PLANETOÏDE 2002 NT7:
BOTSING IN 2019 NU UITGESLOTEN


Don Yeomans

July 28, 2002

Asteroid 2002 NT7: Potential Earth Impact In 2019 Ruled Out

With the processing of a few more observations through July 28, we can now rule out any Earth impact possibilities for February 1, 2019. While we cannot yet completely rule out an impact possibility on February 1, 2060, it seems very likely that this possibility will be soon ruled out as well as additional positional observations are processed. Because the SENTRY system tracks a multitude of test particles in an effort to map the uncertainties of the asteroid's future positions, some of these test particles can take slightly different dynamical paths. Hence there are currently two entries for 2060 in our IMPACT RISK table (http://neo.jpl.nasa.gov/risk). The entry with the higher risk (larger Palermo Technical Scale) would be the value that would then take precedence.


Nieuws uit de astronomie:


Nieuws in de pers:

2002 NY40:

Achtergrondinformatie:



CCNet 91/2002 - 27 July 2002

2002 NT7 IN THE PRESS

From Carl Koppeschaar

Dear Benny and other NEO researchers:

I missed part of the 2002 NT7 hype as I was flying home on July 24 after a 3 weeks vacation on the Galápagos Islands with my family. In a taxi from Schiphol Airport to Haarlem in the Netherlands I heard the story on the radio and was puzzled. 'Great to be home again', flashed through my mind. Just a few hours later Dutch radio and TV kept calling, asking if I would like to comment. I felt sorry that I had not accepted the media's invitation. Astronomical phenomena, spherical astronomy and perturbation theory were my favourite subjects and I had already written a lot on NEO's and the Torino and Palermo scales in Dutch popuar science magazines. But luckily a day later Dutch newspapers were already stating that NASA declared that the chances for a hit were slim and would diminish in time. Repair done.

I do realize that this kind of news raises the public interest in astronomy in general and NEO research in particular. So far no harm inflicted. The general opinion will be that it is good to have astronomers taking care of the world, watching over these kinds of threats.

Crying 'wolf' is yet another thing. I am popularizing astronomy for more than 25 years now and remember all too well a former doomsday (sic) prediction by Brian Marsden as well as exaggerated predictions for comets, Leonid meteor outbursts and other phenomena. After disappointing displays of the Leonids in Europe I already received public complaints like 'Well, it is only astronomy. So it can be 200 to 300 percent off.' These kind of complaints worry me a lot. One reason why I did not want to comment before knowing what exactly was going on.

Well, thanks to Benny for his CCNet updates and to the others for putting into perspective the real risks compared to the inaccuracy of the preliminary orbit. I have put some of the the links and information on my website Astronet to keep the public informed. One last question remaining. Who started all this news? The Asteroid/Comet Connection that I could track in Benny's first CCNet message has been updated already. So original text is no longer shown. How did the BBC get the information? Just like to know out of curiosity. It may be good to learn how things started eventually going to lead their own life.

Furthermore I do agree with David Whitehouse that most of the publications in the press did warn that this was a preliminary prediction only. At the same time I share David Morrison's concern about harm that can be done to the credibility of astronomy or astronomical predictions in general.

Best regards,

Carl

-------------------------------------- 
Carl E. Koppeschaar 
asteroid (7973) and science journalist 
URL: http://www.astronet.nl 
E-mail: carl@astronet.nl 
-------------------------------------- 

MODERATOR'S NOTE: See Bill Allen's report about how ACC broke the 2002 NT7 story. How did the BBC get the story? There are a couple of hundred science writers and space journalists from around the globe subscribed to CCNet. The BBC's David Whitehouse is one of the most attentive and respected among them. I understand that his NT7 report on BBC Online was - by a factor of 20 (yes, 20) - the most hit story on the BBC News website on Wednesday and that it broke all records for a story of ANY category. Sorry folks, but that's how good journalism works! Benny J. Peiser


From David Morrison

"AN ORGY OF MISINFORMATION AND CONFUSION CONCERNING 2002 NT7"

NEO News (07/25/02) Confusion on 2002 NT7

Dear Friends and Students of NEOs:

As you probably all know, we are in the midst of an orgy of misinformation and confusion in the press, concerning asteroid 2002 NT7.

