National prototype kilogram K20, one of two prototypes stored at the US National Institute of Standards and Technology in Gaithersburg, Maryland, which serve as primary standards for defining all units of mass and weight in the United States. This is a replica for public display, shown as it is normally stored, under two bell jars.
In the late 1800’s, a small, well-formed cylinder composed of platinum and a little iridium (the same alloy used in fine platinum jewelry today) was defined by the international scientific community to have a mass of exactly one kilogram. This was not a special rock dug up from the Earth, nor a once-in-a-lifetime meteorite fallen from the heavens, but a man-made object that was bestowed this great and important property to be used by generations of scientists and non-scientists. (Happy 125th Birthday, Kilogram.)
For myself as a student of physics, and likely with many professional scientists in the 20th Century, there was a lingering empty feeling from this type of “pull-it-out-of-the-air” proclamation for something fundamental to so many calculations and theories describing how Nature works. The speed of light, c, is a fundamental number that is directly measurable (try it yourself with chocolate), the definition of a unit of time in seconds, s, is directly measured from a naturally occurring phenomenon with unprecedented regularity (originally based on the rotation of the Earth, with all of its wobbles; now on the energy level transition in an atom near absolute zero temperature), and the meter is marked off (since 1983) by a measurable distance traveled by light in a fraction of a second. So, most other important units are built up from more fundamental definitions. Yet, the kilogram, with its smooth lump of metal, is still thrown into this fundamental mix.
For example, the Newton, N, is a unit of force measured from the well-loved equation F = ma, and carries the units of kilogram · meters per unit second. If the value of one kilogram was set only as the collective whim of humanity well over one hundred years ago, then what does that say about every calculation of force since that time? Well, probably not much, since we’ve been working just fine with it ever since. If the fundamental value changes, it just scales all other values with it. However, it might just be nice, or more reasonable, or more scientific to have the value of the kilogram defined from other measurable fundamental values so it may never be questioned or changed (or stolen for a private collection, or fall through a crevice in the Earth after a quake never to be found again).
The mission of cleaning up the fundamental definition of the kilogram has been underway for many years with an international resolution declared in 1999, at the turn of the century. Now, this latest collective whim of scientists is to derive the value of the kilogram from a very fundamental number found in the realm of quantum mechanics, called Planck’s constant, h.
First described during the turn of the previous century, in 1900, by Max Planck, this constant represents the ratio of the energy (E) of an atomically-small oscillating object to its frequency (f) of vibration. The relationship, called the Planck-Einstein relation, E = hf, became a basic underpin to the development of quantum mechanics. The proportionality constant h made an appearance in a plethora of key equations that came to describe the Universe at its tiniest scales, including the counter-intuitive notion that very small things can behave like a wiggling wave and a bouncing particle simultaneously.
The actual value of the Planck constant is likewise incredibly tiny, measuring in at only 6.626 x 10-34 Joules · seconds. So, to define something else directly from a measurement of this value, insane accuracy is required. This is where the expertise of the National Institute of Standards and Technology (NIST) became a valuable player in establishing the new life of the kilogram.
Bronze weighing dishes from the island of Thera, Santorini, Greece, Minoan civilization, 2000–1500 BC By Norbert Nagel (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Weighing in with h
The advanced measurement technology at NIST to be used for the kilogram is called a watt balance and is a modern-day extension of the classic equal arm balance dating back to at least the second century BC. Since it was originally conceived, an unknown mass is visually balanced by placing a collection of known masses on the opposite side of the device. When the two sides are resting at an equal height — i.e., the same force due to gravity, F = mg, is acting on each tray — then it can be assumed that the unknown mass equals the known mass. This millennial-old approach may have even coaxed the human drive to base any definition of mass from a known sample leading to the double-bell jar and platinum cylinder we find locked away today in a suburb of Paris.
The watt balance sets up a similar arrangement using a comparison of forces. This time, instead of watching gravity do its thing, the device measures electrical and mechanical power, hence the name “watt balance” where watt is the unit of measurement for power (as in 1.21 gigawatts… Great Scott!). Here, a highly controllable measurement of a force resulting from electromagnetism balances the gravitational force on the unknown mass. Flowing a current of electrons through a coil of wire inside a magnetic field on one side of the watt balance will create a force, and if aligned appropriately, this force will shift the two sides into balance for a particular current providing this electrical power.
This initial measurement provides a value of the unknown object’s mass in terms of a current, the magnetic field and the physical dimension of the coil.
