By Duncan Steel 02/05/2019


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Astronauts, astronomers, planetary scientists, space researchers and aerospace engineers are meeting near Washington DC to discuss how we might deal with any asteroid found to be heading for a cataclysmic collision with Earth, perhaps causing a global catastrophe. That is, if it was actually found before it caught us unawares. 

As I type this I am sat in a large, darkened room at the University of Maryland, just north of Washington DC. There are several hundred researchers here (and lots of press), listening in this session to talks about how an asteroid named Apophis is going to make a close fly-by of the Earth in 2029, on Friday April 13th. The world’s media are already full of articles about the prediction, for example here and here and here.

Images of asteroid Apophis obtained using massive radar systems in Puerto Rico and California, and modelled shapes indicting its various spin axes.

This will not be an unlucky Friday the 13th: we know it is going to miss, as we have done for some years. It will come so close, though, that it will be visible to the naked eye if you are in Europe or Africa. Expect many people to travel to watch it, just as many chase eclipses, because this is (we hope) a once-in-a-lifetime opportunity.

Certainly there will be astronomers diligently watching Apophis as it passes us by, and the talks I am listening to this morning concern plans for such observations, the possibility of sending one or more spacecraft to rendezvous with the asteroid (which is only about 340 metres in size), and also theoretical studies concerning whether the body – which (from radar data) appears to be a two-lump peanut-shaped spinning object – might be split apart during the close approach by the tidal force due to Earth’s gravity.


So Apophis will not strike our home in 2029, although an Earth impact by this asteroid in 2068 is still thought to be possible. The conference I am attending, organised by the International Academy of Astronautics, is called Planetary Defense [sic] 2019, and it is the sixth such biennial meeting.

In this context Defense/Defence is concerned with trying to predict impacts on our planet by asteroids or comets, and being able to mitigate their effects. That is, with some warning at least people could be evacuated from the target region of a small impactor; and with plenty of warning we might be able to divert a larger asteroid. As our mantra goes, the dinosaurs went extinct because they didn’t have a space programme.

As evidenced by who is attending the conference, this is a subject that is now taken very seriously by the world’s major space agencies. The meeting was opened on Monday with a keynote address by James Bridenstine, NASA Administrator and a direct appointee of the President.

NASA Administrator James Bridenstine addressing the opening session of the Planetary Defense Conference.

When I started out in this field thirty years ago, people laughed at the idea that an asteroid could slam into our planet and cause mayhem. Surely this is the sort of thing restricted to the distant past, such as the dinosaur wipe-out 65 million years ago?


Unfortunately not. Although really big asteroid or comet impacts on the Earth are extremely rare – the dino-killer was at least 10 km across – hypervelocity arrivals by smaller objects occur more often. The best-known (in terms of public consciousness) was the Tunguska event in 1908, when a rocky body about 50 metres across went bang over Siberia. By ‘went bang’ I mean it exploded in the atmosphere at an altitude above 10 km, releasing energy equivalent to a ten megatonne hydrogen bomb (around a thousand times the Hiroshima atomic weapon), laying waste to some thousands of square kilometres of largely-unpopulated forest.

More recently, on 15th February 2013, a rocky object almost twenty metres across arrived in the early morning just south of the city of Chelyabinsk in eastern Russia. The energy released as the projectile flared far brighter than the Sun was equivalent to about half a megatonne of TNT. Some people were blinded. Over 1,200 were hospitalised with injuries caused mostly by the blast wave that shattered thousands of windows, the flying glass hitting people still looking at the trail left by the small asteroid as it had burned up on atmospheric entry. You see the meteor immediately, at the speed of light; the blast wave follows a couple of minutes later, propagating down at the speed of sound. It’s a wonder that no-one was killed. We may not be so lucky next time.

I knew already of similar events during the past century – a blast over Amazonia in 1935, another near Indonesia in the 1990s, and others – but in just the past 24 hours a kind correspondent (Steve Hutcheon) has alerted me to one that occurred in November 1919 over Michigan and Indiana, being seen across a wide area and causing broken windows and power outages (one effect of massive meteors is that they can generate an electromagnetic pulse that overloads power cables, causing them to trip out). I’ve printed out various reports from the newspapers of the day, including one from the Washington Times, and pinned them to a poster board here. It seems that none of the locals knew about this event, which has its centenary this year.


