The barrage

At the last Tompkins County Friends of the Library Used Book Sale, I picked up a copy of Donald Yeomans's fascinating book titled Near-Earth Objects (which has the rather alarming subtitle, Finding Them Before They Find Us).  Yeomans has impeccable credentials -- senior fellow with NASA's Jet Propulsion Laboratory, manager/supervisor of the Near-Earth Object Program Office and Solar System Dynamics Group, and researcher with the Deep Impact Project that investigates the composition, origins, and trajectories of comets.  His book is about the potential for a significant asteroid or comet strike on Earth -- and, more importantly, how we might find potentially hazardous orbiting objects soon enough to have a chance to avert the collision.

As Canadian astronaut Chris Hadfield put it, "The dinosaurs went extinct because they didn't have a space program."

One of the topics in Yeomans's book is the history of impacts, including the famous one that ended the Mesozoic Era.  But his timeline goes back a great deal further than that; one of the sections is devoted to a period called the Late Heavy Bombardment -- on the order of four billion years ago -- during which it is thought that the Earth got absolutely pummeled.

What caused this barrage?  Well, first of all, it must be stated that not all scientists even think it happened.  The geological processes on the Earth's surface have erased most of the evidence.  Studies of cratering on the Moon (which presumably would also have gotten clobbered during the same period) have yielded conflicting results; Patrick Boehnke and Mark Harrison, of the University of California, wrote a paper back in 2016 suggesting that the radioisotope dating of rocks from the Moon supported a uniformly decreasing impact rate over its history (i.e., no sudden spike about four billion years ago).

Other researchers disagree.  Three of the largest impact basins on the Moon, the Mare Imbrium, Mare Serenitatis, and Mare Nectaris, all appear to date from right around the time of the hypothesized bombardment.  If the same happened on Earth, it was cataclysmic -- turning large areas of the Earth's crust into molten lava, and vaporizing huge volumes of water in the early oceans.

[Image licensed under the Creative Commons CC-BY-SA, from https://ancient-life-and-history-earth.fandom.com/wiki/Late_Heavy_Bombardment]

Where it gets interesting is the explanation for why the Late Heavy Bombardment happened -- if it did.  The whole thing hinges on a bit of physics that falls into the "stuff that I theoretically knew, but never really thought about" department.

The orbital path of a planet (or asteroid, or comet, or whatever) remains stable as long as nothing adds or removes energy from it.  If something subtracts energy, the orbit becomes smaller; if something adds energy, the orbit gets bigger.  Enough added energy, and it achieves escape velocity and is ejected from the system altogether.  But what would itself have enough energy to interact with something the size of a planet in such a way as to make any difference?

Back in the early history of the Solar System, there was a clutter of debris left over from its formation.  We still have three major bands of it left -- the Asteroid Belt between Mars and Jupiter, the Kuiper Belt beyond the orbit of Neptune, and the Oort Cloud way out past the orbit of Pluto.  There are few asteroids left in the vicinity of the planets, because any that were there were swept up gravitationally.  In fact, that's one of the requirements for an object to be classified as a planet; that it clear the space near it of asteroids.  (This is the characteristic that caused Pluto to get demoted.)

But four billion years ago, there was a great deal more debris around.  Any large-ish asteroids that got near a planet resulted in their giving a gravitational yank on each other; if the asteroid was ahead of the planet, it had a bit of its energy stolen by the planet (making the planet's orbital axis get bigger); if it passed behind the planet, the reverse happened (making the planet's orbital axis shrink).  Well, according to the models described by Yeomans, eventually the pushing and pulling by all of the asteroids added up, and a curious thing happened.

The two largest planets, Jupiter and Saturn, had their orbits altered until they were in a highly stable configuration called a 2:1 orbital resonance.  

What this means is that they were in a pattern where Saturn's orbital period was exactly twice Jupiter's.  (They're still close to that; Saturn orbits the Sun once every 29.4 years, and Jupiter once every 11.9 years.)  But when they were in perfect 2:1 resonance, they reinforced each other's gravitational influence on the outer planets, Uranus and Neptune, giving them a kick every time they lined up -- a little like a kid on a playground swing kicking off every time they pass the ground.

This did two things.  First, it gave energy to Uranus and Neptune, making their orbits bigger, moving them outwards.  Second, it subtracted energy from Jupiter and Saturn, making their orbits smaller (and eventually destroying the resonance).  But the important one here is Neptune, because the increase of its orbit moved it out into a region of space that hadn't been cleared of debris.  When Neptune slipped outward into the inner Kuiper Belt, around four billion years ago, this had the effect of slingshotting a great deal of that debris into the inner Solar System...

