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Asteroids: When the time comes to duck

Jonathan Amos | 23:09 UK time, Friday, 29 October 2010

Somewhere out in space there’s a big rock that has our address on it.

Throughout geological history, our planet has been hit by a succession of major asteroids and the probabilities suggest further impacts will occur in the future.

No-one can say today when these might happen; we haven’t yet identified an asteroid of sufficient size and on a path that gives us immediate cause for concern.

Artist's impression of an asteroid mission

If an object was sent to strike the asteroid, the rock's course could be subtly changed

But the evidence hints strongly that something could find us sooner or later, and we need to be ready.

On average, an object about the size of car will enter the Earth's atmosphere once a year, producing a spectacular fireball in the sky.

About every 2,000 years or so, an object the size of a football field will impact the Earth, causing significant local damage.

And then, every few million years, a rock turns up that has a girth measured in kilometres. An impact from one of these will produce global effects.

We know of some Near-Earth Objects (NEOs) today that are several km wide but fortunately none of them comes close enough to make us sweat.

The important thing is we keep looking. The US space agency’s NEO programme has been running since the late 1990s.

It was tasked with finding 90% of the potentially hazardous objects out there larger than 1km and it’s about 80% through this search. A few years back, the US Congress asked Nasa to extend the survey to include rocks down to about 140m in size.

That requires more and better telescopes and these are coming online. You will hear much more information on NEOs in the coming years because of this finer-scale sweep of the skies.

When a potentially hazardous rock is discovered, one of the best ways to determine its true status is to complete a study using radar, an extremely powerful tool.

Facilities such as the Arecibo Observatory in Puerto Rico or the Goldstone complex in California can pin down a rock’s key properties, determining its velocity to a precision of better than 1mm per second, and enabling scientists to compute its orbit hundreds of years into the future.

One of the more interesting facts that I became aware of recently is just how many of these objects are actually binaries – that’s to say, when the radar observations are done it becomes apparent that the asteroid is really two asteroids, or even a trio.


Contact binary: Toutatis (4.5km long) frequently gets to within a couple of Earth-Moon distances

Some of these are what are termed contact binaries – they touch each other. These are the objects that look like giant peanuts. (My favourite contact binary is the “dog bone” asteroid, 216 Kleopatra, although this is a long way from Earth and no threat to us).

About a quarter of all the objects investigated by radar turn out to be binaries of some kind.

So the inevitable question arises, what do we do if we find that huge rock with our address on it?

The powers that be are on the case. A lot of this work goes under the aegis of the United Nations, and in this context a meeting took place this week hosted by the European Space Agency.

The Mission Planning and Operations Group (MPOG) workshop included astronauts and space scientists.

It was the latest in a series organised to report to the UN's Committee on the Peaceful Uses of Outer Space.

The gathering of experts urged the world’s space agencies to improve their search and tracking capabilities, and to start developing concepts to deflect asteroids.

One of the leading figures in this initiative is the Apollo 9 astronaut Rusty Schweickart. He’s the chairman of the B612 Foundation, which campaigns on the NEO topic [PDF], and was one of the attendees at the MPOG meeting. He characterises the threat thus:

“At the upper end, you’re talking about wiping out the dinosaurs and most of life on Earth 65 million years ago; at the smaller end you’re talking about a million objects that hit the Earth last night – we call them shooting stars. It’s the objects in between that occur every few hundred years that we’re concerned with.”

Schweickart is convinced the solutions are within reach to deal with most hazardous asteroids on a collision path with Earth. In the majority of cases, the preferred concept would look much like Nasa’s Deep Impact mission of 2005 which saw a shepherding spacecraft release an impactor to strike a comet.

This gentle nudge, depending when and how it's done, could change the velocity of the rock ever so slightly to make it arrive “at the intersection” sufficiently early or late to miss Earth.

According to Schweickart, rear-ending an asteroid may be the easy part, however. Getting the world’s bureaucracy to act on the threat in a timely fashion may be the bigger challenge, he believes. And here’s why.

Consider the 300m-wide asteroid Apophis. For a while, before the calculations were detailed enough, there was some concern this object might hit Earth in 2036. The odds now are thought to be pretty slim.

But just imagine for a moment that it was headed right for us and we needed to do something about it.

