You may have, or will soon hear about the asteroid 2004 MN4. What is significant about 2004 MN4 is that it has reached an all-time hazard level on the Palermo Scale, and the Torino scale .. two scales that measure the hazard rating of an asteroid.

The most sginificant event is the close encounter between Earth and 2004 MN4 on 2029-04-13 around 21:21 UTC. We currently estimate hit the Earth, it would impact at a speed of 12.6 km/sec. It would hit the Earth, it would impact at a speed of 12.6 km/sec. It would You may have, or will soon hear about the asteroid 2004 MN4. What is significant about 2004 MN4 is that it has reached an all-time hazard level on the Palermo Scale, and the Torino scale .. two scales that measure the hazard rating of an asteroid.

The most significant event is the close encounter between Earth and 2004 MN4 on 2029-04-13 around 21:21 UTC. We currently estimate that there is a 1.6% chance that 2004 MN4 will impact the Earth during that pass. This has given 2004 MN4 a hazard rating of 4 on the Torino Impact Hazard Scale. A 4 means:

A close encounter, with 1% or greater chance of a collision capable of causing regional devastation.

The highest previous was a 1.

2004 MN4 is also rated with a +1.02 on the Palermo Technical Impact Hazard Scale Torino Impact Hazard. No other object has every reached close to +1.0 before.

2004 MN4 appears to be an asteroid that is 420 meters in diameter. It has a mass of about 1.2e+11 kg. Models show that IF it were to hit the Earth, it would impact at a speed of 12.6 km/sec. It would take only 1.4 second to pass from the upper Stratosphere to the surface. The nearly 1/2 km wide asteroid would pass through Earth's atmosphere intact, and strike the surface with an equivalent explosive force of about 2200 Megatons of TNT. Such an impact would cause devastation on a continent sized scale.

All models are is solid agreement that 2004 MN4 has only a 1 in 63 chance of impacting the Earth. So there is a 98.4% chance that it will miss the Earth. On the other hand, no object of this significant size as posed such a known threat to Earth in recorded history. Nothing of even close to this size has ever impacted the Earth during recoded human history.

These models are based on 64 observations made by 10 different observatories over a span of 6 months. That is a long enough observation record confirmed by multiple skilled observers to take seriously.

I'll stress again that there is a 62 out of 63 chance that 2004 MN4 will miss the Earth in 2029-04-13. Even so, this object deserves careful watching. Stay tuned / watch this space for further details.

The 2003-EG16 asteroid had the top position in the current impact risks , but lost to to a new asteroid: 2003-EE16. A writeup of the 2003-EE16 asteroid should appear in this journal soon.

The 50 New observations over 4.6 days is a bit short to create an extremely accurate model.

Based on the new observations, we calculate the following information for 2003-EG16:

• Diameter: 579m (up from 544m)
• Mass: 2.6e11 kg (up from 2.2e11 kg)
• Impact speed (only IF it hits): 23.70 km/s (up from 23.53 km/s)
• Potential impact energy (only IF it hits): 18,000 Megatons (up from 14,000 Megatons)
• Torino impact hazard scale : 0 (no change)
• cumulative Palermo Scale : -2.41 (up from -2.42)
• close Earth approach paths in next 100 yrs: 22 (down from 96)
• Earth impact odds in the next 100 yrs: 1 in 714,000 (up from 1 in 769,000)

Based on the estimated size and mass: IF 2003-EG16 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-EG16 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-EG16 hits the earth remains on the higher end of the typical asteroid approach speed.

The odds of 2003-EG16 impacting Earth means that there is a 99.99986% chance the asteroid will miss the Earth.

We would not be surprised to see additional observations modify the orbit model and reduce the hazard level of this asteroid sometime in the future.

The 2003-EG16 asteroid has taken the top position in the current impact risks .

Because we only have 36 New observations over 2 days, the current orbit model should be considered highly speculative.

Based on the new observations, we calculate the following information for 2003-EG16:

• Diameter: 544m
• Mass: 2.2e11 kg
• Impact speed (only IF it hits): 23.53 km/s
• Potential impact energy (only IF it hits): 14,000 Megatons
• Torino impact hazard scale : 0
• cumulative Palermo Scale : -2.42
• close Earth approach paths in next 100 yrs: 96
• Earth impact odds in the next 100 yrs: 1 in 769,000

Based on the estimated size and mass: IF 2003-EG16 were to hit the Earth on land, its impact would result in sub-continent scale devastation. IF 2003-EG16 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-EG16 hits the earth remains on the higher end of the typical asteroid approach speed.

The odds of 2003-EG16 impacting Earth means that there is a 99.99987% chance the asteroid will miss the Earth. You should still plan to pay your taxes, go to work/look for work, and continue to wait for new South Park episodes. :-)

The asteroid known as 2003-CR20 has been removed from the current impact risks table. The orbit model has been refined by 149 observations to show that there is a nil chance of impact with the Earth in the next 100 years.

Long range models continue to show that both Venus and Mars will continue have close encounters with 2003-CR20 making close encounters with Earth beyond 2103 possible.

Good news!!! With 115 observations over almost 18 days, 2003-CR20 risk has been lowered to the point where is no longer has a Torino impact hazard scale of 1!

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.

The 2003-CR20 asteroid remains at the top position in the current impact risks , and continues to become a higher risk object. Already it as spent more time with a cumulative Palermo Scale value > -2 than any other 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.

The 2003-CR20 asteroid remains at the top position in the current impact risks , and continues to become a higher risk object. The 2003-CR20 asteroid is the 2nd object on the list with a non-zero Torino impact hazard scale value.

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.

The following is a summary of the questions that I have received about 2003-CR20. In addition to this FAQ, you should review the previous " Hazardous NEO Q&A session #0 ".

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.

The 2003-CR20 asteroid remains at the top position in the current impact risks .

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.

From time to time I will present potential impact tables for paths where Earth is within the 5-sigma or less target range. Rather than repeat this same text each time, I will simply refer to this journal entry from now on.

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.

The 2003-CR20 asteroid remains at the top position in the current impact risks .

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.

The 2003-CR20 asteroid has taken the top position in the current impact risks !!!

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.

We have a new entry near the top of the current impact risks . It is an asteroid called 2003-CR20.

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 model for asteroid 2002-XY38 has been refined due to 4 additional observations. We now have 41 observations spanning more than 48 days.

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 .

Yesterday the world lost a great and histroic astronomical facility. See my slashdot posting for details.

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.