Geyser Eruptions on Mars

Every spring on the south polar ice cap of Mars brings violent eruptions of carbon dioxide gas carrying dark sand and dust high aloft.

The seasonal frosting and defrosting of ice results in the appearance of a number of features, such dark dune spots with spider-like rilles or channels below the ice, where spider-like radial channels are carved between the ground and ice, giving it an appearance of spider webs, then, pressure accumulating in their interior ejects gas and dark basaltic sand or mud, which is deposited on the ice surface and thus, forming dark dune spots. This process is rapid, observed happening in the space of a few days, weeks or months.

The geological features called dark dune spots and spiders were separately discovered on images acquired by the MOC camera on board the Mars Global Surveyor during 1998-1999. At first it was generally thought they were unrelated features because of their appearance. The first "Jet" or "Geyser" models start to be proposed and refined from 2000 onwards. The name 'spiders' was coined by Malin Space Science Systems personnel, the developers of the camera. The unusual shape and appearance of these 'spider webs' and spots caused a lot of speculation about their origin. The first years' surveillance showed that during the following Martian years, 70% of the spots appear at the exact same place, and a preliminary statistical study indicated that dark dune spots and spiders are related phenomena as functions of the cycle of CO2 ice condensation and sublimation. Thermal imaging during 2006 revealed that the temperature of these structures are as cold as the ice that covers the area. Soon after their first detection, they were discovered to be negative topographical features: radial troughs or channels of what today are thought to be geyser-like vent systems.

The geysers' two most prominent features (dark dune spots and spider channels) appear at the beginning of the Martian spring on dune fields covered with carbon dioxide (CO2 or 'dry ice'), mainly at the ridges and slopes of the dunes; by the beginning of winter, they disappear. Dark spots' shape is generally round, on the slopes it is usually elongated, sometimes with streams (water?) that accumulate in pools at the bottom of the dunes. Dark dune spots are typically 15 to 46 meters wide and spaced several hundred feet apart. Spider features form a round lobed structure reminiscent of a spider web radiating outward in lobes from a central point. Its radial patterns represent shallow channels or ducts in the ice formed by the flow of the sublimation gas toward the vents. The entire spider channel network is typically 160–300 m across.


Dark dune spots, high resolution color image
by the HiRISE camera (Credit: NASA)

Time-lapsed imagery performed by NASA confirms the apparent ejection of dark material following the radial growth of spider channels in the ice. Small dark spots generally indicate the position of spider features not yet visible; it also shows that spots expand significantly, including dark fans emanating from some of the spots, which increase in prominence and develop clear directionality indicative of wind action.

A number of geophysical models have been investigated to explain the various colors and shapes' development of these geysers on the southern polar ice cap of Mars.

Some teams propose dry venting of carbon dioxide gas and sand, occurring between the ice and the underlying bedrock. It is known that a CO2 ice slab is virtually transparent to solar radiation where 72% of solar energy incident at 60 degrees off vertical will reach the bottom of a 1 m thick layer. In addition, the ice thickness is measured in several target areas, and it was discovered that the greatest thickness of the CO2 frost layer in the geysers' area is about 0.76–0.78 m, supporting the geophysical model of dry venting powered by sunlight. As the southern spring CO2 ice receives enough Sun energy, it starts sublimation of the CO2 ice from the bottom. This vapor accumulates under the slab rapidly increasing pressure and erupting. High-pressure gas flows through at speeds of 161 km/h or more; under the slab, the gas erodes ground as it rushes toward the vents, snatching up loose particles of sand and carving the spidery network of grooves. The dark material falls back to the surface and may be taken up slope by wind, creating dark wind streak patterns on the ice cap.

