Tunguska, Chelyabinsk, Berlin, and New York

(See the previous post.) After my article on the Tunguska Event of 1908 was published, it was removed from This Month in Astronomical History (https://had.aas.org/resources/astro-history) because several members of the Planetary Sciences Division of the AAS sent this letter to the senior editors at the AAS Historical Astronomy Division. 

As senior members of the astronomy community who have spent much of our professional lives studying asteroid impacts and planetary defense, we are concerned by some of the misstatements and omissions in the short article on Tunguska from the AAS Historical Astronomy Division published in the AAS News Digest of 6 June. It fails to represent the currently understood risk from asteroid impacts and the considerable ongoing effort to protect our planet. We request that this article be re-evaluated and either withdrawn or modified to correct these misstatements.

The first half, which is basically a history of the Tunguska event and the early efforts to understand it, does not need much work, although the lengthy discussion of whether this was a strike by an asteroid versus a comet is misplaced; it was a cosmic event by an object in orbit crossing the Earth’s, and further detail hardly matters. There is no established evidence that we know of recovered meteorites associated with Tunguska, and we now know the frequency of impacts of this size. Tunguska was the largest such strike in history of a size expected every couple millennia, which played a critical role in alerting humanity to the real danger from cosmic impacts.

With the comments about the Chelyabinsk impact this story goes off-base. The statement that more than a dozen people were killed by Chelyabinsk we believe is false, and needs to be either documented or removed. The statement that Earth impactors are all on orbits interior to ours is incorrect, it should instead state that impactor orbits must cross the Earth’s orbit, thus are both interior and exterior in different parts of their orbit. Chelyabinsk was not detected by telescopes before impact, it came from close to the dirction [sic] of the sun and could not have been seen in the night sky. The writer seems to have conflated Chelyabinsk with the observations of asteroid 2018 LA, which was observed in the night sky by a survey telescope some hours before impact. In fact, by now 8 small asteroids have been discovered telescopically before impact, a tribute to our ever improving search capabilities.

The size (energy) of the Chelyabinsk impact should be noted, and that we expect something of this size (energy) to hit the Earth about once in a few decades, so it is not unusually large or energetic compared to the observed flux of impactors. It is important to tell readers that the Earth is under constant bombardment by NEOs (Near-Earth Objects, a term chosen to include both asteroids and comets), and that thanks to an international program to detect NEOs we know how often such strikes take place and have a fair chance of predicting the next big one. It is a disservice to imply that astronomers are neglecting this issue or don’t know how to calculate orbits. There is a robust international program studying planetary defense, and the DART experiment" "was notable as the first active defense experiment. The reference to the book “The Asteroid Hunters” is useful, but the other items mentioned at the end of the article are not needed. In particular, any means of diverting an asteroid from a collision course takes time (weeks or months minimum, or even years), so last-minute (or hour) detection cannot prevent an impact.

We are concerned not only by mis-statements of fact in this article, but by basic confusion about the asteroid impact hazard and how astronomers and others are dealing with it. That should be the real lesson of the Tunguska event.

Alan Harris (Former Secretary-Treasurer of DPS, 1995-2001)

David Morrison (Former Secretary-Treasurer of DPS, 1971-1977, and Chair, 1980-1981)

Clark Chapman (Former Chair of DPS, 1982-1983)

We have been further assisted in documenting Tunguska by Mark Boslough, who is not a member of AAS or any Division. We attach an abstract under preparation for an upcoming GSA meeting with him as first author, the other three of us as co-authors, and many additional experts in the field of impact dynamics."

First, I fixed the egregious error. I had accepted the initial news reports from Chelaybinsk at face value and did not go back and check. After the emergency responders worked the scene and victims were sent to hospitals, it was found that no one had been killed. 

I also clarified the language of the celestial mechanics to remove ambiguity. I had written: In addition, they orbit between the Earth and Sun and in the glare of our star are often lost to sight. They also identified the salient fact that the objects are lost to sight: "Chelyabinsk was not detected by telescopes before impact, it came from close to the dirction [sic] of the sun and could not have been seen in the night sky."  

They claimed, "There is no established evidence that we know of recovered meteorites associated with Tunguska..." It is true that no iron or nickel-iron meteorites have been recovered. However, they ignored 100 years of evidentiary reports from the USSR and  Russia.  Every criminologist knows the maxim of Edmond Locard: "Every touch leaves a trace."

