Based on the new observations, we calculate the following information for 2003-CR20:

• Diameter: 604m (up from 560m)
• Mass: 3.0e11 kg (up from 2.4e11 kg)
• Potential impact speed 25.10 km/sec (up from 24.85 km/sec)
• Potential impact energy(only IF it hits): 23,000 Megatons (up from 18,000 Megatons)
• Torino impact hazard scale : 0 (down from 1)
• cumulative Palermo Scale : -3.09 (down from -1.04)
• close Earth approach paths in next 100 yrs: 5 (down from 13)
• Earth impact odds in the next 100 yrs: 1 in 4,167,000 (down from 1 in 20,000)

There is a 99.999976% chance the asteroid will miss the Earth during the next 100 years.

The following is a table of the close Earth approaches by 2003-CR20 where Earth lies within the 5-sigma path. See my explination for the data in this table. The 5-sigma approaches as of the time of this Journal entry are:

1. 2031-09-20.56 1.04 +/-0.353 (Earth inside 3-sigma path)
2. 2043-09-20.19 0.29 +/-0.593 (Earth inside 1-sigma path)

The most significant close approaches have been marked in bold. The ''highest risk'' approach is 2043-09-20.19 0.29 +/-0.593 with only a 1 in 111,111,000 chance that 2003-CR20 will impact the Earth on that pass.

The 2003-CR20 orbit model has become much better for the Earth. It has dropped to 4th place on the current impact risks table. As of 2003-Feb-28 21:00 UTC the refined model's Torino impact hazard scale had dropped to the -2's, but we didn't have time to port a Journal update. As more data comes in, 2003-CR29 risk seems to be declining further.

It has been shown that 2003-CR20 had an encounter with Venus on 1960-01-23.33 with a pass somewhere under the 1,000,000 km range. This encounter may have been the event to have nudged 2003-CR20 into its current high-risk orbit. This high-risk orbit will not last long as an close encounter with Mars in 2096-01-07.15 and another with Venus in 2097-11-12.28 will move 2003-CR20's orbit further away from Earth's path.

2003-CR20 seems to be a wild slingshot ride among Venus, Earth and Mars. Only time will tell where it ends up, but for the next 100 years it is VERY unlikely that it will hit the Earth. No doubt 2003-CR20 will be watched on future trips near Earth. New data may shed new light in the long term nature of its orbit. But the next few years we seem to be safe from that asteroid.

We hope you have enjoyed watching these updates as much as we enjoyed the challenge of modeling this very unusual orbit.

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only non-zero Torino impact hazard scale object.

New observations bring the observation total to 85 over a period of almost 14.5 days. We need more time to generate an extremely accurate model. Still the 2003-CR20 model is getting better as time goes on.

Over the next few weeks the asteroid will be observable by large telescopes. A number of observatories have responded to the priority call for more observations. We expect that more observational data will allow us to improve the orbit model.

Based on the new observations, we calculate the following information for 2003-CR20:

• Diameter: 560m (same value)
• Mass: 2.4e11 kg (same value)
• Potential impact speed 24.85 km/sec (down from 24.87 km/sec)
• Potential impact energy (only IF it hits): 18,000 Megatons (same value)
• Torino impact hazard scale : 1 (same value)
• cumulative Palermo Scale : -1.04 (up from -1.14)
• close Earth approach paths in next 100 yrs: 13 (down from 15)
• Earth impact odds in the next 100 yrs: 1 in 20,000 (up from 1 in 23,000)

IF 2003-CR20 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-CR20 were to hit the Earth in the ocean, it would create a tsunami the size and speed of which have not been seen in recorded history. Such a tsunami would would inflict total devastation along adjoining coastlines and in some cases spread destruction far inland.

The impact speed, IF 2003-CR20 hits the Earth remains on the higher end of the typical asteroid approach speed.

The impact odds, while low, have become somewhat worse. Even though the number of Earth approaches have dropped significantly with the current model, these that remain yield a slightly greater risk of Earth impact. Still, there is a 99.9951% chance the asteroid will miss the Earth.

The following is a table of the close Earth approaches by 2003-CR20 where Earth lies within the 5-sigma path. See my explination for the data in this table. The 5-sigma approaches as of the time of this Journal entry are:

1. 2034-09-20.23 1.05 +/-0.611 (Earth inside 2-sigma path)
2. 2040-09-19.42 0.91 +/-0.588 (Earth inside 2-sigma path)
3. 2043-09-20.20 0.76 +/-0.593 (Earth inside 2-sigma path)
4. 2046-03-17.53 0.79 +/-0.168 (Earth inside 5-sigma path)
5. 2050-03-15.57 0.43 +/-0.088 (Earth inside 5-sigma path)
6. 2052-03-16.74 0.68 +/-0.139 (Earth inside 5-sigma path)
7. 2061-03-16.75 0.41 +/-0.097 (Earth inside 5-sigma path)

The most significant close approaches have been marked in bold.

The highest risk approaches are 2046-03-17.53 0.79 +/-0.168 and the 2061-03-16.75 0.41 +/-0.097 approach. There is a 1 in 28,000 chance and a 1 in 200,000 chance respectively that 2003-CR20 will impact the Earth on that pass. There is a 99.9964% and 99.9995% chance that 2003-CR20 will miss the Earth on that pass as well.

The 2003-CR20 orbit model has become slightly worse for Earth. As the model continues to be refined, some other previous 5-sigma approaches have dropped off the list. However a number those that remain have been changing less and less as more observational data comes in. This type of refinement suggests that the model is on the way to becoming fairly accurate over the next 75 or so years.