Another model explores the possibility of active water-driven erosive structures, where soil and water derived from the shallow sub-surface layer is expelled up by CO2 gas through fissures eroding joints to create spider-like radiating tributaries capped with mud-like material and/or ice. Data obtained by the Mars Express satellite in 2004, confirmed that the southern polar cap has an average of 3 kilometres thick slab of CO2 ice with varying contents of frozen water, depending on its latitude: the bright polar cap itself, is a mixture of 85% CO2 ice and 15% water ice. The second part comprises steep slopes known as 'scarps', made almost entirely of water ice, that fall away from the polar cap to the surrounding plains. This transition area between the scarps and the permafrost is the 'cryptic region', where clusters of geysers are located.

A team of Hungarian scientists propose that the dark dune spots and channels may be colonies of photosynthetic Martian microorganisms, which over-winter beneath the ice cap, and as the sunlight returns to the pole during early spring, light penetrates the ice, the microorganisms photosynthesise and heat their immediate surroundings. A pocket of liquid water, which would normally evaporate instantly in the thin Martian atmosphere, is trapped around them by the overlying ice. Since their discovery, fiction writer Arthur C. Clarke promoted these formations as deserving of study from an astrobiological perspective.

A multinational European team suggests that if liquid water is present in the spiders' channels during their annual defrost cycle, the structures might provide a niche where certain microscopic life forms could have retreated and adapted while sheltered from UV solar radiation. A British team also considers the possibility that organic matter, microbes, or even simple plants might co-exist with these inorganic formations, especially if the mechanism includes liquid water and a geothermal energy source.


Further reading:
Geology of Mars
NASA Findings Suggest Jets Bursting From Martian Ice Cap
Mars' South Pole Ice Deep and Wide
Water at Martian south pole
Martian spots warrant a close look
Dark Dune Spots: Possible Biomarkers on Mars?

Supermassive Black Holes

A supermassive black hole is a black hole with the mass on the order of hundreds of thousands to billions of solar masses. Most galaxies are believed to contain supermassive black holes at their centers.


This artist's concept depicts a supermassive black hole and its
accretion disk at the center of a galaxy (Credit: NASA)

Supermassive black holes have properties which distinguish them from lower-mass classifications:

• The average density of a supermassive black hole can be very low, and may actually be lower than the density of air. This is because the Schwarzschild radius is directly proportional to mass, while density is inversely proportional to the volume. Since the volume of a spherical object is directly proportional to the cube of the radius, and mass merely increases linearly, the volume increases at a greater rate than mass. Thus, average density decreases for increasingly larger radii of black holes.
• The tidal forces in the vicinity of the event horizon are significantly weaker. Since the central singularity is so far away from the horizon, a hypothetical astronaut travelling towards the black hole center would not experience significant tidal force until very deep into the black hole.

There are several models for the formation of black holes of this size. The most obvious is by slow accretion of matter starting from a black hole of stellar size. Another model of supermassive black hole formation involves a large gas cloud collapsing into a relativistic star of perhaps a hundred thousand solar masses or larger. The star would then become unstable to radial perturbations due to electron-positron pair production in its core, and may collapse directly into a black hole without a supernova explosion, which would eject most of its mass and prevent it from leaving a supermassive black hole as a remnant. Yet another model involves a dense stellar cluster undergoing core-collapse as the negative heat capacity of the system drives the velocity dispersion in the core to relativistic speeds. Finally, primordial black holes may have been produced directly from external pressure in the first instants after the Big Bang.

Astronomers are confident that our own Milky Way galaxy has a supermassive black hole at its center, in a region called Sagittarius A* because:

• The star S2 follows an elliptical orbit with a period of 15.2 years and a pericenter of 17 light hours from the central object.
• Early estimates indicated that the central object contains 2.6 million solar masses and has a radius of less than 17 light hours. Only a black hole can contain such a vast mass in such a small volume.
• Further observations strengthened the case for a black hole, by showing that the central object's mass is about 3.7 million solar masses and its radius no more than 6.25 light-hours.

The Max Planck Institute for Extraterrestrial Physics and UCLA Galactic Center Group have provided the strongest evidence to date that Sagittarius A* is the site of a supermassive black hole, based on data from the ESO and the Keck telescope. Our galactic central black hole is calculated to have a mass of approximately 4.1 million solar masses.