Take a look at the map below. We know enough about the plane of Apophis’s orbit to understand where this rock would intersect the Earth, and it would be somewhere along the red line.

Now imagine the UN meeting convened to discuss whether the mission sent up to deflect the asteroid should try to slow or accelerate the rock. The choice is important because it would determine where on the line the rock would hit if the mission is not entirely successful in getting the asteroid to pass by the Earth.

In other words, one strategy chosen over the other would lessen the risks for some while increasing them for others.

So, you can bet Russia, Venezuela and Senegal would have very different views on which mission profile should be chosen.

That’s why Schweickart believes the geopolitical obstacles need to be tackled now and the mechanisms put in place to deal with thorny issues like the one I’ve just described:

“If we can get past that bureaucratic challenge, we can in fact prevent [large] asteroid impacts from hitting again in our future. This is an amazing and rather audacious statement to make, but if we really do our job right, we should never be hit again by an asteroid that can do serious damage to life on Earth.”
Apophis plane of intersection with Earth




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  • 1. At 11:01am on 31 Oct 2010, Stephen Ashworth wrote:

    I think the key point about near-Earth asteroids is their two-sided nature. Yes, they do represent a potential threat. But at the same time they are a huge resource. Their water content, according to Professor John S. Lewis, is likely to be a key enabler of future space exploration and development. This water should be very much more accessible and useful than the lunar polar water you wrote a news piece about a few days ago, because the lunar water is frozen hard and at the bottom of a modest gravity well. The asteroidal water is likely to be easier to get at and is of course already in space, where the largest demand for refuelling will exist in a space economy.

    Lewis reckons that a fair proportion of near-Earth asteroids are extinct comet cores, with the implication that they are carbonaceous and volatile-rich. (See his inspirational book, Mining the Sky.)

    Therefore any space agency with a serious intention of developing some sort of human future in space should already be prioritising near-Earth asteroid exploration and sample return. When the time comes to divert a threatening asteroid, the technologies to do so should already be well developed for economic purposes.

    It may not be quite as simple as the UN phoning a space trucking company and asking them to move asteroid B612 from its current orbit into a new one, but that is how I see it developing by the time a real threat appears.


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  • 2. At 12:24pm on 31 Oct 2010, Robbwot wrote:

    IF there is a need for man to change the flight path of a space object, you can bet the USA (if involved) will make a total BOG of it. Possibly, hitting the Moon instead with the object, the effects of that on earth would be interesting? Buy big wellie's?

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  • 3. At 12:29pm on 31 Oct 2010, Robert Lucien wrote:

    Steven et al, its funny that this was the subject of the next blog. The one type of asteroid we really cant stop with our current technology are the really big ones 1 km across plus, the bigger the worse.

    A 1km rock (back of envelope) weighing on the order of about 1 to 5 billion tons (lets assume a density of about 1.5 tons per cubic meter giving a total mass of about 1.5x10^12 kg) and moving with a relative speed of say 3 km/s will have a kinetic energy of on the order of 10 Exa joules (10^19 J). Thats huge but it could be stopped or at least turned using a few small nuclear bombs. This is the kind of thing the original project Orion was almost designed for, the Orion pulse warheads were designed to give a concentrated pulse of directional push to a remote object. Whether the object being pushed is an Orion ship or a much heavier asteroid is pretty irrelevant.

    With a really serious object of say 300 km across, the base mass jumps to some 50,000 trillion tons (5x10^19 kg), and at the same speed kinetic energy jumps to some 5x10^25 Joules. That's about 100 million times more than put out by Tsar Bomba the most powerful nuclear bomb ever detonated. So whether such a huge asteroid could be diverted at all is very debatable. But it might be possible to turn it with a few very powerful bombs or very large numbers of smaller bombs. Of course this would be a massively bigger challenge than stopping a smaller object simply because of the size and scale - but I bet it is possible. Bombs like Tsar Bomba are very large and very heavy - Tsar bomba weighed 27 tons and was 8 m long.