So far, a search for an historic image of 2003-CR20 as failed to find anything. The historic image search continues.

We have been running the model backward in an effort to try and learn if this high risk orbit is a long standing or recent phenomenon. Complicating this search is the possibility that 2003-CR20 may have a close encounter with Venus on 2097-11-12.28 when it comes within 2.57 million km of the planet. We are exploring the possibility that an encounter with Venus in the recent past may have shifted 2003-CR20 into its current orbit pattern.

Continue to stay tuned ...

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object.

New observations bring the observation total to 73 over a period of almost 12.5 days. 12.5 days is a bit short to create an extremely accurate model, but the model is getting better as time goes on.

Over the next few weeks the asteroid will be observable by large telescopes. A number of observatories have responded to the priority call for more observations. We expect that more observational data will allow us to improve the orbit model.

Based on the new observations, we calculate the following information for 2003-CR20:

• Diameter: 560m (same value)
• Mass: 2.4e11 kg (same value)
• Potential impact speed 24.87 km/sec (down from 24.88 km/sec)
• Potential impact energy (only IF it hits): 18,000 Megatons (same value)
• Torino impact hazard scale : 1 (same value)
• cumulative Palermo Scale : -1.14 (up from -1.17)
• close Earth approach paths in next 100 yrs: 15 (down from 19)
• Earth impact odds in the next 100 yrs: 1 in 23,000 (up from 1 in 27,000)

IF 2003-CR20 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-CR20 were to hit the Earth in the ocean, it would create a tsunami the size and speed of which have not been seen in recorded history. Such a tsunami would would inflict total devastation along adjoining coastlines and in some cases spread destruction far inland.

The impact speed, IF 2003-CR20 hits the Earth remains on the higher end of the typical asteroid approach speed.

The impact odds, while low, have become somewhat worse. Even though the number of Earth approaches have dropped significantly with the current model, these that remain yield a slightly greater risk of Earth impact. Still, there is a 99.9957% chance the asteroid will miss the Earth.

The following is a table of the close Earth approaches by 2003-CR20 where Earth lies within the 5-sigma path. See my explination for the data in this table. The 5-sigma approaches as of the time of this Journal entry are:

1. 2031-03-18.05 0.52 +/-0.137 (Earth inside 4-sigma path)
2. 2031-09-20.54 0.24 +/-0.900 (Earth inside 1-sigma path)
3. 2034-03-17.73 0.80 +/-0.168 (Earth inside 5-sigma path)
4. 2034-09-20.19 0.23 +/-0.912 (Earth inside 1-sigma path)
5. 2040-09-19.39 1.54 +/-0.876 (Earth inside 2-sigma path)
6. 2043-09-20.20 0.12 +/-0.884 (Earth inside 1-sigma path)
7. 2046-03-17.53 0.85 +/-0.19 (Earth inside 5-sigma path)
8. 2050-03-15.57 0.44 +/-0.114 (Earth inside 4-sigma path)
9. 2052-09-18.83 0.34 +/-0.871 (Earth inside 1-sigma path)
10. 2061-03-16.75 0.28 +/-0.0984 (Earth inside 3-sigma path)

The most significant close approaches have been marked in bold.

The highest risk approaches are 2046-03-17.53 0.85 +/-0.19 and the 2061-03-16.75 0.28 +/-0.0984 approach. There is a 1 in 56,000 chance and a 1 in 100,000 change respectively that 2003-CR20 will impact the Earth on that pass. There is a 99.9982% and 99.9990% chance that 2003-CR20 will miss the Earth on that pass as well.

The 2003-CR20 orbit model has become slightly worse for Earth. As the model continues to be refined, some other previous 5-sigma approaches have dropped off the list. However a number those that remain have been changing less and less as more observational data comes in. This type of refinement suggests that the model is on the way to becoming fairly accurate over the next 75 or so years.

So far, a search for an historic image of 2003-CR20 as failed to find anything. For most telescopes the asteroid would only show up in an photographic image during periods of time when the asteroid was within a few 0.1AU (Earth-Sun distances) or Earth. The historic image search continues.

We have been running the model backward in an effort to try and learn if this high risk orbit is a long standing or recent phenomenon. The backward model suggests that 2003-CR20 made a approach to Earth as recently as 2000-03-19.044 and 1997-03-08.086 of 10.7 million km and 5.9 million km respectively. But those not-so-close approaches would not have had a significant impact on the asteroid's orbit.

To complicate the model even further, 2003-CR20 may have a close encounter with Venus on 2097-11-12.28 when it comes within 2.57 million km of the planet. We are exploring the possibility that an encounter with Venus in the recent past may have shifted 2003-CR20 into its current orbit pattern.

Continue to stay tuned ...

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object.

Q0: When was 2003-CR20 discovered and who discovered it?

A0: The asteroid was discovered by the JPL/NEAT team using the Haleakala-AMOS facility (NEA observatory #608) on 2003-02-11.

Q1: How far is 2003-CR20 from Earth now?

A1: As of 2003-02-24, it is about 78.726 million km from Earth.

Q2: Where is 2003-CR20 headed right now?

A2: It is on its way in toward the Sun. It currently below Earth's orbit plane heading up thru it. On 2003-04-07, 2003-CR20 will pass up thru Earth's orbit plane at which time it will be 54.180 million km from Earth. Earth is somewhat ahead of 2003-CR20 this year.

