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Cosmic Holes July 26, 2012

Posted by hellerphysics48 in Astronomy, Black Holes, Quasars.
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We have gazed out into the sky for thousands of years, with each passing generation developing a deeper understanding how the universe functions.  In the last 100 years, developments in physics have lead to a greater understanding of the actual makeup of the cosmos than ever before.

Albert Einstein, the famous German-American physicist, helped to pioneer this deeper understanding.  Under the postulates of the Special Theory of Relativity, Einstein found that space and time were connected.  Through this connection, variation in space must be accompanied by a variation in time.  Under Newtonian physics, any object with mass has its own gravity, but space itself is “flat”.  Under general relativity, any object with mass will cause curvature in space and time.  This curvature is what we experience as the force of gravity.   As the mass increases, so does the curvature of space and the gravitational force. 

In the life cycles of stars, the more massive the star is, the more interesting its life will be.  Stars that have a mass over eight times the mass of our sun put on one of the most spectacular shows the universe can put on.   For stars greater than this, their end comes with a tremendous bang, in which much of the stars mass is ejected into space.  This phenomena, which can be seen from distant galaxies is referred to as a supernova.  The remnant for a star of such mass leads to high density neutron stars. For more massive neutron stars, the escape velocity becomes begins to approach levels nearing the speed of light.  For a neutron star with a mass high enough, the escape velocity will become so great that a photon will no longer be able to escape.  This stellar fragment is left with a highly dense core referred to as a singularity.  As you approach the singularity, there is a point called the event horizon.  This is the last chance for any particle or photon of light to turn back.  Should one dare to cross into this horizon, no matter your speed, there will be no journey back.

Early on into the history of general relativity, the very concept of this “black hole” was met with skepticism.  In their very nature, black holes are difficult to detect.  Due to a black hole’s possession of greater than the speed of light escape velocity, light itself finds itself helplessly ensnared in the cosmic hole’s grasp.  Thankfully direct detection of these phenomena is not the only way of detecting black holes in the universe.  Our best hope for detection of a black hole comes from the study of the effects black holes have upon other stellar phenomena. They can even lead to other death of nearby stars, flattening the star out as it is pulled towards the more massive objects gravitational well.  The result are X-rays as the doomed star is pulled into the black hole, which can be detected on Earth.

Cosmologists need not only rely of the detection of doomed stars to detect black holes.  We can look for deviations of a star from a predicted orbit of its type.  Another method is to observe stars that seem to periodically “disappear”.  In this case, its light can be seen to periodically disappear from sight of our planet, lending evidence towards the existence of a black hole.

Black holes may only come in one shape, however, there seems to be little limit to the size.  It has been postulated that at the center of our galaxy exists a super massive black hole, one which is thought to measure close to 4.5 x 106 times larger than our own star, the sun. 

Penrose–Hawking singularity theorems

To form a singularity, it was postulated by Roger Penrose and Stephen Hawking potential black holes must qualify for one of these stipulations as solutions to Einstein’s field Equations:

  1. A situation where matter is forced to be compressed to a point (a space-like singularity)
  2. A situation where certain light rays comes from a region with infinite curvature.

One great explanation by Karen Masters, an astronomer at the University of Portsmouth, of the phenomena is:
“In the full and most simple General Relativistic solution for a space-time which has a Black Hole (in a vacuum), there are two singularities. One is in what we call the ‘future-light cone’ and this is the Black Hole. The other is in the ‘past-light cone’, and is called a white hole. This solution is however completely unphysical in many ways and in a real black hole (formed from the collapse of a star for example) we cannot use the vacuum solution as there is matter present, in addition to the fact that the white hole singularity disappears.”

White holes now reside in the undetectable category that black holes were resided sixty years ago.  The history of white holes starts with the study of Quasars, which for many years were postulated much elusive “white holes”.  However, this has proven to be an ineffective description.  Quasars are themselves “powered” by gravitational forces caused by accretion disks.  The ejection of electromagnetic radiation is caused by compression of the matter from the circular motion inside the black holes.


