Originally Answered: Will an asteroid hit Earth on 25 September 2015?
So no need to be concerned about that one!
(It has now done its flyby, 8.40 am GMT on 24th September)
You can keep up to date with potential impact hazards here:
Current Impact Risks
It's easy to check. Just look and see what colour they are.
If there is one that is a significant risk it will be coloured orange or red in the Current Impact Risks table.
If they are all white, blue or green, no need to be worried about it at all.
So far none of them have ever gone orange or red. If that does happen - we will get lots of media frenzy for sure, but be aware, that the chances are very high that it gets gets reclassified to white as more measurements are made.
The way it works is that when you first detect an asteroid, you don't know much about its trajectory, and then as you find out more you refine the orbit. As that happens, then sometimes an object may for a while seem to have a trajectory that has a chance of hitting Earth at a particular date, usually at low probability - and then later on as you constrain the orbit with more observations you find out that it is less likely and finally no chance at all.
One of the objects (29075) 1950 DA , large enough to do serious damage possibly even global in its effects (1.1 to 1.4 kms in diameter) had a 1 in 300 chance of impacting earth in 2880, but that risk has now been reduced to 1 in 20,000. Another object (89959) 2002 NT7 a little smaller but large enough to have potentially global effects, had a risk of 1 in a million of hitting Earth in February 2019, for a while, but it is now known it will miss.
Another object 2013 TV135 when first discovered, with only one week of observations, had a 1 in 63,000 chance of hitting Earth in 2032, leading to scary headlines. It's now known it will miss us on that date by over three quarters of the distance to the sun.
Details: Near-Earth object
To put it in perspective, if you had an image of the Earth with 1600 pixels resolution for its diameter, like a high resolution computer screen, then these asteroids would be a little over 1 pixel in diameter.
The dramatic images you see of huge impactors almost moon sized hitting the Earth are artist drawings of the impacts that happened in the early solar system. Chances of one of those is too tiny to consider and we'd know about it long in advance if there was anything. For instance Mercury being deflected from its orbit by the perturbations of Jupiter - may happen about half a billion years from now and if it did head for Earth it would be devastating - but not something we need to worry about. Long enough for humans to evolve a second time from primitive microbes.
There is a risk, but the chance of a major "dinosaur killer" type impact before the end of this century is around 0.0001%.
Since there are far more of the smaller impacts, I expect the first successful prediction of an impact on the Earth would be something like the Russian meteorite - an impactor maybe of the order of up to 100 meters diameter or so, and you tell people to stay indoors and avoid windows in the target region or at worst might have to evacuate some place.
So far we haven't yet had a successful prediction of an impact. Since we've had several impact craters, really tiny ones, then there are impactors there that we could predict as the program gets more refined.
Impact craters as large as this are likely to be created every 10 to 100 years
Diameter about 45 meters and created by an incoming rock only 1.3 meters in diameter. Pristine Impact Crater Discovered in Egypt Desert (first discovered on google maps :) ).
It's a challenge to track things as small as that. But as we get to smaller and smaller impactors, then eventually we are bound to predict a small impact like this. But most of the Earth's surface is uninhabited.
So just by probability, the most likely first confirmed predicted impact would be a small crater like this in an uninhabited region of the Earth. Just because they are so common.
And as it happens we have managed to predict a small impact. This is 2008 TC3
It was used as a way to test the process of tracking NEOs on impact trajectory to Earth and many observations were made. Wikipedia (which is good on this topic area) summarizes it like this:
t was notable as the first such body to be observed and tracked prior to reaching Earth.[6] The process of detecting and tracking a near-Earth object, an effort sometimes referred to as Spaceguard, was put to the test. In total, 586 astrometric and almost as many photometric observations were performed by 27 amateur and professional observers in less than 19 hours and reported to the Minor Planet Center, which issued 25 Minor Planet Electronic Circulars with new orbit solutions in eleven hours as observations poured in. On October 7, 01:49 UTC,[9] the asteroid entered the shadow of the Earth, which made further observations impossible.
It would be a similar process if we found a big asteroid headed our way.
Amateurs and professionals would collaborate to make as many observations as possible to refine the orbit until we know exactly where it is headed and all we can find out about it. Astronomy is interesting as an area of science where amateurs are of great importance Modern telescopes owned by amateurs are very capable.
And while they don't have giant telescopes of tens of meters in diameter, they do have them up to a meter or so in diameter, and some a bit larger. And have the advantage that there are many amateurs to take observations when the pros are few in number by comparison.
BTW here is a telescope built by an amateur astronomer (truck driver) using a mirror from an old spy satellite he got hold of, that was nearly 2 meters in diameter (70 inches). He had to silver it himself. It is basically a giant "dobsonian" steered by hand I think.
At the time anyway, says he was the largest amateur built telescope in he world.
Here is a list of some other large amateur telescopes larger than 1 meter in diameter: Largest Amateur Telescopes
Astronomy is one of the few areas of science where amateurs continue to make significant on going contributions through their own observations.
