Thursday, April 9, 2015

There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities:



Rima Ariadaeus as photographed from Apollo 10. The crater to the south of the rille in the left half of the image is Silberschlag. The dark patch at the top right is the floor of the crater Boscovich. Credit: NASA


Rima Ariadaeus, a linear rile (a surface channel thought to be formed by lava) on the Moon’s surface, as photographed from Apollo 10. Credit: NASA
Every year since 1970, astronomers, geologists, geophysicists, and a host of other specialists have come together to participate in the Lunar and Planetary Science Conference (LPCS). Jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA’s Johnson Space Center (JSC), this annual event is a chance for scientists from all around the world to share and present the latest planetary research concerning Earth’s only moon.

This year, one of the biggest attention-grabbers was the findings presented on Tuesday, March 17th by a team of students from Purdue University. Led by a graduate student from the university’s Department of Earth, Atmospheric and Planetary Sciences, the study they shared indicates that there may be stable lava tubes on the moon, ones large enough to house entire cities.

In addition to being a target for future geological and geophysical studies, the existence of these tubes could also be a boon for future human space exploration. Basically, they argued, such large, stable underground tunnels could provide a home for human settlements, shielding them from harmful cosmic radiation and extremes in temperature.



The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed (NASA/JAXA)


The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed. Credit: NASA/JAXA
Lava tubes are natural conduits formed by flowing lava that is moving beneath the surface as a result of a volcanic eruption. As the lava moves, the outer edges of it cools, forming a hardened, channel-like crust which is left behind once the lava flow stops. For some time, Lunar scientists have been speculating as to whether or not lava flows happen on the Moon, as evidenced by the presence of sinuous rilles on the surface.

Sinuous rilles are narrow depressions in the lunar surface that resemble channels, and have a curved paths that meanders across the landscape like a river valley. It is currently believed that these rilles are the remains of collapsed lava tubes or extinct lava flows, which is backed up by the fact they usually begin at the site of an extinct volcano.

Those that have been observed on the Moon in the past range in size of up to 10 kilometers in width and hundreds of kilometers in length. At that size, the existence of a stable tube – i.e. one which had not collapsed to form a sinuous rille – would be large enough to accommodate a major city.

For the sake of their study, the Purdue team explored whether lava tubes of the same scale could exist underground. What they found was that the stability of a lava tube depended on a number of variables- including width, roof thickness and the stress state of the cooled lava. he researchers also modeled lava tubes with walls created by lava placed in one thick layer and with lava placed in many thin layers.



The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than 1 kilometer wide could remain structurally stable on the moon. (Purdue University/courtesy of David Blair)


The inside of a theoretical lunar lava tube, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair
David Blair, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon.

“Our work is somewhat unique in that we’ve combined the talents of people from various Departments at Purdue,” Blair told Universe Today via email. “With guidance from Prof. Bobet (a civil engineering professor) we’ve been able to incorporate a modern understanding of rock mechanics into our computer models of lava tubes to see how they might actually fail and break under lunar gravity.”

For the sake of their research, the team constructed a number of models of lava tubes of different sizes and with different roof thicknesses to test for stability. This consisted of them checking each model to see if it predicted failure anywhere in the lava tube’s roof.

“What we found was surprising,” Blair continued, “in that much larger lava tubes are theoretically possible than what was previously thought. Even with a roof only a few meters thick, lava tubes a kilometer wide may be able to stay standing. The reason why, though, is a little less surprising. The last work we could find on the subject is from the Apollo era, and used a much simpler approximation of lava tube shape – a flat beam for a roof.



Mons Rümker rise on the Oceanus Procellarum was taken from the Apollo 15 while in lunar orbit.


Mons Rümker, an extinct volcanic formation on the Moon’s surface, as imaged by the Apollo 15 spacecraft while in orbit. Credit: NASA
The study he refers to, “On the origin of lunar sinuous rilles“, was published in 1969 in the journal Modern Geology. In it, professors Greeley, Oberbeck and Quaide advanced the argument that sinuous rilles formation was tied to the collapse of lava flow tubes, and that stable ones might still exist. Calculating for a flat-beam roof, their work found a maximum lava tube size of just under 400 m.

“Our models use a geometry more similar to what’s seen in lava tubes on Earth,” Blair said, “a sort of half-elliptical shape with an arched roof. The fact that an arched roof lets a larger lava tube stay standing makes sense: humans have known since antiquity that arched roofs allow tunnels or bridges to stay standing with wider spans.”

The Purdue study also builds on previous studies conducted by JAXA and NASA where images of “skylights” on the Moon – i.e. holes in the lunar surface – confirmed the presence of caverns at least a few tens of meters across. The data from NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) – which showed big variations in the thickness of the Moon’s crust  is still being interpreted, but could also be an indication of large subsurface recesses.

As a result, Blair is confident that their work opens up new and feasible explanations for many different types of observations that have been made before. Previously, it was unfathomable that large, stable caverns could exist on the Moon. But thanks to his team’s theoretical study, it is now known that under the proper conditions, it is least possible.



The thickness of the moon's crust as calculated by NASA's GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic


NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) mission calculated the thickness of the moon’s crust. Credit: NASA/JPL-Caltech/S. Miljkovic
Another exciting aspect that this work is the implications it offers for future exploration and even colonization on the Moon. Already, the issue of protection against radiation is a big one. Given that the Moon has no atmosphere, colonists and agricultural operations will have no natural shielding from cosmic rays.