Physicist Richard Steiner adjusts the electronic kilogram, an experimental apparatus for defining mass in terms of the basic properties of nature. (NIST)
However, we are looking for more: a direct relationship with the tiny and fundamental value of Planck’s constant. So, a second measurement is taken on the exact same setup of coil, alignment, and magnetic field to determine the voltage generated in the circuit when the coil moves through the magnetic field. This is the mechanical power generated during the balancing experiment.
Finally, the math representing these two measurements are merged together giving a relationship between the mass of the unknown object and the current and voltage. Replacing the current and voltage with their “quantum” mathematical versions (via the Josephon effect and the quantum Hall effect), which both contain the fundamental Planck constant, the mass can be directly expressed in terms of h. (If you are interested, check out an overview of the math.)
Historically, this mathematics and experiment on the watt balance has been used with a known mass to accurately calculate the value of h. Flipping the same equation on its head, if a “known” value of h is instead plugged in, then a value for the “unknown” mass, m, may be calculated.
And just with that one mathematical flip, we now have a fundamental definition of the kilogram based on Nature with quantum mechanics being used to describe a macroscopic quantity.
Extreme Accuracy Makes a New Standard
NIST has been building and operating watt balances since the early 1980s in order to nail down our “known” value of h. The latest generation, dubbed NIST-4, began operation in 2015 with specialty modifications to become an international standard for measuring mass. To be a standard, ultimate precision is the goal and NIST-4 is working to master its measurements with an uncertainty to 0.00000003.
The international scientific community is serious about this new definition and there is a deadline to complete all of this work. In late 2014, the International Committee for Weights and Measures (CIPM) established a roadmap of effort toward officially agreeing on the new definition of mass. This plan includes consistent measurements of the Planck constant to within 0.00000005 — placing NIST’s goal into comfortable territory. The end of the road will occur at the 26th Meeting of the General Conference on Weights and Measures (CGPM) in 2018 during which the new unit of mass is expected to be adopted.
Good Accuracy Makes for Extreme Science at Home
This level of extreme accuracy should certainly be left to the extreme scientific national labs such as NIST. However, the foundational idea behind the balance is still one that has been around for centuries. It is with the advancement of our appreciation of the quantum world that we now have mathematics that can relate this type of measurement with one of the most fundamental values representing our Universe, Planck’s constant, h.
So, what if we could now measure — with reasonably good accuracy — h at home? You can … just try building it with LEGO®.
The same team working on the NIST-4 developed a recipe for designing and building an at-home version of the watt balance. For around $400 and with 0.01 (1%) accuracy, masses may be measured at home by using the same technical concept NIST will use in 2018 to provide internationally accepted scientific measurements of the kilogram. The shopping list includes LEGO® (of course), copper wire, off-the-self laser pointers, free data acquisition software, a data acquisition interface (this is the major expense–but you will open up to an enormous new world of experimental opportunities at home!), several permanent magnets, and lots of building and testing fun with the family.
While this might seem a bit over-the-top for an at-home utility, the same device can also take a known value of a mass and measure the fundamental value of Planck’s constant. Tiny physics with big ideas right in your own basement or garage.
Now that the idea of building with LEGO® while doing some excellent experimental physics has you ready to jump right in to start ordering parts, you might first get way more in-depth with the NIST efforts to develop the new standard for the kilogram (download article*). Then, go ahead and dive into the instructions for building it all at home, which is included below for your immediate reference.
Chao, L. S., et al. “A LEGO Watt Balance: An apparatus to determine the mass based on the new SI” [ download ]
* R. Steiner, E.R. Williams, D.B. Newell and R. Liu. “Towards an electronic kilogram: an improved measurement of the Planck constant and electron mass.” Metrologia. 42 (2005) 431-441. [ download ]
A note to the reader: This article requires following special instructions to watch the videos below. It’s also recommended you be on a desktop computer, but if you are on a mobile device (which won’t let you play two videos simultaneously), simply partner with a friend to play the second video.
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There is a long-standing urban legend claiming toilets situated in the Northern Hemisphere flush the draining water with a counter-clockwise rotation, while in the Southern Hemisphere it all spins down clockwise. The Coriolis effect — a real observable effect described by physics — is said to be the culprit. However, if you have experimented with this observation in the past (yes, take a moment to go and check your toilet bowl now), you may have been disappointed to discover just the opposite. You might have tried a different drain and seen even a different rotation in the same house.
