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 We request that this article be re-evaluated and either withdrawn or modified to correct these misstatements.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/.

https://au.news.yahoo.com/preparations-underway-as-planet-killer-
asteroid-the-size-of-cruise-ship-nears-earth-233328582.html

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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