“Geologically stable lava tubes would absolutely be a boon to human space exploration,” Blair commented. “A cavern like that could be a really ideal place for building a lunar base, and generally for supporting a sustained human presence on the Moon. By going below the surface even a few meters, you suddenly mitigate a lot of the problems with trying to inhabit the lunar surface.”

Basically, in addition to protecting against radiation, a subsurface base would sidestep the problems of micrometeorites and the extreme changes in temperature that are common on the lunar surface. What’s more, stable, subsurface lava tubes could also make the task of pressurizing a base for human habitation easier.

“People have studied and talked about all of these things before,” Blair added, “but our work shows that those kinds of opportunities could potentially exist – now we just have to find them. Humans have been living in caves since the beginning, and it might make sense on the Moon, too!”

In addition to Melosh, Blair and Bobet, team members include Loic Chappaz and Rohan Sood, graduate students in the School of Aeronautics and Astronautics; Kathleen Howell, Purdue’s Hsu Lo Professor of Aeronautical and Astronautical Engineering; Andy M. Freed, an associate professor of earth, atmospheric and planetary sciences; and Colleen Milbury, a postdoctoral research associate in the Department of Earth, Atmospheric and Planetary Sciences.

Further Reading: Purdue News



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Author, freelance writer, educator, Taekwon-Do instructor, and loving hubby, son and Island boy!

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Was This Past Weekend’s Lunar Eclipse Really Total?

Was This Past Weekend’s Lunar Eclipse Really Total?:



Totality... or not? Image credit and copyright: Héctor Barrios


Totality… or not? Image credit and copyright: Héctor Barrios
Millions of viewers across the western United States and across the Pacific, to include Australia and New Zealand were treated to a fine Easter weekend lunar eclipse on Saturday. And while this was the third of the ongoing tetrad of four lunar eclipses, it was definitely worth getting up early for and witnessing firsthand.

But was it truly total at all?

To Recap: The April 4th eclipse featured the shortest advertised duration for totality for the 21st century, clocking in at just four minutes and 43 seconds in length. In fact, you’d have to go all the way back to 1529 to find a shorter span of totality, at one minute and 42 seconds. And you’ll have to wait until September 11th, 2155 to find one that tops it in terms of brevity.



The April 4th lunar eclipse over the Las Vegas strip. Image credit and copyright: John Lybrand


The April 4th lunar eclipse over the Las Vegas strip. Image credit and copyright: John Lybrand
We wrote recently about the saros cycle, and how this past weekend’s eclipse was the first in lunar saros series 132 to feature totality.

A fascinating discussion as to whether this was a de facto total lunar eclipse has recently sprung up on the message boards and a recent Sky and Telescope article online.



The geometry that creates a total lunar eclipse. Credit: NASA


The geometry that creates a total lunar eclipse. Credit: NASA
It all has to do with how you gauge the shape and size of the Earth’s shadow.

This is a surprisingly complex affair, as the Earth’s atmosphere gives the umbra a ragged and indistinct edge. If you’ve ever taken our challenge to determine your longitude using a lunar eclipse — just as mariners such as Christopher Columbus did while at sea — then you know how tough it is to get precise contact timings. There has been an ongoing effort over the years to model the size changes in Earth’s shadow using crater contact times during a lunar eclipse.

Many observers have commented in forums and social media that the northern limb of the Moon stayed pretty bright throughout the brief stretch of totality for Saturday’s eclipse.



What happens (in the skies over) Vegas... the lunar eclipse captured from the Luxor Hotel. Image credit and copyright: Rob Sparks


What happens (in the skies over) Vegas… the lunar eclipse captured from the Luxor Hotel. Image credit and copyright: Rob Sparks
“There are 3 ways of computing the magnitude of a lunar eclipse,” Eclipse expert David Herald mentioned in a recent Solar Eclipse Message List (SEML) posting:

The ‘traditional’ way as used in the Astronomical Almanac is attributed to Chauvenet – where the umbral radius is increased by a simple 2% – with the radius being based on the Earth’s radius at 45 deg latitude (and otherwise the oblateness of the Earth is ignored). For this eclipse the Chauvenet magnitude was 1.005.

 The second way (used in the French Almanac, and more recently by Espenak & Meeus in their ‘Five Millennium Canon of Lunar Eclipses’ is the Danjon method. It similarly uses the Earth’s radius at 45 deg (and otherwise the oblateness is ignored), and increases the Earth’s radius by 75km. For this eclipse the Danjon magnitude is 1.001

The most recent approach (Herald & Sinnott JBAA 124-5 pgs 247-253, 2014) is based on the Danjon approach; however it treats the Earth as oblate, allows for the varying inclination of the Earth relative to the Sun during the year, and increases the Earth’s radius by 87km – being the best fit to 22,539 observations made between 1842 and 2011. For this eclipse the magnitude is computed as 1.002.



“As for eclipses, to me it is total when sliver of light comes through the edge of the Earth’s profile,” eclipse chaser Patrick Poitevin told Universe Today. “Once a minimum of light passes through any of the lunar dales (as it does during a total solar eclipse) I do not concede it as a total. Same for a lunar eclipse.”