In the mathematical theory of general relativity, there is a component which has lead scientists to the possibility of a time-inverted black hole, dubbed a white hole.  The idea behind a white hole is an “action-reaction” connection between black holes and their white hole counterparts.  For each particle that enters a black hole past the event horizon, there is corresponding emission of a particle from the white hole. From this it is postulated that each of these particles would exist in their own universe, one particle on “each side”.  It has been postulated Schwarzschild wormholes or Einstein-Rosen bridges could be theoretically formed connecting these to particles.  These would allow some object, for example a photon, to try to cross in the center at which the event horizons meet.  At this point, it could be possible to travel to the other corresponding hole.  The concept of such a bridge was approached by John A. Wheeler and Robert W. Fuller in 1962.  They found that such a path, such a wormhole would be too quickly pinched off, so much so as to not allow light from one exterior region (universe) to travel to another.

Sources

Karen Masters January 2002 http://curious.astro.cornell.edu/question.php?number=108

Hawking, Stephen & Penrose, Roger (1996). The Nature of Space and Time. Princeton: Princeton University Press. ISBN 0-691-03791-4.

John Roach  November 2, 2005 http://news.nationalgeographic.com/news/2005/11/1102_051102_black_hole.html

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Gamma Ray Bursts by Danielle Thompson July 24, 2012

Posted by missthompsondhs in Astronomy, Gamma Ray Bursts, General.
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In an extremely distance galaxy far far away, billions of light years away from Earth, something remarkable happens nearly every day. The brightest and most energetic events known to the universe perform an electromagnetic lightshow. This extravagant phenomenon releases as much energy in a few seconds as the Sun does in its entire lifetime. This amazing occurrence is thought to be connected to the explosive death of a massive star or the collision of neutron stars. These spectacular incidents, known as gamma ray bursts, that only occur on average for 20-40 seconds produce sudden intense flashes of gamma radiation that outshines everything else in the sky.

Image Gamma Ray Burst

The discovery of the first gamma ray burst was a fortunate derivative of nuclear war defense using U.S. Vela satellites in the late 60’s. The US military satellites were carrying gamma ray detectors because nuclear reactions from bomb tests would give off gamma radiation. The satellites detected a flash of gamma radiation uncharacteristic of any nuclear weaponry. Surprisingly, this discovery was not of urgent concern to the US and over the next ten years with improved technology more information was collected and finally published in a scientific journal.

A later version of an Italian-Dutch satellite, BeppoSAX, launched in 1996 was equipped with not only a gamma ray but an x-ray detector allowing for the observation of the first “afterglow” of a gamma ray burst. An afterglow is caused from the burst colliding with the interstellar gases emitting longer wavelengths. Today NASA satellites are used to create the Gamma-ray Burst Coordinates Network (GCN) which coordinates space and ground-based observations to allow for better viewing of gamma ray bursts’ afterglows.

Image NASA

Further investigation into gamma ray bursts due to the improvements of satellites has allowed for the classification of long and short duration bursts. Long bursts have to last for more than 2 seconds and astronomers are fairly certain the cause of long duration gamma ray bursts is a rapidly rotating massive star, greater than 100 solar masses, and known as a supernova that is collapsing to form a black hole. Short duration bursts make up 30% of all bursts and are thought to be caused by neutron stars colliding. While studying long and short duration bursts, it has been discovered that no two bursts have the same light curve, this is a mystery that still plaques astronomers today.

ImageLight Curves

A new possible explanation for gamma ray burst is a hypernova. Scientists refer to a hypernova as a “failed supernova”, which is still a massive star whose core has collapsed but didn’t go boom. The hypernova’s shock wave doesn’t blow off the outer layers like a supernova does. The outer layers fall into the central neutron star or black hole and produces enormous amount of heat and radiation with an outcome of higher luminosity than a supernova. A hypernova has become the favored possible explanation because gamma ray bursts are more luminous than a supernova. The actually existence of hypernovae is still a hot debate.