... turning Earth into a gigantic bullseye for meteor strikes.

So it's fascinating that if the Late Heavy Bombardment actually did occur, there's a good model for what might have caused it.

The good news is that now that Jupiter and Saturn are no longer in resonance, Neptune is more or less staying put, so any further target practice is unlikely.  Doesn't mean we're out of the woods completely, of course.  Yeomans's whole book is about the possibility of asteroid strikes.

But at least it looks like the barrage is a thing of the past.

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Missing the target

Lately I've been seeing a lot of buzz on social media apropos of the Earth being hit by a killer asteroid.

Much of this appears to be wishful thinking.

Most of it seems to focus on the asteroid 2007 FT3, which is one of the bodies orbiting the Sun that is classified as a "near-Earth object" -- something with an orbit that crosses Earth's, and could potentially hit us at some point in the future.  It bears keeping in mind, however, that even on the scale of the Solar System, the Earth is a really small target.  This "deadly asteroid," we're told, is "on a collision course with Earth" -- but then you find out that its likelihood of its actually striking us on the date of Doomsday, March 3, 2030, is around one in ten million.

Oh, but there's "an altogether more sinister estimate" that 2007 FT3 could hit us on October 5, 2024, but the chances there are one in 11.5 million.  Why this is "altogether more sinister," I'm not sure.  Maybe just because it's sooner.  Or maybe the author of the article doesn't understand how math works and thinks that the bigger the second number, the worse it is.  I dunno.

Then there's the much-hyped asteroid 99942 Apophis, which was first thought to have a 2.7% chance of hitting the Earth in April of 2029 (more accurate observations of its orbit eliminated that possibility entirely), and then gets a second shot at us in April of 2036.  The 2036 collision depends on it passing through a gravitational keyhole during its 2029 close approach -- a tiny region in space where the pull of a much larger planet shifts the orbit of a smaller body in such a way that they then collide on a future pass.  Initially, the keyhole was estimated to be eight hundred kilometers in diameter, and this caused the physicists at NASA to rate Apophis at a four out of ten on the Torino Impact Scale -- the highest value any object has had since such assessments began.  (A rating of four means "A close encounter, meriting attention by astronomers.  Current calculations give a 1% or greater chance of collision capable of regional devastation.  Most likely, new telescopic observations will lead to reassignment to Level 0.  Attention by public and by public officials is merited if the encounter is less than a decade away.")  If it hit, the impact site would be in the eastern Pacific, which would be seriously bad news for anyone living in coastal California.

The close approach in 2029 [Image licensed under the Creative Commons Phoenix7777, Animation of 99942 Apophis orbit around Sun, CC BY-SA 4.0]

This, of course, spurred the scientists to try to refine their measurements, and when they did -- as the scale suggested -- they found out we're not in any danger.  The gravitational keyhole turns out to be only a kilometer wide, and Apophis will miss it completely.

In fact, there are currently no known objects with a Torino Scale rating greater than zero.

It's always possible, of course, that we could be hit out of the blue by something we never saw coming.  But given that we're talking about an unknown risk from an unknown object of unknown size hitting in an unknown location at an unknown time, I think we have more pressing things to worry about.  Sure, something big will eventually hit the Earth, but it's not going to happen in the foreseeable future.  NASA and the other space monitoring agencies in the world are doing a pretty good job of watching the skies, so maybe we should all just turn our attention on more important matters, like trying to figure out how nearly half of Americans think the best choice for president is a multiply-indicted, incompetent compulsive liar who shows every sign of incipient dementia.

In any case, I'm not concerned about asteroid impacts, and all the hype is just more clickbait.  So if you live on the West Coast and were planning on moving inland, or are considering cancelling your plans for a big Halloween bash this year, you probably should just simmer down.

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The Earth's dance partner

Ever heard of 3753 Cruithne?

I hadn't, which is surprising considering my obsession with astronomy.  It's an asteroid which is in a 1:1 orbital resonance with Earth -- in simpler terms, it is co-orbital.  It's sometimes been called "Earth's second moon," which is inaccurate because it doesn't orbit the Earth; in fact, its actual orbit is highly elliptical.  At its perigee, 3753 Cruithne is near the orbit of Mercury, and is outside the orbit of Mars at its apogee.

