1. As far as we know, it is not possible to have life on any other planets other than our own earth. But, there are some factors like frozen ice caps, subsurface water resources, and atmospheric conditions on other planetary bodies that could affect their habitability . Why aren't we able to explore those places? As far as the cost of exploration is concerned, nations of the world could unite to explore each and every inch of any potentially habitable planet.

    Answered Tuesday November 12, 2013 9:05AM PST by Sanjoy Som

    Thanks for your question. Life as we know it requires three main ingredients to be supplied by the environment: i) water, ii) organic material, iii) some form of energy. Earth indeed does supply these, but so do other bodies in our solar system (Enceladus, a moon of Saturn, being a great example, and Mars to an extent). All three ingredients need to be present to allow life as we know it to take hold. Many of the environments that you mention have only one or two of the above ingredients, so while many are exciting targets for research, they are only fair to poor targets to explore for extant life. But who knows? They may well have extinct biosignatures – chemical signatures of past life – within them. The study of biosignatures is an active field of research in astrobiology.

    An Earth-like atmosphere is not necessarily needed for life to exist. In fact, many microbes on Earth cannot live in the presence of atmospheric oxygen. Likewise, water alone does not make an environment habitable. It is exciting when water is indeed found beyond Earth, but water is not in itself a sign of habitability. Yet, the presence of water has indeed guided the exploration of other worlds. Mars, for example, is being actively explored for organic materials (among other things) by the Curiosity rover because the planet has a confirmed history of liquid water present on its surface. So far no organics have been detected.

    With regard to extrasolar planets, all scientists know about them are essentially their densities, from which compositions (either gas, rock, or water) are inferred, not measured. Those planets are many light years away, the closest being around the star Alpha Centauri B, which is still 4.4 light years away. As you know, we as a civilization have a long way to go technologically before we can explore those worlds in situ.

    Space probes are designed and built to answer specific questions about an environment, and so are built with focus. Exploring “each and every inch” of a planet without thinking carefully ahead of time about the scientific worth of exploring certain areas would be a colossal waste of time and money. Because many space agencies are funded by taxpayers, you can imagine the problems this would cause. Think of it this way: even Earth has not been completely explored because it is expensive to explore remote areas and the value to the sponsors of explorations is not always evident. Exploring the entirety of another planet would be far more costly than exploring the entirety of Earth. The cost concern is particularly relevant in these times of financial caution, where national budgets are being scrutinized. So while you are correct that several nations coming together to build an ambitious space probe would be beneficial for exploration, the financial status of different nations varies greatly, and governments must set priorities for allocating funds.

    My question involves planetary science as well as astrobiology (it is for a science-fiction story). Would a planet of 3 earth masses be too large to be terrestrial? Also would it be possible for it to only have a radius of 8,000 kilometers despite its mass?

    Answered Friday November 8, 2013 12PM PST by Michael Busch

    The answer to your questions depends on what you mean by "terrestrial." I'll talk about that, but for the moment consider a planet with the same bulk composition as the Earth, just three times more massive.

    If this planet had the same average density as Earth does, it would have 3 times the volume and so 3^(1/3) the radius - about 44 percent larger. Earth's mean radius is about 6370 kilometers, and 1.44 times that distance is about 9170 km.

    However, a planet with the same composition but 3 times the mass of the Earth would _not_ have the same density as Earth, because it would have greater pressures and higher temperatures in its interior. Materials are compressed to different densities depending on their particular chemical structure as well as pressure and temperature. By way of illustration, the Earth's core is mainly made of iron and nickel, with a bit of sulfur, platinum, iridium, and other things - basically steel. On the surface, at nearly zero pressure, that mixture would have a density of about 8 grams per cubic centimeter. At the center of the Earth, pressure is such that that steel is compressed into a bit less than two thirds of its surface volume, with a density near 13 grams per cubic centimeter. On a super-Earth, the central pressure would be higher still.

    A lot of work has been done to figure out what radii planets made of various mixtures settle down to as a function of mass. There is significant uncertainty in these mass-radius curves - it's hard to produce the temperature and pressure conditions at the center of a planet in the lab. That said, for an object with the same composition as Earth but 3 times its mass, we would expect a radius only 25-30 percent larger - at or just a bit above the 8000 km that you had estimated.

    But such a planet won't just be Earth scaled up. Its surface gravity would be 75-90 percent higher than Earth's. Depending on how old the planet is, it could have several times greater geothermal heat driving much greater mantle convection. Under those circumstances, while plate tectonics would probably be active, the plates would be moving faster and might also be smaller. With higher gravity crushing mountains down, continents would not develop the same way they have on Earth.

    Given an equal mass fraction of water and other volatile compounds, the oceans and atmosphere of such a planet would have roughly three times the mass of Earth's oceans and atmosphere. Such a planet would orbit around its host star in an orbit where greenhouse warming would be enough to keep the ocean liquid at the surface without boiling it into steam. Given its deeper oceans, such a planet might not have any land above the waterline, even if its ocean was liquid at the surface.

    If you change the composition of the planet, things can be different.

    Turn the volatile fraction down a bit and you'll have a thinner atmosphere and less of a steamhouse. But depending on how plate tectonics plays out, you still might not have much surface above the waterline - unless volatile content were lower still. Add _more_ volatiles and you get a waterworld, with an ocean covering the whole surface, potentially to depths of thousands of kilometers.

    Water is less dense than rock or metal at almost any pressure, so these planets would be far larger given the same mass. The Kepler extrasolar-planet-finding spacecraft has found a number of examples of this sort of planet. The surface of a waterworld may be an ice shell, a liquid ocean - although those may not be stable - or an atmosphere so hot and thick that it is impossible to mark the transition from high-temperature steam to high-temperature liquid.

