Asteroid Impacts and an Approaching Anniversary

by Paul Gilster on June 27, 2008

With the 100th anniversary of the Tunguska impact in Siberia coming up on Monday (and we’ll look at it closely then), several items seem germane to the topic of asteroid deflection. Yesterday, a technical briefing at the University of Calgary outlined the Canadian NEOSSat (Near Earth Orbit Surveillance Satellite) mission, a space telescope designed to track small objects near Earth, some of which may pose a collision threat. The suitcase-sized NEOSSat (launch date 2010) capitalizes on technology developed for Canada’s MOST (Microvariability and Oscillation of STars) satellite, which was designed to measure stellar ages in our galaxy.

While NEOSSat’s asteroid-hunting capabilities draw most media attention, the satellite is also going to act as a monitor on other satellites orbiting the Earth, contributing to the worldwide Space Surveillance Network. Satellite-tracking tests using the MOST instrument have proven that a microsatellite can track other satellites, but tuning the technology for asteroids takes another leap. David Cooper, general manager of Ontario-based Dynacon, the prime contractor for NEOSSat and the manufacturer and operator of MOST, puts the issue this way:

“NEOSSat requires remarkable agility and pointing stability that has never before been achieved by a microsatellite. It must rapidly spin to point at new locations hundreds of times per day, each time screeching to a halt to hold rock steady on a distant target, or precisely track a satellite along its orbit, and image-on-the-run.”

‘Rock steady’ is an exquisitely apt phrase for an asteroid hunter. And while the mission’s telescope, at 15-centimeters, is an instrument smaller than that used by many amateurs, placing it 700 kilometers about the atmosphere should offer great advantages. In a fifty minute polar orbit, the satellite will, according to team members, be able to detect asteroids delivering as few as 50 photons in a 100-second explosure. The more asteroid cataloging we can do, the better, and NEOSSat’s unique vantage point also offers the possibility of identifying non-threatening, slow-moving asteroids close to Earth for possible rendezvous missions.

Although it demands a sunshade for the satellite, NEOSSat’s polar orbit will allow it to search the sky to within 45 degrees of the Sun, a region hard to observe from the ground but the place where near-Earth asteroids are concentrated, and the only part of the sky where asteroids that orbit entirely inside Earth’s orbit can be discovered. With current estimates of 100,000 asteroids greater than 140 meters in diameter in near-Earth space, finding those on Earth-crossing orbits should be a high priority for a space-capable civilization, one to which even a small aperture telescope can make a contribution.

Add to this the new analyses of Martian terrain published this week in Nature, three letters that examine the Borealis basin, which covers about forty percent of the planet’s surface, and find it to be the remains of a huge impact early in the Solar System’s formation. Mars is home to abundant testimony of the effect of collisions, but the 5300-mile width of the Borealis basin is four times that of the Hellas basin, also on Mars, that had been the largest impact crater identified in the Solar System before now. Every sign points to the Borealis event having been caused by an object larger than Pluto, with an impact at least 3.9 billion years ago.

The early Solar System was rife with such impacts, but we have seen in our own time that much smaller objects (think Comet Shoemaker-Levy on Jupiter in 1994, or Tunguska in 1908) continue to pose a threat to our planet. Every battered landscape we see on the moons of the outer planets, not to mention our own Moon, bears witness to the violent history of our surroundings. Ensuring planetary security will lead us not only to improved asteroid cataloging but, inevitably, to missions to nearby asteroids as we develop the technology needed to adjust a threatening trajectory. Defense alone pushes us deep into the Solar System, from which point we should have the infrastructure needed to stay.


ljk June 27, 2008 at 11:21

House passes bill mandating a plan for asteroid warning and deflection June 27, 2008

In recently passed H.R.6063, The
U.S. House of Representatives would
direct the NASA Administrator to
develop plans for a low-cost space
mission to rendezvous with the
Apophis asteroid and attach a
tracking device (subject to Senate
approval). The Apophis is expected
to pass at a distance from Earth
that is closer than geostationary

ljk June 27, 2008 at 11:42


Monday, June 30 marks the 100th anniversary of the Tunguska
incident in 1908, in which a meteor or comet fragment entered the
atmosphere over Tunguska in Siberia producing an enormous

“We know that a rather massive body flew into the atmosphere
of our planet,” said Boris Shustov of the Russian Academy of

“It measured 40 to 60 meters in diameter. Clearly, it did not
consist of iron, otherwise it would have certainly reached the Earth.
The body decelerated in the atmosphere, the deceleration being
very abrupt, so the whole energy of this body flying with a velocity
of more than 20 meters per second was released, which resulted
in a mid-air explosion, very similar to a thermonuclear blast,” he
told Tass news agency yesterday.