Illustration for the Coriolis effect article. A hypothetical situation. The circles are inertia circles. Air mass that is in motion would, if no other forces are present, turn full circle. Credit: Anders Persson
Unfortunately, toilet bowls, sink drains and household bathtubs are too small in scale to allow the effects of the rotation of the Earth to be visible for everyday observation. In fact, if you were standing at the equator, you’d be moving over 1,000 miles per hour, and this rotation speed gets slower as you get closer to each of Earth’s poles. It is this constant rotation, which you don’t even notice, that provides a rotating reference frame for any object moving about the surface of the Earth. Since one full rotation takes 23 hours, 56 minutes, 4.0916 seconds (called a sideral day, per the full rotation of a single spot at the Earth’s surface, whereas the full 24 hour definition is based on the observation of the Sun returning to approximately the same location in the sky), the effect of this rotating frame of reference is quite small on most objects we might observe in our daily lives, like our flushing toilets. On the other hand, physical events on the scale of cyclones clearly demonstrate the clockwise vs counter-clockwise rotations depending on the hemisphere of the storm.
Hurricanes might be incredible to watch on the news, but they are too frightening to experience directly. So, an at home physics experiment was conducted on each half of the world by Destin Sandlin from Smarter Every Day and Dr. Derek Muller from Veritasium, which were cleverly recorded for simultaneous viewing of the results.
Now, here is where the important instructions come in: If you are on a desktop computer, click play on the upper video (occurring in the Northern Hemisphere) and watch for the count down. At just the right moment, click play in the lower video (occurring in the Southern Hemisphere) and watch both videos simultaneously. If you are on a mobile device, have a friend click play on the second video at the end of the countdown. You might also try expanding your desktop web browser to full screen mode (try hitting the key F11) to make sure you can see both clearly. The videos and music are synchronized, so if you don’t think you have them rolling at the same time, reload this page and try again. It will be worth it.
Discover the truth about toilets and see first hand what it really is like to live in a rotating frame of reference (since you probably didn’t realize it before).
This evening just after sunset, the crescent Moon was positioned in a beautiful triangular alignment with Venus and Jupiter. (view the skymap) I took the kids out to try using the binoculars to see the Moon — which they certainly also just used to walk around the yard finding one another! — and to talk a little about the two planets and how cool it is that we can see them with our own eyes.
These slightly in-focus images were taken with a very simple Nikon CoolPix S8100 auto focus in night landscape mode on a tripod.
The HUDF includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, are some of the most distant galaxies to have been imaged by an optical telescope, existing at the time shortly after the Big Bang.
The Hubble Ultra Deep field image, taken in 2003, is considered to be the most amazing image ever created by human beings. A direct view of the Universe 13 billion years ago, it contains over 10,000 galaxies, each of which can contain 100 billion stars, or even more.
The enormity of what this image represents is so awesome and so amazing, it’s really impossible for any one human being to comprehend not only its meaning, but that it can actually be.
And, although this image represents something so spectacular, there is still another image closer to home that is infinitely more special to me, as a husband and father. This might be because it is actually possible to comprehend its meaning, it is possible to understand that it is real, and it is felt deep within my heart that it is the most important and wonderful thing that exists in the Universe.
My two children, now five and two years old, are amazing, and it is simply incredible that they exist. There is almost nothing more exciting and wonderful than the fact that these two children were created and will grow up to be fabulous human beings.
My sense of wonder and awe is amplified because of my many previous experiences with wonder and awe while I’ve spent many years of my life learning about how the Universe works, experimenting in that Universe, and trying to express these exciting understandings to others. As a citizen scientist who thoroughly enjoys a continuous advancement of ones own appreciation and understanding of Nature, it is all that more satisfying to be able to share this appreciation with ones own children.
Sister and Brother, the Princess and Prince.
But, what is even more amazing than my children is that my wife, Michelle, created them. What she went through to nurture these babies and bring them both into the world was absolutely insane. And, this is what makes her so incredible. This is what makes all mothers quite incredible. I think that my wife is so amazing for having created our children and this is one reason why I love her more than anything else. It really was an outstanding feat, and only she could have done it: no one else in this infinite Universe could have created exactly our children. They would never have come to be without my wife, and their entire lives and our lives together as a family could have never existed with her.
