- Status Report
- Mar 21, 2023
NEO News (06/04/09) Planetary Defense at Granada pt 2
The edition of NEO News is a continuation of my last message, which was sent 05/29/09.The focus here is on international political support, as well as technical issues associated with protecting our planet from asteroid impacts. A future message will summarize the conclusions and recommendations from the conference. – David Morrison
INTERNATIONAL ORGANIZATIONS AND STUDIES
The International Academy of Astronautics was the primary sponsor of this planetary defense conference, which was held April 27-30 in Granada, Spain. Jean-Michel Contant welcomed the attendees on behalf of the IAA and committed the organization to support future Planetary Defense Conferences at two-year intervals. The next meeting will be in Bucharest, Romania, on May 9-14, 2011.
The IAA has recently completed its own study of the impact threat, summarized at this meeting by Ivan Bekey, called “Dealing with the Threat to Earth from Asteroids and Comets” (2009, 140 pages). The abstract of this document says “The Earth has been struck by asteroids and comets many times throughout its history. This report of the International Academy of Astronautics addresses the nature of the threat, expected future impacts, and the consequences of impacts from various size NEOs. It reviews current programs to detect, track, and characterize NEOs, and the future improvements required in order to take responsible and timely action. It identifies a number of techniques that could alter an incoming NEO’s orbit so as to avoid an impact. It addresses the organizational aspects that will have to be dealt with if a serious international capability is to be developed and employed to mitigate the threat. It then addresses behavioral factors and the sociological and psychological aspects of the threat and attempts at its mitigation before, during, and after an intercept attempt, whether successful or not. Lastly the report examines some of the principal international policy implications that must be dealt with if the world is to act in a timely, unified, and effective way with the very real threat due to NEOs.” To access full text go to this website: http://iaaweb.org/content/view/229/356/. The report contains useful information, but since it was 4 years in preparation, parts of it are rather dated.
D. Koschny of ESA (the European Space Agency) reported on an initiative to include asteroid impacts within the European Space Situational Awareness Programme. Situational awareness is concerned with perception of the environment critical to decision-makers in complex, dynamic areas such as aviation, air traffic control, and military command and control. The objective of the European Space Situational Awareness initiative is to support the European independent utilization of and access to space for research or services, through providing timely and quality data, information, services and knowledge regarding the environment, the threats, and the sustainable exploitation of the outer space. The components of this initiative are space surveillance, space weather, and NEOs. For NEOs, they intend to study tracking, orbit determination, orbital databases, and identification of impact risks. The main objective is to issue impact warnings. They intend to provide information on the impact probability and/or miss distance of NEOs. To do this, they will assess impact analyses and perform their own risk assessments. As these are all tasks that are already being addressed by the NASA NEO Program, the initial ESA activity may be to transmit this information to European decision-makers. No independent European detection or orbital analysis plans were suggested.
Rusty Schweickart provided an update to this meeting on the “Call for Global Response” of the international panel on Asteroid Threat Mitigation of the Association of Space Explorers (made up of astronauts and cosmonauts who have flown in space). Their report has been submitted to the UN committee on the Peaceful uses of Outer Space (COPUOS) and is currently entering a process of deliberation and potential action within the UN. We will be reporting on it in the future.
UNITED STATES STUDIES AND PLANS
Mike A’Hearn of the University of Maryland summarized the current study of the NEO Hazard being carried out by the National Research Council of the National Academy of Sciences. This study, chaired by Irwin Shapiro, the Director emeritus of the Harvard College Observatory, is primarily addressing requests from Congress. They are considering the challenge of surveying potentially hazardous NEAs at smaller sizes, to reach 90% completeness at a diameter of 140 m. They are also considering a wide variety of techniques for characterization and mitigation. Congressional staff members have told the NAS-NRC steering committee that the Congress is interested in understanding how international collaboration should work in this area. This NRC study and recommendations should be completed at the end of 2009.
The capabilities of two large ground-based survey projects were discussed: Pan-STARRS presented by M. Granvik (with the first of four survey telescopes near completion in Hawaii, funded by the U.S. Air Force), and LSST presented by Z. Ivezic (a single wide-field 8-m telescope to be constructed in Chile, with detailed studies underway supported by the U.S. National Science Foundation and the U.S. Department of Energy). Space-based asteroid detection in the thermal infrared was discussed by Amy Mainzer of JPL, who described the capabilities of WISE (the NASA Widefield Infrared Survey Explorer), which is to be launched in November 2009, and of a possible dedicated infrared NEA survey called NEO-CAM to follow.
Peter Garretson (Lt. Col., US Air Force) reported the results of a scripted multi-agency deflection and disaster exercise. Participants included middle-level representatives of U.S. Air Force, NASA, National Security Council, Department of Defense, Department of State, Department of Homeland Security, Navy, Coast Guard, Federal Emergency Management Agency, and Defense Threat Reduction Agency. The objective was to better understand how responsible government organs would respond in the absence of clear policy on roles and missions. The table-top simulation involved two specific threats: a binary asteroid the size of Apophis targeted in the Atlantic Ocean off the coast of Nigeria, and a 50-m metallic asteroid targeted on the Eastern U.S. near Washington DC. They studied possible mitigation of the ocean impact given 7 years warning, and disaster management for the U.S. impact given 72 hours warning. The participants were aware of lack of previous planning. While a number of useful analogs exist, as well as procedures that could be used or adapted, attempts or do so in the moment are likely to be much less successful than advance preparation. Participants recommended that the NEO scenario should be elevated to higher levels with more senior players. They also concluded that proper planning and response to a NEO emergency requires delineation of organizational responsibilities including lead agency and notification standards, but they were not able to agree on which should be the lead agency. This was the first time such a multi-agency exercise had taken place in the U.S. Dealing with similar issues on an international scale would be even more problematic.