A partial phase for the April 4th lunar eclipse above a silo. Image credit and copyright: Brian who is called Brian


A partial phase for the April 4th lunar eclipse above a silo. Image credit and copyright: Brian who is called Brian
Michael Zeiler at the Great American Eclipse also had this to say to Universe Today about the subject:

This is a complex question because the shape of the Earth’s umbra upon the Moon is diffuse due to the effects of the Earth’s atmosphere. The various models used (with corrected radii for the Earth) are empirically based on crater timings of past lunar eclipses, of which there is some uncertainty. I’m sure this accounted for the difference between the USNO duration of eclipse and NASA.

The comment (in the recent Sky & Telescope post online) by Curt Renz is valid; correcting for the Earth’s flattening (meaning that the Earth’s radius from pole to pole is about a third of a percent shorter than the radius across the equator) might influence whether this very low magnitude eclipse is total or not. I haven’t made the calculation whether the Earth’s flattening tips this eclipse from total to partial, but it’s plausible.



Totality! Image credit and copyright: Rolf Wahl Olsen


Totality! Image credit and copyright: Rolf Wahl Olsen
 There is another wrinkle: due to parallactic shifts of the Moon when observing from either pole of the Earth, it might be that for a lunar eclipse right on the knife edge of total/partial, that it may indeed be total from one polar region and partial from another. This is a kind of libration, but it would be a very subtle difference and probably unobservable. 

 It is only possible to conclusively define Saturday’s eclipse as total or partial if you define a brightness threshold for the Sun’s photosphere illuminating an edge of the Moon. The problem here is that this line is indistinct and fuzzy. I watched the lunar eclipse carefully with this question in mind and I could not decide for myself whether this lunar eclipse was total or partial. I think it would require a photometer to make this distinction.

 Certainly, there’s little record of just how the 102 second long lunar eclipse of 1529 appeared. Ironically, it too was a total eclipse near sunrise as seen from Europe. On the other side of the coin, the deep partial eclipse of August 26th, 1961 just missed totality at 98.6% obscuration… and the two lunar eclipses in 2021 have similar circumstances, with a barely total lunar eclipse just 15 minutes long on May 26th and a 97.4% partial lunar eclipse on November 19th.



The circumstances for the 1529 total solar eclipse. Image credit: F.Espenak/NASA/GSFC


The circumstances for the 1529 total solar eclipse. Image credit: F.Espenak/NASA/GSFC
So maybe we won’t have to wait until 2155 to see another brief lunar eclipse that blurs the lines and refuses to play by the rules.



The eclipse as seen from Coral Towers Observatory. Image credit and copyright: Joseph Brimacombe


The eclipse as seen from Coral Towers Observatory. Image credit and copyright: Joseph Brimacombe
What do you, the readers think? What did you see last Saturday morn, a bright total lunar eclipse, or a deep partial?


About 

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.

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Venus and the Pleiades – See the Spectacle!

Venus and the Pleiades – See the Spectacle!:



Venus glides up to the Pleiades or Seven Sisters star cluster this week. This was the view at dusk on April 4. Credit: Bob King


Venus glides up to the Pleiades or Seven Sisters star cluster this week. This was the view at dusk on April 4 when they were still about 10° apart. Credit: Bob King
If you’ve ever been impressed by the brilliance of Venus or the pulchritude of the Pleiades,  you won’t want to miss what’s happening in the western sky this week.  Venus has been inching closer and closer to the star cluster for months. Come Friday and Saturday the two will be only  2.5° apart. What a fantastic sight they’ll make together — the sky’s brightest planet and arguably the most beautiful star cluster side by side at dusk.

No fancy equipment is required for a great view of their close conjunction. The naked eye will do, though I recommend binoculars; a pair of 7 x 35s or 10 x 50s will increase the number of stars you’ll see more than tenfold.



Map showing Venus' path daily from April 6-15, 2015 as it makes a pass at the Pleiades. Created with Chris Marriott's SkyMap


Map showing Venus’ path daily from April 6-15, 2015 as it makes a pass at the Pleiades.  The close pairing will make for great photo opportunities . Created with Chris Marriott’s SkyMap
Just step outside between about 8:30 and 10 p.m. local time, face west and let Venus be your guide. At magnitude -4.1, it’s rivaled in brightness only by the Moon and Sun. Early this week, Venus will lie about 5° or three fingers held together at arm’s length below the Pleiades. But each day it snuggles up a little closer until closest approach on Friday. Around that time, you’ll be able to view both in the same binocular field. Outrageously bright Venus makes for a stunning contrast against the delicate pinpoint beauty of the star cluster.



Venus on April 3, 2012, when it last passed over the Seven Sisters cluster. Credit: Bob King


Venus on April 3, 2012, when it last passed right in front of  the Seven Sisters. The Pleiades  is a young cluster dominated by hot, blue-white stars located 444 light years from Earth. Credit: Bob King
Every 8 years on mid-April evenings, Venus skirts the Pleiades just as it’s doing this week. Think back to April 2007 and you might remember a similar passage; a repeat will happen in April 2023. Venus’ cyclical visits to the Seven Sisters occur because the planet’s motion relative to the Sun repeats every 8 years as seen from Earth’s skies. No matter where and when you see Venus – morning or evening, high or low – you’ll see it in nearly the same place 8 years from that date.

