Going to the Beach at Sunset?

Astronomers have observed a distant planet (upsilon Andromedae b), with a hot spot in an unexpected place. This gas-giant planet, in the hot Jupiter category, orbits its star with one face perpetually facing it. One would expect that this face would be the hottest part of the planet, but to the observers surprise, the hot spot was actually offset by a whopping 80 degrees, so that it was located on the side of the planet instead of directly under the star's glare.

The planet was observed from NASA's Spitzer Space Telescope, which was the first telescope to directly detect photons from an exoplanet (2005). Upsilon Andromedae b does not cross in front of its host star, so it was detected by measuring the total combined light from the star and the planet, as the planet orbited the star (with a period of 4.6 days). Spitzer could not see the planet directly, so it detected variations in the total infrared light from the system that occur when the hot side of a planet comes into Earth's field of view. The hottest part of the planet gives off the most infrared light, and this occurred when the planet was not directly towards or away from us, but rather when the hot Jupiter had its side facing the Earth. This would be equivalent to the Earth being warmest during sunset, as opposed to when we are directly under the sun!

Previous observations have shown slight variations in the hot spots of these so-called hot Jupiters, which were thought to be due to fierce winds pushing around hot material, but this observation may throw this theory into question. The findings show that astronomers understand less about the atmospheric energetics than they previously thought, and this is opening the floor for some new theories. One speculation involves star-planet magnetic interactions, but the several emerging theories will be tested against a growing pool of examined hot Jupiters.

Studying how these distant solar systems form and evolve can provide us with crucial information that will help astrobiologists determine where to search for habitable worlds.

More on Titan

So, we've been getting a ton of information on Titan--for good reason--since it gives strong evidence of Earth's burgeoning atmosphere in the throes of planetary formation several billion years ago, in the Hadean eon, named for how ruthlessly chaotic it was.

Titan: not so much.

A few facts we know right off the bat about Titan we've learned, tying it closer to our own planet:

Largest moon of Saturn.

It is the only moon we know of with a fully developed atmosphere.

When it comes to atmospheric pressure, Titan is the Earth's closest relative, just one and a half times thicker (1).

It was the site of the first ever, up close picture of extra-terrestrial liquid (whaat?)

It's still really cold (-178 celsius?!) (2)

So let's get to the heart of astronomy: what could it be?

Already, many astronomers are itching to find out how similar the atmosphere is to Earth and what it can tell us about our early Earth's atmosphere.

We've figured out that its atmosphere is "controlled by five major processes: CH4 photolysis and photosensitized dissociation, H-to-H2 conversion and hydrogen escape, higher hydrocarbon synthesis, nitrogen and hydrocarbon coupling, and oxygen and hydrocarbon coupling" (3). We've learned about photolysis/photosensitized dissociation--the process by which compounds are broken up by photons, as well as the basics of escape due to thin atmospheric conditions and low-gravity--and the combinations here contribute to its familiar atmospheric composition.

However, there's also something to look for in Titan's haze. Many point to it as the lifeblood of the planet--a haze that could have very easily influenced our own planet's life-origin. In fact, scientists have begun working on trying to imitate the haze of Titan through analogous lab-produced aerosol (4). They explain that when sunlight hits a methane/nitrogen atmosphere, this type of aerosol is produced--so this could be the start of an experiment much like the aforementioned Miller-Urey experiment.

With all of the similarities seen, including Galia's recent post mentioning the possible similarities between a methane weather cycle and our own Earth's water cycle as well as last week's discussions of Mars, it seems that we could afford to spend more money looking at Mars and Titan to understand our own origins.

1. http://www.astrobio.net/index.php?option=com_retrospection&task=detail&id=1755

2. http://www.wired.com/wiredscience/2008/02/titans-organic/

3. http://adsabs.harvard.edu/abs/1984ApJS...55..465Y

4. http://www.universetoday.com/908/the-early-earths-atmosphere-was-similar-to-titan/

Sailing on seas of methane?

As of November of last year, NASA researchers have started planning a 2015 mission to go sailing on a lake… composed entirely of methane and ethane… over 1300 million kilometers from our planet. This ambitious adventure involves the use of a raindrop-flecked camera placed on a nuclear-powered capsule directed to land on Ligeia Mare – one of the largest lakes on Titan, Saturn’s largest moon.