    The point is that stopping a big object is possible but imagine it actually happening, the current approach is that we don't do anything until there is an actual threat. So the only real question in a real scenario is can we design and build and activate a complete system in the time between detecting a threat and it getting to close to stop it hitting us. It would be more sensible obviously to have things in a state much nearer to readiness before the need arises.
    There is another potential type of threat - objects moving at 100 km/s plus. In this case the danger level is basically unknown and pretty much unknowable, the base chance is probably very low though because we don't seem to have any such objects on record. However there is a possibility that the 'Tenguska' event was caused by a very small very fast object so they shouldn't be totally dismissed.
    At higher velocities much small objects start to pose a real danger, and of course it also tends to mean much shorter detection spans. Such objects might be easier to destroy though because their own kinetic energy works against them in any collision.

    At relativistic speeds of say 100,000 km/s even detecting an object before it hits gets very difficult. - To have the same destructive yield as the 1 km diameter object I mentioned above an object moving as 100 km/s would only need to weigh about 100,000 tons (ie be 40 m across).

    PS I'm sure that I have at least one figure wrong, and these are very crude simple estimates - apologies in advance.

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  • 4. At 12:33pm on 31 Oct 2010, Robert Lucien wrote:

    Oops Johnathon I apologize, I dyslexically transposed yours and Stevens names. Sorry to both.

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  • 5. At 1:10pm on 31 Oct 2010, Phil_o_the_North wrote:

    Robert.... my (meagre) understanding of astromechanics is that because we are talking n-body problems here, the motion is chaotic; presumably that accounts for the 'chance' nature of potential impact possibility (like weather forecasting).
    That being the case we can presumably use sensitivity to initial conditions to our advantage (as in some industrial chemical processes) and deflect the asteriod from its path with a (relatively) minor event. Can anyone out there (!) confirm this line of reasoning .. or rubbish it?!

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  • 6. At 6:30pm on 31 Oct 2010, techi4life wrote:

    Phil_o_the_North... In this context I think an n-body problem isn't necessarily a chaotic one. The orbits of planets etal are quite predictable despite it being n-body. Your sort-of right in suggesting about "the sensitivity to initial conditions":- a very slight change in the asteroids velocity can, over time, produce a noticeably different outcome (eg not hitting the Earth!). That difference is still predictable, not chaotic, and thus worth trying.

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  • 7. At 7:21pm on 31 Oct 2010, Robert Lucien wrote:

    Phil and tech4life I certainly wouldn't rubbish chaotic trajectories. In any of the methods I was talking about we would almost certainly be trying to use them, but the problem with them is that they tend to take longer to work. The really big problem with threat asteroids is time- first we have to detect the danger, design and build a response, fly it out to meet the asteroid, then actually do the work of shifting its trajectory. A very crude general rule about orbital manoeuvring is that the less time there is to make a change the more actual physical work that will be needed.

    The sheer size of most likely serious threats is the whole reason for looking at nuclear weapons as propulsion. Pulse (bomb) type systems might seem rather crude and ugly but they are the only technology on the near horizon that is anywhere near to having enough power to actually push a 1 or 10 km wide asteroid.
    Another even bigger advantage of that power is that an Orion ship is very fast. For Orion - journey times might be about a month from Earth to Mars orbit or six to ten months to Jupiter orbit. Compare that to today’s rockets - nine months minimum to reach Mars orbit or several years to reach Jupiter orbit. - That time difference could be crucial.

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  • 8. At 8:19pm on 31 Oct 2010, Kenneth Brown wrote:

    Robbwot- I agree that many times the US GOVERNMENT has gotten involved in world affairs and has made a total mess of things,eg Vietnam, Afghanistan, Iraq. The US has even had a recent President who acted without the UN approval and many Americans are so glad that he is no longer in office! However, when it comes to outer space, NASA is to commended on their accomplishments.They are among the world leaders in space research and have shown their ability and willingness to work along side other space programs-eg The International Space Station.
    The detection and removal of life threatening asteroids is of great importance. A cohesive preparedness plan is essential. Mr Amos clearly points out how it will take time for the nations to debate and argue and then finally agree on a plan. The name calling has already begun. Tragic!

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  • 9. At 8:58pm on 31 Oct 2010, Jonathan Amos wrote:

    For some good follow-up reading, I recommend the National Research Council report called Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies which was published earlier this year. You can download it for free here.