[Nota bene: the name "Cruithne" is from Gaelic, and because of the strange letter-to-phoneme correspondence in the Gaelic language, is pronounced "kroo-in-ya."  It's the name of an obscure king of the ancient Picts; its discoverer, astronomer Duncan Waldron, is Scottish, which probably explains the choice.]

Orbital resonance is one restricted solution to the more general three-body problem, which has yet to be solved by physicists.  The orbital interactions between two objects is thoroughly understood; add a third, and suddenly the math kind of blows up in your face.  You can run computer simulations starting with three objects of specific masses and velocities and see what happens, but a general set of equations governing any three (or more) body system has proven to be impossibly complex.  It's known that a few starting points generate stable orbits (resonance being one of those), and lots more of them prove unstable and eventually result in the objects colliding or flying apart, but trying to come up with the overarching mathematical scheme is currently out of reach.

3753 Cruithne's orbit, at least from our vantage point here on Earth, is a strange one.  If you were out in space, looking down on the Solar System, it wouldn't seem odd; an ellipse, tilted at a little less than twenty degrees away from the orbital plane of Earth:

[Image licensed under the Creative Commons Derivative work: User:Jecowa, Orbits of Cruithne and Earth, CC BY-SA 3.0]

But because of the weird perspective of being in a non-inertial (accelerated) reference frame, what we see on Earth is quite different.  As we watch 3753 Cruithne, it appears to be traveling in a bean-shaped orbit, first approaching us and then backing away as if we'd said something inappropriate:

[Image licensed under the Creative Commons User:Jecowa, Horseshoe orbit of Cruithne from the perspective of Earth, CC BY-SA 3.0]

Makes me realize how hard it is to come up with any reasonable model of moving objects in non-inertial reference frames.  Looking at 3753 Cruithne's strange wanderings almost leaves me sympathetic with Ptolemy and his nested epicycles.  (Isaac Newton, who understood the problem better than just about anyone else, wasn't nearly so forgiving, and called Ptolemy "an outrageous fraud.")

Its orbit classifies it as an Aten asteroid, a group of asteroids whose orbits cross that of the Earth.  For those of you who are of an apocalyptic bent, however, no need to lose sleep over 3753 Cruithne; its orbital tilt makes it no threat.  Its position has been run forward by computer models for thousands of years, and it has a zero chance of striking Earth.

That's assuming the orbital resonance remains stable, of course, and there's no guarantee it will.  There are other players in this gravitational game of pinball besides the Earth and the Sun; Venus and Mercury also come close to 3753 Cruithne on occasion, and a near pass could give the asteroid enough of a gravitational tug to destroy the resonance and destabilize the orbit.  The great likelihood if this happens, though, is it falling into the Sun or being flung out of the Solar System entirely; the chance of some gravitational slingshot effect propelling it into the Earth is about as close to zero as you can calculate.

So that's today's astronomical oddity that I, at least, had never heard of.  An asteroid in an ongoing celestial dance with the Earth.  Just goes to show that to find strange new stuff out in space, you don't need to peer out at the far reaches of the universe -- there's enough right here near home to keep the astronomers busy for a long while.

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Forensic geology

I've been interested in rocks since I was a kid.  My dad was a rockhound -- more specifically, a lapidary, who made jewelry from such semiprecious stones as turquoise, agate, and jasper.  The high point of my year was our annual trip to Arizona and New Mexico, when we split our time between searching for cool rocks in the canyons and hills of the southwestern desert and pawing through the offerings of the hundreds of rock shops found throughout the region.

Besides the simple beauty of the rocks themselves, it fascinated me to find out that with many rocks, you could figure out how and when they formed.  A lot of the gem-quality rocks and minerals my dad was looking for -- malachite, azurite, and opal amongst them -- are created by slow precipitation of layers of minerals from supersaturated water; others, such as lapis lazuli, rhodonite, and garnets form when metal-bearing rocks are metamorphosed by contact with magma far underground.

[Image licensed under the Creative Commons Olga Semiletova, Минералы горных пород, Creative Commons Attribution-Share Alike 4.0 International license]

Once I found out that the "when" part was also often knowable, through such techniques as radioisotope dating and stratigraphy, it was always with a sense of awe that I held pieces of rock in my hand.  Even around where I live now, where there are few if any of the lovely gem-quality stones you find in the southwest, there's still something kind of mind-boggling about knowing the layers of limestone and shale that form the bedrock here in upstate New York were formed in the warm shallows of a warm ocean during the Devonian Period, on the order of four hundred million years ago.