Lance Benner (JPL) provided an update on the always-spectacular discoveries using the Arecibo and Goldstone radars, which are our most powerful tools for both orbital and physical characterization of NEAs (if they come with radar range). He showed an interesting comparison between the radar and spacecraft images of Itokawa; the radar got the size and shape right but could not resolve the fine detail, including the many boulders on the surface. Among the newly imaged objects were 1992 UY4, 1998 CS1, and the binary NEA 2000 DP107. Radar data indicate that about 10% of NEAs are actually contact binaries, and he stressed how different NEAs are, with “no such thing as a typical NEA.”
Rick Binzel (MIT) reviewed telescopic data on the physical properties of NEAs. Large telescopes are being used to obtain visible and near-infrared colors, spectrophotometry, and polarimetry. He introduced a more accurate classification of 42-channel spectrophotometry to create what he calls the Bus-DeMeo taxonomy, with more than 20 classes. Reminding the audience that we have thousands of direct samples of NEAs in the form of meteorites, Binzel noted that one of the objectives of telescopic studies is to link the remote measurements of NEA spectra with specific meteorite types. He used such an analysis to conclude that Apophis has the surface composition of a LL Chondrite. If this is correct, we can use lab study of meteorites to estimate that Apophis is composed primarily of olivine and pyroxene with relatively low metal content. The bulk density of this material is 3.2 g/cc. Similar telescopic data for 2008 TC3 can be calibrated from the recovered meteorites. Binzel called this classification of NEAs from telescopic data “our first line of defense against NEOs.”
The use of small spacecraft for detailed physical characterization of NEAs was the subject of several presentations and poster papers. The Japanese Hayabusa mission to Itokawa is an outstanding example of this approach. David Morrison stressed that flybys are of little use for small NEA targets, with a rendezvous required to determine such key properties as mass, density, and surface topography. He described a low-cost mission called MAAT that has been studied at NASA Ames Research Center. Another paper described the Didymos explorer mission designed to explore a binary NEA. Another proposed Apophis mission called Foresight is intended to tag Apophis with a radio transponder for very precise orbit determination, and PROBA-IP is an ESA technology demonstration mission targeted to Apophis. There was considerable discussion of the great value of a combined rendezvous and ballistic impact mission. Such a mission called Don Quijote was studied by ESA but now seems to have been dropped. However, ESA is working with Japan on an alternative NEA rendezvous mission without the impactor.
MORRISON COMMENTARY ON THE CONFERENCE
This was an excellent meeting: well attended and with some fine technical and policy papers presented. Most of the leaders in the NEO defense arena were present, as well as many new participants, especially many young scientists from Europe.
Several speakers assumed that the current estimates of the impact rate are greater than previously thought, adding urgency to this threat. Judging by some of the presentations at this meeting, these assessments were based on faulty or misinterpreted data. As Al Harris (Space Science Institute) showed (discussed in NEO News 05/29/09), at least 90% of the risk associated with impact by an unknown asteroid has been eliminated by the Spaceguard Survey, and in addition the NEO population data summarized by Harris indicate fewer sub-km asteroids by at least a factor of 2, relative to previous power-law estimates. It is curious to see claims by policy analysts that the impact threat is increasing while the scientific community comes to the opposite conclusion.
There was thus a certain unreality about some of the discussions. Many international and European organizations are becoming concerned about the impact hazard just at the time it is being rapidly reduced by the Spaceguard Survey. While there have been some excellent paper studies (for example, the U.K. impact hazard study in 2001), so far only two nations have made significant contributions to actually mitigating the impact hazard: the United States and Japan. The U.S. has financed the Spaceguard survey, the Minor Planet Center, the NEO Program Office at JPL, the planetary radar systems at Arecibo and Goldstone, studies of the next generation of survey telescopes (including construction of the Pan-STARRS-1, casting the 8-m mirror for the LSST, building the WISE infrared survey satellite, and sending the NEAR-Shoemaker mission which orbited and landed on Eros). Japan has carried out the only spacecraft study of a sub-km NEA, Itokawa, including brief landing and collection of a sample now en route back to Earth.
Three surprising new results presented at this meeting stand out in my mind. (1) The strange case of the Carancas meteorite fall on the Altiplano at the Peru-Bolivia border on September 15, 2007, which was described by Tancredi. A stony (ordinary chondrite) meteorite with an original mass of a few tons hit at a few km/s speed and formed a 15-m wide crater. This should not happen according to conventional models. (2) Boslough’s supercomputer simulations of the Tunguska impact indicate that stony objects <40m in diameter can produce highly destructive airbursts, and somewhat larger airbursts can also generate substantial melting of silicates at the surface when their fireball reaches the ground. (3) The unique case of 2008 TC3 showed that even with the current survey systems it is possible to detect a small NEA very close to impact, accurately predict the impact time and place, and recover meteorites. This is also our first chance to directly compare remote sensing observations of the parent object in space with "ground truth" from recovered samples. TC3 has greatly increased interest in detection of small asteroids within a few days of impact. NEO News (now in its fourteenth 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 [email protected] For additional information, please see the website http://impact.arc.nasa.gov. If anyone wishes to copy or redistribute original material from these notes, fully or in part, please include this disclaimer.