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Chicken Little learns to forecast

By adiffer in Science
Thu Jul 25, 2002 at 08:47:22 AM EST
Tags: Science (all tags)
Science

Over the last few years, the news media has had more and more opportunity to report on a certain class of events that could lead to the 'End of the World' as we know it.  These opportunities are not born of conspiracy theories, religious Armageddon, or ancient prophecies.  They are based upon the hard work of many astronomers hunting for large rocks traveling about the sun at high speed on paths that can intersect our world.

The level of alarm in recent stories has generally been trending downward among the more reputable news sites.  The level of exposure to these stories among the general public has been trending upwards.  In the interests of understanding for everyone involved, a lesson for learning to read the forecast is provided here.


The celestial objects with which we are at risk of collision are referred to a 'minor planets' and cover a range of classes including comets, asteroids, and the trash left over from earlier space flights.  The types that get the most attention by the media are the ones typically referred to as 'Near Earth Objects' (NEO's).

When it comes to scenarios that could conceivably lead to the end of our species on Earth and mass extinctions on the scale of the disappearance of the dinosaurs, the group of NEO's consisting of rocks larger than one kilometer in diameter are referred to as 'Potentially Hazardous Asteroids' (PHA's) if they are also known to have a close approach to Earth in the foreseeable future.

Numerous objects smaller than one kilometer have been found, but most scientists currently feel that the damage one could do to the Earth in a collision is somewhat less than our extinction. The collapse of our civilization, death by starvation and disease of a very large percentage of the human population, and massive geopolitical upheaval are all quite possible, though, for some of the PHA's that are not quite large enough to be dinosaur killers.

Fortunately for us all, there are many who are concerned with knowing where these PHA's are and where they are going.  Some funding is available to astronomers to hunt the night sky for these disasters waiting to happen.  Anyone who knows the places on the internet where these scientists collect their findings can look into the future and know when the sky is going to fall on them.

Our Crystal Ball

One such site is known as the Minor Planet Center.  It isn't a flashy site that will draw the typical web surfer to revisit its pages often.  It is meant mostly for those researchers who are hunting for the rocks.  Among the many links on its pages, though, are ones that an interested forecaster can use to know what is where and when it will come crashing by.

One of the second level pages is The NEO Page.  This page is also unexciting, but it does sport links to a couple of active plotters that will draw gif images of the inner solar system with the locations of all the known asteroids including those not classified as NEO's.  Any reader that wants to get an idea of just how cluttered our solar system is encouraged to have a look.

From the NEO Page is a more interesting page that may be used to predict a bit of your future.  The first is the  
Forthcoming close approaches
page.  This page includes a basic timeline with a naming of NEO's, how close they will approach us, and when the opposition will occur.  Included below is a snippet of their page including events to come in our immediate future.  (The table has been massaged a bit and an extra column added to show the approach distances in terms of the size of the Moons orbit around the Earth beside the distances in terms of the size of the Earth's orbit around the Sun.  Know that the diameter of the Earth's orbit is about 384.6 times the diameter of the Moon's orbit.)

Object Name Encounter Date Distance (AU) Distance (LU) Oppositions Observed Time Span
2001 TE2 2002 July 26.03 0.180700 69.5000 3 2000-2002
2002 AL14 2002 July 26.58 0.084650 32.5577 1 233 days
2000 RV37 2002 July 29.20 0.162800 62.6154 2 2000-2001
2002 LV 2002 July 30.03 0.112400 43.2308 1 53 days
1999 NB5 2002 Aug. 05.68 0.105900 40.7308 2 1999-2002
2002 NY40 2002 Aug. 18.32 0.003518 01.3531 1 9 days
2002 NV16 2002 Aug. 22.87 0.038040 14.6308 1 11 days
2002 HK12 2002 Aug. 27.34 0.048690 18.7269 1 94 days
2001 EB18 2002 Aug. 30.07 0.033770 12.9885 1 432 days
2000 OK8 2002 Sept.14.47 0.169100 65.0385 2 2000-2001
2001 WT1 2002 Sept.25.08 0.165400 63.6154 1 53 days
1998 RO1 2002 Sept.29.73 0.183800 70.6923 5 1996-2001

Note that most of the entries show close approaches that are well outside our Moon's orbit.  If we wish to focus only upon the more harrowing examples, we can visit a different page at PHA Close Approaches.  This page displays the close approach events sorted by how close the shave is.  Included below is a small snippet from the top of the page.

