near-Earth Research Articles

3 μm Phase Curves of Main-belt Asteroids from NEOWISE Photometry

The shapes of asteroid phase curves are influenced by the physical properties of asteroid surfaces. The variation of an asteroid’s brightness as a function of the solar phase angle can tell us about surface properties such as grain size distribution, roughness, porosity, and composition. Phase curves are traditionally derived from photometric observations at visible wavelengths, but phase curves using infrared data can also provide useful information about an asteroid surface. Using photometric observations centered near ∼3.4 μm from the W1 band of the Near-Earth Object Wide-field Infrared Survey Explorer mission, we construct thermally and rotationally corrected infrared phase curves for a sample of main-belt asteroids, which includes asteroids observed by the AKARI satellite, as well as subsets of the Themis and Flora dynamical families. We calculate the linear slope of the phase curves as a measure of their shape and compare W1 phase slopes to band depths of absorption features associated with hydrated materials, spectral slopes, visible albedos, W1 albedos, and diameters. We observe a steepening of the W1 phase slope of C-type asteroids with increasing 2.7 μm band depth but little correlation between the phase slope and 3 μm band depth or 3 μm spectral slope. The C-types in our sample exhibit steeper average W1 phase slopes than M- or S-types, similar to visible-light phase slopes. We also observe steeper W1 phase slopes for smaller-diameter objects within the Themis family and explore comparisons to Jupiter-family comets in phase slope versus albedo space.

Ultraviolet and infrared luminescence of near-Earth objects

ABSTRACT This work deals with a possible ultraviolet and infrared luminescence of the solid substance of the near-Earth objects. In particular, features of the phenomena of photoluminescence and cathodoluminescence of substance of these objects are considered. It is shown that ultraviolet and infrared luminescence of these objects can be revealed by orbital-based instruments. It is demonstrated that detectability of luminescence of near-Earth objects opens up the possibilities for determination of the physical–chemical properties of their solid substance and finding of the dark small low-albedo bodies, which could approach dangerously closer to the Earth. Equations for calculation of luminescence intensity of these objects are proposed. Data on the luminescence of the corresponding minerals and the numerical values of the yields of luminescence and albedo, as the conditions for the detectability of the luminescence of near-Earth objects are presented as well.

Toward a European Facility for Ground-Based Radar Observations of Near-Earth Objects

In this work, we present the preliminary results of radar observations of Near-Earth Objects (NEOs) carried out by European radio telescopes in the framework of the European Space Agency (ESA) project “NEO observation concepts for radar systems”, aimed at deriving the functional requirements of a planetary radar system, evaluating the available European assets to perform NEO radar observations, and carrying out test radar campaigns. In the first part of the project, we executed the performance analysis of a possible European planetary radar system. Instrumental features, as much as issues like the impact of weather conditions on signal propagation at different radio frequencies, were considered. This paper focused on the test campaigns, performed in the years 2021–2022 in collaboration with the Jet Propulsion Laboratory (JPL), which led to the observation of several asteroids including 2021 AF8, (4660) Nereus, and 2005 LW3, which allowed us to derive astrometric measurements, as well as to measure physical properties, such as rotation periods, and observe how one of the targets is actually a binary asteroid. The obtained results demonstrated that European radio astronomical dishes, although employed only as receivers (in bistatic or multistatic configurations) and for a limited amount of time, are able to provide a significant contribution to the constitution of a European network to increase the opportunities for NEO monitoring and studies, if a transmitting antenna—equipped with a suitable high-power transmitter—were made available.

Baked before Breaking into Bits: Evidence for Atira-type Asteroid Splits

Current near-Earth asteroid orbital models cannot reproduce the observed populations close to the Sun. Supercatastrophic and tidal disruptions may explain the differences between theoretical models and observational data. Here, we explore the distributions of mutual nodal distances and the angular separation of perihelia of the known Atiras looking for evidence of past splittings. We find a number of pairs, trios, and one quartet of Atiras with mutual nodal distances as short as 0.001 au at the orbits of Mercury and Venus. The smallest of these highly correlated objects is 2023 WK3. Fragmentation or binary disruption may have triggered the recent formation of the unusual pair made of 594913 ’Ayló’chaxnim (2020 AV2) and 2012 VE46 with both mutual nodal distance and angular separation of perihelia in the first percentile of the distribution, making 2012 VE46 a robust candidate to being a former moon or piece of ’Ayló’chaxnim.