    Add more metal and less rock and volatiles and you get a denser and more compact planet. Kepler has found a couple of examples of this type of planet, too. These bodies should form quite close in to their host stars, where temperatures are too high for volatiles to be accreted. You could think of them as larger versions of Mercury or of Alpha Centauri Bb. Some could be so hot that they might have surfaces made of lava and atmospheres of vaporized silica.

    A planet with the same amounts of metal and rock and volatiles as the Earth in the nominal habitable zone of its host star, but with more carbon than oxygen, would have rocks that would be carbides rather than oxides. The surface of such a planet would be covered in hydrocarbons rather than water, so the place would be very different from both Earth and an object with the same composition as Earth and 3 times Earth's mass. The geophysics of such possible carbon planets has not been investigated in detail, and while some exoplanets have been identified that might be carbon-dominated, this claim has not been confirmed.

    Again, the answer to both of your questions is "yes, depending on what you mean by terrestrial."

    I recently read about a theory that soon the Andromeda galaxy and the Milky Way galaxy are going to collide with each other. What do you think? Could this collision happen? What would be the impact on our galaxy and, most importantly, our Earth in this event?

    Answered Monday August 12, 2013 12PM PDT by Michael Busch

    The Milky Way and Andromeda are indeed predicted to collide with each other, but this collision will only happen "soon" in comparison to the lifetime of the universe. Andromeda is currently 2.54 million lightyears away, and the galaxies are approaching each other at ~300 kilometers per second. It will take several _billion_ years for the two to reach one another. The exact timing and progression of the collision is uncertain, because we do not know exactly how much the galaxies are moving sideways relative to one another. The sideways motion determines the path and time the galaxies will take prior to colliding, as well as their orientations during it. The current best estimate is that the collision will happen in about 4 billion years.

    During the collision, the discs of both galaxies will be disrupted and eventually merge. The smaller satellite galaxies that orbit both the Milky Way and Andromeda will be scattered onto new orbits around the combined large galaxy and many will eventually collide with it themselves. The central black holes of the two galaxies are likely to combine with each other. And a number of interstellar gas and dust clouds will be compressed slightly. Those that become dense enough will collapse under their own gravity, producing a large population of new stars.

    None of this will have any particular effects on the Earth or the other planets. Stars are very thinly spaced, and increasing their density by a factor of two will not lead to any stellar collisions or to any significant fraction of planetary systems being disrupted. There is a small-but-significant probability of the Sun being ejected into intergalactic space during the collision, but even this would not impact the Earth or the other planets beyond changing what the night sky looks like.

    By 4 billion years in the future, barring any large-scale intervention, there will be no life on Earth. The Sun will not yet have become a red giant star, but it will have increased in brightness far enough by that time that the Earth's oceans will have boiled to steam and that steam and the rest of the atmosphere will have escaped to space. In comparison, changes in what the night sky looks like are insignificant.

    Are there planets revolving around all stars, as there are eight planets revolving around our sun ?

    Answered Monday August 5, 2013 2:46AM PDT by Jacob Haqq-Misra

    About twenty to thirty years ago, no one really knew the answer to your question. Astronomers have long known of the eight planets (plus asteroids, Kuiper belt objects, and comets) that comprise our Solar System, but it was not until very recently that planets orbiting other stars have been discovered. The first such planets discovered were very large, bigger than Jupiter, because these are the easiest to find. Over the past ten years or so, astronomers have improved their techniques and are getting better at detecting smaller and smaller planets around nearby and distant stars.

    These new results all seem to indicate that planets are commonplace around stars in our galaxy, and that many, if not most, stars seem to have at least one planet in orbit. Some stars will likely be devoid of planets (such as older stars that have exploded as supernovae, or multiple stars that orbit one another), but astronomical surveys and statistical analysis all seem to indicates that planets are the rule, rather than the exception. As astronomers continue searching for extrasolar planets, we will arrive at an even better understanding of the frequency of planets around stars--and perhaps even the likelihood that such planets might be habitable.

    Dr. Jacob Haqq-Misra, Blue Marble Space Institute of Science

    The discovery of amino acids and carbonate compounds in comets and the current speculation that comets delivered these necessary ingredients for life to a "barren" Earth prompts my question. How did amino acids and the other complex compounds found in cometary bodies get there? For that matter, where did all the water that comprises the majority of the ort cloud come from? Two questions, I know, but they seem related.

    Answered Friday August 2, 2013 2:49AM PDT by Michael Busch

    The water ice in the Oort Cloud, like almost all of the material in the solar system, came originally from a large interstellar cloud of gas and dust called the presolar nebula. Due to the particular mixture of elements injected into the presolar nebula from earlier stars, there was more oxygen than carbon or nitrogen but far more hydrogen than anything else. This produced a large amount of water, carbon dioxide, carbon monoxide, ammonia, and methane - what astronomers call ices or volatiles. As the cloud collapsed to form the solar system, it formed a disc around the young Sun. The inner parts of the disc (out to what would eventually be the inner asteroid belt) were hot enough that those compounds were gases rather than solids, so the planetesimals that later formed the terrestrial planets only had relatively little ices in them. But the outer parts of the disc were cold enough for water to be a solid, with CO2, CO, NH3 and CH4 becoming solid even further out. That's why the objects in the Oort Cloud and the giant planets and their satellites have large quantities of water and other ices in them.

    The amino acids and other carbon compounds in meteorites and comets formed as those ices reacted with each other, and the smaller quantities of many other compounds that were produced in the presolar nebula and before that in the stellar winds of earlier stars. These were then later delivered to the Earth as the orbits of comets and asteroids were perturbed to bring them into the inner solar system. This still happens, but much of the material that was delivered to Earth arrived during a time 3.8 billion years ago called the Late Heavy Bombardment, caused by the orbits of the giant planets changing rapidly.

