Are we really doing enough to find asteroids, especially the smaller ones that could destroy a city? A private initiative urges a rapid ramp-up of the search effort — but not everyone agrees.

"There are a million asteroids in our solar system that have the potential to strike Earth and destroy a city, yet we have discovered just 1% of them."

This is the premise behind Asteroid Day, a private initiative backed by well-known science communicators, celebrities, astronauts, and scientists that calls for a "rapid hundred-fold acceleration of the discovery and tracking of Near-Earth Asteroids to 100,000 per year within the next ten years." To raise the public's awareness of the threat from space, they've declared June 30th "Asteroid Day" — as a reminder of the Tunguska event, during which a 40-m-size space rock devastated a large, but mainly uninhabited area in Siberia on that same date in 1908.

Asteroid Day logo
Asteroid Day is intended as a global day of education and awareness about asteroids — especially those that threaten Earth.
Sentinel / B612 Foundation

Asteroid Day's 100X Declaration, an online petition, does not include details on the means or cost of the proposed goal — or about who should pay the bill. Eric Christensen, who leads the NASA-financed Catalina Sky Survey, is already bothered by its premise that "millions" of asteroids potentially threaten our cities. "The vast majority of these objects have essentially zero chance of impacting our planet within our lifetime," he explains, "and if one were to impact, there is only about a 3% chance that it would impact over a populated area."

"The most likely effect would be a spectacular light show that nobody sees, and a few meteorites that get dropped into the ocean," Christensen adds. He sees the B612 Foundation as one of the driving forces behind Asteroid Day. Established by former astronauts Ed Lu and Rusty Schweickart, this organization is trying to raise funds to build and launch a space-based infrared survey telescope to search for NEOs. "The B612 foundation has provided a steady stream of fear-based press releases over the last few years in order to scare up funding for their project," says Christensen. This tone is also found in Asteroid Day's declaration, he adds. "It is full of language that turns asteroids into menacing killers, injecting an inordinate amount of fear into what could be a reasoned discussion about the asteroid-impact threat."

Sentinel spacecraft in orbit
If private funding can be found, the B612 Foundation plans to launch its Sentinel spacecraft in 2017 to scan for near-Earth asteroids from a Venus-like orbit around the Sun.
Sentinel / B612 Foundation

Timothy Spahr, former director of the IAU's Minor Planet Center, concurs: "Much of the B612 Foundation commentary on smaller objects is fear-mongering. Yet its proposed Sentinel space-based telescope, Spahr notes, is designed to discover larger objects — not the 30- to 50-m "city killers" that are being spotlighted. "In my opinion there is no need for an Asteroid Day," Spahr states flatly, "and if there is to be an Asteroid Day, then including other scientists such as experts in the NEO field would make sense."

Asteroid Insurance

Signatories of the 100X Declaration disagree, of course. Schweickart disputes that the initiative is just a fundraising stunt for Sentinel: "Asteroid Day does not propose any particular system or project. It is an event to help educate the general public about the asteroid impact threat that recognizes the current low rate of asteroid discovery and calls for a significant acceleration."

Asteroids in the inner solar system
This plot of known near-Earth asteroids (shown in red) looks menacing. But space is a big place, and none of these are predicted to strike Earth within the next two centuries
Minor Planet Center

The actual risk of a small asteroid hitting a city might be small, but investing in asteroid research is like investing in car insurance, Schweickart explains: you might never need it, but you probably would not take the risk and do nothing. "And this 'insurance' can preclude the accident itself, not just mitigate the cost of it should it occur," he says. "Furthermore, economic judgments (sound and unsound) are traditional when tax dollars are involved, but donors to privately funded systems should be loudly thanked for their public service."

"I suppose 'hype' is inevitable when you are trying to promote something", adds Clark Chapman, a senior scientist at the Southwest Research Institute in Boulder, Colorado. Chapman has signed the declaration, too: "It is not a scientific publication but a call to the broader public to consider asteroids and their potential harm." Even a very low risk should not be ignored: "I believe that society should make some attempt to address all threats, even low-probability ones, like deaths from airliner crashes, terrorist attacks, or asteroid impacts."

Thanks to NASA's Spaceguard search effort, started in the 1990s, we know the orbits of 95% of all NEOs at least 1 km across. Not one of them is on collision course with Earth — for now there's no danger of a mass-extinction event. But our knowledge of the smaller ones is still fragmentary, a fact beyond dispute among experts. And even small ones locally can cause severe harm.

Pay Less, Wait Longer?

