This area will cover relevant news of the threat to the planet from Near Earth Objects (NEOs) including concepts and designs for mitigation. All opinions are those of the author.

12 November 2007

NEO News (11/12/07) More on Congress NEO Hearings

Note: The following is the 10/12/07 Edition of NEO News, an email newsletter distributed by David Morrison.

NEO News (11/12/07) More on Congress NEO Hearings

This edition of NEO News contains some additional material on the hearings held last week by the House Subcommittee on Space and Aeronautics dealing with advanced NEO searches and related topics. I have (1) posted a news story on the hearing from, (2) selected several very nice summary comments taken from the testimony, and (3) also added a few comments of my own on some misunderstandings that can arise in these discussions, misunderstandings that apparently caused the NASA NEO study to limit itself to technologies for deflecting NEAs between 140m and 1km in diameter, neglecting both the most dangerous (>1km) and the most common (<140m) cases. Also, unrelated to the hearings, there is (4) a post on the strange story off how the Rosetta spacecraft was mistaken for a NEA.

David Morrison



AFP, 8 November 2007

NASA penny-pinching risks exposing humankind to a planetary catastrophe if a big enough asteroid evades detection and slams into Earth, US lawmakers argued Thursday. But the US space agency said the chances of a new "Near-Earth Object" (NEO) like the one that wiped out the dinosaurs were too remote to divert scarce resources.

Scott Pace, head of program analysis and evaluation at NASA, said the agency could not do more to detect NEOs "given the constrained resources and the strategic objectives NASA already has been tasked with."

Pace and other NASA officials were grilled at a congressional hearing on the existing NEO program, which seized the public imagination in the late 1990s through the movies "Armageddon" and "Deep Impact." Lawmakers decried the threatened closure of a giant radio telescope in Puerto Rico run with NASA's assistance that is the world's foremost facility for tracking space objects.

"We're talking about minimal expense compared to the cost of having to absorb this type of damage," Republican Congressman Dana Rohrabacher said. "After all, it may be the entire planet that is destroyed!"

Puerto Rico delegate Luis Fortuno fretted over the economic impact on his impoverished US territory, but also warned of the broader consequences for the entire planet. The National Science Foundation has earmarked the Arecibo Observatory, which featured in science-fiction movie "Contact" and the James Bond installment "Goldeneye," for closure after 2011 if new private-sector money is not found.

NASA officials said they would get by with new monitoring systems, including a network of four telescopes being built in Hawaii by the US Air Force.

Critics say NASA has imposed big cuts on many research programs in a bid to meet President George W. Bush's goal of returning astronauts to the Moon by 2020 and use it as a stepping stone for manned missions to Mars and beyond.

The hearing of the House of Representatives space and aeronautics subcommittee highlighted one small asteroid named Apophis, about 250 meters (273 yards) wide, which some scientists say could swing by Earth on Friday, April 13, 2029. NASA says there is a one in 45,000 chance that Apophis could pass through a "gravitational keyhole" and return to hit the planet in 2036. "It's a very unlikely situation and one we can drive to zero, probably," said Donald Yeomans, who manages the NEO program at NASA's Jet Propulsion Laboratory.

NASA now only tracks NEOs larger than one kilometer (0.62 miles) in diameter, which come near Earth only once every few hundred thousand years. Objects of that size can cause global disaster through their immediate surface impact and by triggering rapid climate change. "Extinction-class" objects measuring at least 10 kilometers, such as the object that crashed into Mexico's Yucatan peninsula about 65 million years ago, would be rarer still.

Lawmakers complained that NASA had failed to come up with a budget in line with a 2005 act of Congress that mandated an expanded search for NEOs that are at least 140 meters in diameter. The agency's annual NEO budget of 4.1 million dollars was attacked as being too meager to cover this goal.

There are about 20,000 smaller objects with the potential to hit home, according to NASA, and Republican Representative Tom Feeney said "they could still inflict large regional impacts if they struck the Earth."

Options to divert space rocks on a collision course with Earth include slamming nuclear missiles into them, although scientists believe that in most cases involving smaller debris, conventional rockets would do the job.

Yeomans said also that while the European and Japanese space agencies are stepping up their own NEO programs, more than 98 percent of the work is now done by NASA.