There have been "false alarm" stories in the past about threatening asteroids, some originating in poorly informed or misguided statements made by astronomers. The general pattern has been that a warning is issued and a day or two later retracted, reflecting either improved calculations or new data or both. It is entirely normal that a very low probability prediction of impact will go to zero as more information is processed. This is not a "failure" of the system, but rather the normal working of the Spaceguard Survey and supporting dynamical calculations. However, the press sometimes portrays this as a "mistake" by astronomers. Consequently, most of us prefer to see no press coverage of such low-probability predictions. It was in this spirit that no formal announcement was made concerning 2002 NT7, since new observations are accumulating and the whole situation is likely to resolve itself within a few days.

Unfortunately, the media themselves seem to have created the current flood of publicity surrounding NT7. Initial statements from the British press stated that 2002 NT7 was on a collision course with Earth with the impact predicted for February 1, 2019. The only qualification was that the prediction of an impact was still somewhat uncertain. There was no hint of the true situation, in which the probability of impact was at the 1-in-a-million level. As noted by Don Yeomans and others, the position of 2002 NT7 on February 1, 2019, is actually uncertain by many millions of kilometers!

The situation has been made more complex by press references to the Palermo technical scale for classifying an asteroid risk. Astronomers use this Palermo scale in communicating among themselves, but several years ago they agreed to use the simpler Torino risk scale in talking to the press and public. The Torino scale was invented to facilitate such communication. As recently noted by Rick Binzel: The largest rationale for the Torino Scale is that we all have a common lexicon for communicating with the public. If each and every one of us would say: "That object is only zero (or one) on the Torino scale, meaning we are carefully monitoring it, with no cause for public concern." eventually the responsible press and responsible people would learn to categorize these "events" as being the same as the last ones that "just went away."

David Morrison
NASA Ames Research Center

==========================================

NOTE TO CONCERNED CITIZENS

This newly discovered asteroid (2002 NT7) is very unlikely to hit the Earth. The current odds are a million to one against hitting. In any case, astronomers are continuing to measure its position, and within a few days we should know for sure what the circumstances are for 2019. Meanwhile, the story has been blown out of proportion. Statements from the press that the asteroid is on a collision course with Earth are simply false.

The probability of impact is so small that this asteroid remains at a risk level on the Torino scale of 0 or 1 - meaning that the chances of impact from another unknown NEA of the same size or larger is similar to the chances of being hit by 2002 NT7. However, the impact probability is not yet zero, and additional observations are needed to ensure that this object will not hit the Earth in 17 years.

Although 2002 NT7 is unlikely to pose any danger, the long-term risk of asteroid collision is real.

The Earth orbits the Sun in a sort of cosmic shooting gallery, subject to impacts from comets and asteroids. It is only fairly recently that we have come to appreciate that these impacts by asteroids and comets (often called Near Earth Objects, or NEOs) pose a significant hazard to life and property. Although the annual probability of the Earth being struck by a large asteroid or comet is extremely small, the consequences of such a collision are so catastrophic that it is prudent to assess the nature of the threat and prepare to deal with it.

Studies have shown that the risk from cosmic impact increases with the size of the projectile. The greatest risk is associated with objects large enough to perturb the Earth's climate on a global scale by injecting large quantities of dust into the stratosphere. Such an event could depress temperatures around the globe, leading to massive loss of food crops and possible breakdown of society. Such global catastrophes are qualitatively different from other more common hazards that we face (excepting nuclear war), because of their potential effect on the entire planet and its population. Various studies have suggested that the minimum mass impacting body to produce such global consequences is several tens of billions of tons, resulting in a groundburst explosion with energy in the vicinity of a million megatons of TNT. The corresponding threshold diameter for NEOs is between 1 and 2 km. Smaller objects (down to tens of meters diameter) can cause severe local damage but pose no global threat.

We don't know when the next NEO impact will take place, but we can calculate the odds. Statistically, the greatest danger is from an NEO with about 1 million megatons energy (roughly 2 km in diameter). On average, one of these collides with the Earth once or twice per million years, producing a global catastrophe that would kill a substantial (but unknown) fraction of the Earth's human population. Reduced to personal terms, this means that you have about one chance in 20,000 of dying as a result of a collision. Such statistics are interesting, but they don't tell you, of course, when the next catastrophic impact will take place-next year or a million years from now.