But if you think that's impressive, wait till you hear about the research out of the University of Johannesburg that was published in the journal Icarus last week.

The research centered around a stone in the desert of western Egypt called Hypatia, given the name by Egyptian geologist Aly Barakat in honor of the brilliant, tragic polymath whose career was cut short when she was brutally murdered by a mob on the orders of Cyril, bishop of Alexandria.  (The aftermath, although infuriating, is typical of the time; Hypatia was largely forgotten, while Cyril went on to be canonized as a saint by the Roman Catholic Church.)  The stone, fittingly considering Hypatia's contributions to astronomy, turns out to be extraterrestrial in origin, later falling as a meteorite to the surface of the Earth.

But "extraterrestrial" is a big place, as it were.  Where exactly did it form?  Chemical tests on the rock found that it didn't match the composition of any known asteroid or comet; then, the mystery deepened when it was found to contain nickel phosphide, which has never been found on any solid material tested in the entire Solar System.

Further tests only made the rock seem more anomalous.  Silicon, second only to oxygen as the most common element in the Earth's crust (a little over 28%, to be exact), was almost absent, as were calcium, chromium, and manganese; on the other hand, there was far more iron, sulfur, phosphorus, copper, and vanadium than you'd expect.  The ratios were far off not only from rocks in our Solar System, they didn't match the composition of interstellar dust, either.

The researchers decided to go at it from the other direction.  Instead of trying to find another sample that matched, they looked at what process would create the element ratios that Hypatia has.  And they found only one candidate that matched.

A type 1a supernova.

Type 1a supernovas occur in binary star systems, when one of the stars is relatively low mass (on the order of the Sun) and ends its life as a super-compact white dwarf star.  White dwarf stars have an upper limit on their mass (specifically about 1.4 times the mass of the Sun) called the Chandrasekhar limit, after Nobel Prize winning astronomer Subrahmanyan Chandrasekhar.  The reason is that at the end of a star's life, when the outward pressure caused by the fusion in the core drops to the point that it can't overcome the inward pull of gravity from the star's mass, it begins to collapse until some other force kicks in to oppose it.  In white dwarf stars, this occurs when the mutual repulsion of electrons in the star's constituent atoms counterbalances the pull of gravity.  In stellar remnants more than 1.4 times the mass of the Sun, electrostatic repulsion isn't powerful enough to halt the collapse.  (The other two possibilities, for progressively higher masses, are neutron stars and black holes.)

In binary stars, when one of the members becomes a white dwarf, the gravitational pull of its extremely compact mass begins to siphon material from its companion.  This (obviously) increases the white dwarf's mass.  Once it passes the Chandrasekhar limit, the white dwarf resumes its collapse.  The temperature of the white dwarf skyrockets, and...

... BOOM.

The whole thing blows itself to smithereens.  Fortunately for us, really; a lot of the elements that make up the Solar System were formed in violent events such as the various kinds of supernovas.  But the models of the relatively rare type 1a (only thought to happen once or twice a century in a typical galaxy of a hundred billion stars) generate a distinct set of elements -- and the percent composition of Hypatia matches the prediction perfectly.

So this chunk of rock in the Egyptian desert was created in the cataclysmic self-destruction of a white dwarf star, probably long before the Solar System even formed.  Since then it's been coursing through interstellar space, eventually colliding with our obscure little planet in the outskirts of the Milky Way.

When I was twelve, holding a piece of billion-year-old limestone from the Grand Canyon, little did I realize how much more amazing such origin stories could get.

I think the real Hypatia would have been fascinated.

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Asteroid astrology

I've written more than once about astrology, a slice of woo-woo that has never failed to impress me as the most completely ridiculous model on the market for explaining how the world works.  I mean, really.  Try to state the definition of astrology in one sentence, and you come up with something like the following:

The idea that your personal fate and the course of global events are controlled by the apparent movement of the Sun and planets relative to bunches of stars that are at varying (but extreme) distances from the Earth, patterns which some highly nearsighted ancient Greeks thought looked vaguely like scorpions and rams and lions and weird mythical creatures like "sea-goats."

It definitely falls into the "how could that possibly work?" department, a question that is usually answered with vague verbiage about vibrations and energies and cosmic resonances.

Like I said, all of that is old territory, here at Skeptophilia.  But yesterday, thanks to a loyal reader and frequent contributor, I found out something that I didn't know about astrology; lately, astrologers have been including the asteroids in their chart-drawing and fortune-telling.

