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Planetary News: Asteroids and Comets (2002)

Asteroid 2002 NT7 Under Watch, But Probably Not Coming Our Way

by A. J. S. Rayl
25 July 2002

Asteroid experts are continuing to observe asteroid 2002 NT7, which was under watch because preliminary calculations indicated it could be on a collision course with Earth. But the experts are now reporting that the probability it will impact Earth on February 1, 2019 is even lower today than it was yesterday, despite some sensational news headlines to the contrary.

"We are still monitoring 2002 NT7, but it appears that the impact probability might have already started the typical, inexorable decline that we normally see in these cases," says senior engineer, Steve Chesley, of NASA's NEO program office at JPL. "We picked up more observations yesterday and ran them through the impact probability and risk scales and all have declined."

So why was there so much ado about in the media about this hurtling hunk of rock? The news about 2002 NT7 was everywhere yesterday and from some of the accounts it seemed almost as if 'the sky might falling' - rather that the asteroid was on its way, edges blazing.

"It was picked up from our pages (http://neo.jpl.nasa.gov ) and disseminated and some of the news organizations apparently decided to get a little sensational headline out of the deal," suggests Chesley, "which is really quite inappropriate in this case."

Asteroid 2002 NT7 still tops the list of NASA/JPL NEO Impact Risks because of the low-probability Earth impact prediction for 2019. But Chesley and other asteroid experts assure that the sky is not falling, and the rock will, in all probability, at this stage, orbit safely on by come 2019. "While this prediction is of scientific interest, the probability of impact is just not large enough to warrant public concern," reassures Chesley. "It is unusual, but it's not anything that would deserve as much attention as it's gotten."

In fact, Chesley adds: "We've seen much higher probabilities, but since this asteroid is quite large, its moderately high probability combined with its great size raises it to a higher level on our risk scales. In other words, this one went over the threshold on one of the risk scales we use, someone noticed and said, 'Hey that's never happened before.' There's your story."

NASA's Near Earth Object program gives the asteroid a rating of "1" on the Torino impact hazard scale one of two such scales for determining the potential risk of asteroids and other objects. That ranking means it is within the range of "events meriting careful monitoring" but not of great concern.

Indeed, 2002 NT7's crossing the "threshold" may have been, in part, cause for the media alarm yesterday, says another asteroid expert, Dan Durda of the Southwest Research Institute in Boulder, Colorado. "This is the first time an asteroid has ranked at something above the 'don't even think about it' level on the Torino or Palermo scale, the two measurements that calibrate these objects," points out Durda. "It means simply that 2002 NT7 has hit the green level (Level1 on the Torino scale} where it warrants close attention."

Asteroid 2002 NT7, which was first detected earlier this month by the Lincoln Near Earth Asteroid Research Project in New Mexico, orbits the Sun every 837 days, traveling in a tilted orbit from about the distance of Mars to just within the Earth's orbit. The recent detailed calculations of 2002 NT7's orbit suggest numerous potentialities for its projected path through space to intersect the Earth's orbit.

More observations in coming weeks will help scientists to more precisely plot the course of the 1.2-mile-wide asteroid and determine the true risk. "With every new observation you help tie down the orbit a little better," Durda explains. "There's an error ellipse - a 'line' that passes through somewhere in space which is our projection of where the orbit goes for this particular asteroid. More often than not, that 'line,' which represents our best guess as to where the asteroid is going to go, is outside the actual sphere of the Earth itself." That error-ellipse is what astronomers will be watching.

Although the latest observations indicate the asteroid is becoming less and less of a threat, if that error ellipse shifts to include the Earth, "then the bells and whistles go off and we would need to look at this object even more carefully," says Durda. "We would then need to get more position observations of the asteroid, not only through optical telescopes, but radar if possible, which is a good way to very tightly constrain the orbit. More than likely," he reiterates, "we're going to find out that with more observations this object is going to make a clean miss and it won't be a problem."