Some astronomers suffer from ergophobia, the fear of energy, and the fear that our galaxy the Milky Way could experience a bad day. The scenario of a gamma ray burst firing its extremely energetic radiation at planet Earth is dishearting. The intense gamma rays would be stopped by the Earth’s stratosphere but the ozone layer would be destroyed. Would the depletion of the ozone layer inevitable cause a mass extinction? Gamma ray bursts fuel the speculation that there is a conceivable end to life as we know it on Earth.

Image The Milky Way

LIVE UPDATE OF GAMMA RAY BURSTS AND THEIR AFTERGLOWS

Commercial Space Flight July 23, 2012

Posted by stemtastic in Space Craft.
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Imagine traveling in space like you have seen on Star Trek, Star Wars, and other space adventure movies. What used to seem like a far-fetched idea only possible in science fiction is now becoming a possibility. While we may not be able to hop in our personal spaceship and head to another planet or galaxy, commercial space flights are a reality. Private companies are now able to transport cargo into space and very soon, people will be able to take flights into space.

After 30 years of service, NASA ended the Space Shuttle program in 2011 with the final flight of Space Shuttle Atlantis. Although NASA retired the Space Shuttle program, it still needs to accomplish missions in space. The development of NASA’s Commercial Crew Development (CCD) program has been designed to create partnerships with United States industry to develop safe and efficient space vehicles to transport astronauts and cargo to the International Space Station (ISS) and other Low Earth Orbit (LEO) destinations. Companies such as Boeing, Sierra Nevada, and SpaceX are working with NASA engineers to design, test, and certify transportation systems that will provide transportation for astronauts and cargo to places like the ISS.

SpaceX recently reached a major milestone in the history of space travel. On May 31, 2012, the spacecraft Dragon became the first commercial spacecraft to complete the mission of successfully transporting cargo to the ISS. The unmanned Dragon lifted off from Cape Canaveral Air Force Station on May 22. After being docked to the ISS on May 25, it spent 6 days being unloaded and loaded with new cargo to be returned to Earth.

The Dragon spacecraft was propelled into space by the Falcon 9 launch vehicle. Falcon 9 is a two stage, liquid oxygen and rocket grade kerosene powered vehicle.  Dragon is a reusable spacecraft designed to transport both pressurized and unpressurized cargo as well as crewmembers from LEO. The only mission completed so far has been unmanned.

In 2008 SpaceX’s Falcon 9 launch vehicle and Dragon spacecraft were selected by NASA to supply the ISS through a minimum of 12 flights for a contracted $1.6 billion. Based on the successful first delivery of cargo, it appears that SpaceX is well on its way to fulfill their obligation.

Commercial space transport helps NASA in a couple of ways. First, it allows NASA to send astronauts to the ISS without needing to hitch a ride on Russian spacecraft. Once the Shuttle program was retired, NASA had no way of sending astronauts to space. SpaceX and companies like it will once again make that a possibility in the near future. Commercial space transport also frees up resources for NASA to develop its deep space exploration program including the Orion Multi-Purpose Crew Vehicle and heavy lift Space Launch System (SLS).

Another area of commercial space flight that is gaining attention is space tourism. Virgin Galactic is one company providing the opportunity for people to experience sub orbital flight. The company claims to be on track for powered flight by the end of 2012. On June 26, 2012, they successfully completed a glide flight test and rocket motor firing. For a mere $200,000, you can purchase a ticket for the experience of a lifetime.

SpaceShipTwo is Virgin Galactic’s air launched glider with a rocket motor. In space, it will use small thrusters to maneuver. Since safety is a top priority, the spacecraft will use a hybrid rocket. This type of rocket uses the advantages of two types of rocket propulsion. It has the simplicity of a solid fuel rocket and the ability to be throttled or shut down like a liquid fuel rocket.