It is from this point that the astronomers, as they say, "go off-base." They wrote: "The writer seems to have conflated Chelyabinsk with the observations of asteroid 2018 LA, which was observed in the night sky by a survey telescope some hours before impact." My grammar was quite clear. There was no conflation. I wrote: Asteroid 2018 LA exploded over Botswana (2 June 2018) and was only the second asteroid detected in space prior to impacting over land.¹⁷  And that is the plain truth. 

In an email to my editor, I said that from there, they sound like the government scientists in a science fiction movie. "We have this under control," they say, and then Godzilla comes out of the sea. The astronomers wrote: "In fact, by now 8 small asteroids have been discovered telescopically before impact, a tribute to our ever improving search capabilities." 

I confess that I soft-pedaled the re-write by acknowledging the work of NASA. 

[quote] On 21 January 2024, NASA’s Scout Impact hazard assessment system identified a meter-sized asteroid (later designated 2024 BX1) 95 minutes before it impacted the atmosphere over Germany, possibly leaving debris 60 km away in the Czech Republic.¹⁸ [close] 

I did not point out that the asteroid was first spotted by an amateur who reported it to the International Astronomical Union 27 minutes earlier. From there, NASA picked up the report and tracked the object. NASA did not detect it first. (See: "Asteroid 2024 BX1: From a Light in the Sky to Rocks on the Ground" by Bob King, Sky & Telescope, 26 January 2024 here: https://skyandtelescope.org/astronomy-news/asteroid-2024-bx1-from-a-dot-of-light-to-fireball-to-rocks-on-the-ground/.

More to the point, their complaint of 12 June 2024 could not have predicted the explosion of a meteor over New York City on 16 July 2024.

As for planetary defense, there is no doubt that any mission would require preparation, which is lacking now. 

I had the good fortune to meet Dr. Claudio Bombardelli when he was a visiting researcher here at the University of Texas. I attended a lecture on the DROMO orbit plotting program. In that, he spoke of rescuing Mumbai by diverting a meteorite to strike in Kazakhstan, the lesser of two evils (absent a consultation from that government). What impressed me most was the synthetic (theoretical; mathematical) solution to orbit plotting with minimal data and minimal time. 

I sent my rewrite forward to the editorial committee of the AAS HAD and there was no reply from them or the Planetary Division. 

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PROBLEMS WITH POP SCI (PART 2)

The Tunguska Event of 1908

[This article was accepted and published by the Historical Astronomy Division of the American Astronomical Society for webpages "This Month in Astronomical History" for June 2024. It was then pulled on the insistence of several members of the Planetary Sciences Division of the AAS. See above for September 19.]

Ten thousand kilometers from the blast site in central Siberia, particulates in the atmosphere rendered the night sky in London bright enough read a newspaper.¹ Seismographs at Irkutsk and Kirensk (1200 km and 500 km distant, respectively) recorded the impact which was assumed to have been a meteorite.² Nearly twenty years passed after that morning on 30 June 1908 before scientists could trek over 3000 km from Moscow to the Tunguska river area of what is today Krasnoyarsk Krai in the Evenk Autonomous Okrug. (See Fig. 1.) Expeditions and field work from 1927 to 1932 gathered remembrances from witnesses; occasional explorations into the 21^st century still have provided little evidence to classify the impacting object as a meteor, asteroid, swarm, comet, or black hole.^{3,4,5,6,7,8,9} Parsimony and the standard of extraordinary evidence to support extraordinary claims have brought most astronomers to assert only that a stony meteoroid about 30 to 50 meters in diameter exploded 10 to 20 kilometers above the ground.^10,11

Leonid Alexyevich Kulik led the first astronomical expedition to the region beginning in February 1927 and arriving in late March. Kulik found the blast site in June. The initial challenge was to identify the exact location. Sending his report to Moscow where it was read to the Russian Academy of Sciences by Academician Vladimir I. Vernadsky, Kulik wrote: “On account of the absence within hundreds of kilometers of any astronomical points and because of the complete unreliability of the maps available for this region, I can only approximately determine the place of the fall as lying in 61°north latitude and in 71° east longitude from Pulkovo.” (Pulkovo Observatory is 30° 19’ 54” east of Greenwich.) An earlier investigation (1924) by Vladimir Obruchev, who extensively explored Siberia, estimated the locale center as 60° 20’ north and 102° 0’ east.³  The fall site is now accepted as 60° 57’ north and 101° 57’ east.¹³

Although latitude and longitude were in some doubt, the site itself was unmistakable. Twenty years after the event, the fallen trees were radii pointing to a depression. The image is iconic. (See Wikipedia, Encyclopedia Britannica, etc.) Destruction covers 680 sq. km.³ and damage to the terrain covers 8000 sq. km.¹³ The blast site was obvious by inspection. However, finding the actual fall site, crater, or craters, and the attendant debris has proved less tractable. Over the past century, several expeditions and research projects have unearthed some evidence and more clues to support various theories—but little else.  