How much warning will we have? With nearly half of even the larger NEOs remaining undiscovered, the most likely warning today would be zero -- the first indication of a collision would be the flash of light and the shaking of the ground as it hit. In contrast, if the current surveys actually discover a NEO on a collision course, we would expect many decades of warning. Any NEO that is going to hit the Earth will swing near our planet many times before it hits, and it should be discovered by comprehensive sky searches. This is the purpose of the Spaceguard Survey. In almost all cases, we will either have a long lead time or none at all.

Meanwhile, the Spaceguard Survey has already discovered more than half of the near Earth asteroids 1 km or larger, and we are on track to find 90% of them before the end of this decade.

For more information see the NASA websites: impact.arc.nasa.gov and neo.jpl.nasa.gov.

David Morrison
NASA Ames Research Center


ANIMATED GIF OF THE MOTION OF ASTEROID 2002 NT7


NASA Science News for July 26, 2002

Caveat Impactor

An asteroid with almost no chance of hitting Earth made big headlines this week.

July 26, 2002: I slid a dollar bill across the counter, and the cashier handed back a lottery ticket. The odds for winning: 1-in-250,000. A long shot, but you never know.

Walking out of the store, ticket in hand, I glance at a newspaper. "Tony Phillips wins the lottery!" the headline declared. Gosh, I thought, that seems premature ... not to mention weird.

Indeed, it's fiction. For one thing, I never buy lottery tickets. But mainly, no one would write such a headline based on such slender odds.

Yet that's what happened this week, in real life, to an asteroid.

On July 9, 2002, MIT astronomers discovered 2002 NT7, a 2 km-wide space rock in a curious orbit. Unlike most asteroids, which circle the Sun in the plane of the planets, 2002 NT7 follows a path that is tilted 42 degrees. It spends most of its time far above or below the rest of the solar system. Every 2.29 years, however, the asteroid plunges through the inner solar system not far from Earth's orbit.

After a week of follow-up observations, researchers did some calculations. There was a chance, they concluded, that 2002 NT7 might hit our planet on February 1, 2019. The odds of impact: 1-in-250,000.

"Space Rock 'on Collision Course'," a headline declared days later. "Asteroid Could Wipe Out a Continent in 2019," another one warned. Really.

"In fact," says Don Yeomans, the manager of NASA's Near-Earth Object Program at JPL, "the threat is minimal. One-in-250,000 is a very small number."

The odds are not only low, but also uncertain. Yeomans explains: "We've been tracking 2002 NT7 for a very short time--only 17 days so far," Meanwhile, the asteroid takes 2.29 years to orbit the Sun. Predictions based on such a small fraction of an orbit are seldom trustworthy.

It's becoming a familiar routine: Astronomers discover a near-Earth asteroid. With only meager data at hand, they can't rule out a collision in the distant future. Headlines trumpet the danger. Finally, the alarm subsides when more data lead to a better orbit--one that rules out an impact.

"As far as the public is concerned," says Jon Giorgini of JPL's Solar System Dynamics Group, "it just isn't worth getting worked up about an object with a couple weeks of data showing a possible Earth encounter many years from now. Additional measurements will shrink the uncertainty by a large amount--and Earth will (almost certainly) fall out of the risk zone."

Already this is happening for 2002 NT7. The calculated probability of a collision with Earth is shrinking as astronomers add new data each day. "I suspect it will take only a few more weeks (or maybe months) to completely rule out an impact in 2019," says Yeomans.

Giorgini explains further: "When we calculate an asteroid's position (based on measurements made at a telescope), the result isn't a single point in space. Instead, it's a volume of space where the asteroid could be with some probability. We deal with probabilities, not absolute answers, because the measurements contain errors." For example, optical data can be corrupted by twinkling and refraction in Earth's atmosphere. (Radar is better, notes Giorgini, but no radar data have yet been obtained for 2002 NT7.)

"When you project this initial probability region years into the future, it naturally expands. For a newly discovered object with only a few days tracking, the uncertainty region can easily grow to cover a big part of the inner solar system. Because Earth is in the inner solar system, and can potentially cut through this volume of smeared out probability, we end up with finite impact probabilities."