    One note on nomenclature: you referred to "carbonate compounds in comets". You likely meant "carbon compounds". "Carbonate" refers specifically to salts of carbonic acid (CO3), and few are found in comet or asteroid samples.

    Dr. Michael Busch, Blue Marble Space Institute of Science

    How does prebiotic chemistry help us to understand how life started?

    Answered Friday July 26, 2013 3:39AM PDT by Grasshopper Illangkoon

    This is a great question, as those of us in the origins of life community ask this very question every time we sit down to work at the lab bench, microscope or telescope.

    Let's start by defining prebiotic chemistry as chemical reactions that happened before the emergence of life as we know it. There are many theories for the origins of life on Earth, but we have yet to connect all the dots to complete the story. One theory as to how life originated on our planet points to an “RNA World” where molecules of the genetic polymer RNA (Ribo Nucleic Acid - similar to DNA, Deoxyribo Nucleic Acid) formed. According to this theory, these molecules of RNA had the ability to copy themselves and were later encapsulated by lipids (certain types of organic molecules) to form what we call "proto cells."

    Here we ask the question: where did the RNA come from in the first place? To answer this question, we study the structure of nucleotides, the building blocks of RNA. A nucleotide has three components: a sugar (ribose), a phosphate, and a heterocycle (a certain type of organic compound). Let’s focus on one of these components, ribose (a molecule of this sugar has five carbon atoms).

    As a chemist, I'm interested in what kind of molecules might have been present on the early Earth or in interstellar space, billions of years ago, to assess what chemical building blocks for life might have been available to start with. To gain a better understanding of what molecules I can add to my toolbox of prebiotic chemistry, I collaborate. I ask fellow scientists - astrochemists, geochemists & geologists - who have a better understanding of what is out in deep space and what may have been on the early Earth, when the planet cooled just enough to enable water to be liquid on its surface.

    For example, astrochemists have confirmed the presence of simple organic molecules such as formaldehyde, glycolaldehyde, and glyceraldehyde in interstellar gas clouds. These three molecules contain one, two and three atoms of carbon respectively. Using chemistry, we can mix these molecules in the lab in various ratios, at different temperatures, and at varying pH levels, and we can include a variety of elements or minerals that we think were present on an early Earth. One prebiotic chemistry experiment, for example, showed that we could mix these simple organic molecules with borate to form stable sugars including the five-carbon ribose. Another molecule present in interstellar gas clouds is cyanide, which can undergo a chemical reaction to evolve into the heterocyclic molecule adenine. Here we now have two pieces of a nucleotide. The next step is to understand how these molecules join together to form the backbone or RNA.

    As you can see, the field of origins of life research is very exciting! One of my favorite perks of being an astrobiologist is the opportunity to collaborate with scientists in other fields and the perpetual learning we all engage in while we answer some of the most important questions relating to our own existence.

    Dr. Grasshopper Illangkoon, Blue Marble Space Institute of Science

    Why it is said that on another planet, if there is no oxygen or water then there is no possibility of life? Is it possible that life may exist on another planet that does not need water or oxygen to live? Is it possible that on another planet , the definition of "life" does not match with our concept? Might be there the living things elsewhere that do not have chromosomes or genes? I am a student studying biology, so out of curiosity this question came into my mind.

    Answered Wednesday July 10, 2013 3:43AM PDT by Jacob Haqq-Misra

    Astrobiologists have not yet discovered any forms of life outside of Earth, and so Earth-life remains our only know example of possible biological systems. On Earth, all living organisms require liquid water during some part of their life cycle, which has suggested that one way of searching for extraterrestrial life is to “follow the water” in space. We do know of plenty of examples of life on Earth that does not require oxygen (known as anaerobic life), and astrobiologists do actively consider both oxygenated and oxygen-free environments when thinking about life elsewhere.

    That said, some scientists study the possibility of life that could use other liquids--such as alcohol solvents—or other chemical backbones—such as arsenic or silicon, rather than carbon. We also cannot discount the possibility that extraterrestrial life might be so completely different from what we can imagine that it could be undetectable by our current search techniques. Until we discover an example of extraterrestrial life, we cannot known for certain, but thinking about the commonalities of Earth life is at least one step toward refining our search for life elsewhere.

    Dr. Jacob Haqq-Misra, Blue Marble Space Institute of Science

    Is it possible to build a tricorder that can detect life on other planets, using a portable system. And if so, how would you do it? Laser spectroscopy, lab on a chip etc.

    Answered Wednesday June 5, 2013 3:27AM PDT by Jacob Haqq-Misra

    A “tricorder”, as depicted in "Star Trek," is a multi-purpose technological device used by human explorers. Present-day human space exploration has not yet taken any astronaut further than the Moon, although some initial planning for human missions to Mars is in progress. Only when humans are able to set foot on the surface of another planet will there be a need for a mobile tricorder-like device that explorers can use to detect life as they explore other planets.

    That said, the technology that might go into such a device has real-life analogues with scientific instruments fitted to robotic planetary exploration rovers. The robotic Mars Exploration Laboratory mission now under way, for example, includes a search for chemical signatures in rocks or soil that could indicate that Mars is or was habitable to present or past life. This roving lab is outfitted with drills and scoops to collect samples, which are then fed into chambers that allow for the composition of the material to be analyzed according to its mass (using a mass spectrometer), its volatiles (using gas chromotography) or its laser-induced signature (using a laser spectrometer). The Mars Science Laboratory (named "Curiosity", see: http://mars.jpl.nasa.gov/msl/) even includes an instrument that shoots a laser at a distant rock and observes its chemical composition from afar! Scientists compare the results of these chemical analyses with their knowledge of environments on Earth to understand whether or not these Martian environments are consistent with the presence of biology (for example, by looking for organics, carbon, amino acids, or other remnants of life). Although we cannot predict what technology in the future will look like, we can at least be sure that the techniques used in the present-day robotic exploration of Mars will be available for future human exploration of the Solar System.

