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RE: NEO
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Asteroid sleuths go back to the future

Spotting a previously unknown asteroid for the first time always raises the big question: is there a risk it will impact Earth?
Yet, upon discovery, analysts often have very little to go on. The initial image from the observatory, survey team or individual backyard astronomer who spotted the rock typically gives only basic information - its location in the sky and its brightness - and sometimes these aren't known terribly accurately.

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Title: Orbital Simulations on Deflecting Near-Earth Objects by Directed Energy
Author: Qicheng Zhang, Kevin J. Walsh, Carl Melis, Gary B. Hughes, Philip M. Lubin

Laser ablation of a Near-Earth Object (NEO) on a collision course with Earth produces a cloud of ejecta which exerts a thrust on the NEO, deflecting it from its original trajectory. Ablation may be performed from afar by illuminating an Earth-targeting asteroid or comet with a stand-off "DE- STAR" system consisting of a large phased-array laser in Earth orbit. Alternatively, a much smaller stand-on "DE-STARLITE" system may travel alongside the target, slowly deflecting it from nearby over a long period. This paper presents orbital simulations comparing the effectiveness of both systems across a range of laser and NEO parameters. Simulated parameters include magnitude, duration and, for the stand-on system, direction of the thrust, as well as the type, size and orbital characteristics of the target NEO. These simulations indicate that deflection distance is approximately proportional to the magnitude of thrust and to the square of the duration of ablation, and is inversely proportional to the mass. Furthermore, deflection distance shows strong dependence on thrust direction with the optimal direction of thrust varying with the duration of laser activity. As one example, consider a typical 325 m asteroid: beginning 15 yr in advance, just 2 N of thrust from a ~20 kW stand-on DE-STARLITE system is sufficient to deflect the asteroid by 2 R_e. Numerous scenarios are discussed as is a practical implementation of such a system consistent with current launch vehicle capabilities.

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After Chelyabinsk European experts assess asteroid options

This week, Deimos Space, an industrial partner working for ESA on SSA, has invited top researchers from universities, research institutes, national space agencies and industry in Europe and the USA to discuss the state of the art in NEO impact effects and threat mitigation.
The meeting is taking place in Tres Cantos, Spain, near Madrid.

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Scientists unveil new detectors in race to save Earth from next asteroid

The extraterrestrial double whammy that Earth only partially avoided on Friday has triggered an immediate response from astronomers. Several have announced plans to create state-of-the-art detection systems to give warning of incoming asteroids and meteoroids. These include projects backed by Nasa as well as proposals put forward by private space contractors.
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Explained: Near-miss asteroids

On May 29, an asteroid the size of a bus came whizzing past Earth at 10 times the speed of a fired bullet. The near-miss asteroid, named 2012 KT42 - streaked across the orbits of weather and television satellites, 22,000 miles above Earth's surface, making it the sixth-closest asteroid approach on record. While the object had little chance of colliding with Earth, its approach gave scientists an opportunity to run a rapid-response program - or as MITs Richard Binzel calls it, an asteroid-tracking "fire drill" - to gain as much information as possible from the incoming space rock.
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Near Earth Objects
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Title: Characterising Subpopulations within the Near Earth Objects with NEOWISE: Preliminary Results
Authors: A. Mainzer, T. Grav, J. Masiero, J. Bauer, R. S. McMillan, J. Giorgini, T. Spahr, R. M. Cutri, D. J. Tholen, R. Jedicke, R. Walker, E. Wright, C. R. Nugent

We present the preliminary results of an analysis of the sub-populations within the near-Earth asteroids, including the Atens, Apollos, Amors, and those that are considered potentially hazardous using data from the Wide-field Infrared Survey Explorer (WISE). In order to extrapolate the sample of objects detected by WISE to the greater population, we determined the survey biases for asteroids detected by the project's automated moving object processing system (known as NEOWISE) as a function of diameter, visible albedo, and orbital elements. Using this technique, we are able to place constraints on the number of potentially hazardous asteroids (PHAs) larger than 100 m and find that there are ~47001450 such objects. As expected, the Atens, Apollos, and Amors are revealed by WISE to have somewhat different albedo distributions, with the Atens being brighter than the Amors. The cumulative size distributions of the various near-Earth object (NEO) subgroups vary slightly between 100 m and 1 km. A comparison of the observed orbital elements of the various sub-populations of the NEOs with the current best model is shown.