Object Name Encounter Date Distance (AU) Distance (LU) Oppositions Observed Time Span
2000 WO107 2140 Dec. 1.75 0.000542 0.2085 2 2000-2002
2001 WN5 2039 June 26.96 0.001485 0.5712 1 301 days
1999 AN10 2027 Aug. 7.29 0.002652 1.0200 3 1955-1999
2002 NY40 2002 Aug. 18.32 0.003518 1.3531 1 9 days
2001 WN5 2028 June 25.74 0.004367 1.6796 1 301 days
2002 CU11 2080 Aug. 31.01 0.004427 1.7027 1 132 days
1999 RQ36 2060 Sept.22.96 0.005548 2.1338 2 1999-2000
2001 YB5 2002 Jan. 7.32 0.005571 2.1427 1 11 days
4660 Nereus 2166 Feb. 13.30 0.005725 2.2019 8 1981-2002

On both of these pages, a reader may find examples of potentially world killer events.  That same reader may wonder why we aren't all running around scared to death about what we are learning.  Some will tell that reader 'Trust in the scientists to figure out how to protect us.'  Such trust makes for some interesting (and some bad) science fiction has Hollywood has proven over the last few decades.  Some will tell that reader 'Trust in your faith to bring about the correct future.'  That statement may work for some of the more faithful among us, but what of the rest?

For the rest of us, we must learn to read more on these pages than the closest approach columns and the related date.  We must also learn to understand what the number of observed oppositions means and the amount of time covered by the orbit arc.  These last two pieces of information tell us how confident the astronomers are in the results of their observations and how reliable the data is for predicting a future path for these rocks.

Our Crystal Ball is fuzzy

Any time a scientist makes a measurement of something, there is always a little bit of uncertainty involved with the accuracy of their numbers. Anyone who has looked through a telescope knows the astronomers are faced with measure the positions of fuzzy, faint dots of light. Modern astronomers have an advantage over their predecessors due to the fact that digital electronics has taken over the job of image recording from photographic plates. However, that advantage does not entirely eliminate observational uncertainties.

Imagine drawing two large dots on a page and connecting them with a line.  The larger the dots are the more choices are available for the slope of that line.  At the middle of the range is a line that connects the centers of the two dots, while the extreme slopes are represented by lines that run tangent to the upper (lower) edge of one dot and the lower (upper) edge of of the other.  The range of possible slopes is greatly reduced, however, if the dots are moved far apart from each other.

The information available in the columns concerning orbit arc is the information we need to understand how far apart the observations are that lead to the predicted orbit for each NEO.  If the number of oppositions is large, the observations are far apart.  If the time span covered by the observations is large, the information deduced about the orbit of the NEO is reasonably accurate and has small uncertainties..  Therefore, the most trustable entries on the pages describing close approaches are those that have either a large number of observed oppositions or a large time span for the measurements.

The PHA page shows in its first two entries examples of close calls that each are predicted to pass within the Moon's orbit.  The first one has the smallest approach distance, but it is also likely to be the more accurate one due to the larger number of observed oppositions.  The third entry may seem a little strange.  1999 AN10 was discovered in 1999 yet the time span covered by observations is from 1955 to 1999.  How can this be?  Even without looking up the notices concerning this asteroid, we can know the most likely thing is some astronomer discovered someone else had taken a picture of the same rock during 1955 and then lost it or never knew it.

Our Crystal Ball is being upgraded

One bit of encouraging information to be found on other pages at the Minor Planet Center shows the number of discoveries by different teams over the years.  While the number of NEO's and PHA's has been climbing at an ever-faster rate, our ability to know about them is transitioning from complete ignorance to an understanding that there is a lot of dangerous material out there.  Many people have dedicated a lot of their work to discovering these hazards even if we don't know how to deal with the dangers when we find them.

Some of the groups engaged in this work can be found at the bottom of the NEO Page.  Both NEAT and LINEAR are listed among them.

There is a project at the Space Frontier Foundation designed to get more non-governmental money to continue the research and get more astronomers the equipment they need at THE WATCH.  Read up on it if you want to try to make a difference.

With these tools and a bit of practice, the readers can decide for themselves what level of alarm they wish to feel with each new announcement.  The readers can also decide if they wish to do anything on a more personal level to change the future they read in the forecasts.

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Poll
How would you deal with a PHA?
o Pray it will go away 0%
o Pray it won't go away 19%
o Blow it up 19%
o Strip mine it 42%
o Build a tractor beam somehow 19%

Votes: 42
Results | Other Polls

Related Links
o report
o Minor Planet Center.
o The NEO Page.
o Forthcoming close approaches
o PHA Close Approaches
o NEAT
o LINEAR
o THE WATCH.  
o Also by adiffer


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Chicken Little learns to forecast | 21 comments (16 topical, 5 editorial, 0 hidden)
Heh (5.00 / 1) (#3)
by carbon on Thu Jul 25, 2002 at 03:24:21 AM EST

So, what happens if one of these PHAs looks to be very likely to hit? Would it be possible for us to destroy it beforehand, ala the unfortunately unpopular Lucasarts game 'The Dig'? Or, would we simply get to enjoy a few weeks of anarchy and chaos before the planet either blows up, or returns to normal, or the economy collapses as a result of the chaos, thus forming a sort of self-fulfilling prophesy?