    Dr. Jacob Haqq-Misra, Blue Marble Space Institute of Science

    Are there any living examples of LUCA (Last Universal Common Ancestor), or would it be possible to reconstruct one? I assume the recent research in creating bacterial DNA artificially, might be used to construct DNA that matches the common elements of all life.

    Answered Monday June 3, 2013 3:22AM PDT by Sara Walker

    As far as we know, there are no living examples of the Last Universal Common Ancestor (LUCA) – it would be really great if there were! It would certainly provide a lot of information about the early evolution of life.

    Instead of finding a living sample of such ancient life, we’ve inferred the existence of LUCA by comparing DNA from all kinds different organisms alive today – the commonalities in the DNA of organisms as diverse as bacteria and humans suggest that all life on Earth is related (the fact that all known organisms on Earth have DNA is a powerful statement in its own right about common ancestry).

    However, the phylogenetic record (the record of the history of life on Earth) that is preserved in DNA is really limited, in that we can only compare the DNA of organisms that exist today. Anything that went extinct in the past is not going to contribute to the DNA sequence data banks that we generate now. The information is simply lost from history. It’s only by using data from modern organisms that we’ve been able to figure out that a common ancestry relates all known life – at the base of the “tree” is LUCA.

    BUT (and this is purposefully a big BUT) we don’t know what information might be missing about LUCA from all of the lineages that went extinct in the 3+ billion years since LUCA lived. So while it would be really cool if we could reconstruct all of the DNA of LUCA, and in principle it is definitely possible with modern technology as you suggest, it may not be possible in practice. We may have lost too much information over the course of evolutionary history to ever know exactly what LUCA looked like. The situation is so challenging when looking that far back in time (more than 3 billion years) that we are not even quite sure where to locate the root of the tree of life.

    Known life is divided into three major domains: Eukaryotes, Bacteria, and Archaea. These three very different kinds of organisms are still related by common ancestry (that is, LUCA), but we don’t know which is most closely related to LUCA. Depending on how you construct your tree (i.e. which DNA sequences you look at) you end up with different relationships of the three domains near the root. So even though we know LUCA existed, there is lots more work to be done to understand what early life looked like. It’s certainly an exciting field of research.

    Dr. Sara Imari Walker, Blue Marble Space Institute of Science

    Is it possible to remove an oxidizing agent after it is used? ex. Chloride (Cl^-) + any oxidizing agent capable of = (Cl). I am having a "fight" with my brother because he stated that you cannot remove an oxidizing agent after it was used, which i honestly cannot believe.

    Answered Monday June 3, 2013 2:56AM PDT by Elizabeth Percak-Dennett

    That's a good question, because understanding how chemical elements interact on Earth helps us to understand how chemical processes can take place in space and on other planets.

    Yes, once an oxidizing agent has oxidized a chemical, it can potentially be removed from the system.

    To better understand this, lets consider an example of the element iron. If you were to buy an iron nail at a hardware store, it would be black in color, and have a reduced oxidation state. If you left that nail outside in the rain and elements for a few months it would develop a rusty orange coating, and that rust is the iron becoming oxidized.

    Most chemical elements, such as the iron making up the nail, have the potential to exist in either a reduced or oxidized state depending on the number of electrons in those elements. The new nail has a reduced oxidation state, and after several months outside the oxygen removes electrons, causing it to rust.

    On Earth, oxygen is the main element driving oxidation of elements, and since oxygen exists as a gas in the atmosphere, the gas is free to diffuse away after oxidation, thus being removed.

    I hope this sheds some light onto the “fight” you’re having with your brother. Let me know if you have any other questions.

    Dr. Liz Percak-Dennett, University of Wisconsin Madison

    I'm doing a world building project on a tidally-locked planet that is still habitable. While I won't bore you with the details, I was wondering, do you think that life forms that use piezoelectricity as an autotrophic metabolic function could possibly inhabit the dark side of the planet?

    Answered Friday May 31, 2013 2:03AM PDT by Morgan Cable

    Very interesting question! The short answer is, I'm not sure. Piezophilic (pressure-loving) bacteria can survive extremely high pressures (like in the Mariana Trench), and bacterial spores with tough spore coats can survive very low pressures (like the vacuum of space), but I'm not aware of any bacteria that take advantage of pressure gradients to generate energy for metabolism. My guess is that in places with pressure gradients, you will most likely have other gradients as well (thermal, chemical, etc.) that would be easier for a bacterial cell to extract energy from. But who knows? If you can figure out a mechanism for it, there's probably a bug out there that is doing it right now, and we just haven't discovered it yet.

    I hope this answers your question. If you'd like more detail about piezophilic bacteria and how they mitigate pressure effects, let me know!

    Dr. Morgan Cable

    I am a chemistry student of 7th semester who´s part of an Astrobiology group in the National University of Colombia. Recently, we have decided to make a book, which pretends having some important topics like alternative biochemistry routes and extremophile organism looking for having a little, but complete compendium about this kind of topics that allows an easy but scientific introduction for interested people. For that reason, I have decided to ask your opinion respect to the topics we can not forget and, more specifically, your opinion about which compounds are the most important to be discussed as probable partaker in a hypothetical life form that use different compounds from those which are used by forms of life in our planet. I am going to be very grateful for your time and your answer.