But this is where it gets interesting. On closer inspection, we soon learn that not every Venus-Pleiades passage is an exact copy. There are actually 3 varieties:

* Close: Venus passes squarely in front of the cluster
* Mid-distance: Venus passes ~2.5° from the cluster
* Far: Venus passes ~3.5° from the cluster



The three flavors of varieties of Venus-Pleiades conjunctions. Created with Stellarium


The three varieties of Venus-Pleiades conjunctions . Created with Stellarium
And get this — each has its own 8-year cycle. This week’s event is part of a series of mid-distance passages that recurs every 8 years. Venus last passed directly through Pleiades in April 2012 and will again in April 2020. The next most distant meeting (3.5°) happens in April 2018 and will again in 2026.



Venus circles between Earth and the Sun, causing it to go through phases just like the Moon. The planet is currently in gibbous phase as seen through a small telescope. Credit: Wikipedia with additions by the author


Venus circles between Earth and the Sun and experiences phases just like the Moon from our perspective. The planet is currently in gibbous phase. It reaches its greatest apparent distance from the Sun on June 6 and inferior conjunction on August 15. Credit: Wikipedia with additions by the author
Why three flavors? Venus’ orbit is tipped 3.4° to the plane of the ecliptic or the Sun-Earth line. During each of it 8-year close passages, it’s furthest north of the ecliptic and crosses within the Pleiades, which by good fortune lie about 4° north of the ecliptic. During the other two cycles, Venus lies closer to the ecliptic and misses the cluster by a few degrees.

Fascinating that a few simple orbital quirks allow for an ever-changing variety of paths for Venus to take around (and through!) one of our favorite star clusters.



About 

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. Every day the universe offers up something both beautiful and thought-provoking. I also write a daily astronomy blog called Astro Bob.

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Beyond “Fermi’s Paradox” II: Questioning the Hart-Tipler Conjecture

Beyond “Fermi’s Paradox” II: Questioning the Hart-Tipler Conjecture:



The Milky Way Galaxy. Astronomer Michael Hart, and cosmologist Frank Tipler propose that extraterrestrials would colonize every available planet. Since they aren't here, they have proposed that extraterrestrials don't exist. Sagan was able to imagine a broader range of possibilities. Credit: NASA


The Milky Way Galaxy. Astronomer Michael Hart, and cosmologist Frank Tipler propose that extraterrestrials would colonize every available planet. Since they aren’t here, they have proposed that extraterrestrials don’t exist. Sagan was able to imagine a broader range of possibilities. Credit: NASA
It’s become a legend of the space age. The brilliant physicist Enrico Fermi, during a lunchtime conversation at Los Alamos National Laboratory in 1950, is supposed to have posed a conundrum for proponents of the existence of extraterrestrial civilizations.

If space traveling aliens exist, so the argument goes, they would spread through the galaxy, colonizing every habitable world. They should then have colonized Earth. They should be here, but because they aren’t, they must not exist.

This is the argument that has come to be known as “Fermi’s paradox”. The problem is, as we saw in the first installment, Fermi never made it. As his surviving lunch companions recall (Fermi himself died of cancer just four years later, and never published anything on the topic of extraterrestrial intelligence), he simply raised a question, “Where is everybody?” to which there are many possible answers.

Fermi didn’t doubt that extraterrestrial civilizations might exist, but supposed that interstellar travel wasn’t feasible or that alien travelers had simply never found Earth in the vastness of the galaxy.

The argument claiming that extraterrestrials don’t exist was actually proposed by the astronomer Michael Hart, in a paper he published in 1975. Hart supposed that if an extraterrestrial civilization arose in the galaxy it would develop interstellar travel and launch colonizing expeditions to nearby stars. These colonies would, in turn, launch their own starships spreading a wave of colonization across the galaxy.

How long would the wave take to cross the galaxy? Assuming that the starships traveled at one tenth the speed of light and that no time was lost in building new ships upon arriving at the destination, the wave, Hart surmised, could cross the galaxy in 650,000 years.

Even allowing for a modicum of time for each colony to establish itself before building more ships, the galaxy could be crossed in two million years, a miniscule interval on a cosmic or evolutionary timescale. Hart asserted that because extraterrestrials aren’t already here on Earth, none exist in our galaxy.

Hart’s argument was extended by cosmologist Frank Tipler in 1980. Tipler supposed that alien colonists would be assisted by self-reproducing robots. His conclusion was announced in the title of his paper ‘Extraterrestrial intelligent beings do not exist’.

Why is it important that Hart’s argument wasn’t really also formulated by the eminent Enrico Fermi? Because Fermi’s name lends a credibility to the argument that it might not deserve. Supporters of the search for extraterrestrial intelligence (SETI) want to search for evidence that alien civilizations exist by using radio telescopes to listen for radio messages that extraterrestrials may have transmitted into space. Interstellar signaling is vastly cheaper than a starship, and is feasible with technology we have today.

Hart drew public policy consequences from his argument that extraterrestrials don’t exist. His paper concluded that “an extensive search for radio messages from other civilizations is probably a waste of time and money”.

Our political leaders heeded Hart’s advice. When Senator William Proxmire led the successful drive to kill funding for NASA’s fledgling SETI program in 1981, he used the Hart-Tipler argument. A second NASA SETI effort was scuttled by congress in 1993, and no public money has been allocated to the search for extraterrestrial radio signals ever since.



