Planetary Defense Research Articles

Optical and acoustic ground effects simulations from terminal defense asteroid disruption via the PI method

Our simulations suggest that Pulverize It (PI), a NASA Phase II NIAC study, is an effective multi-modal approach for planetary defense that can operate in extremely short interdiction modes (with intercepts as short as hours prior to atmospheric entry) as well as long-interdiction time scales with months to years of warning. The basic process is complete disruption of the threat via fragmentation. In scenarios with sufficiently long warning time, the fragment cloud spreads enough to miss Earth, resulting in no ground effects. In “worst-case” scenarios with short warning times (“terminal” scenarios), the fragments (typically <10 m in diameter) will enter Earth’s atmosphere, where their energy is dissipated in a series of ground-level optical pulses and de-correlated shock waves, mitigating any significant damage. We investigate the optical and acoustic ground effects through a set of simulation codes that model the interaction of asteroid fragments with Earth’s atmosphere following terminal threat interception. Even in such cases where fragments enter the atmosphere, our simulations suggest that threats mitigated by PI produce vastly less damage on the ground when compared to an equivalent unfragmented case, yielding optical energy deposition below 200 kJ/m2 and shock wave over-pressures under 3 kPa. Our simulations support the proposition that threats like 2023 PDC, the hypothetical 800 m diameter asteroid from the 2023 Planetary Defense Conference impact exercise, can be effectively mitigated through fragmentation. We find that a terminal defense mitigation scenario that disrupts 2023 PDC into 1 million fragments with an intercept of 60 days before ground impact results in reasonable ground effects with minimal damage.

Optimal combined impulsive/low-thrust trajectories for asteroid deflection via kinetic impact

This work considers the trajectory optimization of a kinetic impactor spacecraft, which is sent to collide with a threatening near-Earth asteroid. It is assumed that Earth departure is done impulsively, by the upper stage of a launch vehicle, and is then followed by low-thrust electric propulsion until impact. For a given spacecraft, all of the important decision parameters, such as the date of departure, the direction of the hyperbolic departure, the thrust program, i.e. the history of the low-thrust pointing angles, and the date of impact are all chosen by the optimizer to maximize the perigee radius of the asteroid at its closest approach. Normally a trajectory optimization problem of this type would need to be described by many hundreds of decision parameters, e.g. if formulated to be solved by an optimization package (such as GPOPS) using nonlinear programming. We show that a successful and accurate optimization of the mission is possible using the heuristic method, particle swarm, and only 16 decision parameters, and present results for the deflection of 99942 Apophis at its 2029 close approach.

Collective action problems in planetary defense

In recent years, growing awareness of potential threats posed by near-Earth objects (NEOs) has led to increased interest in developing and implementing planetary defense measures. International cooperation and public support are crucial to ensuring the long-term success of planetary defense initiatives. However, a number of economic, political, legal, and social issues stand in the way of effective large-scale cooperation in pursuing planetary defense. This article examines the major challenges to international cooperation in planetary defense. The article begins by considering the major types of collective action problems facing international collaboration toward planetary defense. The article then examines the way in which adjacent space-related aspects of international affairs influence the arena of planetary defense. The article then analyzes the legal aspects of these cooperation problems, focusing on sources of perceived uncertainty that interfere with effective development of norms for cooperation. The article then proposes various possible strategies for avoiding cooperation problems and increasing collective buy-in. Noteworthy examples include the use of treaties as pre-commitment devices (which parties agree to undertake in order to limit their future options and commit themselves to pre-established lines of conduct) and amendments to existing legal frameworks to decrease perceived uncertainty and promote objective standards of cooperation. The article concludes by reflecting on the importance of promoting a widespread cultural perspective that emphasizes the pursuit of collective planetary welfare over competing national interests.

DART Impact Ejecta Plume Evolution: Implications for Dimorphos

The NASA Double Asteroid Redirection Test (DART) spacecraft impacted the moon Dimorphos of the [65803] Didymos binary system and changed the binary orbit period, demonstrating asteroid deflection by a kinetic impact and indicating that more momentum was transferred to Dimorphos by escaping impact ejecta than was incident with DART. Images of the DART impact ejecta plume were obtained by the Light Italian cubesat for Imaging of Asteroids (LICIACube) in the first few minutes after the DART impact. The ejecta plume imaged by LICIACube 158 s after the DART impact prior to closest approach shows no evidence for plume clearing at low altitude. The ejecta plume imaged 175 s after the DART impact is optically thick up to projected altitudes of 200 m above the surface of Dimorphos. These observations are compared with models of the impact ejecta plume optical depth, structure, and evolution, which are developed from point-source scaling models fitted to numerical simulations of the DART impact into a rubble pile Dimorphos with different material strengths. The observations of the impact plume optical depth and the high momentum transfer from the DART impact are not consistent with impact and ejecta plume models assuming the Dimorphos cohesive strength to be as high as 5000 Pa. Models with 5 and 50 Pa Dimorphos cohesive strength provide the overall best consistency with plume opacity observations and high momentum transfer.