    Answered Wednesday May 29, 2013 2:08AM PDT by Rebecca Turk MacLeod

    As you may know already, life on Earth is incredibly diverse and uses a variety of different compounds for metabolism and survival. We do not even need to look outside our planet to find microbes that eat and breathe compounds like methane and sulfur, and/or live in environments completely devoid of oxygen. These organisms have evolved certain “tricks” in their physiology and sometimes made slight modifications to their biochemistry that allow them to live in extreme (by human standards) conditions, but as far as we know, the fundamental biochemistry of all living things on Earth is the same. That is to say, we all use DNA, RNA, and proteins as the basis of all our cellular functions.

    But what may exist outside of our standard Earth biochemistry? Scientists have already proposed alternative backbone structures for nucleic acids, which may give us a clue as to where present-day DNA and RNA came from; some of these structures are known as TNA (threose nucleic acid), and PNA (peptide nucleic acid). The behavior of these molecules demonstrates that in principle, anything with a repetitive backbone and “sticky” internal units could function as a genetic polymer; we can also infer that anything that folds up into a 3D structure and affects other molecules can be a catalyst.

    If we want to get really creative, we can look at the periodic table and imagine substitutions for the commonly used atoms in our biochemistry. For example, we can look at the atoms that are directly beneath those used for Earth-based life, and imagine that we can substitute sulfur for oxygen, arsenic for phosphorus, or even silicon for carbon. These kinds of compounds do not make up life on Earth as far as we know (with the exception of sulfur, which is incorporated in some amino acids), sometimes due to issues of instability (or maybe just incompatibility with other biologic compounds), but may be of interest on other worlds with vastly different environmental conditions and chemical makeup from what we are used to on Earth.

    We can also look at the chemical compositions of other worlds, and propose what kinds of compounds could be used by organisms living there. For example, the atmosphere and surface of Titan may have a large proportion of methane and hydrocarbons; we already know of microbes that metabolize methane on Earth, but how might an organism on Titan incorporate hydrocarbons (which generally do not mix with water) into its cellular structure? Would life on Titan be “hydrophobic?”

    When thinking about life on other worlds, we can imagine infinite possibilities, but we are also bounded by chemistry. However, we still have a lot to learn about the environments of other worlds and how chemistry and (exo)biology would behave in conditions unlike those on Earth.

    Dr. Rebecca Turk MacLeod

    What is the purpose of discovering exoplanets? and if we do find an Earthlike planet light-years away, where will studies go from there?

    Answered Wednesday May 22, 2013 6:15AM PDT by Jacob Haqq-Misra

    In the context of astrobiology, which is the study of life in the universe, the purpose of searching for exoplanets is to understand the processes that contribute to the formation of planets, atmospheres, oceans, and life. This ultimately helps us learn two things. First, exoplanet discovery is one of the first steps in the scientific search for life outside of the Solar System, which helps us to understand whether life is a rare or common occurrence. Second, the more we understand about the diversity of planetary systems in nature, the more we will understand the past, present, and future of our own planet. Our continually improving knowledge of planetary systems, planet formation, and the limits of habitability also directly help us to understand our own planet and make better informed decisions.

    Once extrasolar planets have been detected, the next step is to characterize them according to their potential habitability. A telescope outfitted with a spectrometer can identify individual gaseous components of an extrasolar planet's atmosphere, which provides at least some information about the planet. Using the past and present of Earth as a proxy, scientists think that certain combinations of atmospheric gases are likely due to the presence of life. The presence of oxygen, ozone, and methane, for example, is due to widespread life on Earth; if scientists were to observe an extrasolar planet with a similar composition, then it would be evidence for an inhabited Earth-like planet orbiting another star. Scientists have not yet discovered any such planets, but the telescopes to properly conduct this search are still in their infancy. As newer generations of telescopes come into being, we will eventually be able to conduct more careful searches that let us peer into the atmosphere of extrasolar planets—in an effort to find signs of life.

    Dr. Jacob Haqq-Misra, Blue Marble Space Institute of Science

    It seems that members of the animal kingdom can live a plant like existence (e.g. sponges), but you would not expect members of the plant or fungus family to evolve into something that could grow legs and walk around. So fundementally what is the difference between plants and animals, such that animals can move around independently?

    Answered Monday May 20, 2013 2:25AM PDT by Betül Kacar

    Hi Glyn! To answer your question, let’s consider this: moving behavior is not solely attributed to animals. We know not all plants are sedentary - consider, for example, slime molds, or choanoflagellates, which exhibit similar morphological properties to sponges.

    Therefore we cannot list moving as a fundamental distinctive property distinguishing plants from animals. To understand why some organisms are sedentary and some are not, we need to take the environment into consideration. Remember: environment selects!

    Think about the lifestyle of a plant, for instance, and what it needs to survive: nutrients, sufficient soil, air and light. Therefore it would make sense for a plant not to move in order to survive and to satisfy its basic needs. A plant does not have to actively pursue its food like animals must do.

    We often see some closely related species exhibiting different properties. For those cases, we need to keep in mind that the divergence between these species may have occurred millions of years ago. Thus the organisms had a really long time to selectively adapt to their local environment.

    I hope this answers your question, feel free to send in any follow questions you may have.

    Dr. Betul Kacar, Blue Marble Space Institute of Science

    I have read multiple articles on Europa due to a project I have. In multiple articles there are conflicting information about liquid water under the ice. Is it liquid water or another form of liquid?

