Asteroid close approaches: keeping things in perspective



On July 25, the Sydney Morning Herald reported on a close approach of a newly discovered near-Earth object (NEO), asteroid 2019 OK. The asteroid was detected at what might appear, to the non-expert, the last minute (a couple of days before fly-by, I believe.) In actuality, the detection and observation of this NEO as it passed by Earth at 70,000 kilometers (43,496 miles) was routine – certainly nothing to panic about.

The Sydney paper quoted four Australian scientists – understandably, since it’s an Australian news outlet. None of those scientists actually observed the asteroid, as far as I can tell. Two of them, in my humble opinion, made much ado about nothing.

“[If it hit Earth] it makes the bang of a very large nuclear weapon – a very large one.”

It didn’t, and it posed no risk of doing so.

“It would have hit with over 30 times the energy of the atomic blast at Hiroshima.”

It didn’t hit. And it posed no risk of hitting. Not to mention that when asteroids do impact Earth, they do not release any nuclear radiation.

“It’s a city-killer asteroid.”

No it’s not. It did not pose any risk of impact with Earth.

“Definitely too close for comfort.”

This close approach did not make me uncomfortable.

Nonetheless, several other news outlets, ranging from (usually) reliable – such as the Washington Post – to flaky (U.K. tabloids), picked up this story, repeating the sensational framing.

On July 26, the Washington Post picked up on this story, surprisingly interviewing only the two seemingly panic-stricken Australian scientists who generated the comments above. The Post’s story reiterated the “city killer” and “nuclear” tropes, which most asteroid scientists I know tend to avoid. It seems odd that a Washington news outlet would not check in with Washington-based experts – such as my colleagues with the planetary defense program at NASA headquarters (for which I am a consultant, and, for the record, no one asked me to write this post). Oh well….

According to NASA’s public web site for planetary defense:

  • A near-Earth object (NEO) is an asteroid or comet whose orbit brings it into or through a zone between approximately 91 million and 121 million miles (195 million kilometers) from the Sun, meaning that it can pass within about 30 million miles (50 million kilometers) of Earth’s orbit.”
  • A potentially hazardous object (PHO) is a near-Earth object whose orbit brings it within 4.7 million miles (7.5 million km) of Earth’s orbit, and is greater than 500 feet (140 meters) in size.”
  • “A NEO close approach is of particular interest when it passes within the distance from the Earth to the Moon…. The Jet Propulsion Laboratory’s Center for NEO Studies maintains close approach tables that are updated daily.”
  • “Small asteroids a few meters in size are detected passing between Earth and the Moon’s orbit several times a month.”

According to NASA’s Center for NEO Studies (CNEOS), 2019 OK was estimated to be between 59 and 130 meters in size. Yes, an asteroid in this size range could cause damage IF it were to explode in the atmosphere or impact water or land. But, again, 2019 OK didn’t, and it posed no risk of doing so.

A global system is in place for finding, tracking, and characterizing asteroids and predicting their future orbits and any possible impact hazards. Detection and tracking of asteroid 2019 OK – though it may have seemed last-minute to some – is evidence that this global system is working just the way it’s supposed to.

Observers around the world – both professional and amateur – report detections to the Minor Planet Center (MPC), which is funded by NASA’s planetary defense program. The MPC analyzes and archives data received and relays observations to CNEOS, also funded by NASA’s planetary defense program. This is what occurred in the case of 2019 OK.

CNEOS verifies observations and predicts future orbits of the asteroid. (No known asteroid is on an impact course with Earth for the next 100 years.) In the case of asteroid 2019 OK, SONEAR, a Brazilian observation team, first detected this NEO and reported its observations to the MPC. Astronomers at McDonald Observatory in Texas also detected 2019 OK and reported its observations to the MPC. Other astronomers received notification of these observations and conducted follow-up observations, also reported to the MPC. The MPC has a public recordof these observations.

In addition to the MPC and CNEOS, the European Space Agency funds the NEODys-2 system, which performs the same functions as NASA’s CNEOS does using different methods, providing further verification of observational and orbit-prediction data.

The Sydney paper reported, “Asteroids this size tend to pass by once every decade.” According to CNEOS director Paul Chodas, a close approach by an object of the size of 2019 OK is predicted to occur perhaps a couple of times each century, and an impact of an object of this size might occur once every few thousand years. It’s important to note, as always, that considerable uncertainty underlies such predictions.

The International Asteroid Warning Network (IAWN) is a multinational organization of space agencies and observatories involved in finding, tracking, and characterizing asteroids, predicting their future orbits, and identifying any possible future impact hazards.

The multinational Space Mission Planning Advisory Group (SMPAG) is responsible for preparing for an international response to an actual asteroid impact threat (none have, as yet, been identified) through the exchange of information, development of options for collaborative research and mission opportunities, and the conduct of asteroid impact mitigation planning activities.

All of these organizations are in close communication with each other (and I have worked with representatives of all of them).

I realize that in the global, 24-7, news and information environment, where journalists’ deadlines are always NOW, we can’t expect to see as much careful and thorough reporting as we’d like to. In the case of the Sydney paper’s story, I don’t know who reached out to whom: reporter to scientists, or scientists to reporter…. I also realize that we’ll likely never wean journalists off grabby headlines and leads (city killer etc.).  After working on four workshops for the media on planetary defense over the past year, I can only hope that, over time, we might see some improvement.



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