Another major safety design involves the way the spacecraft will re-enter Earth’s atmosphere. Before descending to Earth, the tail structure can be rotated up to about 65°. This allows the pilot to easily control altitude while keeping the spacecraft parallel to the horizon. This is accomplished without complicated fly-by-wire systems. Once the spacecraft has re-entered the atmosphere, the feather lowers to its original position and it is a glider to complete the trip home. According to their website, Virgin Galactic’s Burt Rutan designed SpaceShipTwo “uses aerodynamic design and the laws of physics for a carefree and heat free re-entry followed by a glide runway landing.” For safety, the spacecraft will be transported to an altitude of 50,000 ft by its launch vehicle WhiteKnightTwo. At this altitude, the spacecraft will be above most of Earth’s atmosphere thereby reducing the amount of drag the spacecraft has to overcome. Once SpaceShipTwo has been released, it will fire a rocket and ascend at 2500 mph to 62,000 feet. At this altitude, the passengers will be able to see some of the curvature of Earth and experience five minutes of weightlessness.

It may have seemed like the United States was giving up on space exploration and opportunities but the new age of commercial space flight has turned that around. More than ever before, we have the opportunities to provide more efficient space transportation systems to further research in space labs, explore deep space, and provide thrill seekers with a once-in-a-lifetime opportunity.

References

http://www.nasa.gov/exploration/commercial/index.html

http://www.spacex.com/index.php

http://www.virgingalactic.com/

Fata Morgana and Mirages July 22, 2012

Posted by pswanso233 in Astronomy, physics.
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I was scanning through the archives of the Astronomy Picture of the Day, and I saw this one which I thought looked really cool:

This is the cool picture I saw cruising through the APOD archives.

(http://apod.nasa.gov/apod/ap120415.html)

Interested, I looked up Fata Morgana and learned that it was a type of superior mirage.  Not knowing what a superior mirage was, I had to understand what causes mirages and what the difference between an inferior and a superior mirage was.

A mirage is a real optical phenomenon, rather than a hallucination.  Mirages can actually be photographed, whereas hallucinations cannot be.  Mirages are caused by temperature differences in the Earth’s atmosphere.  It’s here that I should probably introduce Snell’s Law and refraction, which is the bending of light through different materials.  Every transparent subtance has what’s called an index of refraction, which is the ratio of the speed of light in vacuum to the speed of light in that substance.  A high index of refraction indicates that light travels very slowly through the substance, whereas a low index means it doesn’t slow down much.  For example, the index of refraction of water is 1.33.  This means that light travels 1.33 times slower through water than it does air or vacuum.  This is why a pencil looks bent if you put it in a water filled beaker while still allowing part of it to be in the air.

A pencil looks bent when placed in water at an angle to the vertical because of refraction.

(http://library.thinkquest.org/27066/lightrays/nlrefraction.html)

A high index of refraction also means light will bend more if it travels through that substance.  So how exactly does this apply to mirages?  Cold air is denser than warm air, so light has a harder time going through it; therefore its index of refraction is higher.  If light rays from a distant source travel from cold air to hot air, they will bend away from the direction of the temperature gradient.  As these light rays reach your eye, your brain traces it as though they came from a line straight ahead, similar to your eye interpreting a virtual image through a convex lens.

An inferior image is a type of mirage where an image appears to be below a real object.  A common example would be a desert mirage, where the viewer thinks that there’s an oasis on the horizon.  This is caused because sand tends to heat up quickly, so the air around the sand is hot and the air above it is cooler.  The image you’re actually seeing is actually the sky, which is why it looks like water.

Inferior Image Formation

(http://www.islandnet.com/~see/weather/elements/mirage1.htm)

A superior image is the opposite case, where the image appears above the horizon.  This is caused by what’s called a temperature inversion, where hot air exists above cold air.  This tends to be more common at sea.