Scientists have particular interest in Titan as it is the only natural satellite to contain a dense atmosphere, as well as the only celestial object other than Earth for which clear evidence of stable bodies of surface liquid have been found. Titan itself is primarily composed of water ice and rocky material. Prior to 2005, however, the physical characteristics of Titan were largely unknown due to its dense, opaque atmosphere that prevented man-made spacecrafts from gaining visual access to its surface. However, with the arrival of the Cassini-Huygens mission to Titan, scientists discovered the abundant liquid, hydrocarbon lakes in the satellite’s polar regions. Additionally, the spacecraft revealed a mountainous terrain, including several possible cryovolcanoes on the planet’s surface.

Since, the Cassini-Huygens mission arrived in Saturn’s ring system, a much greater understanding of Titan has been gained in the past five years. We now know that the atmosphere of Titan is largely made up of nitrogen and minor components of methane and ethane gas. It’s these hydrocarbon gases that lead to the formation of the orangey clouding and smog that prevented visual access to Titan in years past. Titan’s climate includes wind and occasional rain which contribute to the shockingly similar surface features to Earth, such as: sand dunes and rivers, lakes, and seas of liquid methane ethane, as well as shorelines dominated by seasonal weather patterns. With the existence of liquids and robust nitrogen atmosphere, Titan is considered to be a model of early Earth but at a much lower temperature. It has been cited as one of four bodies in our galaxy that could potentially host microbial extraterrestrial life, or at least, as a prebiotic environment rich in complex organic chemistry.

Thus, for all of these reasons, NASA scientists want to know more. This nuclear-powered “boat” that they are proposing to send to Titan would float about on Ligeia Mare while radioing photos and other data to Earth for a period of about six months. The scientists picked Ligeia Mare in particular as it is over 300 miles wide, which they believe is a big enough target for them to accurately direct their probe straight into the methane sea. The mission is called TIME for Titan Mare Explorer. The probe itself is to be built by the same scientists that created the Beagle 2, the British craft that crashed on Mars on Christmas Day of 2003, as well as the US company, Proxemy Research of Maryland. This British group is being led by Professor John Zarnecki, head of the Centre for Earth, Planetary Space and Astronomical Research at the Open University in Milton Keynes. In regard to the TIME mission he says:

“We want to discover more about Titan's methane weather cycle - like the water cycle on Earth… We want to determine the depth of the lake and if it is murky or clear and what is floating in it, plus look at the shorelines. We'd also want to look for organic materials. Understanding Titan better might also tell us more about whether it is possible for life to develop there."

As I learned from the research I did for my presentation last week, Titan is absolutely swimming with organic chemicals necessary for life, so if the TIME mission could just find some sort of energy source in these methane lakes, the idea of extraterrestrial life could suddenly be much more feasible.

The role of carbohydrate polymers in chemical evolution

This blog entry is on the same topic as the presentation that I gave in class a couple weeks ago concerning some of the possible chemistry that was involved in the beginning of life on Earth. As emphasized by the other presentations that week, it is fairly well established that life is sustained and perpetuated through the DNA/protein world that we know to exist today. Additionally, we now understand some theories regarding the RNA world that pre-dated this DNA/protein world as well.

I presented a literature review that contended that a carbohydrate polymer world most likely existed before modulating into the RNA world, which eventually then gave way to the DNA world we know today. Personally, I really enjoyed reading about the chemistry of the origin of life. Although I don’t know nearly enough about chemistry to have fully understood all that this article was saying, just considering how the complex array of chemical life seen today came to existence from simple building blocks amazes me. We had all heard of the Miller-Urey experiment which attempted to recreated those early Earth conditions; Methane, ammonia, and hydrogen were circulated over boiling water, electrodes were introduced to mimic lightning, and then after a certain period of time, the composition of the mixture was analyzed and a number of amino acids were detected. But this article questions: did that really recreate the conditions of early Earth?

This paper includes some interesting conditions that hadn’t really occurred to me before. It’s pretty widely accepted that the reducing conditions of early Earth didn’t include significant amounts of oxygen. No oxygen means no ozone. No ozone means no protection from high energy UV light. And UV light perhaps provided a significant amount of energy that was needed to drive these early reactions.