    Answered Friday May 17, 2013 3:53AM PDT by Britney Schmidt

    A lot of what we know about Europa comes from looking at the surface, but some of the data we have also tells us about its interior. Even from telescopes on Earth, we could tell that Europa's surface was extremely reflective, like that of ice or snow, and its infrared spectrum, the pattern of infrared light it reflects, tells us the surface is made of water ice.

    We know from gravity measurements that Europa is mostly rocky inside, with an outer layer about 150 km thick with a rocky mantle and iron core just like the Earth. When the Voyager spacecraft flew by Europa in 1979, the first images were returned showing a complex icy surface, with different geology from any place we'd seen in the solar system. Scientists then debated whether the ice was solid all the way through to Europa's rocky interior, or was there a water layer in between the ice and rock? It was the Galileo spacecraft that answered this question, not with images but with a magnetometer that measured Europa's magnetic properties.

    The magnetometer detected an induced magnetic field, meaning that Jupiter's magnetic field was inducing currents in a layer right below Europa's icy surface. The strength of that field tells us that a conductive layer of salty water exists within about 50km of Europa's surface, proving that there is an ocean, much like the Earth's, just below the ice. There's lots of evidence for other pockets and small amounts of water within the ice shell as well, but most of the water is down in the ocean. We know it's water because of its density, the contact with the ice shell, and how the layer conducts, other liquids wouldn't behave the same way or be expected there! Hopefully the next mission to Europa will confirm the ocean, and tell us even more about shallow water in the shell.

    Dr. Britney Schmidt, University of Texas at Austin

    It is said that dying red giant stars could act like a defibrillator and bring icy planets back from the dead & that this rebirth could also lead to new breeding grounds for life. My question is that how can new life survive without light?

    Answered Wednesday May 15, 2013 3:52AM PDT by Thomson Fisher

    While most life on Earth is powered by photosynthesis, it's not the only way for an organism to survive. Organisms can get their energy from chemical reactions as well as sunlight, and these organisms are known as chemotrophs There are actually a surprising number of ecosystems in places that never see the sun. The most famous of these, perhaps, are the communities found around hydrothermal vents, which are volcanic fissures in the ocean floor. Being on the bottom of the sea, they get essentially zero sunlight, but nonetheless, they host a thriving ecosystem, which is based on bacteria that "eat" the sulfur emitted by the vents, rather than on plants. If you want to learn more about these fascinatingly strange communities, Searching For Life Where the Don't Shine is a terrific five-part series of articles examining how things live without sunlight, and our efforts to learn more about them.

    Dr. Mason Fisher

    What would the Earth look like to scientists if it were observed by the Kepler Observatory orbiting the planet Kepler 62e? What would they presume about the Earth's capacity to develop life?

    Answered Monday May 13, 2013 2:44AM PDT by Shawn Domagal-Goldman

    If Kepler were in orbit around Kepler-62e, Earth would look a lot like what Kepler-62e looks like from Kepler as it currently orbits Earth. There are some important differences: Kepler-62e is about 40% bigger than Earth, and it gets more energy from its star compared to what Earth gets from the Sun. And it might be a little too hot for life as we know it. However, its neighbor-planet, Kepler-62f, gets less energy, and none of its known properties are "surface-life killers." So based on what we know, Kepler-62f could potentially harbor Earth-like life. We have no evidence of life on Kepler-62f, the mere possibility is tantalizing.

    The other point to note is that we aren't really "seeing" Kepler-62e, Kepler-62f, or any other exoplanets of a size similar to Earth. For a planet detected by Kepler, all we can usually "see" is the amount of light the planet blocks from its star when the planet passes in front of it. Most of these planets are too far away for us to take pictures of them with a telescope. Someday we exoplanet searchers hope to be able to do that for similar planets that are closer to us. We don't yet know of any exoplanets that would be suitable to this type of study, but the existence of Kepler-62e, Kepler-62f, and other planets suggests we'll find some soon.

    Dr. Shawn Domagal-Goldman, Blue Marble Space Institute of Science

    How could Earths atmosphere be transformed to Titan like environment?

    Answered Friday May 3, 2013 10:06AM PDT by Michael Busch

    This is a good question with an unfortunate answer: it could not.

    The temperature of the Earth's surface is set by the thickness and composition of the atmosphere and by the amount of incoming light from the Sun. Titan's atmosphere is a little denser than that of the Earth. It is predominately nitrogen and methane, and is sufficiently thick to give the surface a temperature of 94 K / -179 C. All other things being equal, an object with a similar atmosphere at the Earth's distance from the Sun would be heated to an average surface temperature of 290 K / 18 C, a few degrees hotter than the Earth is right now. But not all other things are equal: Titan's atmosphere has the composition that it does because Titan is so cold. Warming it up to the temperature of Earth would melt Titan's current icy surface, putting a huge amount of water vapor into the atmosphere in the process. That would warm the place further, and since Titan's surface is the outer surface of a thick shell of water ice, you would end up with a very hot and humid atmosphere which blended seamlessly into a very deep global ocean.

    Nor would moving your Titan-Earth out to the distance of Saturn let you give it a Titan-like atmosphere. The height of an object's atmosphere is determined by its surface gravity and the temperature: at the same temperature, less gravity gives a taller atmosphere. Titan's surface gravity is 14% that of Earth, giving a very tall atmosphere. Something the mass of Earth at the same temperature would have a much shorter atmosphere.

    Finally, the composition of Earth makes an atmosphere like Titan's impossible. Both objects have nitrogen-rich atmospheres. But Earth's overall composition is dominated by silicate oxides (rocks), with only a little bit of water mixed in and floating on top. Titan has a rocky core, but that is covered by thick layers of high-pressure ice, a global subsurface ocean, and the outer ice crust. The methane in the atmosphere, lakes, and near-surface is steadily, albeit slowly, destroyed by the chemical reactions that produce the haze. It is replenished only by slow leaking of a primordial supply of methane from Titan's deep interior. The Earth has no such large reservoir of methane.