Q3: How close will 2003-CR20 come to Earth this year?

A3: On 2003-04-24, it will be only 50.139 million km away from Earth.

Q4: What is being done to improve the orbit model for 2003-CR20?

A4: Observatories continue to track the asteroid and feed position sightings back to orbit modelers. Because of 2003-CR20's unusual orbit, positional observations are being frequently made.

For the next few months while the object is somewhat near Earth's orbit, 2003-CR20 will be studied in considerable detail. We hope, in the next few months, to learn how fast it revolves about its axis. We also hope to learn the orientation of the axis of 2003-CR20. Additionally we hope to learn if the asteroid has any surface detail that suggests non-uniform light absorb ion or reflection by making a detailed study of the brightness curves of 2003-CR20. Such information will be very important in attempting to establish a long range orbit model beyond 100 years. (See the FAQ #1 from the Hazardous NEO Q&A session #0 , and in particular the Yarkovsky effect ).

While looking forward 100 or more years is important, looking backward in time is also important. Establishing an accurate model over the previous 100+ years will help archivists look thru old telescope photos in the hopes of spotting an image of 2003-CR20 years ago. Finding a mid-1900's image would allow us to establish a very accurate orbit model with a long baseline. Without such a historic photo, we will have to track it forward for a number of years (and not lose it) to improve the model.

Going backward a few hundred years might provide insight into questions such as:

• Has 2003-CR20 been in this high risk orbit for a long time?
• Did it slowly shift into this high risk orbit, or did something else nudge/pull it into its present orbit?
• How long has 2003-CR20 been a hazard? Does recent history suggest that the orbit is continuing to evolve? If so, it is evolving into a higher risk object, or a lower risk orbit? Will be get worse before it gets better?

Q5: How the original error-bar ("Center line miss of 29147km +/- 154080 km") is calculated?

What I'm actually trying to understand are the (unpublished) error bars around the odds estimate. They're obviously huge, that's why the odds change so much with each additional week of observation. Here are the things I can think of that contribute to that error:

1. Uncertainty about the position/momentum of the asteroid. Additional observations help a lot here.
2. Uncertainty about the position/momentum of the rest of the solar system.
3. Roundoff and other numerical errors in the N-body solver used to predict future position/momentum of Earth and asteroid.
4. Modeling error in the N-body solver. For example, it might ignore relativistic effects. And it is a good bet it incorrectly models the Yarkovsky effect, if it even tries.

The first three points should be straightforward to deal with in the error analysis. But the fourth one is a lot harder, since modeling error is usually thought of as bias, not a source of variance. However the magnitude of the modeling error increases with time so one might try to fold it into the error bars.

I'm trying to get a feel for how accurate the odds are and what can be done to make them more accurate.

A5: You have listed a number of the more important factors that contribute to orbit model uncertainty. Although factor #3 (numerical errors) is fairly minor with respect the other factors.

The "odds" estimate for a given close approach might very well be off by a factor of 2x or 3x in the short term (the next dozen or two years, or before the first few close approaches) and 5x to 10x in the longer term (up to 100 years, or beyond several close approaches). An approach nearly 100 years from now with "1 in a 1,000,000" odds could actually be anywhere from "1 in 100,000" to "1 in 10,000,000".

The overall odds in the next 100 years depends on how the close approaches are distributed throughout the time-span. The "error bar for the odds numbers" is typically of by a factor of 2x to 5x.

To improve model accuracy, we seek more observations, better observations, more accurate physical information.

With additional time and observations, we then work the model backward in the hopes of being able to find the object on several old photographs / photographic plates / digitized images. If a good set of historic images can be found, then a much longer baseline can be used to improve the model. By a good set we mean several quality images, with reasonable information such as accurate exposure times. We also hope to find several images spread over a number of days to years.

In a quite a few cases, useful historic data cannot be found. Without historic images, the only thing we can do is track the asteroid over an extended period of time ... assuming that you can continue to track it (you don't lose it).

Q6: How difficult is it to see the asteroid? How big of a telescope do I need to be able to view it?

A6: As of 2003-02-24, 2003-CR20 is at an apparent visual magnitude of +19.16. A +19 magnitude object is about 300,000 times fainter than the typical human eye can see. It is more than 150 times fainter than Pluto.

A typical 35 year old person with reasonable sky conditions in a very dark location with the Moon set would need a 2-meter (79-inch) reflecting telescope to visually see 2003-CR20 right now. Telescopes of that size or larger are only found at major observatories.

With a CCD or astro camera, a moderate to large amateur telescope can record an image of the asteroid.

Q7: If 2003-CR20 hits the Earth, where on Earth it is likely to hit?

A7: At the present time, we do not have enough information to predict impact locations. First of all, the odds of 2003-CR20 impacting the Earth is low, so talking about impact locations is very pre-mature.

Second, the error in time is frequently as much as +/- 12 hours. So in many cases, we don't even know which side of the Earth is facing the asteroid path.

Third, even if we know what side of the Earth is facing the in-bound asteroid, the margin of error off of the model's center line is frequently as large or larger than the Earth itself! Q8: How long does it take 2003-CR20 to complete one orbit around the sun? How close and how far away from the Sun does it get.

A8: The orbit period of 2003-CR20 is currently about 1112.43 days (3.045667 years).

It currently comes within 0.5734 AU of the Sun at Perihelion (closest approach to the Sun), and 3.6289 AU at Aphelion (farthest distance from the Sun). An AU is the average Earth-Sun Distance.