Don't believe me?  Listen to this lady, Kim Falconer, who tells us that we should consider the asteroids in our astrological calculations -- but only use the ones we want.  There are too many asteroids, she said, to track them all; "Use the asteroids that have personal meaning to you."

Falconer is right about one thing; there are a great many asteroids out there.  Astronomers currently think there are between 1.1 and 1.9 million asteroids in the belt between Mars and Jupiter alone, and that's not counting the ones in erratic or elliptical orbits.  So it would be a lot to track, but it would have the advantage of keeping the astrologers busy for a long time.

As far as which ones to track, though -- this is where Falconer's recommendations get even funnier, because she says we should pay attention to the names of the asteroids.  Concerned about money?  Check out where the asteroids "Abundantia" and "Fortuna" are.  Would you like to find out what changes you can expect in your sex life?  Look for "Eros" and "Aphrodite."  And I'm thinking; where does she think these names came from?  All of them were named by earthly astronomers, more or less at random.  I mean, it's not like the names have anything to do with the actual objects.  For example, here's a photograph of Eros:

[Image is in the Public Domain courtesy of NASA]

Anything less sexy-looking is hard to imagine, especially given all of the craters and pits and warts on its surface.

But that's missing the point, from Falconer's view, and I realize that.  She and her cohort believe that when Auguste Charlois and Gustav Witt discovered the thing way back in 1898 and gave it its name, they somehow were tapping into a Mystical Reservoir of Connectedness and linked it to Quantum Energies of Love.  Or something like that.

But even so, the "choose the asteroids you like" thing more or less comprises drawing up the astrological chart you want and then acting as if what you got is some sort of profound and surprising revelation.  Because, after all, if there are over a million to choose from, there are bound to be some that have names and positions that are favorable to whatever direction you wish your life was taking.  It's a little like drawing up your Tarot card hand by going through the deck and pulling out the cards you like, and arranging them however you want, and claiming that's your reading and that it has deep implications for your future.

Yes, I know that the actual way Tarot cards are read is equally ridiculous.  It was just an analogy, okay?

Anyhow, that's the latest from the world of horoscopes.  But I better wrap this up, because the asteroid Hygiea is currently crossing into the constellation Horologium the Clock, which probably means it's time for me to take a shower or something.

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Author Michael Pollan became famous for two books in the early 2000s, The Botany of Desire and The Omnivore's Dilemma, which looked at the complex relationships between humans and the various species that we have domesticated over the past few millennia.

More recently, Pollan has become interested in one particular facet of this relationship -- our use of psychotropic substances, most of which come from plants, to alter our moods and perceptions.  In How to Change Your Mind, he considered the promise of psychedelic drugs (such as ketamine and psilocybin) to treat medication-resistant depression; in this week's Skeptophilia book recommendation of the week, This is Your Mind on Plants, he looks at another aspect, which is our strange attitude toward three different plant-produced chemicals: opium, caffeine, and mescaline.

Pollan writes about the long history of our use of these three chemicals, the plants that produce them (poppies, tea and coffee, and the peyote cactus, respectively), and -- most interestingly -- the disparate attitudes of the law toward them.  Why, for example, is a brew containing caffeine available for sale with no restrictions, but a brew containing opium a federal crime?  (I know the physiological effects differ; but the answer is more complex than that, and has a fascinating and convoluted history.)

Pollan's lucid, engaging writing style places a lens on this long relationship, and considers not only its backstory but how our attitudes have little to do with the reality of what the use of the plants do.  It's another chapter in his ongoing study of our relationship to what we put in our bodies -- and how those things change how we think, act, and feel.

[Note:  if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Catch a falling star

Today's post is a scientific puzzle that -- so far -- doesn't have an answer.

I'm sure you've all had the lovely experience of seeing meteors in the night sky.  Some of you might even have seen meteor showers, when there can be hundreds of "shooting stars" per hour.  Bright as they are, most meteors are the size of a small pebble; the intense light comes from the heating caused by the friction of passage through the atmosphere.  The speed they're traveling determines how fast they heat up, and that's controlled by the angle with which the meteor intersects with the moving Earth; they can be going anywhere between 11 and 72 kilometers per second.