In 1988, Andrei E. Zlobin, visited the area, and he wrote: “During the expedition of 1988, in July 24 the author arrived at Pristan camp near the coast of the Khushmo River. He was there from July 24 to July 26. Before returning to Kulik's Zaimka main camp, the author investigated the shoal of the Khushmo River near Pristan with the purpose to find stones which looks [sic] like meteorites.”¹⁴ Zlobin collected 100 samples, three of which were strongly suggestive of being meteor fragments (Fig. 2). 

Approaching the centenary year, motivations were reinforced and another expedition was launched, headed by Luca Gasperini, a marine geologist from the Italian National Research Council. They were rewarded with a “magnetic anomaly” at the bottom of Lake Cheko, which itself has an intriguing conical cross-section.^4,5Yet another exploration and reconsideration apparently dashed those hopes. Lake Cheko is not unique: other depressions in the area also filled with water share its geomorphology and age of 1200 years.¹⁵  Less surprising than the event itself, Gasperini, et al., quickly published a reply.¹⁶ The details of the Tunguska Event remain unsettled and open to continued investigation.

Another such event could be probable within our lifetimes, certainly within the next 200 to 1000 years.⁵ Smaller landfall strikes and near-surface impacts with the atmosphere are more common.

On 15 February 2013, a superbollide meteor in Chelyabinsk, Russia, injured over 1200 people. (Reports were has high as 1500.) The injuries are considered secondary, the result of broken windows and other debris, rather than from the meteor per se. Asteroid 2018 LA was the second asteroid detected in space prior to impacting over land¹⁷exploding over Botswana 2 June 2018. In that case, images had been captured by NASA’s Catalina Sky Survey eight hours earlier, although no determination of the path of asteroid had been computed. On 21 January 2024, NASA’s Scout Impact hazard assessment system identified a meter-sized asteroid (later designated 2024 BX1) 95 minutes before it impacted the atmosphere over Germany, possibly leaving debris 60 km away in the Czech Republic.¹⁸

Astronomer Carrie Nugent published her appeal, The Asteroid Hunters (TED Books Simon & Schuster, 2017) and recorded a TED Talks lecture. First, few researchers are actively scanning the solar systems for “Earth grazers.” Also, of necessity, the objects are small and therefore difficult to detect. Then, there is problem of what to do about any detection. NASA’s Double Asteroid Redirection Test (DART) of 8 October 2022 was successful¹⁹ but the Planetary Defense Coordination Office was created only in 2016 and this was its first proof of concept mission.²⁰

Rapidly calculating the intersection orbits for such a mission is critical to any last-minute attempt to deflect an asteroid. Among the scientists working on new solutions to celestial mechanics is Claudio Bombardelli of the Universidad Politécnica de Madrid who in May and June 2024 was a visiting researcher in the Department of Aerospace Engineering and Engineering Mechanics at the University of Texas, Austin. (See Fig. 3). Bombardelli is a member of a team that developed a fast orbit propagator, called DROMO, a generalizable method, which makes use of high speed computers to solve complicated problems in orbital mechanics such as the interception of near-Earth objects.²¹ Their work allows energy-efficient, low-thrust solutions that can be critical to the rapid-deployment scenario of shepherding an asteroid away from contact with Earth.²²

References

1.  Sagan, Carl. (1980). Cosmos: New York: Random House. page 73. 

2.  Bobrovnikoff, N. T. (1927). “A Remarkable Meteorite,” Publications of the Astronomical Society of the Pacific, 39, 382-384. 

3.  Astapowitsch, I. S., (Lincoln LaPaz and Gerhard Wiens, translators). 1940. “New Data Concerning the fall of the great [Tungusk] Meteorite on June 30, 1908, in Central Siberia,” Popular Astronomy. Vol. 48 p. 433- 1940 

4.  Gasperini, Luca; et al. (2007). “A possible impact crater for the 1908 Tunguska Event,” Terra Nova, 19: 245-251. https://doi.org/10.1111/j.1365-3121.2007.00742.x

5.  Gasperini, Luca; Bonatti, Enrico; and Longo, Giuseppi. (2008). “The Tunguska Mystery—100 Years Later,” Scientific American, June 30, 2008. https://www.scientificamerican.com/article/the-tunguska-mystery-100-years-later/  

6.  Foschini, L; Gasperini, C; et al. (2018). “The atmospheric fragmentation of the 1908 Tunguska Cosmic Body: reconsidering the possibility of a ground impact,” arXiv:1810.07427v2 [astro-ph.EP]

7.   Gladysheva, Olga G. (2020). “Swarm Fragments from the Tunguska Event,” Monthly Notices of the Royal Astronomical Society, 496. 1144-1148.