We say "currently" because close encounters with the Earth will be altering the orbit over time.

Questions, comments and corrections welcome.

New observations bring the observation total to 61 over a period of almost 12 days. 12 days is a a bit short to create an extremely accurate model. However, these 61 observations are from observers/observatories with a good track record of accurate observations.

Based on the new observations, we calculate the following information for 2003-CR20:

• Diameter: 560m (same value)
• Mass: 2.4e11 kg (same value)
• Potential impact speed (only IF it hits): 24.88 km/sec
• Potential impact energy (only IF it hits): 18,000 Megatons (same value)
• Torino impact hazard scale : 1 (same value)
• cumulative Palermo Scale : -1.17 (up from -1.32)
• close Earth approach paths in next 100 yrs: 19 (down from 22)
• Earth impact odds in the next 100 yrs: 1 in 27,000 (up from 1 in 37,000)

The 2003-CR20 asteroid is the 2nd object on the list with a non-zero Torino impact hazard scale value.

IF 2003-CR20 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-CR20 were to hit the Earth in the ocean, it would create a tsunami the size and speed of which have not been seen in recorded history. Such a tsunami would would inflict total devastation along adjoining coastlines and in some cases spread destruction far inland.

The impact speed, IF 2003-CR20 hits the Earth remains on the higher end of the typical asteroid approach speed.

The impact odds, while low, have become somewhat worse. Even though the number of Earth approaches have dropped significantly with the current model, these that remain yield a slightly greater risk of Earth impact. Still, there is a 99.9963% chance the asteroid will miss the Earth.

The following is a table of the close Earth approaches by 2003-CR20 where Earth lies within the 5-sigma path. See my explination for the data in this table. The 5-sigma approaches as of 2003-Feb-23 23:00 UTC, are:

1. 2028-09-19.80 0.73 +/-1.09 (Earth inside 1-sigma path)
2. 2031-03-18.05 0.45 +/-0.169 (Earth inside 3-sigma path)
3. 2031-09-20.05 1.03 +/-1.17 (Earth inside 1-sigma path)
4. 2034-03-17.73 0.77 +/-0.161 (Earth inside 5-sigma path)
5. 2034-09-20.15 1.63 +/-1.19 (Earth inside 2-sigma path)
6. 2040-09-19.36 2.48 +/-1.14 (Earth inside 3-sigma path)
7. 2043-09-20.17 0.83 +/-1.15 (Earth inside 2-sigma path)
8. 2046-03-17.53 0.80 +/-0.49 (Earth inside 2-sigma path)
9. 2049-03-16.96 0.91 +/-0.174 (Earth inside 5-sigma path)
10. 2050-03-15.57 0.43 +/-0.138 (Earth inside 4-sigma path)
11. 2052-03-16.74 0.73 +/-0.151 (Earth inside 5-sigma path)
12. 2052-09-18.73 0.43 +/-1.01 (Earth inside 1-sigma path)
13. 2055-09-18.73 3.28 +/-1.12 (Earth inside 3-sigma path)
14. 2061-03-16.75 0.27 +/-0.108 (Earth inside 3-sigma path)
15. 2073-03-16.43 1.11 +/-0.26 (Earth inside 5-sigma path)

The most significant close approaches have been marked in bold.

The highest risk approach remains the 2046-03-17.53 0.80 +/-0.49 approach. There is a 1 in 50,000 chance that 2003-CR20 will impact the Earth on that pass. There is a 99.998% chance that 2003-CR20 will miss the Earth on that pass as well.

The 2003-CR20 orbit model has become slightly worse for Earth. Stay tuned ...

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object.

Here is a typical example:

2035-09-19.13 3.07 +/- 2.55 (Earth inside 2-sigma path)

The following provides a more detail about such tables:

1. date (YYYY-MM-DD.DD)
   
   The .00 start of a day is with respect to midnight UTC (think GMT +0 hrs, +5 hrs EST, +8 hrs PST).
2. close approach distance (in 6420 km units)
   
   The distance will be given in Earth target size units of 6420 km (slightly larger to account for the thickness of the atmosphere). So a distance of 6.78 means 6420*6.78 = 43527.6 km.
3. +/- error term (in 6420 km units)
   
   The +/- error is also given in the 6420 km Earth target size. The error represents a ~68.3% (1 sigma) certainty. So a +/-2.47 means that there is a ~68.3% chance that the asteroid will be within 2.47 * 6420 = 15857.4 km of the 6420*6.78 = 43527.6 km center close approach distance.

NOTE: Even if the Earth is within the ~68.3% (1 sigma) path certainty, the odds of the path impacting the Earth will be less (and almost always FAR LESS) than ~68.3%. This is because one has to take into account the chance that the asteroid will actually follow that given path.

New observations bring the observation total to 47 over a period of almost 11 days. 11 days is a a bit short to create an extremely accurate model. However, these 47 observations are from observers/observatories with a good track record of accurate observations. They come from several independent observatories have provided data that fit well together. Taken as a whole, they allow one to begin to produce an accurate orbit model.

Based on the new observations, we calculate the following information for 2003-CR20:

• Diameter: 560m (u[ from 450m)
• Mass: 2.4e11 kg (up from 1.3e11)
• Potential impact speed (only IF it hits): 24.88 km/sec (up from 22.84 km/sec)
• Potential impact energy (only IF it hits): 18,000 Megatons
• Torino impact hazard scale : 1 (same value)
• cumulative Palermo Scale : -1.32 (up from -1.73)
• close Earth approach paths in next 100 yrs: 33 (down from 34)
• Earth impact odds in the next 100 yrs: 1 in 37,000 (up from 1 in 63,000)

The 2003-CR20 asteroid is the 2nd object on the list with a non-zero Torino impact hazard scale value.