    But before I quote some passages from the report, let me quote something from the interim document, which said:

    “Because asteroid impacts can occur with warning periods ranging from hours to many centuries, and dangerous impacting objects can range from a few tens of meters to many kilometers in diameter, and can be composed of ice, rock, or metallic iron, it is unlikely that any one mitigation strategy will offer a universal defense. Instead, each plausible strategy (and others yet to be conceived) should have its own place in a matrix of possible responses whose elements depend on the parameters of the particular threat. The effectiveness of various technologies could be evaluated by demonstration experiments as budgets permit.”

    Now to the main report. On the subject of impactors like the one I describe above, the report found: “Kinetic impactors are adequate to prevent impacts on Earth by moderate-sized NEOs (many hundreds of meters to 1 kilometer in diameter) with decades of advance warning. The concept has been demonstrated in space, but the result is sensitive to the properties of the NEO and requires further study.

    On the subject of the nuclear option, the report found: “Other than a large flotilla (100 or more) of massive spacecraft being sent as impactors, nuclear explosions are the only current, practical means for changing the orbit of large NEOs (diameter greater than about 1 kilometer). Nuclear explosions also remain as a backup strategy for somewhat smaller objects if other methods have failed. They may be the only method for dealing with smaller objects when warning time is short, but additional research is necessary for such cases.”

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  • 10. At 9:42pm on 31 Oct 2010, Phil_o_the_North wrote:

    Jonathan ... your link (8:58pm post) seems to be dead.

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  • 11. At 9:48pm on 31 Oct 2010, Jonathan Amos wrote:

    @Phil. Thanks. I need new reading glasses. Try here.

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  • 12. At 10:19pm on 31 Oct 2010, Chores wrote:

    I cannot help feeling that another point has been completely over looked.
    Ever since Big Bang, the universe has been 'shaped' to what it is today because of impacts of any kind, small (as in molecules) and large (as in planets). The order and position of the planets in our own little universe has been established because of all these type of encounters and or collisions.
    Considering we only actually know only about 4% of the actual universe who are we to decide that some other planet (with or without some kind of existence) should be more suited to be the recipient of an asteroid that might be a danger to this planet ?
    Isn't our planet part of the universe and its constant development with all its (hidden) dangers or have we decided that this planet is an indispensable cornerstone of the existence of the universe ?

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  • 13. At 11:28pm on 31 Oct 2010, Simonm wrote:

    The comment about using a near visitor for its resources has been made above, I expect the reference was to the asteroid as a source of materials. But, what about using it as a spacecraft? If we are considering nudging it into an alternative orbit, what about an even more ambitious series of nudges into an eliptical orbit taking in the Earth and Mars with regular controlled near misses.

    Outfit the asteroid as a habitat, tunnels for radiation protection (which can be mined for resources at the same time) then rather than build Earth to Mars spaceships, all we need to consider is smaller spaceships matching velocities at the start and end of the journey. A far easier task than the need to accelerate and decelerate very large spaceships. Perhaps the journey might be longer, but surely safer and if something goes wrong, stay on board and come home!

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  • 14. At 08:00am on 01 Nov 2010, manamonkey wrote:

    Chores (#12): So you are suggesting that we should simply allow ourselves to be severely damaged or completely destroyed if such an event were ever to occur? I don't think that's reasonable, cosmic destiny aside.

    On one hand, if we are the only life in the universe, then we have a duty to protect ourselves. On the other, if there is other life out there capable of deflecting asteroids, how can we be sure that the same situation you describe would not result in our own hypothetical predicament?

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  • 15. At 10:13am on 01 Nov 2010, SionH wrote:

    We all think like chimps cracking a nut, "Hit it, hit it!". We need to be more 21st century in our thinking. Don't hit it, pull it. Send up a spacecraft, park it off to the side of the rock and let it gently tug it off-course. Needs some advance warning, sure, but it is considerably easier to do. After all, it doesn't need to miss by much. Missing is what counts.

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  • 16. At 11:57am on 01 Nov 2010, MOONSTRIKE wrote:

    This article on Asteroid impact danger completely ignores equally dangerous possibilities. If asteroid tracking concentrates on Earth as the target then no warning will be given of asteroid strikes on Venus, Mercury, Mars, the Sun itself or indeed the most dangerous of all, our Moon.

    The response of scientists concerned with tracking would be appreciated.