The Arecibo Radio Telescope in Puerto Rico was the site of NASA's High Resolution Microwave Survey, a search for extraterrestrial radio messages. Funding was cut off for the project in 1993 following criticism in congress. Credit: Unites States National Science Foundation


The Arecibo Radio Telescope in Puerto Rico was the site of NASA’s High Resolution Microwave Survey, a search for extraterrestrial radio messages. Funding was cut off for the project in 1993 following criticism in congress. Credit: Unites States National Science Foundation


Just how convincing is the Hart-Tipler conjecture? Like Hart, Carl Sagan was an optimist about the prospects for interstellar travel, and Sagan published his analysis of the consequences of interstellar travel for extraterrestrial intelligence a whole decade earlier than Hart, in 1963. Sagan and his co-author, the Russian astronomer Iosef Shklovskii devoted a chapter to the topic in their 1966 classic Intelligent Life in the Universe.


Like Hart, Sagan concluded that “if colonization is the rule, then even one spacefaring civilization would rapidly spread, in a time much shorter than the age of the galaxy, throughout the Milky Way. There would be colonies of colonies of colonies…”. So why didn’t Sagan, like Hart, assert that extraterrestrials don’t exist because they aren’t already here?

The answer is that Sagan, unlike Hart, considered unlimited colonization as only one of many possible ways that extraterrestrial spacefarers might act. He wrote that “habitable planets lacking technical civilizations will frequently be encountered by spacefaring civilizations. It is not clear what their response will be…Perhaps strict injunctions against colonization of populated but pre-technical planets are in effect in some Codex Galactica. But we are in no position to judge extraterrestrial ethics. Perhaps attempts are made to colonize every habitable planet…A whole spectrum of intermediate cases can also be imagined”.

Besides assuming that interstellar travel is feasible, Hart’s argument is based on very specific and highly speculative ideas about how extraterrestrials must behave. He assumed that they would pursue a policy of unlimited expansion, that they would expand quickly, and that once their colonies were established, they would last for millions or even billions of years. If any of his speculations about how extraterrestrials will act aren’t right, then his argument that they don’t exist fails.

The evolutionary biologist Stephen Jay Gould was scathing in his criticism of Hart’s speculation. He wrote that ”I must confess that I simply don’t know how to react to such arguments. I have enough trouble predicting the plans and reactions of the people closest to me. I am usually baffled by the thoughts and accomplishments of humans in different cultures. I’ll be damned if I can state with certainty what some extraterrestrial source of intelligence might do”.

In 1981, Sagan and planetary scientist William Newman published a response to Hart and Tipler. While Hart used a very simple mathematical argument, assuming that an alien civilization would spread almost as fast as its ships could travel, Newman and Sagan used a mathematical model like the ones that population biologists use to analyze the spread of animal populations to model interstellar colonization.

They concluded that the rates of expansion assumed by Hart are highly unrealistic. Expansion will be drastically slower, for example, if civilizations control their population growth rates on any given planet to avoid ecological collapse, if colonies have a finite life span, and if alien societies eventually outgrow expansionist tendencies. Hart’s assumption that an alien civilization would spread almost as fast as its ships can travel isn’t plausible. It’s possible to walk across Rome in a day, Newman and Sagan noted, but Rome wasn’t built in a day. It grew much more slowly.

If the evolution of intelligent life is at all likely, other civilizations could emerge before any hypothetical first wave of expansion swept slowly over the galaxy. If several worlds produced waves of colonization, they might encounter one another. What would happen then? Nobody knows. The history of the galaxy can’t be predicted from a few equations.

For Newman and Sagan, the absence of extraterrestrials on Earth doesn’t mean that they don’t exist elsewhere in the galaxy, or that they never launch starships. It just means that they don’t behave in the way Hart expected. They conclude that “except possibly in the very early history of the Galaxy, there are no very old galactic civilizations with a consistent policy of conquest of inhabited worlds; there is no Galactic Empire”.

So, Enrico Fermi never did produce a powerful argument that extraterrestrial intelligence probably doesn’t exist. Neither did Michael Hart. The simple truth is that nobody knows whether or not extraterrestrials exist in the galaxy. If they do exist though, it’s possible that discovering their radio messages would give us the evidence we need. Then we could stop speculating and start learning something.

References and Further Reading:

F. Cain (2013) Where are all the aliens? The Fermi paradox, Universe Today.

F. Cain (2014) Are intelligent civilizations doomed? Universe Today.

R. H. Gray (2012) The Elusive WOW, Searching for Extraterrestrial Intelligence, Palmer Square Press, Chicago, Illinois.

R. H. Gray (2015) The Fermi Paradox is neither Fermi’s nor a paradox, Astrobiology, 15(3): 195-199.

M. H. Hart, (1975) An explanation for the absence of extraterrestrials on Earth, Quarterly Journal of the Royal Astronomical Society, 16:128-135.

W. I. Newman and C. Sagan (1981) Galactic civilizations: Population dynamics and interstellar diffusion, Icarus, 46:293-327.

C. Sagan (1963) Direct contact among galactic civilizations by relativistic interstellar spaceflight, Planetary and Space Science, 11:485-489.

