. This is because widespread lava flows over the past billion years probably either destroyed or covered up the inhospitable planet's ancient terrestrial history.
In the scientific search to discover extraterrestrial life, planetary atmospheres beyond Earth's remain almost entirely unexplored. However, one possibility is currently being developed for the purpose of sampling whatever may or may not lurk in the Venusian clouds, according to Dr. Limaye. The Venus Atmospheric Maneuverable Platform (VAMP) is a craft that will fly like a plane but float like a blimp. This craft, which is still on the drawing board, could stay afloat in the Venusian cloud layer for as long as a year collecting data and samples.
VAMP could carry instruments like Raman Lidar, chemical and meteorological sensors, and spectrometers, Dr. Limaye explained in the March 30, 2018 University of Wisconsin-Madison Press Release. He added that it could also carry a type of microscope capable of detecting living microorganisms. Raman Lidar is an active, ground-based, laser remote-sensing instrument that provides measurements of water-vapor mixing ratio, temperature, aerosol, and cloud optical properties. It is sensitive to both molecular and aerosol backscatter.
"To really know, we need to go there and sample the clouds. Venus could be an exciting new chapter in astrobiology exploration," Dr. Mogul told the press.
The research for this study was supported by NASA grants. The VAMP concept is under development by Northrop Grumman Corporation.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, newspapers, and journals. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others some of the many wonders of her field. Her first book, "Wisps, Ashes, and Smoke," will be published soon.