There is no other image ever created in all of human history that is more important to me than an image of our children. And, my wife is the one who made that all possible. No one else could have done this amazing thing for me, and that makes her such an absolutely incredible person.
With much love on Mother’s Day. Matthew T. Dearing
Sign up with SciSpy to contribute observations of critters from your own backyard.
Discovery Communications‘ Science Channel recently launched a new iPhone application to engage citizen scientists as mobile field observers right from their own back yard.
With the “sci.spy” app, users can venture into their little domain of the world, and take images of all of the biodiversity that can be find. By selecting a “mission” to categorize the pictures, from general wildlife and bugs in your backyard to natural invasions and pets, anyone can contribute detailed information about their native biological environment from where ever they live.
This sort of broad repository of location-specific identifications could become a very critical tool for professional scientists studying the evolution of ecosystems in which civilized humans thrive, and for those who monitor the ongoing health of our environments. If sci.spy, or other similar databases created by crowd sourced data, continue to develop into massively-utilized tools by both a large user base and with a high frequency of updates, then the power of this resource could be realized soon.
Although the participatory program is entirely free, it does throw in some little banner advertising for upcoming shows on the Science Channel’s family of outlets. For some recent “best of the bugs” images contributed from the early adopting users, check out the “Gorgeous And Creepy” photo gallery.
Artist's concept of a catastrophic asteroid impact with the early Earth. An impact with a 500-km-diameter asteroid would effectively sterilize the planet. The Earth may have experienced such gigantic impacts in its youth, but fortunately today there are apparently no projectiles this large to threaten our planet. Courtesy Don Davis, NASA.
Many of us while growing up and listening to our bedtime stories learned to not freak out and run screaming through the streets if we thought that the “sky is falling.” As little chickens, we were taught at an early age that it was best to be brave, calm, and rational, else be considered a crazed lunatic.
This childhood behavioral bias infiltrated adulthood in the relationship between professional astronomers, policy-makers and national budget-number crunchers. When a scientist expresses probabilistic concerns about the impending doom of our planet from a cataclysmic change of a major impact event, say, in the next 100, 1,000, or 10,000 years, it requires just too much risk of political capital and tax-payer dollars to divert significant budget resources to something that might only be a concern for our uber-great grandchildren.
The simultaneous efforts of two Hollywood studios in the late nineties of the last century tried to get something stirring in our cultural awareness with their mega-disaster flicks, Armageddon and Deep Impact. These features did bring us through the box office (which was certainly their primary goal!), but they did not push us en masse to the round table to prepare for the ultimate defensive plan for our planet.
Combating Earth-bound asteroids, or “near-earth objects” (NEOs), is an unsolved problem, and one that citizen scientists largely ignore because it’s assumed that this issue must be only approached via the domain that has access to the massive amounts of taxpayer dollars and the international collaborations between those nations who can liberally spend all of that money. It’s this requirement of essentially unlimited funds that is the sticking point to making serious progress on defending against an event that may, or may not, happen in the upcoming budget cycle.
The method of defense presented in Armageddon is physically bogus, and reportedly is used as a game for managers-in-training at NASA to test how many impossible things can be identified in the film. Burley, blue-collar heroes racing a doomsday clock and risking their lives on a speeding asteroid to implant nuclear weapons deep inside an iron core, all the while engaging in a romance with Liv Tyler, certainly makes for exciting film. But, if this scenario was ever pending in reality, this method just can’t get the job done.
Bruce Willis is required to destroy an asteroid the size of Texas, which is an extreme and unlikely case as far as NEOs go these days. If we do a little simplification (as any good physics estimation will do), Texas has a land area of 678,051 square kilometers (or, about 262,000 square miles), and assuming this area forms a neat square it would have a length of about 823 kilometers (or, 512 miles, which is a fine approximation even though Texas’ widest part is a bit over 700 miles). We might also say that Mr. Willis’s asteroid is a nice sphere with this same diameter, so its radius would be one-half this distance, or about 412 kilometers.
Now, to blow this very large chunk of rock to smithereens one might expect it would take quite a punch. It would also be important to make sure that not only is enough energy released so that the rock brakes apart, but that it is destroyed to such an extent that smaller fragments aren’t left around that might still be a threat to Earth.