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  • 17. At 12:54pm on 01 Nov 2010, Stephen Ashworth wrote:

    #13, Simonm, thanks for your suggestion. I actually suggested just this at a British Interplanetary Society one-day symposium on 19 November 2008. The point is that regular passenger Earth-Mars travel should ideally be based on Earth-Mars cyclers, an idea developed by Alan Friedlander, John Niehoff, Buzz Aldrin and others since the early 1980s. But a number of near-Earth asteroids are in orbits which mimic such cyclers -- 4660 Nereus is one such, and I counted over 50 others. Therefore the bulk of the material resources for regular Earth-Mars travel is already in approximately the right location in space, providing we adopt the point of view of utilising those resources, rather than launching everything on giant rockets from Earth (the standard unimaginative NASA-ESA assumption).

    See my report on the meeting in Spaceflight, March 2009, p.116-118.

    Moonstrike, you are quite right to point out the possibility of impacts on the Moon -- and a glance at the Moon through a modest telescope will show the scars of countless impacts over the ages which humanity has been helpless to prevent (not having been in existence at the time). But are such impacts as dangerous to living organisms, if the population density of organisms on the Moon and other planets is less than that on Earth?


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  • 18. At 2:01pm on 01 Nov 2010, Phil Wells wrote:

    While it is obviously important to continue to discuss ways to deal with a NEO threat, the discussions regarding how much time we may have or may require, and using that as a reason to use (or not use) a particular solution, seems somewhat moot right now.

    Space flight, or more accurately space propulsion, is right on the verge of some fairly major breakthroughs largely as a result of the continual development of technologies like the Ion thruster.

    Ion propulsion was more or less static for 40 years, but over the past 10 years it has begun to be taken far more seriously and we're starting to see some big improvements. Its fear to assume that in 10-20 years it may well have improved to the point where even its acceleration could out-match current chemical propulsion - or could even have been replaced entirely with something even more efficient and even faster (and I can garuntee that it won't be Project Orion).

    The more efficient our propulsion technology becomes, the faster the travel time of the space craft, the quicker the response time to the threat of a NEO collision, the more time we have to react to any potential threat.

    So theories like deploying solar sails to drag the asteroid off its collision trajectory or the like become more and more pheasable as the propulsion technology of our space craft continues to improve.

    And this doesn't even take into account the fact that object detection technology has continued to improve at a substantial rate which again increases the time we have to react, again offering the potential of different solutions.

    So while I agree that it is certainly smart to start thinking up certain ways, I think it is a little stupid that several methods are effectively going un-explored simply because people are basing their opinions on current technology - technology that will be out of date next week, nevermind next decade.

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  • 19. At 10:39pm on 01 Nov 2010, I love banks wrote:

    Why dont we go all armageddon on asteroids and just blow them up. it would be a whole lot easier to just shoot a bomb at one because it would dissintergrate into smaller pieces then be no problem. a few nukes and the problem's solved, we've got enough down here, lets get rid of them by shooting them into asteroids.

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  • 20. At 10:13am on 02 Nov 2010, Hally wrote:

    "You can bet the USA (if involved) will make a total BOG of it. Possibly, hitting the Moon instead with the object"


    "Why dont we go all armageddon on asteroids and just blow them up."

    I really hope you are joking. We've got enough problems about nukes and everything down here. If we start shooting them up there who knows what would happen. Might end up being catastrophic. There have got be better ways to deal with the asteroids than this. Probably using laser or something. Or maybe diverting their projectile through magnetic forces or something alike.

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  • 21. At 1:11pm on 02 Nov 2010, michael mcnaughton wrote:

    One of the problems with trying to destroy an asteroid with nuclear weapons, is that you end up with a potential for thousands of smaller chunks of rock with unknown trajectories. Much of this space rock will be radioactive from the explosions used to destroy it but big enoough to make it through our own atmosphere. These then hit the earth spreading radioactive fallout far and wide.

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  • 22. At 2:01pm on 02 Nov 2010, Simon wrote:

    I couldn't resist doing some maths on this, so I've used the 99942 Apophis as an example. I've obtained all the factual data here from Wikipedia. Discovered in 2004 and with a possible impact date of 2029. Let's assume that in 2013, the orbital refinement shows that it's going to hit us in 2029. That's a lead time of 16 years to impact (and it seems likely to me that the larger the object, the earlier we'd know about it).