Sagittarius A* (centre) and two light echoes
from a recent explosion (Credit: NASA)

It is now widely accepted that the center of nearly every galaxy contains a supermassive black hole. The close observational correlation between the mass of this hole and the velocity dispersion of the host galaxy's bulge, known as the M-sigma relation, strongly suggests a connection between the formation of the black hole and the galaxy itself.

The explanation for this correlation remains an unsolved problem in astrophysics. It is believed that black holes and their host galaxies coevolved between 300-800 million years after the Big Bang, passing through a quasar phase and developing correlated characteristics, but models differ on the causality of whether black holes triggered galaxy formation or vice versa, and sequential formation cannot be excluded. The unknown nature of dark matter is a crucial variable in these models.

At least one galaxy, Galaxy 0402+379, appears to have two supermassive black holes at its center, forming a binary system. Should these collide, the event would create strong gravitational waves. Binary supermassive black holes are believed to be a common consequence of galaxy mergers. As of November 2008, another binary pair, in OJ 287, contains the most massive black hole known, with a mass estimated at 18 billion solar masses.

Self-Replicating Robots Might Take Over the World

"Grey goo" is a hypothetical end-of-the-world scenario involving molecular nanotechnology in which out-of-control self-replicating robots consume all matter on Earth while building more of themselves. This scenario is known as "ecophagy" -- the literal consuming of an ecosystem. The term "grey goo" is usually used in a science fiction context. In the worst postulated scenarios, matter beyond Earth would also be turned into goo, a large mass of replicating nanomachines. The disaster is posited to result from a deliberate doomsday device, or from an accidental mutation in a self-replicating nanomachine used only for other purposes, but designed to operate in a natural environment.


A simple form of self-replicating machine (Credit: NASA)

Self-replicating machines were originally described by mathematician John von Neumann. They are artificial constructs capable of autonomously manufacturing copies of themselves using raw materials taken from their environment. The concept of self-replicating machines has been advanced and examined by Edward F. Moore, Homer Jacobsen, Freeman Dyson, and in more recent times by K. Eric Drexler. The future development of such technology has featured as an integral part of several plans involving the mining of moons and asteroid belts for ore and other materials, the creation of lunar factories and even the construction of solar power satellites in space. Von Neumann also worked on what he called the universal constructor, a self-replicating machine that would operate in a cellular automata environment.

Ecophagy is a term coined by Robert Freitas. He used the term to describe a scenario involving molecular nanotechnology gone awry. In this situation out-of-control self-replicating nanorobots consume entire ecosystems, resulting in global ecophagy. However, the word "ecophagy" is now applied more generally in reference to any event -- nuclear war, the spread of monoculture, massive species extinctions -- that might fundamentally alter the planet. These events might result in ecocide in that they would undermine the capacity of the earth's biological population to repair itself. Some scientists suggest that more mundane and less spectacular events -- the unrelenting growth of the human population, the steady transformation of the natural world by human beings -- will eventually result in a planet that is considerably less vibrant, and one that is, apart from humans, essentially lifeless.

In his original paper Freitas wrote:

Perhaps the earliest-recognized and best-known danger of molecular nanotechnology is the risk that self-replicating nanorobots capable of functioning autonomously in the natural environment could quickly convert that natural environment (e.g., "biomass") into replicas of themselves (e.g., "nanomass") on a global basis, a scenario usually referred to as the "grey goo problem" but perhaps more properly termed "global ecophagy".

As the use of industrial automation has advanced over time, some factories have begun to approach a semblance of self-sufficiency that is suggestive of self-replicating machines. Since safety is a primary goal of all legislative consideration of regulation of such development, future development efforts may be limited to systems which lack either control, matter, or energy closure. Fully-capable machine replicators are most useful for developing resources in dangerous environments which are not easily reached by existing transportation systems -- such as outer space. An artificial replicator can be considered to be a form of artificial life. Depending on its design, it might be subject to evolution over an extended period of time. However, with robust error correction, and the possibility of external intervention, the common science fiction scenario of robotic life run amok will remain extremely unlikely for the foreseeable future.