To guarantee this total annihilation scenario, we can calculate the “gravitational binding energy” of the asteroid, which is the amount of energy needed to pull apart all its gravitationally-bound bits out to infinity (or, very, very far away from Earth). For our approximated nicely smooth and solid sphere, we can calculate a back-of-the-envelope estimate from
The value for the mass requires another gross estimation and simplification, even though this value will have a significant influence on the energy required to blow up the asteroid (the energy increases with the square of the mass in the formular above, which can get pretty big pretty fast). Directly verifying composition, density, and actual volumes of asteroids is a critical issue, and is currently a focus of NASA research. In particular, later this year the very large asteroid, or protoplanet, 4 Vesta will be visited by the Dawn mission in July 2011, during which time observations will be taken to learn more about what makes up these tiny almost-planets.
A color image of 4 Vesta taken by the Hubble Space Telescope. Courtesy NASA.
For comparison, 4 Vesta is the largest asteroid body known, right after the much larger protoplanet Ceres, which will also be visited by Dawn in 2015. Coming in at an average diameter of 530 km, 4 Vesta is a pebble in the sky similar to what Mr. Willis is up against. So, for our composition estimation, we’ll use what we already know about 4 Vesta as a reasonable basis for our Armageddon killer.
Again, we’ll approximate that 4 Vesta is also a sphere, so it would have a volume of
V = 4/3 π r3 = 7.8 x 107 km3,
and with its apparent mass of 2.67 x 1020 kg, we have an average density of
Density = Mass / Volume = 3.4 × 1012 kg/km3,
which, after some unit conversions, quite nicely agrees with the published value of bulk density for 4 Vesta of 3.4 g/cm3.
All of this figuring allows us to have a reasonable guess as to the actual mass of the fictional asteroid from Hollywood, which we can head back to the density formula to calculate,
And, finally, the fun part where we plug all of this into our gravitational binding energy formula, being careful to watch the units,
U = 3 (6.67 × 10-11) (9.9 × 1020 kg )2 / 5 (412 × 103 m) = 9.6 × 1025 N m (or Joules).
This seems like a whole lot of Joules (energy), but what is it in comparison to what the human civilization has produced to date? By definition, 1 ton of TNT releases 4.184 giga Joules (109 Joules) of energy, so to reach the gravitational binding energy of Armageddon, we would need to plant a bomb with the power of 2.3 × 1016 tons of TNT. Compare this to the devastating “Little Boy” dropped onto Hiroshima in 1945, which released 15 × 103 tons (kilotons) of TNT, and the largest ever tested nuclear weapon of 57 × 106 tons (megatons) of TNT by the USSR in 1961.
So, a 10-fold order of magnitude increase in energy would be required to save the planet from Armageddon. That’s taking our most extreme explosive technology from megatons to petatons of TNT. This being the case, we might then consider that in the event of a Texas-sized asteroid on a collision course with Earth, we should just hop on the fastest spaceship to Mars and take our chances on the Red Planet.
To be sure, though, asteroids this large just aren’t out there anymore, other than 4 Vesta, which is happily orbiting about the Sun without any intersections with Earth–ever.
You can have some more fun with trying to destroy asteroids–without all of the calculations above–by trying out the tool developed by Michael Wong called the Asteroid Destruction Calculator. Here, the gravitational binding energy is generated, using reasonable assumptions of possible composition, but it also estimates more reasonable energy requirements that would break up an asteroid not to the ultimate safety of infinitely away from Earth, but into small enough particles that would just as safely burn up in our atmosphere upon entry. This “vaporization energy” is determined only as an estimation by extension of actual experiments on Earth of blowing up smaller rocks that might behave similarly to asteroids.
The feature film Deep Impact seemed to be a little more accurate in its scientific basis, but this might largely be due to the fact that the deflection methods didn’t work, and a chunk slams into the Atlantic Ocean killing millions in the ensuing megatsunami.
Of course, movie theatrics aside, the humanity-depleting effects of mega-rocks slamming into the planet cannot be denied. Objects are constantly being sucked into Earth’s gravitational pull everyday, and thanks to our atmosphere and–friction–nearly everything gets so hot that it burns into oblivion long before any living creature can take notice.
Although the movies might make planetary defense seem unreasonable, we must make very clear again that that NEOs the size of Texas on a collision course for Earth are just not present in our Solar System anymore. In the billions of years of our planetary existence, these relics have been devoured by the planets, in particular Jupiter, and their immediate individual impact effects on their collision buddies have settled long ago. In addition, these sorts of enormous objects 1/10 the size of the Moon, if they did exist, would appear rather bright in the night sky, even when still at a safe distance. So, a focused amateur astronomer or one of the several NEO scanning programs in operation today would presumably detect it before it was way too late.