“The yield of the explosion totaled 10 to 15 megatons, which
matches the yields of the largest hydrogen bomb ever tested on
the planet. The explosion felled some 80 million trees [but] it is
generally assumed that the blast did not kill any people,” he

“The Tunguska phenomenon showed that the asteroid-comet
danger is quite real. It happened not in the era of dinosaurs, but
in our recent history. Russia was definitely lucky; had the body
flown up to the Earth several hours later, it would have hit
St. Petersburg. The consequences would have been horrendous,”
he said.

“Impacts such as the Tunguska incident are thought to occur
about once in one hundred years based on the density of impact
craters on the Moon,” according to a White Paper on Planetary
Defense attached to the 1994 U.S. Air Force report Spacecast

A 2007 NASA summary report to Congress on planetary defense
is here:

A longer account is here:

philw1776 June 27, 2008 at 12:23

Great mission, for all mankind.
Let’s just hope that the last photo NEOSS ever transmits is not an extreme closeup of a NEO filling the field of view.

Mang June 27, 2008 at 13:45

Actually, the anniversary date is not Monday, but July 12th unless I’ve miscounted. That being the slight difference between the Julian and Gregorian Calendars.

tacitus June 27, 2008 at 14:37

It’s worth remembering how far we’ve come in 100 years since Tunguska:

In 1908 we knew of about 665 asteroids, all by four discovered in the previous 100 years. In 2008 we passed 400,000 observed asteroids and comets.

In 1908 we knew of just one near-Earth asteroid — Eros. In 2008 over 5400 have been discovered, plus about 65 near-Earth comets.

On the eve of Tunguska, we hadn’t a clue about the danger lurking above us. Today we’re well on the way to understanding precisely what the risks are especially when it comes to the largest, most deadly, asteroids out there.

Yes, the numbers are scary, and there is plenty more work to do, but thanks to the tremendous efforts of a relative few dedicated astronomers and scientists, Earth will be a much safer place to be in the years ahead (concerning NEOs, anyway).

ljk June 27, 2008 at 14:50
Administrator June 27, 2008 at 15:18

tacitus, what does concern me, despite the progress you mention, is the relative complacency about the issue in some quarters. It wasn’t long ago at all that the idea of closing the Arecibo planetary radar was making the rounds to apparent public indifference. So I’m hoping the Tunguska event will get some further publicity to supplement what the public is currently seeing about these issues.

James M. Essig June 27, 2008 at 16:45

Hi ljk;

Thanks for posting the link for Russian space plans for Apophis. At 350 meters across, the near Earth asteroid would weigh about 100 million to 200 million metric tons. At a collision velocity of 30 kilometers/second with Earth the yield of the collision would be roughly (100)(10 EXP 8) to (200)(10 EXP 8) metric tons of TNT or 10,000 to 20,000 megatons. This is multiple times the yield of the entire currently deployed nuclear arsenals of either the U.S. or the Russian Federation. And this rock is probably much smaller than many future NEO objects. Not to fund studies of such bodies is irresponsible in my opinion.



Adam June 27, 2008 at 18:15

Unestimated threat and an under-appreciated resource. How many NEOs are really water-rich comet corpses? Mining them for in-space resources is surely a necessity for any major move off-world – the water alone is reaction mass, bulk shielding, potable water and a hydrogen source. I think it’s a grave mistake to focus on the Moon’s water resources when the NEO water resources are surely more accessible.

tacitus June 27, 2008 at 19:06

Well I think it’s where progress can be a double-edged sword. Obviously, with the funding they have, astronomers are doing a fantastic job or detecting and cataloging potentially dangerous objects, and I guess when people see how many objects we’ve found and how quickly we can determine how much of a risk they are, then some complacency can settle.