Colonization of Jupiter's moon Europa

Europa, the fourth-largest moon of Jupiter, is a subject in both science fiction and scientific speculation for future human colonization. Europa's geophysical features, including a possible subglacial water ocean, make it a strong possibility that human life could be sustained on or beneath the surface.


At just over 3,100 kilometres in diameter, Europa is slightly smaller than Earth's Moon
and is the sixth-largest moon in the Solar System. (Credit: Galileo Project, JPL, NASA)

Europa is primarily made of silicate rock and likely has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This water ice, liquid water, and organic compounds that might be useful for sustaining human life. The young surface is striated by cracks and streaks, while craters are relatively infrequent. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it. Heat energy from tidal flexing ensures that the ocean remains liquid and drives geological activity.


Model of Europa's subsurface structure. (Credit: NASA)

Colonies in the outer solar system could serve as centers for long term investigation of the planet and the other moons. In particular, robotic devices could be controlled by humans without the very long time delays needed to communicate with Earth. The colonization of Europa presents numerous difficulties; one is the high level of radiation from Jupiter's radiation belt, which is about 10 times as strong as Earth's Van Allen radiation belts. As Europa receives 540 rem of radiation per day, a human would not survive at or near the surface of Europa for long without significant radiation shielding. Colonists on Europa would have to descend beneath the surface, and stay in buried habitats. Another problem is that the surface temperature of Europa normally rests at −170 °C. It is also speculated that alien organisms may exist on Europa, possibly in the water underlying the moon's ice shell. If this is so, human colonists may come into conflict with harmful microbes. Even if life on Europa is found to be benign, human colonization of Europa raises ethical questions of ecocide.

Artist's concept of the cryobot, a large nuclear-powered probe, which
would melt through the ice until it hit the ocean below. (Credit: NASA)

Europa plays a role in the book and film of Arthur C. Clarke's 2010: Odyssey Two (1982) and its sequels. Super-advanced aliens aiding the development of life take an interest in the primitive life forms under Europa's ice and transform Jupiter into a star to kick-start their evolution. The aliens grant humans the other three Galilean moons of Jupiter to settle, but the humans are instructed not to land on Europa in order to allow the local life to develop. In 2061: Odyssey Three (1988), Europa has become a tropical ocean world.

Further reading:

Europa, a Continuing Story of Discovery
Moon Miners' Manifesto: Europa II Workshop Report
Preventing Forward Contamination of Europa
Humans on Europa: A Plan for Colonies on the Icy Moon

Effect of Psychoactive Drugs on Animals

Psychoactive drugs, such as caffeine, amphetamine, mescaline, strychnine, LSD, benzedrine, marijuana, chloral hydrate, theophylline, IBMX and others, have a strong effect on animals. At small concentrations, they reduce the feeding rate of insects and molluscs, and at higher doses kill them. Spiders build more disordered webs after consuming most drugs than before. It is believed that some plants developed caffeine in their leaves as a natural protection against insects.


Drugs affect spider's ability to build a web (Credit: NASA)

Spiders

In 1948, German pharmocologist P. N. Witt started his research on the effect of drugs on spiders. The initial motivation for the study was a request from his colleague, zoologist H. M. Peters, to shift the time when garden spiders build their webs from 2am-5am, which apparently annoyed Peters, to earlier hours. Witt tested spiders with a range of psychoactive drugs, including amphetamine, mescaline, strychnine, LSD and caffeine, and found that the drugs affect the size and shape of the web rather than the time when it is built. At small doses of caffeine (10 µg/spider), the webs were smaller; the radii were uneven, but the regularity of the circles was unaffected. At higher doses (100 µg/spider), the shape changed more, and the web design became irregular. All the drugs tested reduced web regularity except for small doses (0.1-0.3 µg) of LSD, which resulted in more ordered webs.

The drugs were administered by dissolving them in sugar water, and a drop of solution was touched to the spider's mouth. In some later studies, spiders were fed with drugged flies. For qualitative studies, a well-defined volume of solution was administered through a fine syringe. The webs were photographed for the same spider before and after drugging.