    If, rather than the big bang approach, we use a long gentle push with something like an ion engine (current technology, nothing new) we'd need to get to the object and then nudge it for a long period of time.

    We only need to change it's location at impact time by the radius of the earth, plus a small margin for error. Let's say 7000km. We'll assume that the object isn't travelling at relativistic velocities and so we can use basic Newtonian mechanics. s = ut + att/2. s is the distance, u, the original velocity, t is time and a is acceleration. For the purposes of our discussion, u is zero. It's the velocity of the object along the vector we're going to push it in order to miss the earth. At the moment, it's zero and so it will hit.

    Let's say it takes the powers that be 5 years to get their act together, and another 5 years to design, build and test the mission and get it to the asteroid. That leaves 6 years of pushing in order to make it miss us.

    By my calculations (a simple spreadsheet rather than a fag packet, but it does the job) the force needed over that time is just 20 newtons. To give you an idea how much that is, a 5Kg bag of spuds exerts a downward force of 50N at the surface of the earth.

    For the planet killing 300km asteroid, the numbers get a lot bigger. A force of 1 million newtons for 1000 years would be needed, or 10 billion newtons for 10 years. For comparison, the Space Shuttle puts out 12.5 million newtons at launch.

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  • 23. At 5:34pm on 02 Nov 2010, knowles2 wrote:

    I just hope when ever we find a rock with our name on it, they do not have just a plan a but a plan b, c, d, e all ready to go to go.

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  • 24. At 7:07pm on 02 Nov 2010, Tarentaal wrote:

    I think the point being made about the moon was not so much threat to organisms but the effect of a change in the moon's orbit.

    One idea I've not heard mentioned how about an orbiting or moon based mass driver? Cosmic snooker anyone? Use rocks against rocks, a very lightly glancing blow should be sufficient to deflect an incoming object...

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  • 25. At 8:04pm on 02 Nov 2010, Trev wrote:

    Get the human race's space program back on track - and we might just reach out and achieve something fantastic again, or at least protect ourselves a little longer.
    Establish a decent moon-base - then you can install mass drivers and play pool,or use thousands of small simple rocket motors - easy enough to have them all trigger in the same direction on a spinning rock by using the sun as a point of reference, the average mobile phone is sophisticated enough to provide control for each unit - just chuck a couple hundred thousand onto the rock then trigger. Meanwhile move onto Mars and get some of humanities eggs into another basket.

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  • 26. At 8:19pm on 02 Nov 2010, sensiblegrannie wrote:

    I have made many frustrated attempts to find out about our NEO flying by today and found very little information. Can anyone direct me to any relevant observations please.

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  • 27. At 8:45pm on 02 Nov 2010, sensiblegrannie wrote:

    Didn't this latest rock get a bit close to the moon?

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  • 28. At 9:27pm on 02 Nov 2010, Robert Lucien wrote:

    #20 Hally, And maybe we could do that using our Robby rocket pants and Robby laser pack - oh except they don't exist.
    If we want to shoot asteroids with a laser we're going to need an awful lot of power ... Lets say as a very rough ballpark figure we build a laser big enough to push/deflect 1 km scale asteroids. As a very very rough estimate that might need about 10,000 terawatts. That laser will be the biggest thing ever constructed on Earth (maybe a several km long - high), and if built in the UK need a power supply a thousand times bigger than the current national grid.
    But the real punchline is that the first malfunction in its primary circuit and it will do a rather good impression of a (large) nuclear bomb exploding anyway.
    #22 Simon 99942 Apophis is an interesting example. 20 newtons certainly isn't much, but over five years it still needs significant mass and energy. For a 10 km/s rocket the mass needed is only 2 g/s but that gives a total of 314 tons of reaction mass and it needs a constant power source of something like 200 to 400 KW. In comparison the ISS solar arrays can produce 128 KW. The big thing with Apophis though is that it gives a relatively long lead time, what if the lead time is only 10 years or less?
    The main problem in stopping a real threat is altering the course of the target - but the other side of the problem is getting out there rapidly enough to actually do it. (The simplest answer is using the same engine for both.) Whatever the plan we're talking about moving hundreds of tons of cargo out to intercept remote targets that might be on pretty much any trajectory (ie further out than Jupiter). Then there is the little task of matching final velocities with the asteroid which ideally needs a very big short pulse of thrust (eg. 1 Gee for 20 minutes).
    - This task is pretty next to impossible using chemical rockets unless the launch weights exceed 20-50 thousand tons.
    - Things like plasma or ion rockets or railguns are still decades away from being powerful and big enough and would still realistically need to be nuclear powered anyway.
    - Solar sails might be a good option but again on the scales needed they are also probably decades away.
    - The only other real option is fusion thrusters - they are maybe only 10 to 20 years away, but thats at huge cost - say $100 billion plus.