NEOMOD 2: An updated model of Near-Earth Objects from a decade of Catalina Sky Survey observations

Catalina Sky Survey (CSS) is a major survey of Near-Earth Objects (NEOs). In a recent work, we used CSS observations from 2005–2012 to develop a new population model of NEOs (NEOMOD). CSS’s G96 telescope was upgraded in 2016 and detected over 10,000 unique NEOs since then. Here we characterize the NEO detection efficiency of G96 and use G96’s NEO detections from 2013–2022 to update NEOMOD. This resolves previous model inconsistencies related to the population of large NEOs. We estimate there are 936±29 NEOs with absolute magnitude H<17.75 (diameter D>1 km for the reference albedo pV=0.14) and semimajor axis a<4.2 au. The slope of the NEO size distribution for H=25–28 is found to be relatively shallow (cumulative index ≃2.6) and the number of H<28 NEOs (D>9 m for pV=0.14) is determined to be (1.20±0.04)×107, about 3 times lower than in Harris & Chodas (2021). Small NEOs have a different orbital distribution and higher impact probabilities than large NEOs. We estimate 0.034±0.002 impacts of H<28 NEOs on the Earth per year, which is near the low end of the impact flux range inferred from atmospheric bolide observations. Relative to a model where all NEOs are delivered directly from the main belt, the population of small NEOs detected by G96 shows an excess of low-eccentricity orbits with a≃1–1.6 au that appears to increase with H (≃30% excess for H=28). We suggest that the population of very small NEOs is boosted by tidal disruption of large NEOs during close encounters to the terrestrial planets. When the effect of tidal disruption is (approximately) accounted for in the model, we estimate 0.06±0.01 impacts of H<28 NEOs on the Earth per year, which is more in line with the bolide data. The impact probability of a H<22 (D>140 m for pV=0.14) object on the Earth in this millennium is estimated to be ≃4.5%.

Orbital evolution and possible parent asteroids of 40 instrumentally observed meteorites

We present the orbital evolution of 40 meteorites with known heliocentric orbits, both nominal and their clones as well. The goal of our work was to determine the stability of their orbits and to find possible connections with known near-Earth asteroids. Stability along with a probability of a random association were used to select probable candidates. We have found stable behaviour of orbits for 21 meteorites in the time interval of 100,000 years to the past (e.g. Neuschwanstein, Jesenice). Twelve meteorites displayed different orbital evolution of the nominal orbit and the clones (e.g. Almahata Sitta, Motopi Pan), but in general they were stable. There were seven meteorites on unstable orbits; 3 meteorites exhibited chaotic clone evolutions (Košice, Maribo and Novato) and 4 were on overall unstable orbits (Příbram, Sutter’s Mill, Flensburg and Arpu Kuilpu). This study suggests possible parent bodies from the currently known NEA population for 27 meteorites with very low DSH values and low probabilities of random association.

On the Chromaticity of the (NEO)WISE Astrometry

The Wide-field Infrared Survey Explorer and its follow-up Near-Earth Object (NEO) mission scan the mid-infrared sky twice a year. The spatial and temporal coverage of the resulting database is of utmost importance for variability studies, in particular of young stellar objects which have red W1 − W2 colors. During such an effort, I noticed subarcsecond position offsets between subsequent visits. The offsets do not appear for targets with small W1 − W2 colors, which points to a chromatic origin in the optics, caused by the spacecraft pointing alternating “forward” and “backward” from one visit to another. It amounts to 0.″1 for targets with W1 − W2 ≈ 2. Consideration of this chromatic offset will improve astrometry. This is of particular importance for NEOs that are generally red.

Planetary Radar—State-of-the-Art Review

Planetary radar observations have provided invaluable information on the solar system through both ground-based and space-based observations. In this overview article, we summarize how radar observations have contributed in planetary science, how the radar technology as a remote-sensing method for planetary exploration and the methods to interpret the radar data have advanced in the eight decades of increasing use, where the field stands in the early 2020s, and what are the future prospects of the ground-based facilities conducting planetary radar observations and the planned spacecraft missions equipped with radar instruments. The focus of the paper is on radar as a remote-sensing technique using radar instruments in spacecraft orbiting planetary objects and in Earth-based radio telescopes, whereas ground-penetrating radar systems on landers are mentioned only briefly. The key scientific developments are focused on the search for water ice in the subsurface of the Moon, which could be an invaluable in situ resource for crewed missions, dynamical and physical characterization of near-Earth asteroids, which is also crucial for effective planetary defense, and a better understanding of planetary geology.