Even so, there is always at this stage some uncertainty, Durda admits. While the Torino scale placed 2002 NT7 within the range of "events meriting careful monitoring" but not of great concern, there is always a remote possibility it could be determined later to be on track and heading toward Earth. "More than likely it's not going to be problem, but we can't say that yet with absolute certainty," he says. "There's an error cloud around the 'line,' if you will, which represents where there's a certain probability it may go. The point is, yes, the Earth is in that error ellipse and it could potentially hit us."

Still, by all accounts, observations and appearances now, it is highly unlikely that asteroid 2002 NT7 will ruin our day come February 1, 2019. "Imagine a chart, and think about a tiny fraction of area where a tiny dot that represents the Earth lies and then compare it to a much larger area of the error ellipse," Durda expounds. "With more observations, the odds are in our favor that the error ellipse will shrink to the point where it doesn't include the Earth and this object is not going to hit. That's where we're at. In terms of odds, colloquially, this is a one-in-a-million kind of odds, that's speaking figuratively, not statistically. But at this point, people should just not worry about it."

Astronomers will be in a mode of observation, says Durda, for the next several months. "But we could get strong enough observations to eliminate any potential threat to the Earth within three to four days."

If by some bizarre chance, 2002 NT7 were found with further observations to be on a collision course, what then?

"Asteroid 2002 NT7 would rise progressively from green to yellow to orange to red priorities on the Torino scale," says Durda. "Then we're in a position of where we have to actually start worrying and thinking and planning as to what we do. We'd have to kick into high gear at that point and figure it out technically. The first thing we'd probably have to do is better characterize this object. How large is it? What is it made out of - is it a rubble pile or big solid rock? What shape is it? And so on. That characterization would determine what we might do." Some of the conceived options include nuking it, or pushing it out of the way with a rocket.

Currently, there is no master response plan for impending asteroid impacts. "A lot of hypothetical plans and ideas and viewgraphs and thoughts have been put out there, but nobody's put anything down into hardware and actually prepared a real honest-to-gosh operational plan to do anything," says Durda. That however, appears to be changing.

Chesley and Durda are members of an unofficial group that has taken it upon itself to think about the asteroid issue. The group -- which has dubbed itself the B612 group after The Little Prince's asteroid, and which includes astronauts Rusty Schweickart and Ed Lu, and Princeton's Piet Hutt, among others -- met last October in Houston, Texas, to discuss what could be done in the event an asteroid is coming Earth's way, and to consider potential options and possible technical fixes.

Virtually all members of the asteroid community agree that there is a need to develop a master response plan for the simple reason that an asteroid collision could cause tremendous damage and loss of life. If 2002 NT7 or any other asteroid of similar size did collide with Earth, the impact velocity would be an estimated 28 kilometers a second. That, according to many scientists, is enough to wipe out a good part of a major continent and cause global climate changes and/or giant, destructive tsunamis.

The closest known approach of a sizeable object occurred just last month when an asteroid the size of a soccer field missed the Earth by 75,000 miles. That may sound like a solid margin, but in planetary distance terms, it is fairly close, less than one-third of the distance to the Moon. If that asteroid had hit terra firma, scientists projected that it would have released as much energy as a large nuclear weapon.

The public is welcome to "put the sensational stories aside" and observe as astronomers observe 2002 NT7 and other near Earth objects at NASA's NEO website. "We in the community relish the opportunity for the public to understand and see better exactly how this process works, to understand that nobody is hiding anything and that we don't necessarily know immediately whether or not something will hit with certitude," Durda says. "Everybody out there has a stake in understanding that this is an issue and considering the options of how we deal with this issue. It's a decision for everybody to make."

"It is important that we track and observe Near Earth Objects - not enough is being done and that is why The Planetary Society has launched the Gene Shoemaker NEO Grants for observing these objects," says executive director of the Society Louis D. Friedman. The Planetary Society NEO Shoemaker grants are awarded to amateur observers primarily to track objects near the planet, especially those that may pose a threat to Earth. The winner of this year's NEO Shoemaker Award will be announced Tuesday, July 30.