    Really nuclear pulse propulsion is the simplest option, the closest to being ready, should have a very good payload capacity, and is relatively cheap. I'd put it at 10 years maximum from being usable and at a coast of about $5 to 10 billion, Its only really the nuclear panic and paranoia that is its big problem. Orion system type bombs are so small that you could use one to demolish the Palace of Westminster and watch it from the Millennium Eye and survive the experience.
    The really funny thing is that solving this problem also solves the basic problem of expanding general space exploration pretty much for free.

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  • 29. At 10:19am on 03 Nov 2010, sensiblegrannie wrote:

    Being a total and absolute beginner at this type of thing I don't know where to look to answer my particular question and I wondered if any of you could answer it.
    If an NEO came within the geomagnetic sphere of influence of either the moon or the earth, at a particular point, could it have the potential to become a new orbiting body and potentially alter the equilibrium of the existing bodies?

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  • 30. At 12:18pm on 03 Nov 2010, knowles2 wrote:


    Interesting question, would love to know the answer myself.

    I would of thought it would be possible but extremely unlikely as it would have to enter at the right angle, enter into a orbit which means it will not crash into the moon or the earth. An have exactly the right mass to achieve a equilibrium. I would think it be extremely unlikely.

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  • 31. At 1:19pm on 03 Nov 2010, Robert Lucien wrote:

    Hi sensiblegrannie. (Yes) The answer is that its very unlikely. The main problem is that something needs to slow the object down and reduce its momentum enough so that the Earth or Moons gravity can hold onto it - and so that it will fall into orbit rather than flying off and escaping. Even if it does go into orbit the orbit is unlikely to be stable and the object may well eventually escape anyway.
    As for changing the equilibrium of the Earth or Moon that would take something very big - at a guess a minimum of maybe several thousand kilometers across. I'm probably wrong here and there are other factors like 'orbital resonance' plus others.
    BTW Although they may be very big any magnetic fields will be absolutely minuscule compared to the gravitational forces or kinetic energy involved. The Earths kinetic energy for instance is an incredible 5x10^33 Joules.

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  • 32. At 4:01pm on 03 Nov 2010, SionH wrote:

    @ #19, alex_thewomanizer_elliott, I'm afraid to say that Armageddon was almost completely wrong in everything that happened. The thing about asteroids is that they carry a lot of kinetic energy, given by the formula; one-half x the mass of the asteroid x the velocity of the asteroid x the velocity of the asteroid.
    Breaking it into smaller pieces doesn't affect that kinetic energy formula at all. The overall energy hitting us is the same.
    The only option is to deflect it. Exploding a bomb near it is also pretty useless as the energy is wasted in several ways. Thrust or pull are the only two viable options.

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  • 33. At 5:55pm on 03 Nov 2010, sensiblegrannie wrote:

    Hi Robert Lucien
    Thanks for your response. What would create a force strong enough to slow the object down enough to reduce the momentum? It is becoming pretty crowded out there in space. What if some of these NEO'S bumped into each other? Apart from a new trajectory surely there would be a new velocity to calculate?

    That is a nice new toy for us to play with and thank you Jonathan Amos. Bookmarked and ready to go when the next NEO gets close enough for us to speculate about outcomes.

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  • 34. At 6:38pm on 03 Nov 2010, sensiblegrannie wrote:

    All the talk about environmental change has set me on a mission. I want to prove that although humans cause environmental change they are not the only cause of change. We egocentric earthlings sometimes forget that there is a whole universe out there, connected and affecting our own little planet along with everything else. Perhaps our planets are little more than magnetic vegetable balls in a swirling magnetic soup.