"A finite probability, however, is not really a prediction of impact," he cautions, "but a statement that one is possible." Of course, many things are possible. Like the newspaper headline "Tony Phillips wins the Lottery!" But most of them do not happen.

JPL lists asteroids like 2002 NT7 on their Internet "risk page" not to raise an alarm, says Yeomans, but to alert astronomers when new discoveries merit attention. "It's important that we continue tracking these asteroids to refine their orbits," he says. The more observers, the better.

Above: Astronomer John Rogers captured this image of 2002 NT7, faint and far away, on July 23, 2002, using a 0.3-meter telescope at the Camarillo Observatory.

What's an ordinary person to do? The next time you see a headline "Killer asteroid threatens Earth!" ask yourself two questions: Have we known about this space rock for more than a week or so? (If not, check again in a month. It probably won't be considered a killer then.) And what are the odds of impact?

If you're more likely to win the lottery, there's probably nothing to worry about.


Near-Earth Object Program

24 July 2002

Asteroid 2002 NT7

Asteroid 2002 NT7 currently heads the list on our IMPACT RISKS Page because of a low-probability Earth impact prediction for February 1, 2019. While this prediction is of scientific interest, the probability of impact is not large enough to warrant public concern.

Discovered on July 9, 2002 by the LINEAR team, asteroid 2002 NT7 is in an orbit, which is highly inclined with respect to the Earth's orbit about the sun and in fact nearly intersects the orbit of the Earth. While the orbits of Earth and 2002 NT7 are close to one another at one point in their respective orbits, that does not mean that the asteroid and Earth themselves will get close to one another. Just after an asteroid like 2002 NT7 is discovered, the limited number of observations available do not allow its trajectory to be tightly constrained and the object's very uncertain future motion often allows a very low probability of an Earth impact at some future date. Just such a low probability impact has been identified for February 1, 2019 and a few subsequent dates. As additional observations of the asteroid are made in the coming months, and perhaps pre-discovery archival observations of this object are identified, the asteroid's orbit will become more tightly constrained and the future motion of the asteroid will become better defined. By far the most likely scenario is that, with additional data, the possibility of an Earth impact will be eliminated.

This is an example of the type of scenario that we can expect as some types of near-Earth objects are discovered. For some objects, their uncertain initial orbits cannot be used to immediately rule out future very low-probability Earth impacts, but when additional observations are used to refine the initial orbit, these low-probability Earth impact possibilities will go away. Other recently discovered near-Earth asteroids will be added to the Risk page until their orbits are refined and they are then dropped off the list of closely watched objects. This is how the system is expected to work and any initial indication of a low-probability Earth impact followed by a removal of that event from our IMPACT RISKS tables should not be considered a mistake. It is a natural result of the on-going process of monitoring the motions of near-Earth objects.


Astronieuws

23 juli 2002 • zonnestelsel – planetoïden

Er is een nieuwe, kleine planetoïde onderweg naar een nabije ontmoeting met de aarde. Het ongeveer 500 meter grote object, 2002 NY40, werd op 14 juli ontdekt met de automatische surveytelescoop LINEAR. De aardscheerder, die een omlooptijd van 3,03 jaar heeft, passeert onze planeet op 18 augustus op een afstand van 530.000 kilometer. Ondanks zijn geringe afmetingen is hij dan met een kleine telescoop waarneembaar. Op dit moment bevindt 2002 NY40 zich in het sterrenbeeld Boogschutter. De kans dat de planetoïde binnen afzienbare tijd met de aarde in botsing komt is (astronomisch) klein.

Een andere planetoïde, 2002 NT7, zou een groter probleem kunnen gaan vormen. Dit twee kilometer grote object lijkt de aarde op 1 februari 2019 op een afstand van ongeveer 25.000 kilometer te gaan passeren, maar zijn baan is nog erg onzeker. Er is een kleine kans – ongeveer 1 op 150.000 – dat het tot een botsing komt. Ook in 2035 en 2051 komt deze aardscheerder dicht in de buurt van onze planeet.

Meer informatie:

Sky&Telescope
Neo Program: Current Impact Risks


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