I. S. Shklovskii and C. Sagan (1966) Intelligent Life in the Universe. Delta Publishing Company, Inc. New York, NY.

F. Tipler (1980) Extraterrestrial intelligent beings do not exist, Quarterly Journal of the Royal Astronomical Society, 21:267-281.

S. Webb (2010) If the Universe is Teeming with Aliens…Where is Everybody? Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life. Copernicus Books, New York, NY.



About 

Paul Patton is a freelance science writer. He holds a Bachelor's degree in physics from the University of Wisconsin Green Bay, a Master's degree in the history and philosophy of science from Indiana University, and a Doctorate in neuroscience from the University of Chicago. He has been interested in space, astronomy, and extraterrestrial life since early childhood.

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Trail’s End: Beautiful New Night-Sky Timelapse by Randy Halverson

Trail’s End: Beautiful New Night-Sky Timelapse by Randy Halverson:



Stunning views of the Milky Way, shimmering aurora, spectacular thunderstorms, flashing meteors, zipping satellies, stirring music, and spooky sprites and gravity waves …. they are all part of this wonderful new timelapse by night-sky guru Randy Halverson.

“Trails End is a compilation of some of my favorite timelapse shots from 2014, with a few aurora shots from early this year,” Halverson told us. “It was shot in Wyoming, Utah and South Dakota.”

A few moments to note in the video:

(...)
Read the rest of Trail’s End: Beautiful New Night-Sky Timelapse by Randy Halverson (90 words)

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Here’s How You Can Watch the SpaceX’s CRS-6 Mission From Your Backyard

Here’s How You Can Watch the SpaceX’s CRS-6 Mission From Your Backyard:



Image credit:


Dragon approaches the ISS during CRS-5. Image credit: SpaceX.
Hunting for satellites from your backyard can be positively addicting. Sure, the Orion Nebula or the Andromeda Galaxy appear grand… and they’ll also look exactly the same throughout the short span of our fleeting human lifetimes. Since the launch of Sputnik in 1957, humans also have added their own ephemeral ‘stars’ to the sky. It’s fun to sleuth out just what these might be, as they photobomb the sky overhead.  In the coming week, we’d like to turn your attention towards a unique opportunity to watch a high profile space launch approach a well-known orbiting space laboratory.

On Monday, April 13th 2015, SpaceX will launch its CRS-6 resupply mission headed towards the International Space Station. As of this writing, the launch is set for 20:33 Universal Time (UT) or 4:33 PM EDT. This is just over three hours prior to local sunset. The launch window to catch the ISS is instantaneous, and Tuesday April 14th at 4:10 PM EDT is the backup date if the launch does not occur on Monday.



Image credit: Andrew


Dragon chasing the ISS over Ottawa. Image credit and copyright: Andrew Symes
Of course, launches are fun to watch up-close from the Kennedy Space Center. To date, we’ve seen two shuttle launches, one Falcon launch, and the MAVEN and MSL liftoffs headed to Mars from up close, and dozens more from our backyard about 100 miles to the west of KSC. We can typically follow a given night launch right through to fairing and stage one separation with binoculars, and we once even had a serendipitous launch occur during a local school star party! We really get jaded along the Florida Space Coast, where space launches are as common as three day weekend traffic jams elsewhere.

And it’s true that you can actually tell when a launch is headed ISS-ward, as it follows the station up the US eastern seaboard along its steep 52 degree inclination orbit.

On Monday, Dragon launches 23 minutes behind the ISS in its orbit. Viewers up should be able to follow CRS-6 up the U.S. East Coast in the late afternoon sky if it’s clear.



Image credit: Orbitron


The position of the ISS during Monday’s liftoff, plus the trace for the next two orbits, and the position of the day/night terminator at the end of the second orbit. Image credit: Orbitron
And of course, SpaceX will make another attempt Monday at landing its Falcon Stage 1 engine on a floating sea platform, known as the ‘autonomous spaceport drone ship’ (don’t call it a barge) after liftoff.

About 15-20 minutes after liftoff, Europe and the United Kingdom may catch the Dragon and Falcon S2 booster shortly after the ISS pass on the evening of April 13th. Observers ‘across the pond’ used to frequently catch sight of the Space Shuttle and the external fuel tank shortly after launch; such a sight is not to be missed!

Spotting Dragon ‘and friends’ on early orbits may provide for a fascinating show in the evenings leading up to capture and berthing. Typically, a Dragon launch generates four objects in orbit: the Dragon spacecraft, the Falcon Stage 2 booster, and the two solar panel covers. These were very prominent to us as they passed over Northern Maine on first orbit in the pre-dawn sky on the morning of January 10th, 2015. Universe Today science writer Bob King also noted that observers spotted what was probably a venting maneuver over Minnesota on the 2nd pass on the same date.



Image credit: the launch of CRS-2.


The launch of CRS-2. Image credit: David Dickinson
And even after berthing, the Falcon S2 booster and solar panel covers will stay up in orbit, either following or leading the ISS for several weeks before destructive reentry.

Orbits on Monday and Tuesday leading up to capture for Dragon on Wednesday April 15th at 7:14 AM EDT/11:14 UT will be the key times to sight the pair. Capture by the CanadaArm2 will take place over the central Pacific, and the Dragon will be berthed to the nadir Harmony node of the ISS. Dragon will remain attached to the station until May 17th for a subsequent return to Earth. With the end of the U.S. Space Shuttle program in 2011, SpaceX’s Dragon is currently the only vessel with a ‘down-mass’ cargo capability, handy for returning experiments to Earth.