Sometimes, larger chunks of rock strike the Earth.  Sometimes much larger.  The meteor that exploded over Chelyabinsk, Russia in 2013 is estimated to have been around twenty meters in diameter, and to have weighed on the order of 12,000 tons.  The explosion released an energy equivalent of 400 kilotons of TNT, which is about thirty times that released from the atomic bomb that destroyed Hiroshima.  

[Image licensed under the Creative Commons Alex Alishevskikh, 2013 Chelyabinsk meteor trace, CC BY-SA 2.0]

Big rocks are the exception, of course.  Most meteors are tiny... but there are lots of them.  Honestly, I didn't realize how much meteoritic material hits the Earth.  Given how small most of it is, the vast majority of it goes unnoticed.  But the current estimates are that 44,000 kilograms of meteorites land on the Earth every day.  Most of it lands in the oceans (which, after all, cover seventy percent of the Earth's surface), but the rest of it becomes part of the dust that's floating in the air, and that we give virtually no thought to.

The origin of meteors and meteorites (as they're known once they hit the Earth) has always been thought to be random bits of rocky junk left over from the formation of the Solar System; meteor showers mostly come from the passage of the Earth through the orbital paths of comets.  (Comets, being basically big dirty snowballs, partly evaporate with each passage near the Sun, and any particles of rock embedded in the ice get left behind in a trail corresponding to the comet's orbit.)  Because the origin of meteoritic material was thought to be pretty random, the expectation was that even similar types of meteorites would differ in composition, as they'd come from different sources in the asteroid belt and elsewhere.

Well, turns out that isn't true.  A group of scientists led by Birger Schmitz of Lund University set about to study the only meteorites that hang around for a while in the geological record -- chondrites, or stony meteorites.  (The other main type, iron-nickel meteorites, tend to oxidize pretty rapidly once they hit the Earth, so there aren't any particularly old iron-nickel meteorites known.)  Even the chondrites break down and erode, but there's a part of them -- grains of a mineral called chrome spinel -- that are resistant enough to degradation that they can last a billion years essentially unchanged.

So Schmitz's group decided to look at the commonness of meteoritic chrome spinel crystals in the geological record (which would tell them how meteor strike frequency had changed over time), and the specific composition of the crystals (which would tell them the origins of the grains).

And that's when they got a surprise.

Not only has the flux of meteorites barely changed over the entirety of geological history, the composition of the chrome spinel crystals hasn't changed, either -- leading Schmitz et al. to conclude that the vast majority of meteors come from the same, and as yet unidentified, source.

The authors write:

The meteoritic material falling on Earth is believed to derive from large break-up or cratering events in the asteroid belt.  The flux of extraterrestrial material would then vary in accordance with the timing of such asteroid family-forming events.  In order to validate this, we investigated marine sediments representing 15 timewindows in the Phanerozoic for content of micrometeoritic relict chrome-spinel grains (>32 μm).  We compare these data with the timing of the 15 largest break-up events involving chrome-spinel–bearing asteroids (S- and V-types).  Unexpectedly, our Phanerozoic time windows show a stable flux dominated by ordinary chondrites similar to today’s flux.  Only in the mid-Ordovician, in connection with the breakup of the L-chondrite parent body, do we observe an anomalous micrometeorite regime with a two to three orders-of-magnitude increase in the flux of L-chondritic chrome-spinel grains to Earth.  This corresponds to a one order-of-magnitude excess in the number of impact craters in the mid-Ordovician following the L-chondrite break-up, the only resolvable peak in Phanerozoic cratering rates indicative of an asteroid shower.  We argue that meteorites and small (<1-km-sized) asteroids impacting Earth mainly sample a very small region of orbital space in the asteroid belt.  This selectiveness has been remarkably stable over the past 500 Ma.

So as baffling as it seems, it looks like most of the stony meteors out there come from one source -- probably the collision of two asteroids in the very, very distant past.  This impact created a huge cloud of fragments of different sizes but of relatively uniform composition, and that's the stuff that's been raining down on Earth for the past billion years.

Think about that next time you see a "falling star" on a clear, cloudless night.  You're seeing a relic of a collision that occurred back when the vast majority of living things were single-celled creatures living in the ocean.  That little pebble creating a streak of light across the sky has been floating around in space ever since, finally intersecting Earth's path and burning up in the atmosphere.

Just in time for you to make a wish.

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I'm in awe of people who are true masters of their craft.  My son is a professional glassblower, making precision scientific equipment, and watching him do what he does has always seemed to me to be a little like watching a magic show.  On a (much) lower level of skill, I'm an amateur potter, and have a great time exploring different kinds of clays, pigments, stains, and glazes used in making functional pottery.