Long-term Monitoring of Didymos with the LCOGT Network and MRO after the DART Impact

The world’s first planetary defense test mission was carried out in late 2022 by NASA’s Double Asteroid Redirection Test (DART) mission. The main DART spacecraft, which was accompanied by the ASI-provided LICIACube cubesat, intentionally impacted Dimorphos, the smaller secondary of the near-Earth object binary system (65803) Didymos, on 2022 September 26. The impact released a large amount of ejecta, which, combined with the spacecraft’s momentum, produced the observed 33 ± 1 minute period change that was subsequently observed from ground-based telescopes. The DART mission, in addition to having successfully changed the orbital period of Dimorphos, also activated the asteroid as a result of the impact but under known conditions, unlike other impacts on asteroids. We have conducted long-term monitoring over 5 months following the impact with the Las Cumbres Observatory Global Telescope (LCOGT) network and Magdalena Ridge Observatory (MRO). This was supplemented by almost 3 months of more sparsely sampled data, primarily from educational users of the LCOGT network during the period from 2022 July 5 to 2022 September 25, prior to the impact date of 2022 September 26. Here we report the observations of the Didymos system and DART impact ejecta with the telescopes of the LCOGT network from T+1.93 days to T+151.3 days after impact, and we study the evolving morphology of the ejecta cloud and evolving tail over the entire length of the data set. In addition, we combined these intensive data sets with the earlier sparse observations over the ∼90 days prior to impact to derive a new disk-integrated phase function model using the H, G 1, G 2 parameterization.

Consequences of asteroid characterization on the state of knowledge about inferred physical parameters and impact risk

Planetary defense scenarios require an assessment of the possible effects of an impact and of the efficacy of different mitigation options in order to provide decision makers with actionable information. Essential inputs to these assessments are the orbital parameters, the likelihood of impact, the possible locations of impact, and the physical properties of the potential impactor. There is a robust framework in place to determine the orbital parameters, the likelihood of impact, and the possible locations of impact (e.g. Milani et al. [1], Sciarra et al. [2], Losacco et al. [3]). While there is a robust suite of potential methods to determine properties of a potential impactor, most of these methods depend critically on the details of the objects observability (e.g. brightness, distance from Earth, …). As a result, in practice it is rare that all the physical properties of interest are measurable. In order to fill this gap, we have developed a property inference network that can be used to generate a set of potential impactors whose properties in aggregate are consistent with the distributions from the available measurements, the distributions derived from population-wide statistics, and the combination of physical properties for each individual impactor is physically plausible. We will describe this Asteroid Property Inference Network (APIN), apply it to the PDC23 scenario, and demonstrate how even limited asteroid characterization can be leveraged to improve impact risk assessment.

DART: Latest results from the Dimorphos impact and a look forward to future planetary defense initiatives

DART, the Double Asteroid Redirection Test, successfully impacted asteroid Dimorphos on September 26, 2022, becoming the first mission to demonstrate asteroid deflection. Shared live via a NASA broadcast, over a million concurrent viewers around the world watched as the DART spacecraft streamed images to Earth up to the final second before its impact with Dimorphos. In this paper, we share the final phases of the DART encounter and the latest results from the DART Investigation Team's analysis of ground and space-based data. This includes measurements on the amount of deflection that DART imparted on Dimorphos, a determination of the momentum transfer enhancement factor, and results on understanding the geology and surface characteristics of the impact site. The success of the DART mission paves the future for a bold international Planetary Defense program. We also share ideas on bolstering international coordination, developing new technologies that can mitigate different types of asteroid threats, and closing identified gaps in our overall preparedness.