The first few orbits on the night of the 13th for North America include a key pass for the US northeast at 1:04UT (on the 14th)/9:04 PM EDT, and subsequent passes at dusk westward about 90 minutes later. NASA’s Spot the Station App usually lists Dragon passes shortly after launch, as does Heavens-Above and numerous other tracking applications. We’ll also be publishing sighting opportunities for Dragon and the ISS, along with maps on Twitter as @Astroguyz as the info becomes available.

Pre-berthing passes next week favor 40-50 degrees north for evening passes, and 40-50 degrees south for morning viewing.



Image credit: Marco


Dragon/CRS-3 passes over the Netherlands. Image credit: Marco Langbroek
The International Space Station has become a busy place since its completion in 2009. To date, the station has been a port of call for the U.S. Space Shuttles, the Soyuz spacecraft with crews, and Progress, HTV, ATV and Dragon resupply craft.

The current expedition features astronaut Scott Kelly and cosmonaut Mikhail Korniyenko conducting a nearly yearlong stay on the ISS to study the effects that long duration spaceflight has on the human body. Kelley will also break the U.S. duration record by 126 days during his 342 stay aboard the station. The future may see Dragon ferrying crews to the ISS as early as 2017.



Image credit:


Our ad-hoc satellite imaging rig. Image credit: David Dickinson
And you can always watch the launch live via NASA TV starting at 3:30 PM EDT/19:30 UT.

Don’t miss a chance to catch the drama of the Dragon spacecraft approaching the International Space Station, coming to a sky near you!



About 

David Dickinson is an Earth science teacher, freelance science writer, retired USAF veteran & backyard astronomer. He currently writes and ponders the universe from Tampa Bay, Florida.

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Sunday, April 5, 2015

Infoporn: The Best Images of the Deep Universe (So Far)

Infoporn: The Best Images of the Deep Universe (So Far):

The European Southern Observatory released an incredible set of images today that give the best-ever view of the deep universe. It’s a stunning new peek at one region of space—the Hubble Deep Field South (HDF-S)—that reveals many previously invisible galaxies, along with new information about how they move and how far away they are.

The new discovery is all thanks to the recently-installed MUSE instrument on the ESO’s Very Large Telescope, based on the very high mountain of Cerro Paranal in the very dry Atacama Desert of northern Chile. (High altitude and dry air make for much better astronomical observations.) Until now, astronomers observing the deep universe—including NASA researchers using the Hubble Space Telescope—had to use separate instruments over the course of days to take images of the sky and measure the physical properties of the stuff in it. MUSE (for Multi Unit Spectroscopic Explorer) is the first instrument capable of doing both.

MUSE is two things: a camera that images celestial light-emitting objects, and a spectrograph that measures the wavelength of that light. Using the instrument, astronomers at ESO don’t just receive an image full of pixels. They also receive information about the intensity of the pixel’s component colors—information that lets them learn about a galaxy’s distance from Earth, its elemental composition, and even its rotation. And thanks to adaptive optics that improve resolution, MUSE can see not just bright nearby galaxies, but very faint ones as well.



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The spectrograph in the MUSE instrument creates thousands of individual images of the sky, sorted by wavelength from violet to red. Many galaxies emit only a specific wavelength, flickering into view when the spectrograph isolates that color.  European Southern Observatory


“It was like fishing in deep water, and each new catch generated a lot of excitement and discussion of the species we were finding,” said MUSE principal investigator Roland Bacon in a press release. “The greatest excitement came when we found very distant galaxies that were not even visible in the deepest Hubble image.”

In the latest data, ESO astronomers used MUSE to measure distances for 189 galaxies, including some that are more than 12.8 billion light-years away. MUSE also found more than twenty very faint objects that Hubble had never been able to see before.

Now that MUSE has shown its stuff, Bacon and his colleagues expect to follow up on this data with observations of the Hubble Ultra Deep Field and other ill-known spaces of the universe. ESO has already used the instrument to track the collision of spiral galaxy ESO 137-001 as it crashes spectacularly into the Norma Cluster. Hopefully the images from those observations turn out just as stellar.

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Chilean Volcano Spews a Spectacular Lava Fountain

Chilean Volcano Spews a Spectacular Lava Fountain:

Chilean Volcano Spews a Spectacular Lava Fountain
Villarrica unleashed an impressive lava fountain as the recent unrest continues at the Chilean volcano.

The post Chilean Volcano Spews a Spectacular Lava Fountain appeared first on WIRED.

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Woman Controls a Fighter Jet Sim Using Only Her Mind

Woman Controls a Fighter Jet Sim Using Only Her Mind:

Woman Controls a Fighter Jet Sim Using Only Her Mind
A brain-computer interface lets a quadriplegic woman pilot an F-35 flight simulator with the power of her mind alone.

The post Woman Controls a Fighter Jet Sim Using Only Her Mind appeared first on WIRED.

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NASA Probe Finally Arrives at an Icy Alien World

NASA Probe Finally Arrives at an Icy Alien World:

NASA Probe Finally Arrives at an Icy Alien World
Larry Lebofsky has always been fascinated with Ceres, the biggest object in the asteroid belt between Mars and Jupiter. Even the license plate on his 2005 Toyota Matrix reads “1CERES.” In the late 1970s, the planetary scientist made some of the first observations that suggested Ceres—which is a dwarf planet, like Pluto—has bits of water ice […]

The post NASA Probe Finally Arrives at an Icy Alien World appeared first on WIRED.