Barringer crater in Arizona
Barringer Crater, near Flagstaff, Arizona, is one of the youngest impact craters on Earth. It was excavated about 50,000 years ago when an iron mass (or perhaps several) struck flat-lying sedimentary rocks at more than 11 km per second. Between 15 and 20 megatons of kinetic energy were released during the impact, which left a bowl-shaped crater 1.2 km in diameter and 200 m deep.
D. Roddy & K. Zeller / USGS

The poster child for What might Happen is Barringer Crater, created 50,000 years ago when a 40-m-wide metallic asteroid slammed into what is now northern Arizona. Had the space rock that exploded over Chelyabinsk, Russia, in 2013 been a little larger than 20 m, instead of 1,500 injured there might easily have been thousands of fatalities, says Alan Harris, coordinator of the NEOShield project financed by the European Union. "If we want to take the risk, then we can sit back and just carry on as most of the NEOs will eventually be discovered by ongoing search programs, but the smaller you go, the longer it takes." For Chelybinsk-type objects, at the present rate and with present telescopes Harris estimates it will take probably hundreds of years.

"Pay less, wait longer, is an option", Harris says. "Pay more" would mean spending a lot more, however. Spahr estimates that to meet the 100× goal within 10 years, the goal of Asteroid Day's proponents, billions of extra dollars would be needed. As part of the existing, "pay less" approach, astronomers are building the Large Synoptic Survey Telescope in Chile. When it begins observations, perhaps by 2019, LSST is expected to provide a sharp jump in NEO discoveries — but maybe not to the extent Asteroid Day proposes.

The 100X goal might be unrealistic or economically unsound, as some critics argue. But it wouldn't hurt to do a little more, says Harris, who has not signed the declaration: "Worldwide we are currently looking at probably $50 or $60 million a year [spent on the NEO threat], which, let's face it, is really a trivially small amount of money for a worldwide effort." More should be spent on follow-up and characterization studies of known asteroids, he says, useful details were one of them comes too close.

OSIRIS-REx spacecraft
A spacecraft called OSIRIS-REx (short for Origins Spectral Interpretation Resource Identification Security Regolith Explorer) will be launched in 2016, land on asteroid (101955) Bennu, and return a sample of its surface to Earth in 2023.

OSIRIS-REx, NASA's forthcoming asteroid sample-return mission, will provide such insight. Ed Beshore, principal investigator of the mission and former CSS collaborator, recommends focusing on intermediate-size asteroids, those massive enough to do considerably more damage than the Barringer-size objects that could wipe out a single city. "Concerning the estimates of the consequences of such small objects impacting the Earth, I think the risk to lives may be overstated," says Beshore. "But I fully support the search for larger objects of a couple of hundred meters and larger, because the consequences of those impacts are very large, even if the likelihood is low."

There is no doubt that asteroids pose a threat for our planet, he affirms. But dramatization does not help: "At the risk of being ignored, science must work very hard to paint an accurate picture of the risks that mankind faces."

For a quick snapshot of the current known threats from potentially hazardous asteroids, check out the risk pages maintained by NASA's NEO office and by the University of Pisa's NEODyS-2 effort.


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Anthony Barreiro

June 26, 2015 at 1:34 pm

Thanks for this clear, thorough, and reasonable report. I too have been put off by the fear-mongering of the asteroid hunters. The costs and benefits of assessing the statistically minuscule but potentially catastrophic risks of death and destruction from asteroids (and comets -- we wouldn't see one coming until a few months before impact) need to be weighed against those of aggressively reducing and remediating the undeniable environmental destruction we ourselves are doing to our planet. Shall we fiddle with satellites while the Earth burns?

By the way, this article doesn't include a bio for author Jan Hattenbach. Here's his profile on about dot me:
Free lance science writer, physicist, passionate amateur astronomer and photographer. Contributed to Sterne und Weltraum, Spektrum der Wissenschaft, Frankfurter Allgemeine Zeitung (Germany), Sky&Telescope (US), and others.
Topics: Everything about astronomy and astrophysics (professional and amateur), light pollution, astroparticle physics, elementary particle physics and cosmology.
Blogs: SkyLights (English), Himmelslichter (German).

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Richard Kowalski

June 26, 2015 at 6:34 pm

Anthony. please note that "Asteroid Hunters" are NOT the ones doing this. It is a private team that is, in my opinion, fear mongering to raise funds. You will notice in the article, that the actual hunters are criticizing this event, not participating.

Richard Kowalski
Catalina Sky Survey
Discoverer of 2008 TC3 & 2014 AA

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Anthony Barreiro

June 29, 2015 at 2:00 pm

Richard, thank you for the clarification. I'm sorry to have tarred you with too broad a brush.

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June 26, 2015 at 11:05 pm

Sorry, but if you look at the people who signed this declaration, there are no active asteroid hunters. In fact, the only person on that list who ever discovered a near earth object is Carolyn Shoemaker, and David Jewiit and Janet Luu codiscovered the second transneptunian asteroid. It's kind of surprising to find David Morrison in that list, while not an observer, he should know better. The others are not asteroid hunters. People who know a bit about asteroid surveys know that first the goal set by this project is not really useful, we really don't need to find all asteroids which are 20m large, and if you wanted to discover them in 10 years, you would need to spend more money that is spent yearly in the whole of astronomical research worldwide for several years. It won't happen. I mean if, like you do, people still have their feet on the earth and look around... Then again, sometimes I have doubts...