IF 2003-CR20 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-CR20 were to hit the Earth in the ocean, it would create a tsunami the size and speed of which have not been seen in recorded history. Such a tsunami would would inflict total devastation along adjoining coastlines and in some cases spread destruction far inland.

The impact speed, IF 2003-CR20 hits the Earth remains on the higher end of the typical asteroid approach speed.

The impact odds, while low, have become somewhat worse. Even though the number of Earth approaches have dropped significantly with the current model, these that remain yield a slightly greater risk of Earth impact. Still, there is a 99.9973% chance the asteroid will miss the Earth.

The following is a table of the close Earth approaches by 2003-CR20 where Earth lies within the 5-sigma path. See my explination for the data in this table. The 5-sigma approaches as of 2003-Feb-23 08:30 UTC, are:

1. 2026-09-19.02 2.07 +/-1.36 (Earth inside 2-sigma path)
2. 2029-09-18.76 2.88 +/-1.35 (Earth inside 2-sigma path)
3. 2031-09-20.47 1.93 +/-1.37 (Earth inside 2-sigma path)
4. 2032-09-18.44 3.90 +/-1.39 (Earth inside 3-sigma path)
5. 2034-09-20.26 1.00 +/-1.33 (Earth inside 1-sigma path)
6. 2035-09-18.99 1.28 +/-1.40 (Earth inside 1-sigma path)
7. 2040-09-19.34 3.19 +/-1.33 (Earth inside 3-sigma path)
8. 2043-09-20.14 1.55 +/-1.35 (Earth inside 2-sigma path)
9. 2046-03-17.53 0.86 +/-1.12 (Earth inside 1-sigma path)
10. 2049-03-16.96 0.80 +/-1.20 (Earth inside 1-sigma path)
11. 2050-03-15.57 0.54 +/-0.16 (Earth inside 4-sigma path)
12. 2055-09-19.96 2.62 +/-1.32 (Earth inside 2-sigma path)
13. 2061-03-16.75 0.15 +/-0.12 (Earth inside 2-sigma path)
14. 2070-09-19.22 4.07 +/-1.26 (Earth inside 4-sigma path)

The most significant close approaches have been marked in bold.

Please keep in mind that even when the Earth is inside the 1-sigma path, the chance of impacting are NOT ~68%! One has to factor in the chance that the model path will be taken at all. The highest risk approach remains the 2046-03-17.53 0.86 +/-1.12 approach. There is a 1 in 83,000 chance that 2003-CR20 will impact the Earth on that pass. There is a 99.9988% chance that 2003-CR20 will miss the Earth on that pass as well.

The 2003-CR20 orbit model has become slightly worse for Earth. Stay tuned ...

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object.

New observations bring the observation total to 23 over a period of almost 9 days. 9 days is a little short to create an extremely accurate model. However, these 23 observations are from observers/observatories with a good track record of accurate observations. They come from 7 independent observatories have provided data that fit well together. Taken as a whole, they allow one to begin to produce an accurate orbit model.

Based on the new observations, we calculate the following information for 2003-CR20:

• Diameter: 450m (down from 520m)
• Mass: 1.3e11 kg (down from 1.9e11 kg)
• Impact speed (only IF it hits): 24.84 km/s (down from 24.95 km/sec)
• Torino impact hazard scale : 1 (up from 0)
• cumulative Palermo Scale : -1.73 (up from -1.86)
• close Earth approach paths in next 100 yrs: 34 (down from 234)
• Earth impact odds in the next 100 yrs: 1 in 63,000 (up from 1 in 233,000)

The 2003-CR20 asteroid is the 2nd object on the list with a non-zero Torino impact hazard scale value.

The refined size and mass, while slightly smaller, is still significant. IF 2003-CR20 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-CR20 were to hit the Earth in the ocean, it would create a tsunami the size and speed of which have not been seen in recorded history. Such a tsunami would would inflict total devastation along adjoining coastlines and in some cases spread destruction far inland.

The impact speed, IF 2003-CR20 hits the earth remains on the higher end of the typical asteroid approach speed.

The impact odds, while low, have become slightly worse. Even though the number of Earth approaches have dropped significantly with the current model, those 34 that remain yield a slightly greater risk of Earth impact. Still, there is a 99.9984% chance the asteroid will miss the Earth, so don't start ''heading for the hills'' (yet). :-)

The current model has a number of close approaches to Earth that require more careful processing. For example, in some cases we need to account for the non-uniform mass distribution of the Earth and the time of day of the close approach. This work is being performed as this journal entry is being written. If this work results in a significantly different orbit model, I will post a journal update on the revised model.