What amazes me, though, is that crafts like these aren't new.  Glassblowing, pottery-making, blacksmithing, and other such endeavors date back to long before we knew anything about the underlying chemistry and physics; the techniques were developed by a long history of trial and error.

This is the subject of Anna Ploszajski's new book Handmade: A Scientist's Search for Meaning Through Making, in which she visits some of the finest craftspeople in the world -- and looks at what each is doing through the lenses of history and science.  It's a fascinating inquiry into the drive to create, and how we've learned to manipulate the materials around us into tools, technology, and fine art.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]

Astronomical Whack-a-Mole

Because we all clearly needed something else to worry about, today we have: the mega-asteroids of doom.

This comes up because of a new program at NASA, now that the Trump administration has freed them from the necessity of worrying about climate change.  Called the "Large Synoptic Survey Telescope," this project involves building a huge telescope in Chile that will be looking for "potentially hazardous asteroids" (PHAs).  The idea is that they'll scan the sky looking for any hitherto-unrecorded astronomical object that shows apparent movement against the background stars in an hour.  "Anything that moves in just one hour," writes project leader Michael Lund, astrophysicist at Vanderbilt University, "has to be so close that it is within our Solar System."

It's not like this is an inconsequential threat.  Barringer Crater, in northern Arizona, is a huge hole in the ground that was caused by collision with a nickel-iron meteorite fifty meters in diameter.  The Chesapeake Bay Impact Event, about 35 million years ago, is 85 kilometers across, and was caused by an object about three kilometers wide -- the impact was enough to cause a tsunami that hit the Blue Ridge Mountains.  The mother of 'em all, though, is the 150 kilometer wide Chicxulub Crater, 66 million years ago, which blew up a layer of dust that settled out as clay all over the Earth -- and is thought to have kicked off the Cretaceous Extinction, the final straw for the dinosaurs (except for the ones who were the ancestors of modern birds).

What is cheering, however, is that these events aren't frequent.  The Chelyabinsk meteor of 2013, which exploded 32,000 meters above the Earth's surface but still was able to generate a shock wave big enough to injure 1,200 people.  The object that caused the blast is thought to have been about twenty meters across -- nothing compared to Chesapeake Bay and Chicxulub, but still a little on the scary side.

[Image courtesy of NASA/JPL]

No one doubts that there are lots of objects out there that could potentially play Whack-a-Mole with the Earth.  The LSST gives us hope of finding them before they find us.  The unfortunate part, however, comes when Lund addresses the question of what we could do about it if we discovered that a huge rock was on a collision course with Newark:

If an asteroid is on a collision course hours or days before it occurs, the Earth won’t have many options.  It’s like a car suddenly pulling out in front of you. There is little that you can do.  If, however, we find these asteroids years or decades before a potential collision, then we may be able to use spacecraft to nudge the asteroid enough to change its path so that it and the Earth don’t collide. 

This is, however, easier said than done, and currently, no one really knows how well an asteroid can be redirected.  There have been several proposals for missions by NASA and the European Space Agency to do this, but so far, they have not passed early stages of mission development.

 So it looks like if you found out that day after tomorrow, your home town was going to get clobbered, you'd have two options: (1) get in your car, drive like hell, and hope for the best; or (2) put your head between your legs and kiss your ass goodbye.  I suppose that's better than nothing, especially considering that the alternative is thinking you're going to take a nice nap in your hammock and instead getting vaporized by an enormous superheated rock.

But even so, there's the problem of what it's going to be like for the rest of the Earth, the ones not in the impact zone.  Any impact -- even a relatively small one, like the one that formed Barringer Crater -- is actually going to have an enormous effect even on very distant places, just from the standpoint of kicking up a crapload of dust.  (Recall that when the volcano Tambora erupted in 1815, it caused "the Year Without a Summer," during which crops froze in mid-July and hundreds of thousands of people died of starvation.)

Nearer to the impact site, things get even worse.  Consider the Chelyabinsk meteor, which by comparison is a popgun -- not to mention the fact that it self-destructed 32,000 meters up, and never hit the surface.  The shock wave would be astronomical.  Pun intended.  Closer still, and the heat blast would flash-fry anything in its way.

You don't even get a pass if the impact is in the ocean, because then you've got hundred-foot-high tsunamis to worry about.

So yeah.  Not fun.