Near-earth asteroids classification using NGBoost classifier

Near-Earth asteroids (NEAs) are celestial bodies that orbit within close to Earth, offering valuable insights into the early solar system's formation and posing potential hazards due to impact events. This work presents a comprehensive overview of NEAs, encompassing their historical significance, characteristics, impact hazards, and prospects. The study outlines the NASA Asteroids Classification Dataset and discusses its importance for research on asteroid classification and risk assessment. Furthermore, the methodology section delineates the utilization of the NGBoost classifier for predictive modeling tasks, detailing data collection, preprocessing, model training, evaluation, and result interpretation. Results from the NGBoost classifier demonstrate high accuracy and performance metrics in classifying asteroids, underscoring its efficacy in advancing asteroid classification efforts and informing planetary defense strategies. NEAs pose a potential threat to our planet, and their classification is essential for understanding their properties and predicting their trajectories accurately. In this research, we explore the application of NGBoost, a powerful gradient-boosting framework, for classifying NEAs based on their orbital and physical characteristics. We present a dataset comprising features extracted from known NEAs and non-NEAs and demonstrate the efficacy of NGBoost in accurately distinguishing between these classes. Our results indicate promising performance metrics with 99.22% accuracy, suggesting that NGBoost holds potential as a valuable tool in asteroid classification.

VADER: Probing the Dark Side of Dimorphos with LICIACube LUKE

Abstract The ASI cubesat LICIACube has been part of the first planetary defense mission DART, having among its scopes to complement the DRACO images to better constrain the Dimorphos shape. LICIACube had two different cameras, LEIA and LUKE, and to accomplish its goal, it exploited the unique possibility of acquiring images of the Dimorphos hemisphere not seen by DART from a vantage point of view, in both time and space. This work is indeed aimed at constraining the tridimensional shape of Dimorphos, starting from both LUKE images of the nonimpacted hemisphere of Dimorphos and the results obtained by DART looking at the impacted hemisphere. To this aim, we developed a semiautomatic Computer Vision algorithm, named VADER, able to identify objects of interest on the basis of physical characteristics, subsequently used as input to retrieve the shape of the ellipse projected in the LUKE images analyzed. Thanks to this shape, we then extracted information about the Dimorphos ellipsoid by applying a series of quantitative geometric considerations. Although the solution space coming from this analysis includes the triaxial ellipsoid found by using DART images, we cannot discard the possibility that Dimorphos has a more elongated shape, more similar to what is expected from previous theories and observations. The result of our work seems therefore to emphasize the unique value of the LICIACube mission and its images, making even clearer the need of having different points of view to accurately define the shape of an asteroid.

Near-Earth Object Observations using Synthetic Tracking

Synthetic tracking (ST) has emerged as a potent technique for observing fast-moving near-Earth objects (NEOs), offering enhanced detection sensitivity and astrometric accuracy by avoiding trailing loss. This approach also empowers small telescopes to use prolonged integration times to achieve high sensitivity for NEO surveys and follow-up observations. In this study, we present the outcomes of ST observations conducted with Pomona College’s 1 m telescope at the Table Mountain Facility and JPL’s robotic telescopes at the Sierra Remote Observatory. The results showcase astrometric accuracy statistics comparable to stellar astrometry, irrespective of an object’s rate of motion, and the capability to detect faint asteroids beyond 20.5th magnitude using 11 inch telescopes. Furthermore, we detail the technical aspects of data processing, including the correction of differential chromatic refraction in the atmosphere and accurate timing for image stacking, which contribute to achieving precise astrometry. We also provide compelling examples that showcase the robustness of ST even when asteroids closely approach stars or bright satellites cause disturbances. Moreover, we illustrate the proficiency of ST in recovering NEO candidates with highly uncertain ephemerides. As a glimpse of the potential of NEO surveys utilizing small robotic telescopes with ST, we present significant statistics from our NEO survey conducted for testing purposes. These findings underscore the promise and effectiveness of ST as a powerful tool for observing fast-moving NEOs, offering valuable insights into their trajectories and characteristics. Overall, the adoption of ST stands to revolutionize fast-moving NEO observations for planetary defense and studying these celestial bodies.

Acoustic ground effects simulations from asteroid disruption via the “Pulverize It” method

Our simulations show that PI (“Pulverize It”), a NASA Phase II NIAC study, is an effective multi-modal approach for planetary defense that can operate in extremely short interdiction modes (with intercepts as short as hours prior to atmospheric entry) as well as long interdiction time scales with months to years of warning. The basic process is complete disruption of the threat via fragmentation. In long warning time cases, the fragment cloud spreads enough to miss Earth, resulting in no ground effects. In cases where the warning time is short, the fragments (typically &amp;lt;10 m in diameter) will enter Earth’s atmosphere where their energy is dissipated in a series of ground-level optical pulses and de-correlated shock waves, mitigating any significant damage. We investigate the acoustic ground effects through a set of simulation codes that model the interaction of asteroid fragments with the Earth’s atmosphere following threat interception. Even in the short warning time cases where the fragments enter the atmosphere, our simulations show that threats mitigated by the PI method produce vastly less damage on the ground when compared to the same unfragmented case, yielding shock wave over-pressures under 3 kPa. Our simulations support the proposition that threats sized 20 m—1000 m in diameter can be effectively mitigated through fragmentation, resulting in acoustic ground effects that are below estimated damage thresholds and yield short- and long-term non-lethal effects.