The following is a table of the close Earth approaches by 2003-CR20 where Earth lies within the 5-sigma path. See my explination for the data in this table. The 5-sigma approaches as of 2003-Feb-21 19:30 UTC, are:

1. 2026-09-19.17 6.78 +/- 2.47 (Earth inside 3-sigma path)
2. 2029-09-18.88 6.87 +/- 2.56 (Earth inside 3-sigma path)
3. 2031-09-20.52 0.65 +/- 2.48 (Earth inside 1-sigma path)
4. 2032-09-18.47 6.22 +/- 2.49 (Earth inside 3-sigma path)
5. 2032-09-18.58 8.36 +/- 2.54 (Earth inside 4-sigma path)
6. 2034-09-20.08 3.93 +/- 2.37 (Earth inside 2-sigma path)
7. 2035-09-19.13 3.07 +/- 2.55 (Earth inside 2-sigma path)
8. 2043-09-20.48 7.43 +/- 2.44 (Earth inside 4-sigma path)
9. 2046-03-17.53 0.82 +/- 0.22 (Earth inside 4-sigma path)
10. 2048-09-19.27 0.01 +/- 2.15 (Earth inside 1-sigma path)
11. 2049-03-16.97 0.92 +/- 0.23 (Earth inside 4-sigma path)
12. 2050-03-15.57 0.09 +/- 0.32 (Earth inside 1-sigma path)
13. 2054-09-19.53 5.66 +/- 2.20 (Earth inside 3-sigma path)
14. 2055-09-20.03 4.49 +/- 2.39 (Earth inside 2-sigma path)
15. 2058-09-19.28 4.74 +/- 2.31 (Earth inside 2-sigma path)
16. 2061-09-18.79 0.48 +/- 2.24 (Earth inside 1-sigma path)
17. 2064-09-18.46 5.29 +/- 2.20 (Earth inside 3-sigma path)
18. 2065-09-18.65 2.33 +/- 2.26 (Earth inside 2-sigma path)
19. 2073-03-16.43 1.16 +/- 0.25 (Earth inside 5-sigma path)
20. 2083-09-19.14 0.23 +/- 2.23 (Earth inside 1-sigma path)

The most significant close approaches have been marked in bold.

Please keep in mind that even when the Earth is inside the 1-sigma path, the chance of impacting are NOT ~68%! One has to factor in the chance that the model path will be taken at all. For example, while the 2048-09-19.27 0.01 +/- 2.15 path may look bad for Earth, the overall probability that the Earth will be impacted on (or near) that date is only ~1 in 83,333,000. So even though that path looks like the Earth is right in the ''bull's eye'', there is still a 99.9999988% chance the asteroid will miss the Earth for that approach.

The highest risk approach is the 2046-03-17.53 0.82 +/- 0.22 approach. Even though the Earth is 4-sigma away, the chance that this given path will be taken is somewhat significant. So you cannot always tell high risk paths from the Earth target sigma. The odds of 2003-CR20 impacting on or near that date are only ~1 in 196,000 chance. Still there is a 99.99949% chance the asteroid will miss the Earth on or near that date.

You notice this entry has gone into a lot of detail about 2003-CR20, it is because the orbit models are getting worse not better as more observational data comes in. Still, it is possible that with the same quality level of observations over a longer period of time (than just 9 days) will change the model. Experience has shown that usually such model changes yields a model with a lower impact risk.

Stay tuned ...

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object.

This asteroid appears be about 520 m in diameter. Its impact velocity, IF it were to hit the Earth is in the high end of the range: 24.95 km/sec.

IF 2003-CR20 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-CR20 were to hit the Earth in the ocean, it would create a tsunami the size and speed of which have not been seen in recorded history. Such a tsunami would would inflict total devastation along adjoining coastlines and in some cases spread destruction far inland.

The 2003-CR20 asteroid has a Torino impact hazard scale value of 0. It also has a cumulative Palermo Scale value of -1.86, mostly because of its many (234) potential close approach scenarios over the next 100 years.

The chance of impacting the Earth in the next 100 years is low: about 1 in 233,000. Even so, at those odds there is a 99.99957% chance that it will NOT hit the Earth in the next 100 years.

The 1st close approach is not until 20 Sep 2006. The model shows over the next 100 years the closest approach could be a close as 875 km. The most of the approaches in the next 100 years range from 10000 km to 700000 km above the Earth's surface.

Normally close approaches occur around one day of the year. That is, the asteroid's orbit crosses near Earth's orbit at only one point as the asteroid comes up thru (ascending node) or drops down thru (descending node) the plane of Earth's orbit. An interesting aspect of this model is that both nodes of 2003-CR20 pass close to Earth's orbit. 2003-CR20's orbit passes close to Earth's orbit near the 20-Sep position AND near the 15-Mar position.

It is very likely that over the next few days or weeks, additional observations will allow the model for 2003-CR20 to be refined. It should be noted that 2003-CR20's listing is preliminary with only 11 observations spanning only about 3 days ... not much on which to form a super accurate model.

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object. The only reason why 2003-CD30 is listed higher than 1997-XR2 is because its cumulative Palermo scale is higher.

The Torino impact hazard scale for 2002-XY38 remains at a 0. The cumulative Palermo Scale has dropped from -2.64 to -6.28.

The size of 2002-XY38 is still estimated to be 90m in diameter. The impact velocity (if it were to hit the Earth) remains in the low to medium range of ~12.95 km/sec.

The odds of 2002-XY38 impacting the Earth in the next 100 years has dropped from 1 in ~1,300 to 1 in ~1,833,333. Even so, at those odds there is a 99.999988% chance that it will NOT hit the Earth in the next 100 years.

The 1st close approach is still 24 Feb 2084. On that date 2002-XY38 will miss the Earth by ~1290 km instead of only 1290 km. The other close approach in the next 100 years occurs on 23 Feb 2090 with a very close pass of only ~125 km!

Currently, 2002-XY38 is #31 on the current impact risks table. It is possible that over the next few months, additional observations will allow the model for 2002-XY38 to be refined.