The best-case outcome, here, is that Lund and his colleagues scan the sky with the LSST for a while, and say, "Welp.  Nothing much out there.  I guess everything's hunky-dory.  As you were."  Or, that any projected impact will take place thousands of years from now.  (I figure that anyone around then will just have to fend for themselves.)  Or, perhaps, that we could use our technology to redirect the asteroid away from colliding with us.  Lund says this is already being looked into:

The B612 Foundation, a private nonprofit group, is also trying to privately raise money for a mission to redirect an asteroid, and they may be the first to attempt this if the government space programs don’t.  Pushing an asteroid sounds like an odd thing to do, but when we one day find an asteroid on a collision course with Earth, it may well be that knowledge that will save humanity.

I'll be watching the results, though, because being a little on the anxious, neurotic side, I definitely need another thing to keep me up at night.  On the other hand, it's at least temporarily taken my mind off all the other problems we're facing.  Which is good, right?

Of course right.

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This week's book recommendation is from one of my favorite writers and documentary producers, Irish science historian James Burke.  Burke became famous for his series Connections, in which he explored the one-thing-leads-to-another phenomenon which led to so many pivotal discoveries -- if you've seen any of the episodes of Connections, you'll know what I mean when I say that it is just mindblowing fun to watch how this man's brain works.  In his book The Pinball Effect, Burke investigates the role of serendipity -- resulting in another tremendously entertaining and illuminating read.

Asteroid astrology

I've written more than once about astrology, a slice of woo-woo that has never failed to impress me as the most completely ridiculous model on the market for explaining how the world works.  I mean, really.  Try to state the definition of astrology in one sentence, and you come up with something like the following:

The idea that your personal fate, and the course of global events, are controlled by the apparent movement of the Sun and planets relative to bunches of stars that are at varying (but extreme) distances from the Earth, patterns which some highly nearsighted ancient Greeks thought looked vaguely like scorpions and rams and lions and weird mythical creatures like "sea-goats."

It definitely falls into the "how could that possibly work?" department, a question that is usually answered with vague verbiage about vibrations and energies and cosmic resonances.

But like I said, all of that is old territory, here at Skeptophilia.  But yesterday, thanks to a loyal reader and frequent contributor, I found out something that I didn't know about astrology; lately, astrologers have been including the asteroids in their chart-drawing and fortune-telling.

Don't believe me?  Listen to this lady, Kim Falconer,  who tells us that we should consider the asteroids in our astrological calculations -- but only use the ones we want.  There are too many asteroids, she said, to track them all; "Use the asteroids that have personal meaning to you."

Falconer is right about one thing; there are a great many asteroids out there.  Astronomers currently think there are between 1.1 and 1.9 million asteroids in the belt between Mars and Jupiter alone, and that's not counting the ones in erratic or elliptical orbits.  So it would be a lot to track, but it would have the advantage of keeping the astrologers busy for a long time.

As far as which ones to track, though -- this is where Falconer's recommendations get even funnier,  because she says we should pay attention to the names of the asteroids.  Concerned about money?  Check out where the asteroids "Abundantia" and "Fortuna" are.  Concerned about love?  Find "Eros" and "Aphrodite."  And I'm thinking; where does she think these names come from?  All of them were named by earthly astronomers, more or less at random.  I mean, it's not like the names have anything to do with the actual objects.  For example, here's a photograph of Eros:

[image courtesy of NASA and the Wikimedia Commons]

Anything less sexy-looking is hard to imagine, especially given all of the craters and pits and warts on its surface.

But that's missing the point, from Falconer's view, and I realize that.  She and her cohort believe that when Auguste Charlois and Gustav Witt discovered the thing way back in 1898 and gave it its name, they somehow were tapping into a Mystical Reservoir of Connectedness and linked it to Quantum Energies of Love.  Or something like that.

But even so, the "choose the asteroids you like" thing seems very much like just drawing up the astrological chart you want.  Because, after all, if there are over a million to choose from, there are bound to be some that have names and positions that are favorable to whatever direction you'd like your life to take.  It's a little like drawing up your Tarot card hand by going through the deck and pulling out the cards you like, and arranging them however you want, and claiming that's your reading.

Yes, I know that the actual way Tarot cards are read is equally ridiculous.  It was just an analogy, okay?

Anyhow, that's the latest from the world of horoscopes.  But I better wrap this up, because the asteroid Hygiea is currently crossing into the constellation Horologium the Clock, which means it's time for me to go take a shower so I can get ready for work.