Superior Image Formation

(http://www.islandnet.com/~see/weather/elements/mirage1.htm)

Anyway, as I said before, a Fata Morgana is a special case of a superior mirage.  They can be seen from anywhere on Earth, but tend to be most common in Polar Regions and higher altitudes.

The special case of the superior mirage of a Fata Morgana occurs when the temperature inversion is high enough such that the light bends through it in such a way that the curvature of the light is higher than the curvature of the Earth.  The viewer should be present in an atmospheric duct, which is where light rays and other electromagnetic waves bend with the curvature of the Earth.  This is why these images tend to be rarer than other types of mirages.

A fata morgana off the coast of Canada

(http://www.sciencephoto.com/media/420314/enlarge)

          A Fata Morgana usually looks very bizarre, and can produce stacked images on top of each other.  They can also change rapidly, as if the temperature gradients change in such a way that the light no longer bends with the curvature of the Earth, they become regular superior mirages and don’t necessarily appear on the horizon anymore.

Another example of a fata morgana

(http://www.fedbybirds.com/2009/03/fata_morgana_in_finland.html)

           Fata Morgana is named for “The Fairy Morgana”, Morgan le Fay, who opposed King Arthur and Queen Guinevere in Arthurian legend.  She was a sorceress who had affairs with some of Arthur’s knights and was also Arthur’s half-sister.

One other cool and (sort of) funny I learned is that, back in the early 1900’s, some explorers found what they called the “Crocker Land”, which was a supposedly large island that existed between Canada and Greenland.  A very expensive team was sent to survey the island, but the mission cost over $100,000 (a huge sum at the time), because the island they saw was, in fact, a Fata Morgana.  They were even warned by some of the natives of Greenland that it was an illusion, but they pressed on anyways and were unable to explore the Crocker Land.

There is also some interest that perhaps a Fata Morgana contributed to the sinking of the Titanic:

http://www.dailymail.co.uk/sciencetech/article-2130598/False-wall-water-created-Fata-Morgana-mirage-hidden-iceberg-Titanic-late.html

Gathering the Wrong Light July 21, 2012

Posted by pjhsscience in Astronomy, Observatory, telescopes.
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Imagine for a moment, driving at night through the vast and unpopulated expanses of the western deserts of North America. Frequently, some of the most amazing photos of our night sky are taken from locations such as these and for very good reason. The only light visible is that which is being projected from the stars above. Back to yourself in the car now, you are approaching a town, a rather large town. As you get closer the lights from above start to fade as your eyes are drawn toward the glowing city. It’s not that street lamps and stoplights are more of an amazing site than our celestial blanket; it’s just that those lights are quickly becoming the only thing visible. You are experiencing the plague of metropolitan exorbitance, a form of pollution, light pollution.

Light pollution is one of the newest forms of pollution plaguing modern society. Before electric grids the night sky, even in large cities, was still an intriguing sight. As technology evolved and electricity flowed we were able to combat our limited night vision by lighting the night. As the world at night become brighter we covered the sky by uncovering what lies beneath us at night.

Lighting too has evolved throughout time. We are becoming more familiar with the glow of HID, or high intensity discharge lights, while becoming less familiar with the arrangement of the heavens. To get a view of just how encroaching light pollution can be we need only look at the animal kingdom. Lighting areas where light is not naturally present at night is having a major effect on nocturnal animals. Sea turtle hatchlings are often confused by brightly lit beaches and wander away from safe havens. Migration patterns of many species of waterfowl have been altered due to excess lighting. Feeding is a naturally performed at night for nocturnal creatures and feeding patterns have brought unwanted guests to our doorsteps due to light pollution. Lights attract bugs and bugs attract bats.

Astronomers from amateur to professional can all agree that light pollution is a great disturbance. Before even viewing a star astronomers without an enclosure cannot expect to have full dark adaption at night. The tools of astronomy are also plagued by light pollution. For instance, the Mt. Wilson Observatory just outside of Los Angeles is now operating at 11% of its original capacity due to the glowing L.A. night sky. While some stars may be visible in areas of high light pollution galaxies and nebula are greatly dimmed and very difficult to see even with advanced telescopes. New observatories are increasingly being constructed in remote areas in order combat light pollution but remote construction brings higher costs.