© 2007 AFP



From testimony of J. Anthony Tyson, LSST

Until recently, the discussion of risk associated with an impact of a NEO has been statistical; what is the probability? This is similar to considerations of risk in many other areas such as weather and traffic accidents. What if it were feasible to deploy a system that would alert me of an impending traffic accident well in advance? That would change the very nature of that risk from a probabilistic worry to a deterministic actionable situation. The ability to detect virtually every potentially hazardous Near-Earth object and determine its orbit with precision transforms that statistical threat into a deterministic prediction. We face many threats, and virtually all of them are either so complex or unpredictable that they are treated probabilistically even though the social and financial consequences are legion. With a comparatively small investment the NEO risk can be transformed from a probabilistic one to a deterministic one, enabling mitigation.

From testimony of Donald Yeomans, JPL

What should be done in the event of an identified NEO Threat? A number of existing technologies can deflect an Earth threatening asteroid -- if there is time. The primary goal of the PHA survey programs is to discover them early and provide the necessary time. An asteroid that is predicted to hit Earth might require a change in its velocity of only 3 millimeters per second if this impulse were applied twenty years in advance of the impact. The key to a successful deflection is having sufficient time to carry it out, whether it is the slow, gentle drag of a gravity tractor or a more impulsive shove from an impacting spacecraft or explosive device. In either case, a verification process would be required to ensure the deflection maneuver was successful and to ensure the object's subsequent motion would not put it on yet another Earth impacting trajectory. While suitable deflection technologies exist, none of them can be effective if we are taken by surprise. It is the aggressive survey efforts and robust planetary radars that must ensure that the vast majority of potentially hazardous objects are discovered and tracked well in advance of any Earth threatening encounters. The first three steps in any asteroid mitigation process are: Find them early, find them early, and find them early!

From testimony of Russell Schweickart, B612 Foundation

In closing I would suggest a personal perspective based on having spent the last 6 years of my life studying this issue. NEOs are part of nature. A NEO impact is a natural hazard in much the same way as are hurricanes, tsunamis, floods, etc. NEO impacts are deceptively infrequent, yet devastating at potentially unimaginable levels. NEOs are however not our enemies. We do not need to "defend" against NEOs, we need to protect ourselves from their occasional impact, as we do with other natural hazards.

Unlike other natural hazards, however, NEO impacts can be predicted well ahead of time and actually prevented from occurring. If we live up to our responsibility, if we wisely use our amazing technology, and if we are mature enough, as a nation and as a community of nations, there may never again be a substantially damaging asteroid impact on the Earth. We have the ability to make ourselves safe from cosmic extinction. If we cannot manage to meet this challenge, we will, in my opinion, have failed to meet our evolutionary responsibility.



David Morrison

Some of the often misunderstood concepts behind NEO surveys concern the meaning of a specified 90% target size, 1km diameter in the case of the current Spaceguard Survey, and 140m for the proposed Spaceguard deep survey. An example from the news story above is this statement: "NASA now only tracks NEOs larger than one kilometer (0.62 miles) in diameter." But the fact is, in Al Harris's often-quoted words, "we don't throw back the small ones." The majority of NEAs found by Spaceguard are less than 1km in diameter. By the time we reach 90% completeness at 1km, we will have found almost ten times more NEAs smaller than this limit, and certainly these smaller NEAs are tracked and cataloged. The best known example is Apophis, the most dangerous NEA found yet, which is only about half the 1km Spaceguard target size. In any such survey, most of the NEAs will be below the index size, but these will be less complete than the index size used for the 90% metric.

Similarly, any survey scaled for 140m NEAs will predominantly find NEAs smaller than this size. In fact, the discoveries from this deep survey will extend down below the atmospheric cut-off at about 30m diameter. Rusty Schweickart in his testimony estimates that when we reach 90% completeness at 140m, we will be 40% complete for Tunguska-size objects. The most likely object to require deflection is actually below the 140m index size.

There are implications of these facts that need to be considered. For example, the data handling must be scaled for nearly 10 times the number of NEAs at 140m size, since again, we won't throw back the small ones. Further, any plans for deflection should recognize that the most likely challenges will come from NEAs less than 140m in diameter. The NASA study apparently focused only on deflecting NEAs between 140m and 1km in diameter, neglecting both the most dangerous (those larger than 1km, of which 10% will remain undiscovered at the nominal end of the current Spaceguard survey) and the most common (those under 140m diameter).