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  • 35. At 11:02am on 04 Nov 2010, Nickthevet wrote:

    Perhaps I'm being a bit stupid here. Aren't all of these asteroids spinning? If so then surely any propulsive "engine" will be using its delta vee in different directions, in fact a complete circle, therefore cancelling any effect on the asteroid? maybe the plan, if it exists is to pulse the engine to only come on to pull or push ata given angle. I can see that this would add yet another layer of complexity & increase any likelihood of failure.

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  • 36. At 8:56pm on 06 Nov 2010, friedemann wrote:

    I am confused somewhat. WE have claimed that the earth and solar system and the other stars are the result of the "BIG BANG" in theory(in the beginning).
    Now I have worked with explosives and have observed what happens when it blows off. Fine particles close to the blast just float up and down, and bigger stones get blasted away farther.
    But I never noticed them pulling up and passing each other(as they all are traveling relatively the same speed.)
    And we are continually separating from the other stars so they are getting farther away. Our sun and solar system is also traveling on its trajectory away from the bBB and from other stars.
    So farther away and coming from one central point. I fail to see how anything can "catch up".

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  • 37. At 12:03pm on 11 Nov 2010, TheyCallMeTheWonderer wrote:

    I've seen this film before. It hits Paris.

    @Friedemann. You are forgetting about gravity. Every object in the universe is pulling on every other object in the universe. In the explosions you have worked with, these small ejected rocks and particles do pull on each other and on do move towards one another but these tiny gravitational pulls are so tiny as to be practially unobservable compared to the pull of the earth which is much, much greater.

    It is true as you say that our universe all began with a big explosion, but as soon as all the matter in the universe was ejected it began to interact gravitationally, each particle pulling on every other particle, eventually forming into clumps that we now call galaxies.

    The asteroids that threaten us are in orbit around the earth (or the sun), the earth orbits the sun and the sun orbits the galactic core. Even galaxies pull on one another from great distances - there are several smaller galaxies orbiting around our milky way and the nearest large spiral galaxy, andromeda, is pulling on our milky way and the two will collide in about 4.5 billion years.

    In truth, the only things that could be said to be still shooting off on their original trajectories are the galactic super-clusters.

    The rocks do not catch up, we are already moving at the same speed, dominated by our sun which contains 99% of all the mass (hence all the gravity) in the solar system.

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  • 38. At 00:58am on 12 Nov 2010, U14684293 wrote:

    The easy Techno-optimism of Randy Schweikart and others will fail at the critical moment. We will be hit. About a third of us will die quickly, markets and brokerage accounts will lose >95% of their value in a day....and then things will get much worse....Survivalism? forget it! yet another useless human fantasy about to be exposed in the rudest way. See "FINDING CHICXULUB 1978, LIVING WITH NEOCATASTROPHISM 2007" at the IBRI website; Chicxulub Crater co-discoverer Glen Penfield laid it out.

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  • 39. At 6:18pm on 13 Nov 2010, SpursCantWinTheMilkCup wrote:

    Well Phil_o_the_North lets hope the English dont start predicting these because if it is as dodgy as Weather Forecasting, we may as well say our prayers now

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  • 40. At 09:57am on 12 Dec 2010, seismo wrote:

    Not that asteroids aren't a threat but we have two other, much more likely ELEs to consider; volcanoes and atmospheric/ocean warming.

    To date the planet has suffered one ELE by asteroid and it is likely that at least one of the other extinctions was a CO2 warming event that triggered oceanic toxic gas production.

    Vastly outnumbering these however have been volcanic super-eruptions.
    Should the 1815 Tambora explosion (that led to the summer of 1816 -- the year without a summer) be repeated today we would have massive crop failures in the northern hemisphere (though a handy diminution in solar capture) and if we had a Tuba level eruption (76ky bp)we could face an extinction threat. Bear in mind that in this modern age we have next to no long term food or seed storage.

    Even a repeat of the 1783 Laki eruption of in Iceland which killed some 23000 people in Britain could scale to devastating loss of life.

    Interestingly the crustal destabilisation and increased volcanic potential engendered by the melting of the Greenland icesheet rarely impinges on the climate debate.

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