That said, we’ll let out some more good news now: for the majority of asteroids and comets zipping around our solar system today, deflection is theoretically and technically possible. The problem is that implementation isn’t free. and it sure would be nice to do a test run or two before being called in for real action. And, tests aren’t free, either.
Recently, the New Yorker published a narrative about the current struggles NASA is experiencing with fulfilling this civilization-saving task. It features the plight of an astronaut-turned-NEO evangelizer, Russell Schweickart, who now heads the B612 Foundation, which is driven by the goal to “significantly alter the orbit of an asteroid in a controlled manner by 2015.” NASA has money to search-and-destroy NEOs, but the alloted budget just might cover snacks and bagels pre-purchased at the grocery store for departmental meetings. So, the NEO program at NASA certainly could use some loud support.
The article overviews one of these meetings held in 2010 to develop a direction for moving NASA forward in the crapshoot that was once only considered to be a popular Atari game (play now! Can you now calculate the energy from each laser shot?). This meeting, called the The NASA Advisory Council Ad-Hoc Task Force on Planetary Defense, was held in two sessions during 2010, and was co-chaired by Mr. Schweickart. The council’s purpose was to review NASA’s current and future role in the issue of near-earth asteroids, and to create a formal recommendation on what NASA should and should not continue to be doing.
The interesting notes from the first of the two sessions are available online: April 15-16, 2010 Minutes [PDF]
There are many issues that NASA must juggle with here, including political, financial, and scientific. Who is willing to risk one’s political capital to champion the destruction of once-in-an-epoch giant fireballs in the sky, albeit one that can destroy our civilization as we know it? How much of taxpayer dollars can be appropriated to a once-in-an-epoch event, albeit one that can destroy our civilization as we know it? And, with deflection technology really already at hand, how professionally interesting is it to track and monitor orbiting rocks, since a Nobel Prize doesn’t target too many rocks these days?
The bottom line is that the political will and the money are not available from the United States federal government, so the financing of advancing technology–well in advance of pending doom–is not really an option right now, and will likely continue to not be an option for some time. Methods of averting potentially impacting objects have already been proposed, and should be reasonable to implement without too much of a technological leap, if any, although the funding factor will always be an application killer. In fact, according the the task force’s minutes, NASA should stay out of the direct defensive activities, and leave that to those who know how to defend, like the Air Force. Of course, the United States is already over-criticized for being the police force of the world, so why should it now have to be the defender of the planet and of all civilization?
Research on methods of saving Planet Earth from an asteroid on a collision course has been in consideration for quite some time. It seems, however, that only within the past decade have more serious efforts toward planning for a global response been accomplished. Assuming we would have enough warning of a future collision generated from extensive tracking and precise, long-term orbit predictions, the focus has been on deflection of asteroids as opposed to all-out destruction. (As suggested above, even if you could blow up an asteroid to some extent, you will likely only fragment it into an unlimited number of additional asteroids, all still right on target.) By 2004, it seemed that a surge of recommendations and proposals came out of the woodwork, probably due in large part to the invigorated efforts of Mr. Schweickart. The threat is certainly real, but the realities of actually doing anything about it might be even more insurmountable.
Basically, deflection can be accomplished by either exploding a bomb near an asteroid and using the radiating energy to nudge its trajectory, or by landing a propulsion system onto the surface of the speeding rock and directly steer it out of the collision path.
Of primary concern with the former method is the significant unknown of how a particular asteroid will absorb the energy from a nearby explosion. Many asteroids are considered to be porous, or can be composed of water-ice, or metals, or other minerals. Creating a predictable and controlled course correction from a precisely positioned detonation could be quickly rendered useless if the composition of the killer rock was incorrectly assumed. For a discussion on this approach, including detailed calculations and a prediction of what sort of asteroids would be favorable candidates for standoff explosions, read Donald B. Gennery’s Deflecting Asteroids by Means of Standoff Nuclear Explosions [PDF] presented at the 2004 Planetary Defense Conference.
Deflection by direct contact might seem a more controllable approach, and we are already developing the skills required to make such a trip to a potentially colliding asteroid or comet through recent NASA missions (in particular, Deep Impact–not the movie) and others, as well as future NASA projects in progress. This general method as a solution is supported by Mr. Schweickart and the B612 Foundation, and a detailed review was published in 2006 by Izzo, et al. in Acta Astronautica from the International Academy of Astronautics.