Limiting magnitude can be described as the faintest apparent magnitude of a celestial body capable of being detected and dependent upon equipment. Light pollution has a direct and sustained impact on the limiting magnitude in a given area. The limiting magnitude of the human eye under a completely dark sky is somewhere in the range of 7.6-8.0. At the other side of this scale, imagine yourself staring up at the night sky in a brightly lit inner-city setting. The limiting magnitude of your eye has been reduced by fifty percent to 4.0 or less. That comparison is simply applied to eyeball astronomy though, what about astronomers looking to make an observation. Under a dark sky with a 32 centimeter reflecting telescope you might just make some observations at the 18th magnitude. Again, we travel to the city where you set up your scope and find that you will only be making observations at the 13th magnitude.

For those in areas affected by light pollution there are some methods of circumventing it. Astronomers often employ narrow or high-band filters that do not allow light of certain spectral lines to pass through a telescope. The spectral lines targeted are those emitted by common vapor lamps including mercury and sodium. Though a good tool, these filters do limit the use of higher magnification.

If you wish to calculate how much light pollution will affect your astronomy work there is a simple equation to employ. The equation, I=0.01Pd-2.5 where I is the increase in sky glow, P is the population of the targeted city and d is the distance to the center of the city, works very well. This law is commonly referred to as Walker’s Law. Merle Walker proposed this relation after taking measurements of sky glow in several California cities. If you used this calculation and yielded a value of .03 that would mean that at the midway point between the horizon and zenith angle in the direction of the city the current sky would be 3% brighter than the natural background.

It is easy to see that combating light pollution would be of great benefit to society in general, the cost savings alone are staggering. Every year we waste one billion dollars lighting the night sky. Remediation of this problem is not as difficult as one might think; in fact, light pollution is the easiest of all forms of pollution to fix. Replacing old style lamps that radiate light in all directions with lamps that focus light downward is one remediation tactic. Also, we have to realize that lighting is not always necessary and we should take steps to remove lighting where it is not needed. Changing output is another effective method. Extremely bright bulbs are used in a number of lighting applications where they are not needed, limiting energy output not only reduces light pollution but also saves money.

We often light outdoor areas without a thought as to what we are losing. We may gain a little extra ease of night time navigation but we lose light at the same time. The light we lose is the light from nebula, galaxies and stars. This light has traveled a great distance, often many light years. This light has traveled those great distances through the vast reaches of outer space. This light ends its journey within our atmosphere at the hands of our lighting. Light pollution is a problem we have created but a problem that we can fix. Take a moment to look at the heavens through a dark sky and ask yourself if it is worth saving. My answer is yes.

Volcanism on Icy Io July 20, 2012

Posted by epscienceblog in Astronomy, moon, Solar and Space weather.
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Io, the closest moon to Jupiter, has an orange-brown
surface containing sulfur, the light areas are an icy
mix of sulfur and the dark areas highlight volcanic areas. Composite picture from NASA

As we have studied the Universe, one of the main ways that we have learned in the past is by using the Earth as a comparison, using all that we know about our planet as a reference for the other galactic bodies that we explore.  What is amazing now is the shift that is taking place, where we are beginning to use what we learn about other celestial bodies and apply that information to our own planet.  We learn even more about Earth as advances are being made in the exploration of our universe.  One example of how we are applying our knowledge of other bodies is Io.  The new information that is being gained from Io gives clues to the processes that occurred on Earth when it was young.

Io is an icy satellite of Jupiter 628,866,000 km from Earth, far enough from the sun that its surface temperature is 175 K (-143°C or -230°F) and is covered in sulfur dioxide frost.  Io’s yellow tinged crust is not fractured, therefore, it is not thought to have tectonic activity.  Despite these two factors, Io has the most volcanic activity in our solar system, spewing out over 100 times as much lava as all Earth’s volcanoes combined and may have as many as 300 active volcanoes.