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only non-zero Torino impact hazard scale object.

P.P.S. The most probable known NEA impactor in the next 100 years is 2000-SG344, with a 1 in ~556 chance is hitting the Earth before the year 2103. This asteroid has a Torino impact hazard scale of 0 and a cumulative Palermo Scale of only -3.08. The 1st close approach is not until 2068 Sep 19 (5975 km), although there is a 450 km close approach on 2073 Sep 12.

Asteroid 2000-SG344 is #3 on the current impact risks table because this it is a small NEA (only 40m in diameter) and any impacts would be somewhat on the lower end of the velocity scale (about 11.3 km/sec). If 2000-SG344 were to hit the Earth, it would produce an event that would compare to the Tunguska event in 1908.

On a different, but astronomy related note: Please consider donating something to the Mt. Stromlo Redevelopment and Bushfire Relief Fund .

It was what I could write up in a short period time. I hope it is OK. I'll post corrections (or pointers to corrections) as replies to this journal entry, if needed.

p.s. As of 13:00 19 Jan 2003: No change in status of Asteroid 2002-XY38. Nor has anyhting changed with Asteroids 1997-XR2 and 2000-SG344.

The Torino impact hazard scale for 2002-XY38 has dropped from 1 to 0. The cumulative Palermo Scale has dropped from -2.53 to -2.64.

The size of 2002-XY38 is still estimated to be 90m in diameter. The impact velocity (if it were to hit the Earth) remains in the low to medium range of ~12.9 km/sec.

The odds of 2002-XY38 impacting the Earth in the next 100 years has dropped from 1 in ~1,300 to 1 in ~1,820. Even so, at those odds there is a 99.945% chance that it will NOT hit the Earth in the next 100 years.

The 1st close approach is still 24 Feb 2084. On that date 2002-XY38 will miss the Earth by ~1290 km instead of only 625 km. On the other hand, the 6 other close approaches in the next 100 years, the closest (on 23 Feb 2090) is only 515 km.

Currently, 2002-XY38 is #2 on the current impact risks table. It is very likely that over the next few days or weeks, additional observations will allow the model for 2002-XY38 to be refined. It would not surprise us to see a refined model reducing the impact risk to the point where this object is removed from the potential Earth impactor table.

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only non-zero Torino impact hazard scale object.

P.P.S. The most probable known NEA impactor in the next 100 years is 2000-SG344, with a 1 in ~556 chance is hitting the Earth before the year 2103. This asteroid has a Torino impact hazard scale of 0 and a cumulative Palermo Scale of only -3.08. The 1st close approach is not until 2068 Sep 19 (5975 km), although there is a 450 km close approach on 2073 Sep 12.

Asteroid 2000-SG344 is #5 on the current impact risks table because this it is a small NEA (only 40m in diameter) and any impacts would be somewhat on the lower end of the velocity scale (about 11.3 km/sec). If 2000-SG344 were to hit the Earth, it would produce an event that would compare to the Tunguska event in 1908.

This asteroid appears be about ~90 m in diameter. Its impact velocity, IF it were to hit the Earth is in the low to medium range: ~12.9 km/sec. If 2002-XY38 were to hit the earth, the collision would result in significant local devastation. The devastation area would be somewhat larger than the Tunguska event in 1908.

The 2002-XY38 asteroid has a Torino impact hazard scale value of 1. It also has a cumulative Palermo Scale value of -2.53, mostly because of its small size and moderate impact speed.

The chance of impacting the Earth in the next 100 years is moderate: about 1 in ~1,300. Even so, at those odds there is a 99.923% chance that it will NOT hit the Earth in the next 100 years.

The 1st close approach is not until 24 Feb 2084. The model shows over the next 100 years the closest approach is about 625 km. The other 7 approaches in the next 100 years range from 1300 km to 5500 km above the Earth's surface.

It is very likely that over the next few days or weeks, additional observations will allow the model for 2002-XY38 to be refined. It would not surprise us to see a refined model reducing the impact risk to the point where this object is removed from the potential Earth impactor table.

It should be noted that 2002-XY38's listing is preliminary with only 33 observations spanning only about 24 days ... not much on which to form an super accurate model.

P.S. There is no change is status for 1997-XR2. That asteroid remains as the only other non-zero Torino impact hazard scale object. The only reason why 2002-XY38 is listed higher than 1997-XR2 is because its Palermo scale is only 0.09 higher.

Further updates on XY38 will be posted to chongo's journal .

See my next Journal entry .

Implied Q #0: I'd say this should be worth a Q&A session on Slashdot's front page.

A #0: Feel free to suggest it to the /. folks. I'd be happy to do a more general Hazardous NEO Q&A.

Q #1: I notice that many potential impacts have 2 dates that are virtually the same. 1997 XR2's 2 impacts, for instance, differ with just 0.01 days. Why aren't they considered the same potential impact (which in some cases could give it a higher Torino scale number)?

A #1: [[UPDATED]] The collection of asteroid observations may not be well defined / may have significant uncertainties require the model to split into parallel paths. If more than one of these paths intersect or closely approach the Earth, then multiple close encounters and/or potential impacts will be listed.

Over a span of 100 years, the Yarkovsky effect has a significant enough affect on 1997-XR2 to warrant its consideration. Our 1997-XR2 model has two major paths. One path assumes a clockwise rotation and the other a counter-clockwise rotation of 1997-XR2. Like JPL, we show two potential encounters whose close approach differs by about 1.4 minutes on 1 June 2101.