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Spaceguard survey
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About 1,000 asteroids big enough to cause catastrophic damage if they hit Earth are orbiting relatively nearby, a NASA survey shows.
In a project known as Spaceguard, the U.S. space agency was ordered by Congress in 1998 to find 90 percent of objects near Earth that are 1 km (0.62 of a mile) in diameter or larger.
The survey is now complete, with 93 percent of the objects accounted for, astronomer Amy Mainzer of NASA's Jet Propulsion Laboratory in Pasadena, California, said at the American Geophysical Union conference in San Francisco on Tuesday.

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Title: NEOWISE Observations of Near-Earth Objects: Preliminary Results
Authors: A. Mainzer, T. Grav, J. Bauer, J. Masiero, R. S. McMillan, R. M. Cutri, R. Walker, E. Wright, P. Eisenhardt, D. J. Tholen, T. Spahr, R. Jedicke, L. Denneau, E. DeBaun, D. Elsbury, T. Gautier, S. Gomillion, E. Hand, W. Mo, J. Watkins, A. Wilkins, G. L. Bryngelson, A. Del Pino Molina, S. Desai, M. Go'mez Camus, S. L. Hidalgo, I. Konstantopoulos, J. A. Larsen, C. Maleszewski, M. A. Malkan, J.-C. Mauduit, B. L. Mullan, E. W. Olszewski, J. Pforr, A. Saro, J. V. Scotti, L. H. Wasserman

With the NEOWISE portion of the Wide-field Infrared Survey Explorer (WISE) project, we have carried out a highly uniform survey of the near-Earth object (NEO) population at thermal infrared wavelengths ranging from 3 to 22 \mu m, allowing us to refine estimates of their numbers, sizes, and albedos. The NEOWISE survey detected NEOs the same way whether they were previously known or not, subject to the availability of ground-based follow-up observations, resulting in the discovery of more than 130 new NEOs. The survey's uniformity in sensitivity, observing cadence, and image quality have permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by NEOWISE during the fully cryogenic portion of the WISE mission to the larger population. We find that there are 981 19 NEAs larger than 1 km and 20,500 3000 NEAs larger than 100 m. We show that the Spaceguard goal of detecting 90% of all 1 km NEAs has been met, and that the cumulative size distribution is best represented by a broken power law with a slope of 1.32 0.14 below 1.5 km. This power law slope produces ~13,200 1,900 NEAs with D>140 m. Although previous studies predict another break in the cumulative size distribution below D~50-100 m, resulting in an increase in the number of NEOs in this size range and smaller, we did not detect enough objects to comment on this increase. The overall number for the NEA population between 100-1000 m are lower than previous estimates. The numbers of near-Earth comets will be the subject of future work.

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Title: NEOWISE Studies of Spectrophotometrically Classified Asteroids: Preliminary Results
Authors: A. Mainzer, T. Grav, J. Masiero, J. Bauer, E. Hand, D. Tholen, R. S. McMillan, T. Spahr, R. M. Cutri, E. Wright, J. Watkins, W. Mo, C. Maleszewski

The NEOWISE dataset offers the opportunity to study the variations in albedo for asteroid classification schemes based on visible and near-infrared observations for a large sample of minor planets. We have determined the albedos for nearly 1900 asteroids classified by the Tholen, Bus and Bus-DeMeo taxonomic classification schemes. We find that the S-complex spans a broad range of bright albedos, partially overlapping the low albedo C-complex at small sizes. As expected, the X-complex covers a wide range of albedos. The multi-wavelength infrared coverage provided by NEOWISE allows determination of the reflectivity at 3.4 and 4.6 \mu m relative to the visible albedo. The direct computation of the reflectivity at 3.4 and 4.6 \mu m enables a new means of comparing the various taxonomic classes. Although C, B, D and T asteroids all have similarly low visible albedos, the D and T types can be distinguished from the C and B types by examining their relative reflectance at 3.4 and 4.6 \mu m. All of the albedo distributions are strongly affected by selection biases against small, low albedo objects, as all objects selected for taxonomic classification were chosen according to their visible light brightness. Due to these strong selection biases, we are unable to determine whether or not there are correlations between size, albedo and space weathering. We argue that the current set of classified asteroids makes any such correlations difficult to verify. A sample of taxonomically classified asteroids drawn without significant albedo bias is needed in order to perform such an analysis.

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NASA Space Telescope Finds Fewer Asteroids Near Earth

New observations by NASA's Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.
Astronomers now estimate there are roughly 19,500 -- not 35,000 -- mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought. However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 100 and 1,000-metre wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.

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