There are so many events and objects to observe that the very few big telescopes can't possibly handle all the observations. It would be absurd to track a newly discovered asteroid with say the Hubble space telescope and such like.
They would be sure to rely on the amateur community as well as pro astronomers world wide. And indeed they do. For more about this see my comment on this answer.
This one broke up in the atmosphere as a dramatic "fireball" type meteor.
Photos were taken of the fireball from space
I expect many more events like this before we get any predictions of a major impact. And when eventually we do, which we are bound to, at least Tungaski sized, it will probably be for many centuries or a thousand years into the future. Just by probabilities. Though it might be for nearer future.
As I said before chance of a really large kilometer scale one hitting Earth before 2100 is about 0.0001%. Still it could happen so is well worth putting a lot of effort into making sure we can predict anything like that.
There are ways we can deflect a meteorite, especially given lots of time we could deflect even a kilometer scale one. Even by a measure as simple as painting one of its hemispheres white.
See Asteroid impact avoidance
As for NASA somehow being able to predict a major impact that nobody else knows about, forget about it, it's an absurd idea :).
MORE ABOUT THE TELESCOPES USED TO DISCOVER AND TRACK NEOS - AND THE PEOPLE WHO OPERATE THEM
Hubble's field of view is measured in arc seconds usually and largest field of view 0.05 degrees or about a tenth of the diameter of the Moon. By comparision PAN-STARRS which is one of the main telescopes used for searching for NEOs has a field of view of 3 degrees, or six times the diameter of the Moon.
You can compare the field of view of various telescopes here: Pan-STARRS
And this is a photograph taken with Pan-STARRS
- full three degrees view, 60 times the diameter, and 3600 times the area of the field of view of Hubble and photographed with a super high resolution a 1.4 gigapixel digital camera. This is what you want for searching for asteroids - wide field of view, lots of photographs, sensitive to low light levels.
To see this image in its full glory go to APOD: 2012 October 12 and then click through to see it full screen. And that's just a fraction of the detail of its original images, which it takes twice a minute, each in enough detail so that if printed at 300 dpi it would cover half a basketball court The 1.4-Gigapixel Camera Standing Between Us and Armageddon
Pan-STARRS is operated by Hawaii University and a team of astronomers from 10 different institutes from four countries in the PS1 Science Consortium
And when you first find the asteroid, you have no idea what its long term trajectory is. You need several weeks of observations to get started, and then they continue to refine the orbits over years of observations.
You need all the help you can get for that task.
Big telescopes are sometimes used when asteroids do flybys of the Earth to get detailed images of them. But apart from that - it's lots of observations by many people including many amateur observations.
The main ones are listed here:
"Most of the NEO Discovery Surveys, including the Catalina Sky survey, Pan-STARRS and Spacewatch provide a substantial number of follow-up observations. Dr. David Tholen, at the University of Hawaii, is particularly efficient in providing the very faint follow-up observations that are often required to prevent small NEOs from being lost.
A substantial number of faint follow-up observations are also made at the Magdalena Ridge Observatory in New Mexico (Bill and Eileen Ryan). Explicit mention should also be made of the prolific number of follow-up observations provided by the Astronomical Research Institute (ARI) under the direction of Robert Holmes and the amateur group at the New Millennium Observatory in Northern Italy."
The new millenium observatory in Italy - run by amateur astronomers - one of the many groups of observers who are involved in the Follow-up Observing Programs to refine the orbits of NEOs. This was built by Luca Cozzi, an engineer, brother of Dr. Elia Cozzi, Italian amateur astronomer and astrophysicist whose idea it was.
That's just to give an example - there are many groups of people and many telescopes world wide involved in this - and as you see - that's an ordinary not that big suburban house in Italy with a telescope built into its roof - the telescopes don't have to be huge monster tens of meters telescopes for this job.
Robert Holmes, amateur astronomer, one of the most prolific follow up observers for the NEO program.
For an idea of some of the other amateur groups involved in the NEO follow up observations see the Planetary Society grants, which they give regularly - to amateur groups who are doing especially good work in this area. See:
Leaders in Asteroid Tracking/Observing Awarded Through Global Grant Program
Bob Holmes again, this time with one of his telescopes - a wide field of view 0.76 m (30 in) telescope with a sensitive CCD camera purchased with a 2013 grant from the Planetary Society. Bob Holmes of the Astronomical Research Institute in Illinois, USA
So, NASA are part of a big global program, and it is all interconnected.
- The sensitive telescopes with a wide field of view that find the asteroids originally (this used to involve amateurs also but is now largely automated) - run by many teams of astronomers from many different countries
- Those telescopes together with amateurs that track them after that to get the long baseline of measurements for the accuracy you need to assess probabilities properly.
- The big telescopes that occasionally take images of them for instance during close flybys of Earth.
- The computing / math geeks who are expert at working out the orbits and dynamics. They all have to work together, it's a big international effort.
- And many others
SUMMARY CONCLUSION
There is nothing in the list that has any probability at all of hitting Earth in the next year.
None at all. Nothing even big enough to be hazardous to a city or cause a tsunami.