Witt's research was discontinued, but it became reinvigorated in 1984 after a paper by Nathanson in the journal Science, which is discussed below. In 1995, a NASA research group repeated Witt's experiments on the effect of caffeine, benzedrine, marijuana and chloral hydrate on European garden spiders. NASA's results were qualitatively similar to those of Witt, but the novelty was that the pattern of the spider web was quantitatively analyzed with modern statistical tools, and proposed as a sensitive method of drug detection.



Other arthropods and molluscs

In 1984, Nathanson reported an effect of methylxanthines on larvae of the tobacco hornworm. He administered solutions of finely powdered tea leaves or coffee beans to the larvae and observed, at concentrations between 0.3 and 10% for coffee and 0.1 to 3% for tea, inhibition of feeding, associated with hyperactivity and tremor. At higher concentrations, larvae were killed within 24 hours. He repeated the experiments with purified caffeine and concluded that the drug was responsible for the effect, and the concentration differences between coffee beans and tea leaves originated from 2-3 times higher caffeine content in the latter. Similar action was observed for IBMX on mosquito larvae, mealworm larvae, butterfly larvae and milkweed bug nymphs, that is, inhibition of feeding and death at higher doses. Flour beetles were unaffected by IBMX up to 3% concentrations, but long-term experiments revealed suppression of reproductive activity.

Further, Nathanson fed tobacco hornworm larvae with leaves sprayed with such psychoactive drugs as caffeine, formamidine pesticide didemethylchlordimeform (DDCDM), IBMX or theophylline. He observed a similar effect, namely inhibition of feeding followed by death. Nathanson concluded that caffeine and related methylxanthines could be natural pesticides developed by plants as protection against worms: Caffeine is found in many plant species, with high levels in seedlings that are still developing foliage, but are lacking mechanical protection; caffeine paralyzes and kills certain insects feeding upon the plant. High caffeine levels have also been found in the soil surrounding coffee bean seedlings. It is therefore understood that caffeine has a natural function, both as a natural pesticide and as an inhibitor of seed germination of other nearby coffee seedlings, thus giving it a better chance of survival.

Coffee borer beetles seem to be unaffected by caffeine, in that their feeding rate did not change when they were given leaves sprayed with caffeine solution. It was concluded that those beetles have adapted to caffeine. This study was further developed by changing the solvent for caffeine. Although aqueous caffeine solutions had indeed no effect on the beetles, oleate emulsions of caffeine did inhibit their feeding, suggesting that even if certain insects have adjusted to some caffeine forms, they can be tricked by changing minor details, such as the drug solvent.

These results and conclusions were confirmed by a similar study on slugs and snails. Cabbage leaves were sprayed with caffeine solutions and fed to Veronicella cubensis slugs and Zonitoides arboreus snails. Cabbage consumption reduced over time, followed by the death of the molluscs. Inhibition of feeding by caffeine was also observed for caterpillars.

(Source: Wikipedia)

IK Pegasi B: The Nearest Supernova Candidate

IK Pegasi is a binary star system in the constellation Pegasus. White dwarf IK Pegasi B, a massive star that is no longer generating energy through nuclear fusion, is the nearest known supernova candidate. When the primary evolves into a red giant, it will grow to a radius where the white dwarf can attract more matter from the expanded envelope. When the white dwarf approaches the limit of 1.44 solar masses, it is going to explode as a Type Ia supernova.


In IK Pegasi binary system, gas is being stripped away
from a giant star to form an accretion disc around
a compact companion (NASA image).

The primary is a main sequence star that displays minor pulsations in luminosity. It is categorized as a Delta Scuti variable star with a period of about an hour. Its companion is a massive white dwarf — a star that has evolved past the main sequence. They orbit each other every 21.7 days with a separation of about astronomical units. This is smaller than the orbit of Mercury around the Sun.