    In other words, to make the atmosphere of the Earth like that of Titan, you would need to: move the object out to the distance Titan is from the Sun, change its mass to be similar to that of Titan, and change its bulk composition to match that of Titan. At that point, you don't have the Earth anymore.

    Dr. Michael Busch, Blue Marble Space Institute of Science

    Amino acids have been found in interstellar dust clouds, in the tail of comet Wild 2 and in the meteorite 2008 TC3. If you asked your colleagues whether amino acids falling onto to the young Earth were a significant source of material for life to start, would there be a consensus? How would you "vote"?

    Answered Wednesday May 1, 2013 3:03AM PDT by Henderson Cleaves

    Let's break this question into two parts. First, did significant amounts of amino acids get delivered to the early Earth by extraterrestrial sources, and second, were amino acids important for the origin of life?

    For the first part, most scientists would agree that it is likely that the flux of extraterrestrial organic materials, including interstellar dust particles, meteorites, and comets was likely much higher early in Earth’s history. The lunar cratering record certainly supports the notion of there being larger amounts of as-yet-unaccreted materials impacting inner solar system bodies early in their history. Whether extraterrestrial organics were a significant source of organics for the origin of life is an open question: this would depend on the yields of organics from other sources, such as atmospheric synthesis and hydrothermal synthesis, among other factors.

    For the second part, it is true that several types of extraterrestrial materials we have studied contain indigenous amino acids, among other types of organic materials. It is also true that amino acids are significant components of all modern terrestrial organisms. Unfortunately, at this point we do not have a unified model for how life started on Earth, so some scientists might say yes, amino acids were important, while others would be more skeptical. I prefer to stay open-minded about these things, until we have more information.

    Dr. Jim Cleaves, Blue Marble Space Institute of Science

    I am a geology student and have some questions regarding the organic compounds in the Solar System. Where the organic compounds are usually found in the solar system? And where can they form in solar system or in galaxy? And how these compounds are formed in the universe?

    Answered Monday April 29, 2013 4:33AM PDT by Svetlana Shkolyar

    Good question. Yes, organics can form in young galactic areas and get delivered to solar systems. (In your question's context, I am assuming organic compounds mean those with carbon in them, that often resemble or even are the same as compounds used or made by life.)

    Some scientists use the method of spectroscopy - analysis of the way light is absorbed and emitted by objects - to study organics in nebulae (huge star-forming clouds of dust and gas the size of galaxies). They have identified organic compounds in these parts of the universe, and they've developed some theories as to how they form. The theory I'm familiar with is that organics are formed in circumstellar areas, where young stars are forming, and escape with other interstellar dust particles into the interstellar medium. They may get sucked into nearby planetary nebulae, which are areas where planets are forming. The formation of stars or planets can incorporate those organic compounds.

    Meteorites, which are sort of like "crumbs" left over from planet formation, can also carry organic compounds through space. When a meteorite strikes a planet, it can deposit those organics. Some scientists theorize that this deposition process may have played a role in the origin of how life on Earth.

    I hope I've answered your question!

    Svetlana Shkolyar, School of Earth and Space Exploration, Arizona State University

    What are the benefits of being an astrobiologist??

    Answered Friday April 26, 2013 2:15AM PDT by Sanjoy Som

    An astrobiologist is a “system scientist”, so although she/he has specialized in a particular field (geology, oceanography, atmospheric science, astronomy, biology etc..), astrobiologists have rounded their education with classes from other discipline to allow them to have an intuition about fields outside of their own specialty. I personally find this a compelling reason to be an astrobiologist: you end up being a well-rounded scientist. I personally like thinking about “system Earth”, i.e. how is the planet interconnected with its biology and solar neighborhood.

    In addition, because astrobiology asks deep questions, such as is there life beyond Earth, and what is the future of life on Earth, it touches a lot on ethics and philosophy, which I find very interesting. For example, what are the ethics of terraforming Mars for human habitation if microbial life is detected? Or what type of message should we send extraterrestrials, and how would it be best represent Earth, as opposed to a culture or country? Those are all very stimulating topics I think, grounded in astrobiology.

    Another compelling reason is that for me, being an astrobiologist has made me a better science communicator. The nature of the astrobiology profession makes it imperative to communicate your science to a very broad audience. As such, you become skilled at communicating complex concepts to people with different levels of understanding.

    Dr. Sanjoy Som, Blue Marble Space Institute of Science

    what technologies do you use to study life on different planets?

    Answered Wednesday April 24, 2013 2:16AM PDT by Jacob Haqq-Misra

    So far scientists have not yet discovered any forms of life on other planets, but they do use a variety of methods to search for evidence of life on other planets. Within our own Solar System, scientists can send robotic rovers to take actual measurements of another planet's geology. Mars exploration, for example, includes a search for chemical signatures in rocks or soil that could indicate present or past life. Scientists outfit these rovers with drills and scoops to collect samples, which are then fed into chambers that allow for the composition of the material to be analyzed according to its mass (using a mass spectrometer), its volatiles (using gas chromotography) or its laser-induced signature (using a laser spectrometer). The recent Mars Science Laboratory (named "Curiosity", see: http://mars.jpl.nasa.gov/msl/) even includes an instrument that shoots a laser at a distant rock and observes its chemical composition from afar! Scientists compare the results of these chemical analyses with environments on Earth to understand whether or not these Martian environments are consistent with the presence of biology (for example, by looking for organics, carbon, amino acids, or other remnants of life). Scientists use these type of analyses to design better experiments that will ultimately help to conclude whether or not Mars has (or had) life. Similar exploration techniques are used, or will be used, in the exploration of other bodies within our Solar System.