Also, the paper presents the idea that as more and more complex molecules were created, the concentration still remained considerably small, even if they were all dissolved in the early oceans. Thus, for these molecules to randomly collide to form polymers would be highly unlikely. The authors of this paper thus contended that maybe these early molecules would adhere to mineral-rich clay particles in water. The clay would enable the reactants to congregate on a common surface and the minerals (aluminum, iron, magnesium, calcium, sodium, and potassium to name a few) would serve as catalysts for these early reactions. Eventually more and more complex molecules would be synthesized, and the authors hypothesized that saccharides would have been among the first complex molecules to be formed. Furthermore, the authors presented the claim that since only the simplest molecules were present on early Earth, it was likely that formaldehyde was one of them present in non-trivial amounts. They speculated that maybe formaldehyde self-polymerizes on these clay surfaces to form small saccharides, which eventually undergo aldol condensation to form more advanced hexoses and pentoses.

With this theory about the origin of chemical life, it isn’t at all difficult to then see how these carbohydrate polymers gave way to an RNA-based world. The authors suspect that carbohydrates polymerized along with abundant phosphates to form longer chain polymers. Several polymers are capable of forming with this method, one of them resembling RNA without the base pairs. So essentially, just a series of ribofuranose units linked by phosphate groups (structure sown below). The highly oxidized purine and pyrimidine bases probably only came about a little later, and when they did arrive, only a simple substitution was need to create the first strands of RNA (also shown below).

With the theories presented in this review, the RNA world hypothesis gains some much-needed support after past failures to experimentally recreate the formation of RNA. Certain bonds are simply unable to bond to sugars to form a complete RNA molecule under early Earth conditions. Now, all that is left to do is to show how these nucleotides produced life in a primitive RNA world…

Can Silicon serve as a replacement for Carbon based life?

So, unfortunately there is really no way I can relate this blog entry to Avatar. From what I remember from the movie, there was no mention of the chemical foundations of Pandora. The trees and plants did form these complex electrochemical connections that effectively acted as neurons, creating some sort of a planet-wide brain that had achieved sentience… which was incredibly awesome, but not really elaborated upon on a chemical basis.

Anyway, this topic of Silicon, as opposed to carbon-based life has major astrobiological implications. All known life on earth is built upon the sixth element, carbon, and carbon-based compounds. Most life forms contain a large majority of the elements hydrogen and oxygen (from water) as well. But the chemical processes that give something the status of “living” require carbon based molecular structures. The human body in particular uses some of carbon’s most unique chemical properties to function, mainly involving the storage of energy and creation of highly complex molecules and structures.

However, as illustrated with the creation of the creature called “Horta” in episode 26 of the original Star Trek series, its been speculated that another element (such as Silicon) could potentially replace carbon to form a very different biological basis of life. In fact, the first count of this speculation came from the German astrophysicist, Julius Scheiner, in 1891 when he suggested the suitability of silicon as a basis for life. Several years later the British chemist, James Reynolds, actually based his opening address to the British Association for the Advancement of Science on the fact that silicon has heat-stabilizing properties that could allow life to exist at extremely high temperatures (as we see with thermophiles on Earth).

Okay, so yeah people are and have been talking about silicon-based life for years, but when it comes down to the biochemistry it’s hard to justify as a potential reality. At first glance it is promising though. Silicon is the second-most common element in the Earth’s crust (far more abundant than carbon), though like carbon, is a “p-block” element of group IV of the periodic table suggesting significant similarities in their basic chemical qualities. For example, just as carbon commonly combines with four hydrogen atoms to form methane (CH4), silicon yields silane (SiH4), and in addition to these tendencies, both elements form long chains (polymers) in which they alternate with oxygen.

However, a significant difference in size and orbital energy between carbon and silicon may be the determining factor in the existence of silicon-based life. A silicon atom has eight more electrons than a carbon atom does, and its’ homogenous bond length is considerably greater than carbon’s: 235 pm in comparison to carbon’s 77 pm. Silicon’s larger electron cloud subjects its’ bonds to a greater magnitude of shielding, thus a silicon bond is generally weaker than a carbon bond. This difference alone is enough to explain why carbon makes life and silicon makes rocks, at least, in standard terrestrial conditions. Additionally, for these reasons, silicon is known to be largely incapable of forming as diverse a range of molecules as carbon under natural conditions, in addition to silicon’s strong affinity for oxygen molecules.

Silicon’s affinity for oxygen would be problematic for life formation, because when carbon is oxidized during the respiratory process of a terrestrial organism, it becomes gaseous carbon dioxide - a waste material that is easy for a creature to remove from its body. The oxidation of silicon, however, yields a solid because immediately upon formation, silicon dioxide organizes itself into a lattice in which each silicon atom is surrounded by four oxygens. Disposing of a substance such as this would pose a major respiratory challenge.