Their calculations are applied to the asteroid “99942 Apophis,” which was discovered late in 2004 with initial trajectory measurements predicting a small chance of impact in 2029. Although the impact probabilities have since been reduced, there is still the possibility of Earth’s gravitational pull nudging Apophis’s orbit just right (called a gravitational keyhole) to move it into a future collision trajectory for 2036. In 2013, Apophis will visit near Earth again, and will provide the next opportunity to more accurately calculate its orbit out to 2070 as well as its physical properties. Apophis’s future trajectories and orbit diagram may be interactively explored at JPL’s Small-Body Database.
Apophis was the focus of another detailed study on potential deflection techniques at the 1st IAA Planetary Defense Conference in 2009 (one of the sequels to the 2004 conference):
This paper outlines very specific simulated scenarios on dealing with Apophis and what sort of issues must be considered for tracking, predicting orbits, and deflecting such an object. Of course, although all of this technological study of deflection is quite critical for the long-term survival of our civilization, it just might be out of the realm of the citizen scientist. But, if one is still interested in learning more about the current state of asteroid deflection techniques, the above referenced articles are must-reads to get started.
On the other hand, since there may be no nobler a cause than saving civilization, it would be grand if the citizen scientist could actually play a crucial role. Since one might not be able to be involved in the actual direct deflection of an asteroid (I haven’t yet met a citizen scientists who is ready to land on an asteroid and plant a nuclear device or two, or a billion), but in a more practical effort through backyard observations.
The discovery of new near-earth objects is obviously important since we have not yet found any guaranteed direct-hitting NEO. But, if it is out there, then it certainly needs to be found much sooner than latter. In addition, the continued monitoring of known objects is equally vital, if not more so, because not only can NEO trajectories change as they interact with the gravitational fields of other bodies, but many known objects are calculated with limited data, which increases the error in future predictions of possible close encounters. Additional observations and measurements need to be compiled each time a particular NEO passes close to Earth so that its current orbit may be more precisely determined thereby providing a more accurate prediction of future orbit trajectories.
From a large-scale national budgetary perspective, a higher resolution in NEO orbit calculations is critical for NASA and other world-wide governmental bodies who are willing to participate in protecting the planet. If actual planet-defending programs are launched, it would be rather expensive if we move forward with low-confidence NEO orbit predictions such that we feel the need to blow up every NEO in the neighborhood. By providing as much observational data as possible, orbit predictions can become quite thorough, and governments–and their populations–will have the confidence to take action only on the very rare NEO of a significant size that is almost certainly inching its way toward Earth’s mesosphere.
NASA’s Near Earth Asteroid Count by Size as of December 2010.
The hunting and tracking of NEOs are certainly already in progress by NASA. Their mandated goal is to identify 90% of all NEOs with diameters larger than 1 km by 2020. Of course, it’s difficult to accurately determine what number to take 90% of to know if the goal has ever been reached. But, the current statistics on known NEOs is updated by NASA on their Discovery Statistics page. As of April 11, 2011, the total count of all near-earth objects of all sizes has reached 7,890 and kilometer-sized “large” NEOs at 824.
Major observatories from around the world are participating in the ongoing hunt for NEOs and partner with NASA on their observations. One of the early programs was developed at the University of Arizona’s Lunar and Planetary Laboratory called The Spacewatch Project. Just over twenty years ago they discovered the first NEO with automated observing technology, and they have booked many other important “firsts” in this growing field. Several years ago, but now closed to the public since 2006, Spacewatch hosted a citizen science program where registered volunteers could visually review digital images of the night sky to try to identify fast moving objects appearing in consecutive CCD views. With 43 discoveries of new objects in two years from 52 volunteer reviewers, this program was a great example of connecting scientists with interested participates to collaboratively accomplish something very important to the rest of humanity.
Much of the searching and monitoring is now largely automated. In a very recent example of new, automatic detection, NASA’s Meteoroid Environment Office established a set of fish-eye-style all-sky cameras that record anything that blazes through our night sky. Software then inputs the images, triangulates the object’s trajectory and calculates its previous orbit. (Check out a live view from the cameras.)
However, all of these efforts still need to expand. NASA is effectively using breadcrumbs to fund the programs, and although they are partnering with willing observatories, the massive amount of observational time required to guarantee we will catch Earth-bound objects well in advance is enormous.
