LIGHT FROM A MORNING STAR
Over a century ago, on 30th June 1908 at 07:17 local time,, Earth experienced an ‘unusual’ event. In a sparsely populated region of the Siberian Boreal forest, located in a large swathe of territory now known as Krasnoyarsk Krai, an object reputedly in the order of 50 – 190 metres in size raced towards our unsuspecting planet. Eyewitness accounts and subsequent scientific studies have suggested that the object was likely a meteorite which, rather than physically impacting the surface, experienced a massive airburst detonation; releasing the estimated energy equivalent of 3 – 30 megatons of TNT above the heavily forested territory. For comparison, the Castle Bravo U.S. thermonuclear test unexpectedly produced a blast equivalent to about 15 megatons of TNT; a detonation that devastated the Bikini Atoll region.In total, the ensuing shockwave would flatten an area of forestry of about 2,150 square kilometres, creating a large radial pattern that centralised around an area of peat bog with scorched trees – but with no discernible impact crater. Due to this forensic discrepancy, other reasonable theories for the devastation have also been suggested, but the event is broadly considered to be an airburst incident.
This curious tale from the remote regions of Siberia would become known as the ‘Tunguska event’ – the largest known collision event on Earth in recorded history – and it continues to be used as an emblematic, cautionary tale to encourage broad international discussions on the perennial hazards, and possible risks, posed by future meteoroid impacts. A concerning rise in similar airburst observations (due to the increasing population density and technological distribution in remote regions – not an increase in the frequency of impact events) reveal that the Tunguska event was not such an ‘unusual’ event after all within the history of our living planet, with Earth experiencing several smaller, less energy-intensive detonations in our protective atmosphere every single year. According to the Centre for Near Earth Observation Studies, Earth’s orbit intersects with a lot of neighbouring objects, and we can only ever observe a limited quantity of this material due to constraining parameters like the opposition arc effect (i.e., sufficient angular illumination of these dark objects by the Sun, to enable telescopes to physically ‘spot them’ from Earth’s shifting position).
The mental impression of a ‘significant collision event’, when it is mentioned in reference to wandering rocky or metallic bodies in outer space, is something all too familiar to those who consume these dramatic literary stories and cinematic depictions as part of popular media. The storylines are all too familiar: an asteroid, or similar astronomical body traversing Earth’s usual orbit, is unfortunately nudged onto a collision course with our planet, leading the protagonists to mount a heroic rescue effort to save our planet (or ensure survival of a select numbers of the human population at least). These pop cultural depictions are usually complete with flashy CGI graphics, spectacular soundtrack, flag waving, and a memorable title – often with dodgy scientific justifications for the unfolding event, or the proposed solutions that will lead to humanities’ salvation (or not).
The reality of Near-Earth Objects (NEO), Potentially Hazardous Objects (PHO), and Earth Crossing Asteroids (ECA) presents abundant reference material for the future of such fantastical, spectacular stories. But, as noted above, there is a very real historical precedent for significant impact events – perhaps not on a planetary-level scale as frequently popularised, but certainly a ‘city-killer’ classified object or volumes of smaller material is more plausible. Earth’s dynamic geology physically covers up most of the visible scars from the Paleolithic record and other earlier periods of geological time. But, some larger trace forensic remnants are still readily apparent; as is the case of sites like the Upheaval Dome (United States), Morokweng (South Africa), René-Levasseur Island (Canada), Shoemaker (Australia), and Barrington (United States) craters, amongst many other identified trace boundaries from past impacts. Moreover, our species presently occupies (or at least controls usage of) a growing amount of our planet’s available landmass, a trend that will likely continue in the future, ensuring that the odds of a significant event over a populated urban area increases across the grand theatres of time. Meteorite collisions are very much a fact of life for Earth and will remain so for the foreseeable future as our planet continues to clear out the debris field in its orbital range – 'left overs' from formation during the Hadean aeon and also through chance encounters with ancient materials occasionally migrating towards the innards of our Solar System. Further to this, the Tunguska episode, and similar incidents widely documented in modern history, demonstrate that the objects need not physically impact the planet's surface to cause enormous, wide-ranging infrastructure damage or far-reaching service disruptions.
Given the relative uncertainties and perennial risks posed by future collisions with asteroids and other proto-planetary bodies, there are already a number of formal Earth-observation programmes established by numerous national space agencies and private monitoring-survey systems. These include NASA’s Centre for Near Earth Object Studies (the successor of the Near-Earth Asteroid Tracking system, itself a successor to the Palomar Planet-Crossing Asteroid Survey), ESA’s Planetary Defence Office, EURONEAR, and China’s Schmidt CCD Asteroid Program (SCAP), amongst many other competing near-Earth object astronomical surveys. Recent (though acknowledged to be severely limited) observations have already uncovered about 25,000 Near Earth Asteroids, over a hundred short-period near-Earth comets, and a number of other solar-orbiting meteoroids large enough to visually register on tracking systems – all of which have been silent companions of our planet’s orbital range since the formation of the Solar System. This is the 'normal' reality of our orbital region.