Additionally, in carbon-based biota, the basic energy storage compounds are carbohydrates in which the carbon atoms are linked by single bonds into a chain. A carbohydrate is oxidized to release energy (and the waste products water and carbon dioxide) in a series of controlled steps using enzymes. These enzymes are large, complex molecules (usually proteins), which catalyze specific reactions because of their shape and "handedness." A feature of carbon chemistry is that many of its compounds can take right and left forms, and it is this handedness (also called chirality) that gives enzymes their ability to recognize and regulate a huge variety of processes in the body. Silicon's failure to give rise to many compounds that display handedness makes it hard to see how it could serve as the basis for the many interconnected chains of reactions needed to support life.

So, ultimately it seems as though it’s pretty unlikely that silicon-based life could exist in a terrestrial setting in an Earth-defined biological sense. However, that hasn’t held back the imaginations of science fiction writers. As mentioned above, the Horta, a silicon-based life formed appearing in Star Trek existed on the planet, Janus IV. Apparently every 50,000 years, all the Horta die except for one individual who survives to look after the eggs of the next generation. Personally, the Horta seems to be the most unlikely form of a functional biological organism in terms of what we define “life” as on Earth. But see for yourself: http://www.youtube.com/watch?v=39roz9jQfzE.

Star Clusters are Rough Neighborhoods

John Debes and Brian Jackson of NASA's Goddard Space Flight Center have some news for planet hunters: stay away from clusters. In their recent publication in Astrophysical Journal, they claim that most of the easily detectable "hot Jupiters" that astronomers search for in star clusters were likely destroyed by their stars.

When the search for planets in star-packed globular clusters began, expectations were high. One cluster, 47 Tucanae, was expected to yield at least a dozen planets from around its 34,000 candidate stars, but the search was unsuccessful. More than 450 exoplanets have been found, but most of them have been detected around single stars.

Why are planets not being found in these neighborhoods? Jackson explains that "there are lots of stars to beat up on them and not much for them to eat." The high density of stars increases the chances that a nearby star will affect a planets orbit and potentially kick it out of its solar system. Additionally, surveys of globular clusters have shown that they are rather poor in metals, which are essential for making planets (this is known as low metallicity). In essence, planets in these neighborhoods get their lunch money stolen and get kicked out of town, which is why the search for planets in these areas have come up short.

The research also suggests that "hot Jupiters" are more likely to be found in younger star clusters than older ones. This is because in addition to the problems listed above, the large planets that are very close to the sun could be destroyed by their cramped orbits. Since the planets are at least 3 times closer to their host stars than Mercury is to our sun, the gravitational pull of the planet on the star can create a tide on the star. This bulge on the star is always just a little behind the planet, and its gravity essentially tugs back on the planet, reducing the energy of its orbit. As this energy drops, the planet becomes closer to the star, and this bulge gets even bigger. Eventually, the planet will crash into the star or it will be torn apart by the star's gravity, according to the researcher's model of tidal decay.

Debes and Jackson modeled this effect on a hypothetical 47 Tucanae, and it predicted that most of the planets would have been destroyed, regardless of metallicity. This would explain the unsuccessful search for exoplanets, especially since the model predicts that more than 96% of the hot Jupiters would be destroyed by the time a cluster was as old as 47 Tucanae (11 billion years). The researchers look forward to the results of the Kepler mission, which is searching for hot Jupiters as well as smaller planets, to test their model. If their model is right, finding planets could be getting harder since the large and obvious ones may be long gone.

Taking this all in, star clusters are tough places for planets to hang out. Perhaps the search for exoplanets should focus on younger, higher metallicity, and less dense clusters that haven't bullied their planets just yet.

Why did life originate?

This entry is based on an article on Physorg.com by Lisa Zurg in 2008 called “Why Life Originated (and why it continues).” Link: http://www.physorg.com/news148050302.html

There are numerous researchers who devote their lives to determining how life evolved in the attempt to discover both the origin of life on Earth but also how life could evolve elsewhere. Much of the public has heard about the primordial soup theory and may have heard of the famous Miller and Urey experiment whereby amino acids where spontaneously created from elemental materials and energy. However, how often do we stop to think not about how life was created but why? Why did life originate and why has it continued to evolve?

We know that based on the theory of Darwinian evolution, we evolve in relation to our ecosystems; that organisms are naturally selected on through the process of reproduction and that over time, those traits that are most advantageous in a population will be increasingly passed down to future generations. We know that evolution is random and chaotic in the sense that there is no defining direction that evolution is heading in. Even if we evolve to become better equipped to live in our habitat, that habitat itself not a static entity.