Green outline shows the limited monitoring region from Earth; Orange shows the proposed monitoring from satellites; and the rest of the circumference of asteroids remain invisible to our observations. From National Academy of Sciences and Space.com
The biggest hurdle that we face is actually unsurmountable without the help of a network of space-based telescopes existing in their own heliocentric orbits: Observers from the Earth looking into our night sky can only see so much of the Universe. There is a limited swath of space that can be observed at any one time, and NEOs that happen to be passing through that swath at that moment can be observed and analyzed. The majority of objects zipping through our solar system, however, are effectively invisible to us at any one moment, and any NEOs trailing the Earth’s orbit can’t be seen by us until they happen to zip into our field of view; and this could presumably take decades. And when it does happen, it might be too late.
There are proposals to launch satellites that will trail the Earth’s orbit and be able to pick out a wider observational window to find and track potential NEOs. Until this proposal actually gets off the ground–literally–more is needed to continuously observe the entire field of view that we do have to maximize the surveying efforts that is possible now.
The typical citizen scientist wanting to add celestial viewing to their science experience shouldn’t be expected to develop a multi-million dollar deep-space observatory in their own backyard. The real issue, however, is that major observatories are overbooked and highly in demand, so professionals are not always offered the luxury of scanning the skies for transient objects. The amateur, on the other hand, is at his or her own command and may leisurely watch the heavens. The important disadvantage for the amateur and their comparatively low-powered instrumentation is that any observed object of significant size should have already been picked up by an existing automated system. In addition, any NEO that is discovered by a backyard amateur that has never been cataloged before might not provide an early enough detection time-frame for deflection if it actually is on an immediate Earth-crossing path.
However, there is so much out there–or, at least potentially out there–that there can never be too much time devoted to detection and monitoring of NEOs. And, what is better than volunteer efforts from citizen scientists around the world that generates data at no additional cost to NASA?
So, with this in mind, citizen scientists can consider contributing their backyard observing time to the important effort of scanning for NEOs. It should not be considered a low-threshold, entry-level project since a minimum level of equipment, skill, and dedicated time will be required. The IAU Minor Planet Center (MPC), operating out of the Smithsonian Astrophysical Observatory at Harvard, is supported by NASA and carries the responsibly of maintaining a database of confirmed minor planets, comets, and near-earth objects. They have an extensive NEO division, which includes the latest updates of NEO observations, requested confirmations, and many online tools to support the surveying of NEOs.
In particular, the MPC has developed a detailed guide on setting up your own observation system for minor bodies and potential NEOs. Following this guide, Dynamic Patterns Research is currently considering how to design and build a low-cost NEO backyard observatory for citizen scientists who are interested in participating in NEO hunting. One requirement for those interested in participating is the official establishment of your viewing position as a registered observatory. This can be completed by anyone, but a “permanent” site is needed; in other words, your personal authorized observatory shouldn’t move around with your portable telescope, since reported observations will be more valuable for MPC if they originate from the same viewing coordinates. Also, several observing tests are required to be submitted and approved before being registered as an observatory.
If you are interested in beginning your own backyard astrometry program now, then begin by reviewing the extensive guide from MPC. Then, contact us at Dynamic Patterns Research so that we may collaborate with you in our development efforts for designing a system geared just for citizen scientists.
As an exciting goal for setting up your own NEO observatory, later this year on November 8-9, we will be able to experience a very close approach of a rather large asteroid, 2005 YU55. About 1,300 feet in diameter, it will pass within 0.85 lunar distances (just a bit inside the orbit of the Moon). Although 2005 YU55 is predicted to not have any significant threat of hitting Earth within the next 100 years, this year’s flyby will be its closest approach until 2028, when it will pass by nearly half-way to the Moon.
The advantage of additional observations during these close encounters, as suggested above, is that more accurate orbit calculations may be determined from measuring its updated trajectory, which can always be influenced by gravitational interactions during close encounters with any other massive body in the Solar System. And, this is where the NEO-tracking citizen science can collaborate by submitting additional data that NASA can’t get enough of to be ever more precise in their predictions of future NEO orbits.
So, come early November 2011, citizen scientists with their newly-established, personal NEO backyard observatory will be ready to experience the most exciting beta-testing event of a lifetime.
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Download the free PDF report from National Academy of Sciences on their 2009 report on the state of the United States efforts in NEO: Near-Earth Object Surveys and Hazard Mitigation Strategies: Interim Report
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