But you also have too look at the overall risks involved. Of all the things that can (and will) kill you, a meteorite/comet strike is still very much a long shot. Yes, if it happens, then it would be a disaster, but many people have a hard time with being told that it’s a imminent danger when there are so many more obviously dangers to life and limb out there. Few people would chose putting $100 million into asteroid defense over, say, putting $100 million into finding cures for cancer or heart disease. And it would be hard to disagree since the majority are almost certainly going to be affected by one or both, whereas dying from an asteroid strike is extremely unlikely.

(I know that’s a false dichotomy since funding one doesn’t preclude funding the other, but I think the point is clear.)

tacitus June 27, 2008 at 19:18

One thing that does seem rather remarkable is how people can be so blasé about asteriod/comet strikes and yet get so worked up about the possibility of a Planet X crashing into us, or some mega-solar outburst consuming the Earth.

They seem to implicitly trust astronomers when say that there are no immediate threats from asteroids (that we know of) and yet when it comes to debunking Planet X, they pour scorn on the astronomers’ disbelief and debunkings.

I guess, as is always the case with pseudoscience, reality just seems to become dull and uninteresting by comparison. Why get excited over a few lumps of ordinary rock when there’s a mysterious planet to track down? I am sure Centauri Dreams has been the target of such dismissals too. If there are aliens among us and our government already has a working superluminal space drive, then why the heck are you writing stories about taking 1,000 years to get to Alpha Centauri?

Cheapening the wonders of the Universe is an unforgivable crime of the pseudoscientists, not far behind that of demeaning the careers of real scientists who toil for years with little reward while they reap the spoils to churning out the nonsense that clogs up the shelves in bookstores.

(You can probably tell what I think of these people :-) )

Adam June 28, 2008 at 0:22

Good points tacitus. I’ve got to wonder what the urge to propagate nonsense achieves – cheap attention getting obviously, but what else?

Ronald June 29, 2008 at 6:49

@tacitus (and Adam): straight from my heart!

Here in the Netherlands there is a (most) popular news site, where people can send in (links to) articles that they consider most relevant and/or interesting. It is just amazing how this site is dominated by ‘news items’ on UFOs, govt. conspiracies and cover-ups, ‘free’ energy, all sorts of superstitions, etc.

I suppose that sensationalism and lack of knowledge dominate the scene.

Sad to notice that, at the same time, it is striking how the same people continuously bash real scientific progress.

Adam June 29, 2008 at 16:46

Hi Ron

People don’t trust governments – particularly the US and UK – because we know they lied to the Nazis in World War II and we know they’ve lied ever since. Thus conspiracies breed in the “veracity vacuum” created by the creative use of truth and facts by Government and, increasingly, Big Business.

There is also a counter-culture cult-mindset that has parasitised young people’s minds since the late 1950s, which causes them to readily accept nonsense as truth.

ljk July 2, 2008 at 21:20

Canada to build World’s First Asteroid-hunting Satellite

Written by Nicholos Wethington

Just yesterday (June 30th) was the 100-year anniversary of the Tunguska event, when a small piece of ice or rock created a huge blast crater near the Podkammenaya Tungus river in Siberia, flattening trees and scaring the heck out of people in the surrounding area. Thankfully, the blast didn’t happen in a populated area and nobody was killed, but there are many more pieces of debris floating around out there in space.

If we want to do something about an asteroid headed our way, or keep astronauts safe from space debris, knowing is half the battle. Thanks to a new microsatellite being built by the Canadian Space Agency, we will soon have a better map of the objects surrounding the Earth’s orbit.

The Near Earth Object Surveillance Satellite (NEOSSat) is a small satellite, about the size of a suitcase and weighing 143 pounds (65 kilograms). This puts it in a class of satellites known as “microsatellites”. Canada has already launched a successful microsatellite mission – Microvariability and Oscillation of STars (MOST) – that measured the light oscillation of stars to determine their age.

NEOSSat will monitor asteroids, comets and space junk in near-Earth orbit – within 100 – 1240 miles (160 – 2000 km) – to create a detailed survey of objects close to the Earth. It will also track other satellites, such as geosynchronous satellites, which orbit further out at 22,400 miles (~36,000 km).

Full article here:

Comments on this entry are closed.