ROAMING THE NEIGHBOURHOOD
The tentative nature of the risks posed by these objects is, perhaps, best illustrated by the highly restrictive observational windows and aggregated knowledge we possess for many flagged bodies of concern; sometimes only consisting of 2–5 static frames taken days apart, and identified only when there is sufficient data available for surveys to reliably plot a measurable trajectory. Concerningly, some city-killer objects have only been discovered days after an unobserved near miss – as with the infamous case of 2002 MN; a 73-metre asteroid, similar in scale to the Tunguska body, which blindly came within 120,000 kilometres of Earth’s surface from the direction of the Sun. Objects from the Sun’s direction are notoriously difficult to detect, due to the overpowering glare from our local stellar body which over saturates a detector's aperture. Taking another, well-studied example, observations and orbital projections for 99942 Apophis – a Near Earth Asteroid, measuring about 370 metres – have recently ruled out a collision probability over the next foreseeable century, despite a number of concerning, but predictable close approaches (including a perilously-close approach of five-times the Earth’s radius expected in 2029). Several other close approaches are predicted over the forthcoming fifty years, however, the future hazards posed by this particular body remain uncertain. Despite the highly unique risks posed by NEO, impact probabilities are low, if not rare, per annum, but across expanses of deep time, these possibilities can fatally add up to real-world implications.
Orbital trajectories are naturally perturbed by any number of gravitational influences, each tugging on a body and its own native gravitational field; drag exerted by the Solar, Earth and Lunar fields, as the target body of interest continues to intersect and interact with these condensed regions of space, in addition to the faint gravitational tugs from the larger outer planets. Over time, these tugs gradually build up and, sometimes, gently nudge Near-Earth Objects onto potentially fatal courses with our homeworld. These ‘dynamical chaos’ effects are accumulative, taking many decades, centuries, or perhaps millennia, to manifest; ensuring that our predicted measures of a chance collision probability will become redundant and, therefore, will need to be periodically revised over protracted timeframes. The trajectory of any NEO today, may have been set forth in motion millions of years ago, by any number of close approaches to another's gravitational fields, before subsequent nudges refined these unfortunate trajectories throughout the ensuing aeons. Our observations today, may one day prove insightful for future astronomical observations to predict the immediate behaviours and measurable perturbations of these hazardous objects – rocky and metallic bodies that, due to the physical limits of our monitoring technologies, may not be physically observed for decades, or perhaps even centuries before they emerge from the interplanetary darkness. Of note, there is already an increasing subset of ‘lost’ astronomical objects that are simply not routinely observable again. Preserving a record of these past observations, therefore, provides a vital data point for posterity to compare and refine their own collision probabilities with next-generation surveys, while ensuring that NEO behaviours and orbital modelling remain accurate. In the very least, such information may enable posterity generations to prepare better assessments of our planetary orbit for future NEO studies as part of a best practice approach under the precautionary principle or, perhaps, take mitigative or preventative actions in the face of anticipated collision events.
FOOTNOTING FOR POSTERITY
The particular focus of our NEO almanac is to simply chronicle our ongoing identification of hazardous asteroids, alongside the risk posed by other types of potentially hazardous objects currently occupying Earth-intersecting orbits, and preserve our measurements of their orbital periods, so that this data may be reliably compared with future observations as part of a dynamic, multi-century NEO observatory archive. The simple nature of the challenges associated with NEO observations, and ensuing predictive scenario analysis, requires the implementation of long-term monitoring for these bodies, and their respective trajectory properties which, more often than not, fall outside of the narrow timescales remits associated with research projects, funding grants, operational lifespans of observational equipment, and also the professional careers of those who devote their lives to this essential field – perhaps, even their entire lifespans. To complement this ongoing archival work, the foundation plans to utilise revised
‘static’ versions of this catalogue, and supporting materials, as a basis for addressing the various semiotical challenges associated with memory-retention customs, in addition to supporting our secondary goals of establishing public outreach, education and creative engagement activities with this unique 'alternative heritage'.
Notes to the catalogue: The NEO Almanac is consolidated to simply preserve past observations of NEO as comparative data for future observations of these same objects. Given the relative distance of these remote observations, and difficulty in establishing trajectories over repeated observation periods, there are some conflicting accounts of information already present for the same objects, measured by independent parties. Any large divergences in figures are noted after the defined ‘formally-accepted’ observation data; properties accepted by a majority of observational institutes. No judgements or independent assessments of the risk profile associated with any of the listed NEO and other lost bodies has been undertaken, nor does the foundation actively employ observational instruments for NEO studies. The entire catalogue remains an active document, subject to updates, amendments, and further peer-review, in addition to future observational data for these objects.
Page last updated: 28 Oct 2021