The NEO Surveyor Near-Earth Asteroid Known Object Model

The known near-Earth object (NEO) population consists of over 32,000 objects, with a yearly discovery rate of over 3000 NEOs per year. An essential component of the next generation of NEO surveys is an understanding of the population of known objects, including an accounting of the discovery rate per year as a function of size. Using a near-Earth asteroid (NEA) reference model developed for NASA’s NEO Surveyor (NEOS) mission and a model of the major current and historical ground-based surveys, an estimate of the current NEA survey completeness as a function of size and absolute magnitude has been determined (termed the Known Object Model; KOM). This allows for understanding of the intersection of the known catalog of NEAs and the objects expected to be observed by NEOS. The current NEA population is found to be ∼38% complete for objects larger than 140 m, consistent with estimates by Harris & Chodas. NEOS is expected to catalog more than two-thirds of the NEAs larger than 140 m, resulting in ∼76% of NEAs cataloged at the end of its 5 yr nominal survey, making significant progress toward the US Congressional mandate. The KOM estimates that ∼77% of the currently cataloged objects will be detected by NEOS, with those not detected contributing ∼9% to the final completeness at the end of its 5 yr mission. This model allows for placing the NEOS mission in the context of current surveys to more completely assess the progress toward the goal of cataloging the population of hazardous asteroids.

The Near-Earth Object Surveyor Mission

The Near-Earth Object (NEO) Surveyor mission is a NASA Observatory designed to discover and characterize asteroids and comets. The mission’s primary objective is to find the majority of objects large enough to cause severe regional impact damage (>140 m in effective spherical diameter) within its 5 yr baseline survey. Operating at the Sun–Earth L1 Lagrange point, the mission will survey to within 45° of the Sun in an effort to find objects in the most Earth-like orbits. The survey cadence is optimized to provide observational arcs long enough to distinguish near-Earth objects from more distant small bodies that cannot pose an impact hazard reliably. Over the course of its survey, NEO Surveyor will discover ∼200,000–300,000 new NEOs down to sizes as small as ∼10 m and thousands of comets, significantly improving our understanding of the probability of an Earth impact over the next century.

Результаты астрометрических наблюдений АСЗ на пулковском 40-см телескопе в обсерватории Ассы-Тургень

We present the results of astrometric observations of two near-Earth asteroids (2005 XY7 and 2007 UM12) performed in September-November 2023 with the 40-cm Pulkovo telescope in the Assy-Turgen observatory. Stellar and asteroid pixel coordinates were calculated by varying the photo center position, background, and flux values for the PSF (point spread function) based on the analysis of the stellar images. The stars within the 4-arcmin asteroid-centered ring were not involved in the astrometric calibration. These stars were used for the asteroid systematic correction calculation. As a result, the internal accuracy of asteroid positions was better than 0.1 arcsec. The estimation of the mean position and the apparent rate components were performed for each set of CCD frames. Finally, the typical accuracy of the coordinates reached values of 0.024 – 0.088 arcsec. In addition, the numerical integration of the asteroid motion was made by varying the components of the state vector and A2-parameter (Yarkovsky acceleration). The unexpected and statistically insignificant A2 value for the 2007 UM12 has been found. It can be explained by the low quality of the data related to the first approach of this asteroid to the Earth and/or the tidal effects that changed the rotational state of the asteroid. The value A2 = (8.1 ± 6.4) · 10−14 a.u. per day2 on the significance boundary has been calculated for 2005 XY7 asteroid. This value does not contradict well-known data for the same size asteroids.

Validation of the Survey Simulator Tool for the NEO Surveyor Mission Using NEOWISE Data

The Near-Earth Object Surveyor (NEO Surveyor) mission has a requirement to find two-thirds of the potentially hazardous asteroids larger than 140 m in size. In order to determine the mission’s expected progress toward this goal during design and testing, as well as the actual progress during the survey, a simulation tool has been developed to act as a consistent and quantifiable yardstick. We test that the survey simulation software is correctly predicting on-sky positions and thermal infrared fluxes by using it to reproduce the published measurements of asteroids from the NEOWISE mission. We then extended this work to find previously unreported detections of known near-Earth asteroids in the NEOWISE data archive, a search that resulted in 21,661 recovery detections, including 1166 objects that had no previously reported NEOWISE observations. These efforts demonstrate the reliability of the NEO Surveyor Survey Simulator tool and the perennial value of searchable image and source catalog archives for extending our knowledge of the small bodies of the solar system.