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Watch a Mesmerizing Animation of NASA Satellites

Watch a Mesmerizing Animation of NASA Satellites:

Watch a Mesmerizing Animation of NASA Satellites
NASA’s Earth-observing satellites get the dubious honor of staring at us all day. Now, this video of the fleet zipping around the planet is just mesmerizing enough to make us want to do the same.

The post Watch a Mesmerizing Animation of NASA Satellites appeared first on WIRED.

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Alien FAQ: 6 questions about strange cosmic radio bursts

Alien FAQ: 6 questions about strange cosmic radio bursts:



The truth is out there (Image: Universal/Everett/REX)

A report that bursts of radio waves from the distant universe exhibit a weird mathematical pattern have freshly raised hopes that ET might be signalling us. But what's really behind it? Here's our ET FAQ.

1. Is this the first time we think we might have found aliens?
Nope, there have been several false alarms. The most famous is the 72-second Wow! signal, so called because an eager astronomer wrote "Wow!" next to it on a printout from the Ohio State Big Ear Telescope in 1977. It didn't seem to be of this Earth, but it was never seen again.

A few years before that, astronomer Jocelyn Bell thought she may have found the beep-beep-beep of "little green men" when she had actually discovered pulsars, the rapidly rotating corpses of stars that sweep a lighthouse-like beam of radiation as they spin. In the 70s, astronomers thought a Citizen's Band radio could be ET, and flagged the SOHO satellite as a possible signal in the 90s. But their double, triple and quadruple-checking rules meant they found the real culprits before making any announcements.

SETI software now weeds out false alarms pretty fast on its own, and there haven't been any major maybes in more than a decade – until now, perhaps.

2. Could the bursts have natural causes?
Fast radio bursts could have a natural, rather than an artificial, flavour. If a star in our galaxy had a massive flare-up, and the radiation had to tunnel through a bunch of cast-off plasma, the signal could look like it came from much farther away.

Also, if two white dwarf stars – the kind of dead sphere our sun will turn into in a few million years – crash into each other, they explode in a supernova. That blast could release a fast radio burst.

Then there are neutron stars. If two neutron stars – the dense cores of collapsed stars – are about to collide, they might release a radio burst right before they violently merge into one. Alternatively, some neutron stars are so massive that they should have collapsed into black holes, but are rotating too fast to do so. If one of these slows down, it will finally form a black hole, maybe blasting out a burst before it disappears forever.

Still, these don't account for the fast radio bursts' pattern according to any physics we know now.

3. How will we figure out if the creepy pattern is real or not?
First, scientists will have to discover more bursts using lots of different telescopes. Based on how much of the sky telescopes stared at and for how long before we found the 10 known bursts, scientists estimate that 10,000 bursts happen every day. Watching the whole sky all the time we'd catch every one of them, but right now we make discoveries when a scope happens to be pointed at the right place at the right time.

Either these new bursts will fit within the same pattern, adding to the eeriness, or they won't. If not, case closed. But, assuming they match up, we can see if they fit any earthly patterns, like appearing at the same parts of the day-night cycle or aligned with our seconds or minutes, which might imply an earthly origin. This may already be throwing some water on the discovery: the researchers published an update on 30 March suggesting that the signals might arrive according to UTC times, which aliens are unlikely to know about.

4. If it's really a signal from ET, how will we know what they're saying?
Google Translate! Just kidding. For the bursts we've already seen, we'll have to dig around in the existing data – which tells us how strong the radio waves were, at which frequencies, at what times – and see if anything is encoded besides 187.5. In the future, we could try to record more information about the bursts, to see if extra signals are embedded.

Some SETI scientists think it could take us centuries to decode any message we received. We won't have a common language, a common culture, or even common sensory organs. For a while, we may have to be happy to assume they're just saying "Hello!"

5. How else can we find ET?
Rogue radio broadcasts are the traditional signs astronomers look for from aliens – basically because these are the easiest to spot - and specifically, those from known exoplanet systems. The Allen Telescope Array currently does this sort of work from northern California. But search options expand as our technology gets better. As astronomer Jill Tarter is fond of saying, "SETI scientists always reserve the right to get smarter."

We could also look for signs of atmospheric and light pollution on other planets, to see if ET is as environmentally unfriendly as we are. We can look for ultrafast laser pulses that, as far as we know, the universe doesn't create naturally, but which humans – and perhaps aliens – can generate. And aliens who harness their star's energy in a super-evolved version of solar panels called a Dyson sphere would leave a heat signature we could see from far away.

6. What is the most likely explanation?
The only thing we know for sure about fast radio bursts – and this potential pattern – is that they're telling us we don't understand something about the universe. Maybe what we don't understand is that we have cosmic cousins. But more likely, we're missing something fundamental about how pulsars work or what our own satellites are doing. Either we'll learn something about physics, or we'll learn something about interstellar biology. It's win-win.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.

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Super-typhoon Maysak looks tranquil from space

Super-typhoon Maysak looks tranquil from space:



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A destructive typhoon currently heading towards the Philippines has been photographed from the International Space Stationmf.gif







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