Summary (Sep 29, 2003): Selected from tens of thousands of questions posed to Astrobiology Magazine, the best ones are culled in a reader dialog that helps guide new areas to explore. Key questions continue to center on some of the most extreme conditions on earth, and the chances for liquid water elsewhere.
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Messages in a BottleThe editors of the Astrobiology Magazine, and its companion Mars Edition, receive a large volume of questions on the new science fields seeking out answers to life elsewhere in the universe.
The magazine periodically enhances this dialog by sharing the best of these questions. This feedback not only gauges the depth of interest and knowledge among those who track this field, but also helps define new vistas for investigation. Many of these areas, by their nature, are imprecisely understood. As with most science, such questions spawn new sets of inquiries.
The first installment was entitled "The Envelope of Life, Please", to underscore the magnitude of interest in extreme environments and the limits to places where no living organism has gone before (and survived). That fascination with extreme life has continued, and is reflected in many of the questions recently submitted.
The magazine received a total of 41,709 questions, and about one in eight (5,731) were not duplicates and ranked most popular. Of these nearly six thousand entrants, the top seventy-five or so are shown below with their reference links for further exploration.
The editors have judged the following question as the most compelling to date, both for its fundamental insight, but also because it is a fertile field of current investigation among astrobiologists.
Do lifeforms exist without water?
Not so far, at least beyond some exotic sporulating, hibernating or dessicated state. This singular question guides a great deal of how scientists look for habitable zones on other planets: can liquid water exist? Frequently Asked Questions What is the most extreme temperature in which life is found? 235 F, a hyperthermophilic microbe called Pyrolobus fumarii What is the most extreme pressure in which life is found? 1200 times atmospheric pressures. In laboratory experiments, around 16,000 sea-level pressures, survival is possible, but it is unknown what kinds of growth and metabolism may be possible under such extreme conditions. What is the biomass below the surface of the Earth? The mass of microorganisms beneath our feet, reaching down miles underground, likely equals or exceeds the mass of all the organisms on Earth's surface What is the definition of a living organism? It must feed, grow and reproduce. Around 102 specific questions can be asked of a given phenomenon if a classification scheme is imposed. Did ancient oceans exist on Mars? Don't know yet. Snow, frost and gully remnants are fascinating clues to what may also be enough subsurface water to cover the planet knee-deep if equally distributed latitudinally. There is a scientific consensus building around the notion of at least transient gushes to the surface.
What were the earliest life forms on Earth? Many think trilobites were the first multi-celled organisms, and cyanobacteria as the first photosynthesizing. Is there life on Europa? Under miles of a frozen ocean, a salty sea may harbor exotic or primitive candidates. What is a galactic habitable zone? A star with planets capable of hosting liquid water. Other constraints may limit the distance the star is away from the high radiation environment of a galactic center vs. periphery. Does Saturn's moon, Titan, have an atmosphere? Yes. The Cassini spacecraft will drop a probe down into what some scientists believe is a biochemically rich atmosphere. What is the Fermi paradox? If there is intelligent life out there, why haven't we found it yet? How did our Moon form? New evidence points to 'a chip off the terrestrial block', although there are other planets which have captured moons around stray asteroids. How are meteorite searches conducted to find Martian fragments? Often times on hands and knees in Antarctica, or even in desert marketplaces where meteorites are sold. What kinds of next generation, planetary rovers are currently being explored? Lots of remote control, autonomous behaviors. Did life originate once or many times on Earth? All life can be mapped to one tree or web of life. Are strong oxidants thought to exist on the surface of Europa? Evidence from the Voyager and especially Galileo spacecraft missions points towards an ocean whose volume is nearly twice that of all the Earth's oceans combined. How is mitochondrial DNA used to construct family trees through maternal genes? The energy center for complex cells called the mitochondria carries forward tracer DNA that allows backtracking, and has recently been found in fossils of interest. Could life be transferred from Mars to Earth or vice versa? Perhaps endospores, or fossils. Radiation may be a bigger constraint that temperatures. How many plant and animal species have gone extinct? The majority. What is the Doppler detection method for finding new planets? A change in color of a star's light to measures changes in the star's velocity caused by the gravitational pull of an orbiting planet How do scientists apply Occam's Razor to resolve questions with little actual data available? A principle of good science, given multiple possible choices, choose the simplest one with the fewest assumptions - to paraphrase. What organic compounds have been found in meteorites? The Murchison meteorite showed evidence for protein building blocks, and some amino acids thought not to occur terrestrially. What space probes are planned to explore Europa? The Europa Orbiter is tentatively planned for 2010. So far much compelling data has been collected by the Galileo spacecraft's fly-by mission. What is considered the one animal that can survive the harshest extreme environment? Tardigrade or water bear What is the saltiest environment that living cells are found to grow? Halophiles, or salt-loving, microbes have been found in water with 25% salt content. What was the Miller-Urey experiment? In the classic 1953 experiment, complex molecules such as amino acids and sugars were produced by electrical discharges in a primeval atmosphere replete with gases such as methane, hydrogen, ammonia and water. What are the three domains of life? Archaea (including life in extreme environments), prokaryotes (lacking a cell nucleus) and eukaryotes (having a cell nucleus) like plants, animals and humans. Some consider viruses a fourth domain. Are their organisms that don't use DNA for code storage? RNA viruses like common cold. What are the most promising Martian landing sites? Dry lakebed or where the water-forming minerals like hematite are expected. More than a hundred sites have been considered relatively promising but differ in mission risks and rewards. What killed the dinosaurs? Climate change and perhaps an asteroid strike where the present day Gulf of Mexico is. This K/T impact occurred 65 million years ago . What science is available to predict what aliens might look like? Not generally, but if advanced intelligence, there are clues to how long such a civilization might need based on what we know about Earth. What was special about the Tagish meteorite? Landed on a frozen lake in Canada, and is considered well-preserved. What was special about the Allan Hills meteorite? Martian meteor which showed curious rod-like deposits and magnetic properties. What was special about the Murchison meteorite? Showed evidence for amino acids. What was on the golden record sent out on the Voyager spacecraft? A combined message-in-a-bottle featuring music, images, and greetings.