Morbid humor sure is fun. :-)

Wasn't Dr. Claus the bad guy on Inspector Gadget? - dirvish
depends (5.00 / 1) (#6)
by adiffer on Thu Jul 25, 2002 at 03:42:10 AM EST

It can depend on a number of things like size, density, and the amount of time we have to think about it.  I suppose it could be treated like global warming too.  8)

-Dream Big.
--Grow Up.
[ Parent ]
chicken littles (4.50 / 2) (#7)
by khallow on Thu Jul 25, 2002 at 04:01:45 AM EST

I was annoyed by the recent report that had a two kilometer asteroid (that could hit us!!!!! Panic!!!!!) that would pass within ten million kilometers of Earth (only fourty times the distance to the Moon) sometime around 2015 or so. It had a positive threat number so it must be dangerous. As the scientists in article point out, it's extremely unlikely to be a danger to Earth and we'd have more than a decade to angst over it even if it were.

Stating the obvious since 1969.

Alarmist billboard (none / 0) (#15)
by thebrix on Thu Jul 25, 2002 at 01:13:02 PM EST

Yesterday the Evening Standard had a billboard ASTEROID APPROACHING EARTH. The story inside was probably less exciting ;)

[ Parent ]
threat numbers (none / 0) (#19)
by adiffer on Thu Jul 25, 2002 at 03:50:16 PM EST

When they pin down its orbit a bit better, they will be able to refine the threat number.  At the time, they could not say what the orbit is with their usual great precision.  Uncertainty, size, and the possibility of an impact wherre enough to drive the threat number positive.

Expect to see positive threat numbers in the future that don't get reduced quickly.  It's just a matter of time.  At the rate they teams are finding rocks, that time will probably be short.

-Dream Big.
--Grow Up.
[ Parent ]

Very interesting, two questions (4.00 / 1) (#9)
by DesiredUsername on Thu Jul 25, 2002 at 08:35:42 AM EST

1) Why are the sizes of these objects listed?

2) For those objects that are passing us at roughly the distance of the moon, how visible will they be? This depends on #1 but also on how visible a "minor planet" is in general.

Play 囲碁

dammit (none / 0) (#10)
by DesiredUsername on Thu Jul 25, 2002 at 08:36:22 AM EST

I mean why aren't the sizes listed.

Play 囲碁
[ Parent ]
Boiled down table (5.00 / 1) (#12)
by thebrix on Thu Jul 25, 2002 at 09:36:13 AM EST

The table misses out a lot to keep it small - most importantly, six orbital elements per asteroid (quantities which allow the orbit to be reconstructed).

[ Parent ]
they don't really know (none / 0) (#16)
by adiffer on Thu Jul 25, 2002 at 03:23:32 PM EST

The size of a rock is guessed at by how bright it appears to be.  We have a rough idea of how reflective certain types of asteroids are and can backtrack to the diameter.  The researchers will sometimes restate their numbers, though, as more information on any one particular rock becomes more refined.

The number of minor planets that have actually been imaged by radar is relatively low.  We know much more about where they are that about what they are or how big they are.

-Dream Big.
--Grow Up.
[ Parent ]

Answers (none / 0) (#11)
by thebrix on Thu Jul 25, 2002 at 09:32:12 AM EST

1. A couple of kilometres at most.

2. Very difficult to tell because albedo (how well the asteroid reflects light) is difficult to calculate when the body is so small.

[ Parent ]

visibility (none / 0) (#18)
by adiffer on Thu Jul 25, 2002 at 03:42:38 PM EST

You probably won't see them with the naked eye.  Comets have the high albedo necessary to be visible at such a small size while the asteroids generally don't.

One thing to remember about these rocks is that they are about as reflective as the typical asphalt road.  Even our own Moon has a low albedo.  Combine a low albedo with a tiny size and you get a stealth rock.

That doesn't mean these things are out of range of the amateur astronomy community, though.  If you have some good equipment and know what you are doing, you have a chance of spotting some of the larger ones when they are close.  There are some rich folks with a love of the hobby who probably have amateur set-ups that can do it.  To know more about where to look and whether you stand a chance of seeing it, you have to dig a little deeper and get ephemerides.