8.   Gladysheva, O. G. (2023). “The Structure of the Tunguska Comet,” Earth and Planetary Science, 3(1), 1–8. https://doi.org/10.36956/eps.v3i1.924

9.  Jackson IV, A, A; Ryan, Michael P. 1973. “Was the Tungusk Event due to a Black Hole?” Nature, vol. 245. September 14, 1973.

10.  Chaisson, Eric; and McMillan, Steve. (2008). Astronomy Today, sixth edition. Pearson Addison Wesley.

11.  Murdin, Paul; and Penston, Margaret (eds). 2004. The Firefly Encyclopedia of Astronomy. Richmond Hill, Ontario: Canopus Publishing. 

12.  Kulik, L. 1935. “On the Fall of the Podkamennaya Tunguska Meteorite in 1908,” Meteor Notes, 1935A, 43. Translated by Lincoln La Paz and Gerhardt Wiens, Edited by Frederick C. Leonard and H. H. Nininger. Published originally in the Journal of the Russian Academy of Sciences, 1927A.

13.  Astapowitsch, Igor. S. (1938). “On the Fall of the Great Siberian Meteorite, June 30, 1908,” Popular Astronomy, Vol. 46, pg. 310, July 1938. 

14.  Zlobin, Andrei E. (2013). “Discovery of Probably Tunguska Meteorites at the Bottom of Khushmo River’s Shoal,” arXiv:1304.8070 [physics.gen-ph]

15. Rogozin, D. Y.; Krylov, P. S.; et al. (2023). ”Morphology of Lakes of the Central Tunguska Plateau (Siberia, Evenkia): New Information on the Problem of the ‘Tunguska Event 1908’, Doklady Rossijskoj akademii nauk., Number 510, May 2023. https://journals.rcsi.science/2686-7397/article/view/135850reported in “New evidence refutes the hypothesis that Lake Cheko is a result of the Tunguska Event,” Russian Center for Science Information, Federal Research Center, 25 May 2023. https://ksc.krasn.ru/en/news/Ozero_cheko/

16.  Gasperini, Luca; Bellucci, Luca Giorgio; et al. (2023) “Comment on Rogozin, et al., (2023), Morphology of Lakes in the Central Tunguska Plateau (Krasnoyarsk krai, Evenkiya): New Data on the Problem of the Tunguska Event of 1908.,” Seismology, Vol 513, p 1200-1203.  

17.  Jenniskens, Peter, et al. (2021) "The impact and recovery of asteroid 2018 LA," Meteoritics and Planetary Science, 56 (4), 844-893.

18.  https://www.jpl.nasa.gov/news/nasa-system-predicts-impact-of-a-very-small-asteroid-over-germany

19.  https://www.nasa.gov/news-release/nasa-confirms-dart-mission-impact-changed-asteroids-motion-in-space/

20.  https://science.nasa.gov/planetary-defense-dart/

21.  Bau, Giulio; Hunh Alexander; Urrutxua, Hodei; Bombardelli, Claudio; Peláez, Jesús. (2011). “DROMO: A New Regularized Orbital Propagator.” International Symposium on Orbit Propagation and Determination, 26–28 September 2011, IMCCE, Lille, France.

22.  Bombardelli, Claudio, et al. (2013). “The ion beam shepherd: A new concept for asteroid deflection,” Acta Astronautica,  Vol. 90, Issue 1.

Fig. 1. Relative distances from Tomsk (pop. 500,000) to Tunguska crater and from Kansas City, Missouri, to the Black Hills of South Dakota, about 12 hours by superhighway or two months by other means. 

Fig. 2. Zlobin’s Figure 2 showing three likely meteorites recovered from the region of the 1908 event. (“Discovery of Probably Tunguska Meteorites at the Bottom of Khushmo River’s Shoal,” arXiv:1304.8070 [physics.gen-ph])

Fig. 3. Claudio Bombardelli explains the DROMO system at the University of Texas (Austin), 9 May 2024.