Double Asteroid Redirection Test (DART): Navigating to obliteration

DART is NASA’s demonstration of an asteroid deflection using a kinetic impactor. The spacecraft launched aboard a SpaceX Falcon 9 on November 24th 2021, on a direct collision with the binary asteroid system Didymos planned for September 26th 2022. By impacting the small moon, Dimorphos, DART’s objective was to alter the moon’s orbit about the larger asteroid by several minutes.The navigation of a ballistic mission is usually relatively simple. Other than heading to a violent demise, this mission had a number of unconventional aspects which gave the navigation team interesting challenges: a tight propellant budget for part of the mission, no reaction wheels which resulted in a noisy spacecraft with the Nav team having to rely heavily on Delta Differential One-way Ranging measurements to identify off line-of-sight Delta-V, and critical operations in the last 30 days of the mission under a new thrusting control mode regime. Optical navigation was a critical element in the success of this mission, contributing to the determination of the spacecraft and target ephemerides for refined targeting maneuvers. After strategic decisions in the final weeks of the missions, DART could have comfortably hit the larger asteroid, Didymos, which increased the probably of impact with its moon Dimorphos.

Sensitivity study of impact risk model results to thermal radiation damage model for large objects

NASA's Probabilistic Asteroid Impact Risk (PAIR) model assesses the likelihood of potential damage for asteroid impact scenarios. Fast-running models are used to capture the effects of different hazards. This paper looks specifically at local ground damage hazards, including blast overpressure and thermal radiation damage, for large object impact scenarios. A sensitivity study is conducted to determine which parameters, and over what ranges, cause impact risks to become sensitive to thermal damage. Two additional thermal models with different approaches are used for comparison. The study determined the current thermal model is most sensitive to the luminous efficiency parameter that reflects the model's uncertainty in the amount of energy contributing to the thermal radiation damage. This sensitivity was most apparent for the highest severity damage levels. Comparisons of the three models showed that, in addition to sensitivities within the models, the impact risks are also sensitive to the choice of thermal model. The study results were applied to the 2023 Planetary Defense Conference hypothetical asteroid impact scenario (800 m diameter, 10.29 Gt energy), and parameter ranges of interest were determined. At the serious damage level, luminous efficiencies above 0.006 (0.6%) showed a small chance of thermal playing an important role, while luminous efficiencies above 0.0008 (0.08%) led to thermal playing a significant role at the unsurvivable damage severity level. Study results are used to identify key areas where additional model refinement and better knowledge of asteroid properties may be important for improving damage estimates.

Achievement of the Planetary Defense Investigations of the Double Asteroid Redirection Test (DART) Mission

NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β, resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

Measurability of the Heliocentric Momentum Enhancement from a Kinetic Impact: The Double Asteroid Redirection Test (DART) Mission

The NASA Double Asteroid Redirection Test (DART) has demonstrated the capability of successfully conducting kinetic impact-based asteroid deflection missions. The changes in the Didymos–Dimorphos mutual orbit as a result of the DART impact have already been measured. To fully assess the heliocentric outcome of deflection missions, the heliocentric momentum enhancement parameter, β ⊙, needs to be determined and disentangled from other nongravitational phenomena such as the Yarkovsky effect. Here we explore the measurability of β ⊙ resulting from DART, which we estimate simultaneously with nongravitational accelerations using a least-squares filter. Results show that successful stellar occultation measurements of the Didymos system in the second half of 2024 in addition to the ones in the 2022–2023 campaigns can achieve a statistically significant estimate of β ⊙, with an uncertainty slightly above 20% for an assumed β ⊙ = 3. Adding additional occultation measurements and pseudorange measurements from the Hera spacecraft operations at Didymos starting in 2027 decreases this relative uncertainty to under 6%. We find that pre-impact occultation observations combined with post-impact occultations would have yielded substantially higher signal-to-noise ratios on the heliocentric deflection. Additionally, pre-impact occultations would also have enabled a statistically significant β ⊙ estimate using only one additional occultation in 2023 September. Therefore, we conclude that future asteroid deflection missions would greatly benefit from both pre- and post-deflection occultation measurements to help assess the resulting orbital changes.