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Anthony Barreiro

June 29, 2015 at 2:02 pm

Alain, I am sorry to have used the term "asteroid hunters" when I should have referred specifically to the people who are promoting this particular scheme. Thank you for the clarification.

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June 26, 2015 at 8:02 pm

As some point an asteroid/comet will pose a threat to Earth; not if but when!?

Humans (and all life on Earth) will ultimately be wiped out by something; not if but when!?

Humans are renown for procrastinating about serious decisions. This is one serious decision. However, knowing that something nasty is going to happen is distinctly different from knowing how to mitigate the problem, be it climate change, an asteroid, a pandemic, the aging/expansion of the sun, a gamma ray burst, whatever... I'm not too sure if I really want to know there is going to be a major extinction event on Earth if we are helpless to do something about it!?

I suspect humans will wait until the last minute and probably be too late to avoid the inevitable. The planet will then start evolving new species to replace all the ones that went extinct in the "big one"...

Humans may be the most advanced species to have evolved on Earth but that doesn't mean we are immune to the worst nature can throw at us! It is always nice to have a little insurance.

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GH Martin

June 27, 2015 at 12:05 am

No one has remarked about the 70% probability of an object impacting in the ocean rather than land. Think about the consequences if the Tunguska object had exploded and created the tremendous pressure wave over the North Atlantic instead of Siberia. The resulting tsunami would have washed over New York City, London, Lisbon, Savannah, Charleston -- everywhere around both sides of the Atlantic. The point is, a "city killer" doesn't have to hit a city to be catastrophic. In fact, the effects are much worse if it doesn't strike land.

It's only been since 1979 and the work of the Alvarezes et al that we have come to recognize the danger. Public awareness of the problem is extremely low. And as Anthony Barreio pointed out above, comets are an even bigger problem because of so little warning time.

We need to not only be looking for these incoming objects, but have a means of intercepting and diverting them as well. We now have the technology to not only see an extinction event coming, but to do something to prevent it -- if we have the political will to spend the money to design and build the craft needed.

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June 27, 2015 at 6:08 am

Tunguska was an airburst, estimated as equivalent to about 10-15 megatons of TNT, similar to (but substantially bigger than) that at Chelyabinsk. It would not have created much of a tsunami had it struck over the oceans (its surface effects were mainly to flatten a great many trees), that would have required a far larger event.

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GH Martin

June 27, 2015 at 1:40 pm

I beg to differ. I realize Tunguska was an airburst -- "...if the Tunguska object had exploded and created the tremendous pressure wave over the North Atlantic instead of Siberia.

That pressure wave was strong enough to completely flatten the forests over a 50 mile diameter, and compressed the air to such a degree that the trees were charred. Such an airburst over an ocean would almost certainly create a large tsunami.

But that's not the entire point. A 40 meter iron siderite hitting land results in a city-killing explosion creating a mile-wide crater. The same siderite impacting an ocean (70% probability, mind you) creates a huge tsunami capable of killing scores of cities as it inundates the coasts on both sides of the target ocean.

Yes, the odds are slim that such an event will happen in our lifetime. But the odds are 1::1 that such an impact will happen at some point in the future -- unless we prevent it.

I believe having an Asteroid Day serves a valid purpose.

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June 27, 2015 at 11:27 am

I respectfully submit that the Chelyabinsk bolide is the "Poster Child" for asteroid threats as this event was extensively studied and reset the bar as to the threat posed by so many similar sized asteroids. Several factors contributed to the lessening of damage and injuries from this event: size (as pointed out in the article), shallow approach angle, the previously fractured structure of the meteoroid.

Chelyabinsk also came in from the Sun and was never detected. There have been numerous instances in which asteroids were discovered AFTER their closest point of approach to Earth which contributes to the value of a asteroid detecting spacecraft in a Venus proximity orbit.

It must also be remembered that this is a "When" and not "If" event. We ARE going to be hit again and one must prepare accordingly. Having multiple space and ground based assets searching the skies will always be a good thing. Adding responsible private assets to the government mix has shown its worth - "Space X" anyone?

A final thought. In today's very dangerous world will a political leader take time to determine that the mushroom cloud over their territory is from an impact and not a nuclear weapon? The late Carl Sagan eloquently posed this question. Fortunately Chelyabinsk had no mushroom cloud and I have never heard or read of what the response was within the walls of the Kremlin in the first moments after the event.

Asteroid Day educates and highlights the very real threat posed by future impacts.

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Peter Wilson

June 29, 2015 at 9:09 am

Found a Happy Asteroid Day card at Walmart yesterday. Opposition is futile...

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