-Dream Big.
--Grow Up.
[ Parent ]

what about a large-body collision with moon? (4.66 / 3) (#13)
by Shren on Thu Jul 25, 2002 at 09:42:56 AM EST

The moon gets hit by plenty of little asteroids because it has no atmosphere to deflect them. But what happens if a planet-killer rogue body hits not the earth, but the moon? Nothing? Could the moon's orbit be shifted? How much would this affect tides?

My mild knowledge of physics tells me that it's implausible for the moon to be knocked out of orbit or into the earth except by an object at least two orders of magnitude larger than the average rogue body. But what could a smaller body do?

Strange events in 1178 (none / 0) (#14)
by thebrix on Thu Jul 25, 2002 at 01:09:35 PM EST

I read about this (a possible asteroid impact on the Moon) some time ago in a 19th century astronomy book ... and, lo and behold, BBC News Online has an excellent account.

It's interesting that the researcher believes a 'meteor shower' is all that would occur; given the Moon's lower escape velocity and lack of atmospheric drag I'd have thought larger bits could've been thrown out (hence meteorites landing on Earth).

[ Parent ]

The meteors fr. moon could be gigantic (none / 0) (#21)
by MickLinux on Fri Jul 26, 2002 at 11:19:01 AM EST

It is not inconcievable that the "meteor shower" from the debris could still be huge.

Indeed, there may have been a large asteroid that was blasted from the surface of the moon.  Read below from an email from my brother, John, who has been hiking and driving around, looking at the geology of Virginia for a while, now:

----QUOTED MATERIAL BEGINS HERE----
A really cool mystery has been the one about the white titanium-rich anorthosite rock in Roseland (Nelson County), VA.  Joe was the first to propose
that maybe it had arrived as a meteor from the moon.  Agreeing with that hypothesis is the fact that geologists say that the rock had to have been
formed at very high temperatures for a very long time--which happens to be the condition the moon used to be at for a long time.  Like moon rock, the
Roseland anorthosite is white, extremely reflective, and grinds together to form white powder.

Finally, today I read that the outer crust of the moon is made of...anorthosite!  It's really funny to think of all these people with white gravel
driveways made of...moonrock!


I make a call to grace, for the alternative is more broken than you can imagine.
[ Parent ]

other evidence (none / 0) (#17)
by adiffer on Thu Jul 25, 2002 at 03:33:35 PM EST

In all likelyhood, a large collision would clutter our immediate neighborhood with debris from the impact.  How much debris would depend on the size of the impactor.  One thing to remember about debris from a lunar impact is that debris would leave the Moon but still retain most of the momentum it had while still attached.  That means it would take up an orbit around the Earth that was similar to the one occupied by the Moon.  That region tends to be a little unstable for small objects, the the orbits would be perturbed over time.  Some of the debris might eventually reach us, but much of it would be ejected from the Earth-Moon system.

Take a look at moons around Saturn and Uranus, though, and you will find evidence for them getting hit by objects large enough to do some serious damage.  When you find a bullseye crater on one side and a big crack on the opposite side, you know they REALLY got hit.  If I remember right, one of the moons of Uranus was supposedly hit hard enough to break it, though it slowly came back together afterwards.

-Dream Big.
--Grow Up.
[ Parent ]

Better mathematical tool (none / 0) (#20)
by MickLinux on Fri Jul 26, 2002 at 10:24:00 AM EST

First, let me qualify this statement:  I know what I am talking about because #1, my father is directly involved in this research, #2, I have performed some calculations with this method, and it is extremely easy.

---Now---

One of the major problems with NEO calculations is that we cannot even properly predict the positions of the planets.  An 11-body problem (or worse, a 121-body problem) is not trivial.

Add to that the lesser fact that there are masses out there which we cannot account (oort clouds?  dark matter?  other planetoids?) and the accuracy of our prediction is ... well, limited.

However, we do have a major improvement, now, that can upgrade the accuracy of our calculations, if not the data -- and that can increase the precision of our accuracy perhaps perhaps 100-fold.

The method is called the parker-sochacki solution to the Picard iteration, and it is easy enough that you can do a 10-body problem with pencil, calculator, and paper (if you have all day) or with a computer (if you want to save about 6 hours, and spare yourself simple errors).  Then, once you have it encoded, you can quickly upgrade it to a 141-body problem, if desired, and output the results in the form of a Taylor series position function, term after term, with about 3 calculations per term per variable.

That's not at all bad.

By the way, a .ps (postscript) paper on this method that makes it clear is here

I make a call to grace, for the alternative is more broken than you can imagine.

Chicken Little learns to forecast | 21 comments (16 topical, 5 editorial, 0 hidden)
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