A new meteor shower from comet 46P/Wirtanen expected in December 2023

Context. Comet 46P/Wirtanen is a near-Earth object (NEO) for which no associated meteor shower has ever been reported. Aims. This study is aimed at improving our understanding of why there has been no observed shower activity for this NEO to date, as well as to consider whether any past activity could be uncovered from the post-prediction results. Methods. The usual dynamic tools for meteoroid streams were used to describe the behavior of the particles ejected by the comet. The resulting modeled meteoroid stream was thoroughly inspected for collisions between the stream and the Earth. Results. The results show a possible encounter forecast for December 12, 2023, between 8:00 and 12:30 UT. The slow entry velocity is typically known to cause dim meteors. The activity level of the shower is highly uncertain due to the absence of reported past showers. Conclusions. Overall, the most optimal observations on the forecasted day would be achieved from Eastern Australia, New Zealand, and Oceania. These observations will help constrain the size distribution of meteoroids from comet 46P/Wirtanen in the millimeter range.

Impact Earth! Protecting the UK and further afield from impacts by Near-Earth objects

Abstract Mark Burchell, Gareth Collins and Massimiliano Vasile report on an RAS Specialist Discussion Meeting dedicated to investigating the effects of potentially hazardous objects colliding with the Earth

The Yarkovsky effect and bulk density of near-Earth asteroids from Gaia DR3

Aims. The primary objective of this study is to utilize Gaia DR3 asteroid astrometry to detect the Yarkovsky effect, a non-gravitational acceleration that affects the orbits of small asteroids. We then computed the bulk densities for the sample of objects for which we obtained an estimation of the Yarkovsky effect. Methods. We used the version of the OrbFit software that is currently developed at the Minor Planet Center (MPC). We utilized the complete astrometric dataset from the MPC, encompassing all radar data and Gaia DR3 observations. The orbital computation was performed for a total of 446 Near-Earth Asteroids (NEAs; including 93 Potentially Hazardous Asteroids (PHAs)), and 54094 Inner Main Belt Asteroids (IMBAs) as well as Mars Crossing asteroids. Furthermore, we used a new validation method which involved computing the A2 (the Yarkovsky effect) using different observational arcs to observe the stability of the result. We applied the Yarkovsky effect to determine the density of the studied asteroids. Results. Thanks to Gaia DR3 we significantly constrained orbital uncertainties and determined reliable A2 values for 49 Near-Earth Asteroids, including 10 new detections and for all improvements in signal-to-noise ratio. Additionally, we successfully determined the density, along with their uncertainties, for all of these objects. However, regarding IMBAs, although we have made progress, we do not detect Yarkovsky drift for any asteroid in the main belt. Conclusions. Adding a relatively small amount of ultra-precise astrometry from Gaia DR3 to the observations from the Minor Planet Center (MPC) not only significantly improves the orbit of the asteroid but also enhances the detectability of non-gravitational parameters. Utilizing this improved dataset, we were able to determine the densities, along with their uncertainties, for the studied asteroids. Looking ahead, with the upcoming release of Gaia DR4, we anticipate even more detections for NEAs and new detections for IMBA and Mars Crossing Asteroids.

Advancement and Challenges in Methods of Predicting the Motion of Near-Earth Asteroids

Advancement and Challenges in Methods of Predicting the Motion of Near-Earth Asteroids

The known large Near-Earth Objects’ highways: dynamical evolution, fates, and lifetimes

The known large Near-Earth Objects’ highways: dynamical evolution, fates, and lifetimes

Erratum to: Determination of the Motion Parameters of Near-Earth Objects from Position Measurements Performed at the Terskol Observatory

Erratum to: Determination of the Motion Parameters of Near-Earth Objects from Position Measurements Performed at the Terskol Observatory