None of the prepared testimony explicitly mentioned uncertainties in the population of small NEAs or in the ability to model the efficiency of survey telescopes. This in understandable, given the limited time available, but it does over-emphasize specific dates and sizes that enter into models of the new deep surveys. It is not unreasonable that both the number of NEAs larger than 140m and the ability of new telescopes (both ground-based and space based) to detect and identify them could be off by as much as a factor of two. We won't know when we are likely to achieve 90% completeness at 140m until the telescopes are built and the new survey is well underway. Therefore I don't worry too much about small differences in the estimated dates of completion. I am more interested in the start date than the completion date for Spaceguard-2.



The Planetary Society Weblog, 9 November 2007
By Emily Lakdawalla

Whenever I am out at night with my husband and I point to the sky and say, "that's Venus" or "look, that's Saturn, see how yellow it is," he likes to burst my bubble by saying "no, it's just a plane." Every great once in a while, I'm sad to say, he's right.

Well, a similar scenario has just unfolded within the near-Earth asteroid community. On November 8 the Minor Planet Center issued a routine Minor Planet Electronic Circular, reporting on observations of a newly discovered object, newly designated 2007 VN84. Several observatories had spotted the faint object, and, based upon those observations, an orbital trajectory was calculated, which placed the object on a very close path by Earth, "0.000081 AU (1.89 Earth radii) on Nov 13.844 UT." Now, that 1.89 Earth radii is measured relative to Earth's center, meaning that the thing was going to fly within 6,000 kilometers of Earth on November 13 at 20:15 UTC. That's pretty close! This is a truly near-Earth object.

Rosetta's second Earth flyby is due to take place Closest approach will take place on 13 November 2007 at 20:57 UTC, at which time Rosetta will speed past at 45,000 km/h (about 12.5 km/s) relative to Earth. At this time, Rosetta will be 5,301 km above the Pacific Ocean, south-west of Chile, at 63° 46' south and 74° 35' west. But a sharp-eyed reader of the MPECs, Denis Denisenko, realized that there was something going on. I'm not sure what tipped him off; whether he noticed that specific date and time and remembered another significant event to happen on that day, or whether he has a habit of checking near-Earth object trajectories against catalogs of manmade objects. However the discovery happened, he realized that 2007 VN84 had a trajectory that was awfully similar to Rosetta, which is due to swing by Earth on November 13 at 20:57 UTC. He posted as much to the Minor Planet Mailing List.

Indeed, today, the Minor Planet Center issued an Editorial Notice stating that further investigation has shown that the object briefly designated 2007 VN84 is, in fact, the Rosetta spacecraft, and that the designation "2007 VN84" will be retired. The editorial notice goes on to say, with notable asperity, "This incident, along with previous NEOCP postings of the WMAP spacecraft, highlights the deplorable state of availability of positional information on distant artificial objects.... A single source for information on all distant artificial objects would be very desirable."

I think it's pretty funny that a very big spacecraft designed to study minor planets in the solar system has itself, however briefly, been named among the minor planets. This episode also goes to show how sensitive our detection capability is. Rosetta is a pretty reflective object, but it's also quite small when compared to near-Earth objects that could do us any damage. And here we had at least several days' warning of this small object's approach. It's actually comforting to me, in a way; it seems that there is now no way we can have less than a few weeks' warning of the approach of an object large enough to do us some harm. Bad things may happen if such an object hits, but that's enough time to get a lot of people out of harm's way.

Of course, all this hubbub is occasioned by Rosetta's upcoming flyby. The Rosetta Blog has some updates, including the nice detail that no further trajectory correction maneuvers are necessary, which bodes well for them accomplishing the acquisition of science data during the flyby.

Copyright © 1993 - 2007 The Planetary Society. All rights reserved.


NEO News (now in its thirteenth year of distribution) is an informal compilation of news and opinion dealing with Near Earth Objects (NEOs) and their impacts. These opinions are the responsibility of the individual authors and do not represent the positions of NASA, Ames Research Center, the International Astronomical Union, or any other organization. To subscribe (or unsubscribe) contact For additional information, please see the website If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.

No comments:

Post a Comment

Note: Any opinions expressed on the blog are solely those of the author. The site is not sponsored by, nor does it represent the opinions of, any organization, corporation, or other entity.