I cannot state for certain that the Varkovsky effect is why JPL lists 2 encounters for 1997-XR2, but it does for our model.

There are other reasons why a model may show multiple close encounters over a short span of time. Sometimes a model's will be split into several unique paths that represent a range of possible outcomes after a close encounter.

Sometimes 2 or more potential encounters within a brief period of time represent different paths (previously split as noted above) with different numbers of revolutions around the sun.

It is also possible that an object is really multiple objects (such as an asteroid with a moon or a fragmented comet) each of which has its own potential impact / close encounter. However this is rare.

Q #2: [[UPDATED]] What's the deal with the Hazardous NEO Technical Reviews Does it mean that a potentially hazardous impact with a Torino value > 1 would be kept off the JPL and NEODyS lists (and even in your journal!) until the Committee find it in its heart to tell the rest of us?

I find it hard to believe that such things could be kept secret since the observations are public and everyone can (in theory) make their own calculations based on them. Right?

A number of years ago, a hazardous NEO was discovered (I forget which one) that was picked up by the press. It was a slow news day. Hollywood had or was about to release several asteroid/comet doomsday movies. The press went wild and blew the report way out of proportion.

Then as usual, a number of new observations came along. Better models were developed. As I also recall, the initial model may even have had an error in it. The result of this was that the object was removed from the Hazardous NEO list.

Some of the press reported that Astronomers had made a blunder. Other press groups continued to publish doomsday reports, finding some person who discounted the revised model (claiming that the new data was part of a cover-up).

Nobody was happy with the result.

At the urging of notable Astronomers (I recall Marsden and Morrison), a new protocol was developed.

One aspect of this protocol is when an objects appears to have a >= 0 Palermo Technical Scale is discovered, the orbit model undergo a review by a technical committee before their results are released. Typically this review takes less than 72 hours.

After the review, the results are published. Additional material is also released help the press more accurately report the finding. The object is also posted on the various NEO lists after the technical review.

A summary of the 20 Dec 2002 Hazardous NEO Technical Review process is available.

Permit me to add a few remarks of my own:

• The ~72 hour review is to improve the accuracy of significant NEO potential impactors.
• A review is not unusual in Science. Many technical publications go through a referee process prior to journal publication. In some cases, the publication delay can be weeks to months. The ~72 hour technical review is a rather rapid review process when compared to most.
• A ~72 hour review / sanity check should not pose a risk to you personally. If we have less then 72 hours before something significant impacts the Earth, then there may be little that anyone can do about it anyway.
• The review process does not include any government approval. There is no censorship. The review team and 2nd level advisers are an International team. So single institution or nation has a lock on the process.
• The review team has promised to keep the information confidential during the ~72 hour review process. While I believe they will keep the information confidential during the ~72 hour period, the risk in the process is that someone will leak data instead of hiding/burying data.
• At the end of the review process, something is always released.
  • It may be that the object shows up as a new entry in the hazard list .
  • It may be that the object is determined to be a re-discovery on a previously known NEO object and only an IAU circular of the observation is published.
  • It may be that the object is a previously lost object that is not a NEO object and an only IAU circular of the observation is published.
  • It may be that the object is a newly discovered object that is a non-NEO object and a IAU circular of the observation and orbit parameters is published, along with perhaps a new entry in the minor planet database.

Q #3: How computational expensive are the the models?

A #3: Models can be somewhat computationally expensive. Detailed models can be computationally expensive.

Sometimes an observer / observatory's data has a systematic error.Discovering and correcting or ignoring bad data can be a combinatorial process that requires multiple models to be run.

Q #4: The JPL model takes the gravitational effects of the 3 biggest asteroids into consideration and I've noticed that 2002NT7 is listed with a close approach to the second largest asteroid, Pallas, in 2020. So I guess even the small masses of these asteroids are worth having in the model. But why do they stop there? Why isn't Juno and other large asteroids accounted for? Is this a trade off of accuracy vs computational time?

A #4: The more bodies that you add to your model, the more complex your model becomes. One must not only take steps to ensure that the new body data is accurate, one must also add the uncertainty of the new body data to the overall model error.

Most of the time, minor planets do not have a significant or even measurable impact on a NEO orbit model over the next 100 years. Most of the time even details about the Earth (such the Earth's non-spherical shape, non-uniform mass distribution, and time of day (how the non-uniform mass is rotated)), and the Moon (nutation, etc.) usually to not matter over a 100 year period.

It is only when an object has a close encounter with an another significant object that one has to resort to more detailed and complex models.

It is somewhat a trade off of accuracy vs computational time. It also an issue of model complexity and accuracy of additional orbits.

Q #5: Watching the hazard lists it seems that the only thing influencing the numbers are more observations, not more time to calculate. How long does it take to calculate a trajectory 100 years ahead given a set of observations?

A #5: The hazard lists produced by the JPL use their standard ephemeris model. Tables can be produced in short amount of time.

When we find that our model that suggests a close encounter with another significant object, we adjust our model. For example, a close encounter with Pallas might warrant adding estimated Pallas positions and mass over a brief period of time. More complex encounters such as the J002E3's 6 orbit eventrequires even more detailed model improvement.

Usually it takes more time to adjust and check a new model than it does to run the new model.

[[recent addition]]

Q #6: Has there ever been a potential impact listed with a Torino value >1?

A: #6: No.

Well that is all.

Corrections and additions to the above are welcome.