    Extrasolar planets present another challenge because they are too far away for even robotic exploration. Scientists must therefore rely on remote observations using telescopes to first identify extrasolar planets and then to characterize them according to their potential habitability. A telescope outfitted with a spectrometer can identify individual gaseous components of an extrasolar planet's atmosphere, which provides at least some information about the planet. Using the past and present of Earth as a proxy, scientists think that certain combinations of atmospheric gases are likely due to the presence of life. The presence of oxygen, ozone, and methane, for example, is due to widespread life on Earth; if scientists were to observe an extrasolar planet with a similar composition, then it would be evidence for an inhabited Earth-like planet orbiting another star. Scientists have not yet discovered any such planets, but the telescopes to properly conduct this search are still in their infancy. As newer generations of telescopes come into being, we will eventually be able to conduct more careful searches that let us peer into the atmosphere of extrasolar planets—in an effort to find signs of life.

    Dr. Jacob Haqq-Misra, Blue Marble Space Institute of Science

    If there exist some life as like in earth. Is there any possibilities that they will have close resemblance with us?

    Answered Monday April 22, 2013 6:26AM PDT by Morgan Cable

    Great question! There are many theories about what kinds of life we may discover elsewhere in the Universe. Some scientists think life will be similar to us - based on carbon, oxygen, nitrogen and similar elements. Other scientists believe we may find life that is completely different - perhaps based on silicon instead of carbon, or able to use in liquid methane or ethane as a solvent, as opposed to liquid water. Based on a chemistry standpoint, I believe any life we find will probably be carbon-based, for several reasons. First, life that uses lighter elements like carbon and nitrogen would be more likely simply because these elements are more abundant in the Universe than heavier elements like silicon and arsenic. Second, we know that carbon-based compounds like methanol, carbon dioxide and amino acids are present on comets, in meteorites and in giant molecular clouds (interstellar clouds of gas in which the formation of molecules can take place), so they're out there already. Third and most importantly, carbon-based life works on a thermodynamic level. In carbon-containing molecules, bonds to carbon atoms are just strong enough to be stable, but not too strong to be unbreakable, meaning that the molecules can store energy in those bonds and then access it later. This is how life on Earth can store energy from sunlight (if it's a plant or photosynthesizing organism), or use the energy from sugars and other compounds in foods. Carbon just makes sense!

    BUT, just because carbon makes sense, that doesn't mean we won't find weird life somewhere! We just need to keep our minds open to new possibilities and not overlook anything in our search for life.

    Dr. Morgan Cable, JPL-Caltech

    Would a certified Astrobiologist be considered a candidate to be sent into outer space? For example, to the ISS, or in the future if there is a manned mission to Mars?

    Answered Friday April 19, 2013 5:55AM PDT by Julia DeMarines

    Astrobiology is a relatively new field that is more frequently becoming incorporated into academia. Because Astrobiology is such a diverse field it is difficult to have a single standard for what an Astrobiologist is, and thus there are only a few PhD programs that offer degrees in Astrobiology (such as the University of Stockholm, Penn State University and the University of Washington) and usually it’s paired with an additional discipline. There are some Universities that offer an Astrobiology Certificate along with a master’s degree or a PhD (such as the University of Colorado), and perhaps more in the future as Astrobiology grows as field. An Astrobiology certificate or degree doesn’t only make you an Astrobiologist; any field of study that relates to the bigger picture of life in the Universe can fall under Astrobiology.

    When talking about Astronaut qualifications, being an Astrobiologist may help your chances depending on the nature of the mission. Perhaps in the future, we will venture to Mars with a goal of finding past, or present life. Then, it would be highly advantageous to be an Astrobiologist! As of now, Astronauts only venture to the International Space Station, which in short, is a very expensive space laboratory. Quoting the NASA Astronaut solicitation: “Qualifications include a bachelor's degree in engineering, science or math and three years of relevant professional experience. Educators teaching kindergarten through 12th grade also are encouraged to apply.” Astronauts that go to the ISS usually have a job of repairing something (for example the Hubble Space Telescope, or the station itself) and/or are in charge of monitoring experiments (sometimes they are the experiments themselves!). Various labs around the world design these experiments and the astronaut’s job is to make sure they function properly. So, it might be advantageous on an Astronaut application to have a background in a science, such as Astrobiology, but it may hold the same weight as being within the physical requirements of an Astronaut, or your abilities to work well with others in isolated conditions. It might be more probable for an Astrobiologist specialized in biology to have an experiment flown on the ISS than to actually fly themselves.

    Julia DeMarines, Blue Marble Space Institute of Science

    Why is the necessities, evolution, and adaptation to life important and relevant to astronomy?

    Answered Wednesday April 17, 2013 3:54AM PDT by Dimitra Atri

    Based on our current understanding of life on the Earth, we can say with a great degree of confidence that life's origin and evolution occurred in a very limited range of physical conditions for a period of a few billion years. Therefore, it is natural to probe the properties of astronomical objects governing the physical conditions leading to the origin and evolution of life on Earth. The search for habitable extraterrestrial environments has generated tremendous interest in the study of planets orbiting stars other than our Sun, or extrasolar planets (exoplanets in short). Such studies are helping us to understand the birth and evolution of stellar systems in our Galaxy and also leading to new developments in astronomical instrumentation. The search for evidence of habitable environments on Mars has lead to a number of scientific missions to the planet which provide insights into the history of the solar system, amongst other things.

    Dr. Dimitra Atri, Blue Marble Space Institute of Science

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