We will get many smaller impacts up to say ten meters or so - we get those all the time. They usually burn up in the atmosphere causing a spectacular but harmless fireball, occasionally some remnant makes it to the ground.
There is a chance of larger impacts up to hundreds of meters, and a tiny chance of larger impacts than that because its work in progress, and it will take a while before they have them all mapped out. Hope to have nearly all mapped out by the 2020s down to a few hundred meters.
Actually 2012 TT5 is not that big anyway as meteorites go, diameter 137 - 307 meters. NEODyS.
At that size it would be only local in its effects, if it did hit the Earth. Devastating to a city and even a state (at the larger end of the diameter estimate) if it hit one. Could cause a tsunami if it hit the sea. If it landed in one of the many deserts or Siberia or Alaska, it probably would just a crater. Crater would be up to 6 km in diameter.
What would happen if a large object hit the Earth
Some time in the future, we may need to do something about it, but at that size it should be pretty easy to deflect or perhaps mine, if it has useful materials for space industry.
For the effects of larger meteorites, see Environmental Damage from Asteroid and Comet Impacts. Also Solar System Fluff From 1 to 10 km then they are large enough to be devastatign world wide (but not extinction causing for humans).
World ending not going to happen, nothing that big for billions of years, probability about zero. For more about that, see Robert Walker's answer to What are the odds of a bigtime asteroid hitting the Earth a la Armageddon and Deep Impact?
Dinosaur extinction scale - i.e. that many humans could survive because of our technology but dinosaurs couldn't - chances are minute of that happening in the near future, say before 2200.
Impacts as big as that happen every few million years. So, the best guess, at this stage before they complete the survey is that we probably have to wait at least a few million years before we have an impact as big as that.
With thousands, or millions of years to prepare for the impact, we may be able to divert it quite easily. Even with a century or two we may find a way to divert it, or if worst comes to the worst, have many decades to prepare e.g. building shelters etc to protect us, or identifying areas of the world that are safe to migrate to until the impact is over.
See also
Sizing Up the Threat from Near-Earth Objects (NEOs)
Entertaining TED talk about asteroid impacts and what we can do
How to defend Earth from asteroids
by Phil Platt (of Bad Astronomy blog fame)
One of several blog posts about one of the many meteorite scare stories (we get them every year or so, and sometimes they are published by large distribution newspapers that should know better) by Phil Platts - there's a nice video debate with experts about asteroid impacts at the end
Reports of an Asteroid Impact in 2106 Are Greatly Exaggerated
Also please see the Asteroid Scares topic.
I've just written this up as an article for my Science20 blog here:
Is It True That An Asteroid Will Strike Earth On [Insert Date Here]? - Truth Behind Asteroid Scare Stories
DEFLECTING ASTEROIDS
If you are curious about how painting an asteroid white can deflect it, here is a short video of professor Dave Hyland talking about the idea:
And article
Asteroids No Match For Paint Gun, Says Prof | Texas A&M Today
(or How to Deflect Killer Asteroids With Spray Paint | WIRED)
Amongst the most favoured approaches are, direct kinetic (non nuclear) impact (obvious thing to do really) - and the gravity tractor
But a huge number of other ideas have been explored, some in a great deal of detail. For some of them see the wikipedia article: Asteroid impact avoidance
ASTEROID DETECTION
So far our asteroid detection is done from Earth. But if we can send space telescopes into independent orbit around the sun, especially if they are closer to the sun, then they will be able to spot faint close NEOs much more quickly, so that we can complete the search for them sooner.
This is the idea of the B612 foundation (named after the "Little Prince"'s planet) which has been working for some time on its Sentinel telescope idea
It would sit inside of Earth close to Venus's orbit giving it a good field of view of NEOs close to the sun. It looks away from the sun to avoid being blinded by it - and it can then see faint NEOs that are in between the Earth and the Sun which is the hardest place to spot them from our current Earth based surveys. Eventually it would spot just about everything out there that's in the vicinity of the Earth orbit.
Idea is that it would find nearly all potential impactors down to 40 meters diameter. And recently announced, that it should be able to spot them down to 20 meters diameter.
Anyone who is really keen to support them with their work can help them out with a donation on their website.
You can also sign this petition to increase funding of asteroid detection by 100 times
100x Declaration
See also: Robert Walker's answer to Is the act of drilling into an Earth-bound asteroid to blow it up with a nuclear weapon (as seen in Armageddon) technically feasible? If so, how much would it cost and how many nukes would you need? (The answer is, it could be possible to deflect it or destroy it with a nuclear weapon, but it's far more likely that we have many close flybys of Earth first, and then gentle nudges by just a fraction of a meter per second are all that is needed, so you can use much lower cost and simpler methods).
Also Robert Walker's answer to Is NASA presently capable of fending off a collision if a meteor or any other celestial body were to strike the earth?
I've written up this answer as a science blog post here Is It True That An Asteroid Will Strike Earth On [Insert Date Here]? - Truth Behind Asteroid Scare Stories
And I've now made a kindle booklet which expands on this with a lot more detail here:
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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