Image from New Horizons, highlighting the Tvashtar volcanic plume reaching 300 km above the horizon.
Credit: NASA

The surface of Io is much different than previous expectations had dictated, and contains potential clues to the history of Earth.  When the Voyager spacecraft missions took images of Io in1979, NASA was surprised to see that Io was not full of craters, as had previously been thought.  It was assumed that Io would be cratered much like our moon.  Yet Io hardly had any craters at all, instead it had irregular pits and blotches of color.  When the images were carefully examined, volcanic plumes and lava flows were discovered.  Infrared spectrometry also detected abundant sulfur and sulfur dioxide in the volcanic plumes.

The sulfur on Io’s cold crust is solid, though when heated inside the crust, it explodes much like steam in a geyser on Earth.  The sulfur cools as it is ejected and may fall back down as “snow” on Io’s surface.  The lava flows on Io can range in color from orange to red to black and are found around the active vents.  The Galileo spacecraft monitored volcanic areas in the late 90s and found that the active lava flows of Io were between 1700 to 2000 K (around 1450 to 1750°C, or 2600 to 3150°F).  Earth’s lava temperatures are around 1300 to 1450 K.  The lava on Io is probably ultramafic, containing magnesium and iron that have higher melting points.  Ultramafic lava is found on Earth, but was formed when the Earth was young and the interior was much hotter than today.

A blue-tinged volcanic eruption forcing out rock and sulfurous gas,
taken from the NASA Galileo spacecraft.

The volcanoes on Io are mostly caldera-like, containing  large pools of lava, though some are fissures or cracks where the molten material can flow over the surface.  Loki Patera is a caldera with a diameter of 200 km, which makes it the largest in the solar system.  Some of the volcanoes form fountains, umbrella-shaped flows that spread up and out over large distances.  The Prometheus plume is a volcanic region that has been seen in almost every image taken of Io from 1979 to 1997, suggesting that it has been continually erupting for years.

Jupiter’s four largest moons (from left to right: Io, Europa, Ganymede, Callisto)
with sizes to scale. Credit: NASA

Aside from the similarities, we can also learn from the stark differences between Earth and Io.  While the heat in Earth’s core is mainly due to the radioactive decay of uranium, thorium and potassium, Io’s extreme internal temperature is caused by gravity.  Io is the closest natural satellite to Jupiter and is one of Jupiter’s four largest moons.  Due to the close proximity to Jupiter and the slightly elliptical orbit of Io, the gravitational pull on Io ebbs and flows, creating contraction and expansion on Io’s crust.  The next two moons closest to Io, Europa and Ganymede, also interact gravitationally with Io and increase the forces on Io as they routinely pass by.  The speed of the moon’s orbits are not the same; during the same period of time Ganymede orbits once, Europa orbits twice and Io orbits four times around Jupiter.  The differences in the orbits cause the moons to line up often.  This increases the gravitational pull on Io from both Europa and Ganymede as well as from Jupiter.  This continual pull creates tidal heating causing temperatures that melt the rock within Io and fuels the intense volcanic activity.  The process of squeezing and flexing is similar to how a ball of clay will soften and warm as a person kneads it.  However, the heating of Io is unlike what we have ever experienced on Earth.  The tidal heating on Io adds as much energy as 24 tons of TNT exploding every second.  Io’s surface receives 2.5 watts of power to each square meter, compared to 0.06 watts per square meter on the Earth’s crust from global heating.  The only areas on Earth that are comparable to Io’s average are in Earth’s volcanic areas.

GUEST POSTS THIS WEEK July 20, 2012

Posted by jcconwell in Astronomy.
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Over the next few days we will have a special treat. Some guest bloggers from my summer astronomy class for science teachers will be commenting on some cosmic and terrestrial topics that caught their interests this summer.