But, according to Arto Annila of the University of Helsinki and Erkki Annila of the Finnish Forest Research Institute, this is not the most basic understanding of evolution and of life. The guiding principle of the universe, and thus of life as well, is the tendency to reduce energy differences. The process of natural selection is at its most fundamental level, nothing more than the drive to increase entropy and decrease energy differences. It is understood that chemicals will spontaneously mix and that elements can spontaneously organize into molecules. All this is done within the context of thermodynamics. All life is merely an assembly of molecules via chemical reactions. The molecules involved in the origin of life likely “underwent a series of more and more complex reactions to minimize mutual energy differences between matter on Earth and with respect to high-energy radiation from Sun. The process eventually advanced so far that it cumulated into such sophisticated functional structures that could be called living.”

Could be called living…That is an interesting concept in and of itself. Because if the principles that operate within living creatures are the same that operate everywhere else in the universe, what exactly distinguishes living from non-living. Indeed, the Annilas stress that there is no distinction between animate and inanimate; that “processes of life are, in their principles, no different from any other natural processes.” Biologists would argue that the most fundamental component of life, indeed the definition of the beginning of life, was the creation of a self-replicating molecule capable of storing information. But is this only a concept that we have since imposed on this molecule. What in reality separates it from its most basic physical and chemical elements?

What this means for us is a substantial de-significance of what it means to be not just an individual, or a human, or an animal, but to be alive itself. What is life really but the product of the tendency to increase entropy? “Our “purpose,” so to speak, is to redistribute energy on the Earth, which is in between a huge potential energy difference caused by the hot Sun and cold space.” Cells, genetic code, cellular metabolism all originated as ways to increase entropy and decrease energy differences. Thus, “the order and complexity that characterize modern biological systems have no value in and of themselves, but structure and hierarchical organization emerged and developed because they provided paths for increasing energy flows.” Though this makes sense at some fundamental level, what does this mean for things like the human brain. Is the ability to think, to write, to cry merely a way to increase entropy, or is there a distinction between the fundamentality of thermodynamics to the origin or life and to the continued evolution of life now? Or is this something we want to believe only because it gives us comfort to think of ourselves as special, as being in some fundamental way different from a pot of boiling water?

This is getting us closer to the philosophical conundrum of the definition of life, however, this also relates to the search for the origin of life. And thus relates to the biological foundations of life, and indeed the meaning of “biological” foundations in the first place. Because, “’according to thermodynamics, there was no striking moment or no single specific locus for life to originate, but the natural process has been advancing by a long sequence of steps via numerous mechanisms so far reaching a specific meaning – life.’” So how are we supposed to determine a particular moment, compound or reaction that distinguishes animate from inanimate? We can look at the structures and processes that we know occur in life and try to figure out how they came to evolve, but we may never be able to define the point at which life originated. At least, not if life itself is indefinable. There is no definite beginning.

This makes the title of the article I’m describing inconsistent. While the article argues that there can be no single point of origin of life, the title implies that there was. Despite this inconsistency, the article does take an interesting but also disconcerting look at the “origin” of life from a different perspective. Whether this perspective is irrelevant to the study of astrobiology is unanswered.
It is a fundamental principle of science to conceptualize nature and to define things in an arbitrary but significant way, indeed that is a tendency of humanity itself, and thus to conceptualize ‘life’ may not only be inevitable but also essential. I would argue that this tendency is pivotal to the ability to do science and learn about the world. So perhaps it is not so important to get stuck on the fact that life is indefinable, but it is important, I would argue, to understand the point of this article and the fundamentals of the argument that life is just a human concept. Indeed, this way of thinking about life may be important for astrobiology as we begin to get closer to discovering the origin of life, only to discover that there is no concrete origin. It also may help us to think outside the box in terms of what we consider to be possibilities of life on other planets; taking a step back to look at life as the product of thermodynamics (another concept and label we impress on nature though obviously based on true phenomena) may help us search for life elsewhere.

It is also important to note that this is not a new perspective on life; Buddhists, Taoists and many philosophers in history have conveyed the understanding that everything is made out of atoms and that at the most basic level, everything is of the same and life is only a human construction.

As the Anillas say, “To ask how life started would be the same as to ask when and where did the first wind blow that quivered the surface of a warm pond.”