The International Astronomical Search Collaboration (IASC)—Citizen Scientist System for Asteroid Discovery

We describe a citizen science asteroid detection system developed by the International Astronomical Search Collaboration (IASC) and the Institute for Astronomy at the University of Hawaii, utilizing data from the Pan-STARRS telescopes. The goals of this project are to (i) educate and engage citizen scientists (mostly high school students) in science and astronomy, (ii) search for new asteroids to extend the limiting magnitudes of existing asteroid surveys, and (iii) find missed Near-Earth Objects (NEOs—objects with perihelia q < 1.3 au) to support planetary defense efforts. Over the past 15 yr, 50,000 citizen scientists from 96 countries around the world have detected ∼12,000 main-belt asteroids and ∼5 NEOs. Citizen scientists use the software Astrometrica during scheduled campaigns to search for and measure asteroid astrometry and photometry, and submit the data to IASC for vetting. Candidate detections not already submitted by Pan-STARRS are then submitted to the Minor Planet Center, and are typically ∼0.30 ± 0.07 mag fainter.

Photometry of the Didymos System across the DART Impact Apparition

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

Modeling Binary Asteroids: Integrating Orbital and Rotational Motion for Physical Property Inversion

The field of space science places significant emphasis on deep space exploration, with a particular focus on asteroids as a potential hazard to humanity. Inverting their physical characteristics from photometric observations is essential for uncovering their origins and evolution. This article attempts to present a solution to the challenging task of estimating the physical properties of binary asteroids, which are common in near-Earth asteroids larger than 200 meters. A novel model for binary asteroids is proposed, which integrates orbital and rotational motions to simulate brightness variations based on two Cellinoid shapes. The model combines the projection and occultation effects of the shapes to generate the simulated brightness. The inversion of determining physical properties is optimized based on the Levenberg–Marquardt algorithm through a simulation process involving several parameter corrections. Finally, the performance of the proposed model is demonstrated through numerical experiments and applications to two real binary asteroids, namely, asteroid (317) Roxane and asteroid (624) Hektor. The derived results are nearly identical to those from other publications, which confirms that the proposed model provides reliable and accurate estimations of the physical properties of binary asteroids. Additionally, this method has a potential application in supporting the development of effective strategies for the Double Asteroid Redirection Test (DART) project, the first planetary defense experiment in space undertaken by humans.

Dynamics and control of sun-facing diffractive solar sails in displaced orbit for asteroid deflection

A gravity tractor spacecraft propelled by a diffractive sail tracking a displaced orbit offers a potential option for deflecting near-Earth asteroids. This study delves into the preliminary dynamics, evaluates the deflection capabilities, and investigates the stability and control of the diffractive sail on the displaced orbit near the asteroid. Unlike reflective sails, diffractive solar sails generate tangential radiation pressure force, offering multiple advantages. These include the elimination of tilt attitude requirements, no offset angle restrictions from the target asteroid's flight direction, and superior deflection performance with an equivalent area-to-mass ratio when the diffraction angle surpasses 50deg. To maintain position, a controllable diffractive sail model using spatial light modulators, coupled with a feedback control law, is proposed. This control design stabilizes the periodic displaced orbit without necessitating tilt attitude adjustments towards the sun, as validated by our numerical simulations.

The identification of airbursts in the past: Insights from the BIT-58 layer

Airbursts are estimated to be the most frequent type ofdestructive impact events. Yet, confirmation of these events is elusive, resulting in a major gap in the impact record of Earth. The recent discovery of igneous chondritic spherules produced during a new type of touchdown airburst 430 thousand years (kyr) ago over Antarctica, in which a projectile vapor jet interacts with the Antarctic ice sheet, provided the first trace of such an impact in the geological record. In terms of petrology and geochemistry, particles constituting the BIT-58 dust horizon, which was found in surface ice at near Allan Hills in Antarctica, are almost identical to those produced 430 kyr ago. We demonstrate here that BIT-58 particles were indeed formed during a touchdown event between 2.3 and 2.7 million years (Myr) ago. This represents the oldest record of an airburst on Earth identified to date. Slight geochemical differences with 430 kyr old airburst spherules provide additional constraints on spherule condensation in large airburst plumes. Finding confirmation of airbursts in the paleorecord can provide insight into the frequency of the most hazardous impacts and, thus, has implications for planetary defence.