The distance to the IK Pegasi system can be measured directly by observing its parallax shifts against the distant stellar background as the Earth orbits around the Sun. This shift was measured to high precision by the Hipparcos spacecraft, and the distance was estimated as 150 light years. Hipparcos also measured the proper motion — the small angular motion of IK Pegasi across the sky because of its motion through space. The combination of the distance and proper motion of this system was used to compute the transverse velocity of IK Pegasi as 16.9 km/s.

The interior of IK Pegasi B may be composed wholly of carbon and oxygen, or alternatively, it may have a core of oxygen and neon, surrounded by a mantle enriched with carbon and oxygen. The exterior is covered by an atmosphere of almost pure hydrogen. Any helium in the envelope will have sunk beneath the hydrogen layer. The entire mass of the star is supported by electron degeneracy pressure — a quantum mechanical effect that limits the amount of matter that can be squeezed into a given volume.


A comparison between the IK Pegasi B (center), its companion
IK Pegasi A (left) and the Sun (right). (Credit: RJHall)

IK Pegasi B is considered to be a high-mass white dwarf, at an estimated 1.15 solar masses. Its radius can be estimated from known theoretical relationships between the mass and radius of white dwarfs, giving a value of about 0.60% of the Sun's radius. Thus this star packs a mass greater than the Sun into a volume roughly the size of the Earth. The massive, compact nature of a white dwarf produces a strong surface gravity — over 900,000 times the gravitational force on the Earth. The surface temperature is about 35,500K, making it a strong source of ultraviolet radiation. Under normal conditions this white dwarf would continue to cool for more than a billion years, while its radius would remain unchanged.

At some point in the future, IK Pegasi A will consume the hydrogen fuel at its core and form a red giant. The envelope of a red giant can extend up to a hundred times its previous radius. Once IK Pegasi A expands to the point where its outer envelope overflows the Roche lobe of its companion, a gaseous accretion disk will form around the white dwarf. This mass transfer between the stars will also cause their mutual orbit to shrink. Should the white dwarf's mass approach the Chandrasekhar limit of 1.44 solar masses it will no longer be supported by electron degeneracy pressure and it will undergo a collapse. If the core is made of carbon-oxygen, increasing pressure and temperature will initiate carbon fusion in the center prior to attainment of the Chandrasekhar limit. The dramatic result is a runaway nuclear fusion reaction that consumes a substantial fraction of the star within a short time. This will be sufficient to unbind the star in a cataclysmic, Type Ia supernova explosion.

A supernova would need to be within about 26 light years of the Earth to effectively destroy the Earth's ozone layer, which would severely impact the planet's biosphere. IK Pegasi system is not likely to pose a threat to life on the Earth, however. It is thought that the primary star is unlikely to evolve into a red giant in the immediate future. As shown previously, the space velocity of this star relative to the Sun is 20.4 km/s. This is equivalent to moving a distance of one light year every 14,700 years. After 5 million years, this star will be separated from the Sun by more than 500 light years. This is outside the radius where a Type Ia supernova is thought to be hazardous.


This video shows a thermonuclear flame burning its way through a white dwarf star. The flame produces hot ash, which buoyantly rises as the flame burns. The ash breaks out of but remains gravitationally bound to the surface of the star and collides at a point on the opposite side of the star from the breakout location. The blue shows the approximate surface of the star and the orange shows the interface between the star and the hot ash produced by the flame. (Credit: DOE NNSA ASC/Alliance Flash Center at the University of Chicago)

The Story of Gamma-ray Bursts

Gamma-ray bursts are flashes of gamma rays connected with extremely energetic explosions in distant galaxies. They are the most luminous electromagnetic events occurring in the universe.

This illustration shows the life of a massive star as nuclear fusion converts lighter elements into heavier ones. When fusion no longer generates enough pressure to counteract gravity, the star rapidly collapses into a black hole. Energy may be released during the collapse along the axis of rotation to form a gamma-ray burst. (Credit: Nicolle Rager Fuller/NSF)

"The death star": BBC documentary on the first stars in the universe and gamma-ray bursts.