It’s now Wednesday here, and there is a series of talks being presented about a space mission called DART: Double Asteroid Redirection Test. This is due for launch in 2021, and in 2022 it will ‘attack’ a small asteroid. More precisely, the idea is that the spacecraft will impact the smaller component of a binary or double asteroid named Didymos. An amazing discovery in recent years is that many asteroids have moons, or might comprise binary pairs whereby there are two large rocks which are gravitationally-bound to each other, looping around their mutual centre-of-mass, whilst also orbiting the Sun. Didymos was thought to be a single body about 800 metres across after it was first spotted in 1996, but some years later it was realised that apart from that main component there is also a smaller companion around 170 metres in size. This is sometimes informally referred to as ‘Didymoon’.

The target of the DART mission, then, is Didymoon. The idea is to slam the spacecraft into that object, excavating a crater and throwing some material outwards. The overall effect will be to impose a force on the body, perturbing its orbit around the main part of Didymos (‘Didymain’), and how much that orbit alters will enable us to work out the overall effect of the impact. With such information it is hoped that we will gain a better understanding of how to go about diverting an asteroid heading for Earth, should such an object ever be identified. It’s unlikely we would need to do so anytime soon (say, the next century), but with advance knowledge we’ll be better prepared to intervene should we need to do so.


This post is intended as a status report, and I will provide an update later. One part of the NZ media has rather belatedly recognised that this conference is occurring, copying a report from the AAP. However, there is no-one from Australia here. Out of around 300 attendees, there are just two from the southern hemisphere: myself from New Zealand, and my old friend Gonzalo Tancredi from the University of the Republic in Montevideo, Uruguay. We’ve joked that we could form a voting bloc in a hemisphere versus hemisphere debate, and force those up north to do what we think is right.

That is written just in jest, but there could be a serious undercurrent. As part of the Planetary Defense Conference there is a day-by-day exercise underway, in which an evolutionary scenario is examined in which a small FICTITIOUS asteroid has been discovered, and considered to be on a collision course with Earth in 2027. Thing is, although it quickly becomes almost-certain (based on astronomical measurements) that the asteroid will strike the Earth, it is not known precisely where the impact will be. The line that defines possible impact locations stretches from near Hawaii eastwards and across the United States, and then across the Atlantic and parts of Africa. The pertinent question here is this: if the actual impact point eventually were identified, and it was long enough in advance (a few years) such that the asteroid might be nudged, then what are the implications of doing that nudging? What if the ‘natural’ impact point were in the U.S., but the nudge (conducted by instruments of the U.S. Government) resulted in an impact onto an African nation? Or perhaps the nudge results in the asteroid hitting the Atlantic, causing a tsunami that deluges European coastlines facing onto that ocean. That is, any intervention could have wide international (humanitarian and legal) implications.

Ed Lu makes a point at the Planetary Defense Conference. Lu was a NASA astronaut, flying on space shuttle missions in 1997 and 2000 before spending six months on the International Space Station in 2003. He is now the CEO of the B612 Foundation, which is dedicated to assisting the protection of humankind from NEO impacts.

The AAP report I mentioned above begins with a paragraph saying that “A US conference that opened in Washington Monday will include an exercise to test how Nasa and the international community would respond to an asteroid found to be on a collision course with Earth.” So, we’re discussing “how the international community would respond” to something that could cause global effects, and there are just two of us here from the southern hemisphere.

For some years the U.S. has been encouraging other countries to engage, and get involved with plans and strategies for dealing with any potential impact by a near-Earth object (NEO: an any asteroid or comet coming close by Earth’s orbit around the Sun). Last year the (U.S.) Executive Office of the President published a National Near Earth Object Preparedness Strategy and Action Plan. Five broad goals are described, of which one reads as follows:

Increase International Cooperation on NEO Preparation: Agencies will work to inform and develop international support for addressing global NEO impact risks. International engagement and cooperation will help the Nation to prepare more effectively for a potential NEO impact.

Two facts about New Zealand:

(1) This country is especially at risk from the effects of asteroid impacts, because we sit on the edge of the largest target on Earth (the Pacific Ocean) and an impact into the sea would cause a phenomenal tsunami.

(2) NZ is at a uniquely-important geographical location because we are just to the west of the major NEO search facilities in Hawaii, Arizona and Chile, so that most discoveries made there could be promptly taken over for tracking by telescopes in this country; indeed the telescopes at Mount John Observatory are the southernmost year-round optical facilities of this type globally. It is widely-recognised by space scientists working in this field that a much-needed addition to the international effort is greatly-expanded tracking of NEOs from the southern hemisphere.

Just a few things to think about.


For clarity, before someone gets the wrong idea: I am attending the Planetary Defense Conference at my own expense, and I have taken annual leave in order to be present. I am here because it is clear that the long-term future of humans on Earth is dependent on the development of suitable systems to defend ourselves against major asteroid and comet impacts. Anyone wanting to contact me in this regard can do so via my eponymous website.