 | | The Earth is our only example of planetary life. This makes it difficult to unravel what is universal and what is accidental about the nature and history of life. |
What is the 'typical' weather like on Mars? Atmospheric pressure at 0.6 percent that of the Earth's surface, an average temperature of -60 degrees C (-140 F) and a thin atmosphere of 95 percent carbon dioxide. The lack of a protective atmosphere may make radiation hazards considerable. What is the expected lifetime of our Sun? Around another 7 billion years before it enters its Red Giant phase of rapid expansion. What are the scientific chances of a large meteor or comet striking Earth? Around 1000 near earth objects a kilometer or larger in size, with an impact capable of killing 100,000 people occurring about once every 40,000 years. Have any comets or asteroids ever hit planets besides Earth? In 1994, the Hubble Telescope photographed the dramatic impact of Comet Levy/Shoemaker as it exploded into Jupiter's atmosphere. What are the prospects for life on Jupiter's moon, Io? Europa is a better bet because of its salty ocean, and Io is volcanic. What is meant by the panspermia hypothesis? Sowing the seeds of life with organic molecules or simple life transported on meteors or comets. Are electrical storms on Mars a risk for spacecraft and rover electronics? Mission planners are testing against this hazard. What is the driest place on Earth? At high altitude between northern Chile and Bolivia (Atacama), and Antarctica. Could bacteria survive on present-day Venus? The surface is too hot, but cloud colony theories have been proposed. Who is Matthew Golombek? Mars Pathfinder (1997) Project Scientist, Jet Propulsion Laboratory. What are nanobes? What is the smallest organism on the planet? Nanobacteria, or life at the limits of being able to encapsulate its own DNA. What are the two typical structures for viruses? Rods or icosahedral. What will animals will like in a million years? Impossible to speculate, but some scientists imagine on time scales as short as a thousand years, humans will be frequently space-faring which introduces rapid adaptations in a hostile environment. Is there water on Venus? The surface is hot enough to melt lead, but atmospheric layers may be temperate in a stratified way. What is Dollo's law in evolution? An organ never returns to an antecedent structure What is meant by the Snowball Earth theory? A geological phase where the oceans freeze. Was there life on earth before the formation of our own Moon? Unlikely, since the Earth was hot and molten, and above the boiling point of liquid water. What are the individual probabilities for intelligent life based on the Drake equation? A series of probabilities based on the number of stars, but with the least well-known factor may well be the lifetime of a technological civilization. What is the age of the universe? 13.7 billion years, according to levels of background microwave radiation. What happened to cause the Cambrian explosion of different life forms on Earth? Don't know exactly, but genetic cross-over of material played a larger role compared to just mutations in evolving species more rapidly.
 | Europa is one of the primary focuses in the search for life in the universe.
Credit: NASA |
What do planet discoverers mean when they refer to 'hot Jupiters'? Gas giants very close to their parent star, and unlikely to harbor habitable conditions. Could life form today from 'scratch' given current the current Earth's atmosphere, composition and temperature? Life scientists are trying some ambitious lab experiments. What weather modifications are needed to terraform Mars? Greenhouse creation, most likely with chlorofluorocarbons, or CFCs. It might take at least 40 years depending on the inputs, and how well-controlled a runaway hot Mars might behave. The greening of a rusted, red planet is being actively studied, although the requirements for bacteria are quite different from more complex life.. How many extrasolar planets have been found so far? Around 105. Why is the mineral hematite considered important to finding evidence for ancient water on Mars? Red hematite is found in certain regions and on Earth is formed in combination with water deposits. What are psychrophiles? Cold-adapted bacteria that often lives in permafrost at -20 C. How are tidal forces considered an alternative heat source when solar heat is insufficient? Akin to frictional heating, strong tides provide a heat source particularly for Jupiter's moons, such as Europa.
Honorable mentions. A new honorable mention category is appended for specialty categories, such as the most humorous and the most surprising:
Can humans live after being frozen? Is a camel just a horse designed by a committee? Intra-species Human CommunicationThe most unexpected lines of questions hold future promise for humans communicating with our own species, as a large number of readers seek out new space-related ringtones for their cellphones. These requests have come from around the world, including Serbia, Turkey, Marathi (India), Armenia, Japan, Telugu (southern India), Punjabi, Persia, Cantonese, Vietnam, Nepal, Kannada (India), Korea, Poland, Arabic, and Uganda. Fortunately all these are available from adaptations of the Voyager spacecraft's golden record that was sent as a partial history of diverse languages and greeting to a future receiver of that message-in-a-bottle.
Note: Extrasolar Life: [2002-04-26]
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