Gaia Focused Product Release: Asteroid orbital solution

Context. We report the exploitation of a sample of Solar System observations based on data from the third Gaia Data Release (Gaia DR3) of nearly 157 000 asteroids. It extends the epoch astrometric solution over the time coverage planned for the Gaia DR4, which is not expected before the end of 2025. This data set covers more than one full orbital period for the vast majority of these asteroids. The orbital solutions are derived from the Gaia data alone over a relatively short arc compared to the observation history of many of these asteroids. Aims. The work aims to produce orbital elements for a large set of asteroids based on 66 months of accurate astrometry provided by Gaia and to assess the accuracy of these orbital solutions with a comparison to the best available orbits derived from independent observations. A second validation is performed with accurate occultation timings. Methods. We processed the raw astrometric measurements of Gaia to obtain astrometric positions of moving objects with 1D sub-mas accuracy at the bright end. For each asteroid that we matched to the data, an orbit fitting was attempted in the form of the best fit of the initial conditions at the median epoch. The force model included Newtonian and relativistic accelerations to derive the observation equations, which were solved with a linear least-squares fit. Results. Orbits are provided in the form of state vectors in the International Celestial Reference Frame for 156 764 asteroids, including near-Earth objects, main-belt asteroids, and Trojans. For the asteroids with the best observations, the (formal) relative uncertainty σa/a is better than 10−10. Results are compared to orbits available from the Jet Propulsion Laboratory and MPC. Their orbits are based on much longer data arcs, but from positions of lower quality. The relative differences in semi-major axes have a mean of 5 × 10−10 and a scatter of 5 × 10−9.

THEO & MUFN: Defending Earth against the 2023 PDC hypothetical asteroid impact

Planetary defense is an emerging field among the aerospace community. As the rate of near-Earth object (NEO) discoveries increases, so too does the probability that we will discover a NEO on a collision course with Earth. This paper documents a planetary defense mission campaign design to defend against the hypothetical Earth impactor 2023 PDC. At its 90th percentile mass estimate, the asteroid could have a diameter of approximately 1120 m. The asteroid makes no close approaches until Earth impact and has the potential to affect over a billion people, depending on its actual size. This paper describes a mission campaign consisting of both reconnaissance and mitigation missions that will be deployed to neutralize the threat posed by the asteroid. The reconnaissance orbiter named THEO (Terrestrial Hazard Exploration Orbiter) will survey the asteroid to clarify its morphological, gravitational, and dynamical properties. This information will be used to inform the design of the subsequent mitigation mission. THEO will be designed to have a mission lifetime of 12 years which will enable it to observe the mitigation mission and confirm its success. Two 21-day launch periods have been identified that minimize post-launch ΔV requirements and include current launch vehicle capabilities. For the purposes of this paper, the mitigation mission has been designed assuming a geocenter impact for the 90th percentile mass estimate of the asteroid because a precise impact location and an accurate mass estimate will not be available until THEO reconnoiters 2023 PDC. The mitigation mission, named MUFN (Mitigation Using a Fission Nuclear device), will send three spacecraft to rendezvous with 2023 PDC and alter the asteroid’s trajectory prior to Earth impact through a series of standoff nuclear detonations. The MUFN spacecraft are identical in design, each employing a hypergolic bi-propellant thruster. Each MUFN spacecraft launches on a SpaceX Falcon Heavy Expendable launch vehicle between 2028 and 2030 and carries four 340 kt nuclear explosive device (NED) equipped orbiters, named BELA-Os (“Bull’s Eye, Later Asteroid” Orbiters). The BELA-Os are designed to sequentially deploy, maneuver to an optimal standoff distance anti-parallel to the asteroid velocity vector, and detonate the NED to impart a change-in-velocity to the asteroid. After arrival at 2023 PDC, each MUFN spacecraft will station-keep above the asteroid. The NED-equipped BELA-Os will deploy from the MUFN spacecraft and maneuver 180 degrees out of phase from MUFN to the ‘front’ of the asteroid. Once there, each BELA-O will detonate and impart 2.32 mm/s of velocity change to the asteroid. After the ablation debris has cleared, MUFN will complete a single orbit around the asteroid to survey the blast site and assess the effectiveness of the detonation. After MUFN has completed its survey, it will release another BELA-O. This process will repeat until all BELA-Os have been released by all MUFN spacecraft. All denotations will occur between 2029 and 2031. After all BELA-Os have detonated their NED payloads near the 2023 PDC asteroid to deflect its orbit, the asteroid will safely fly by Earth at a minimum altitude of 3500 km instead of colliding on October 22, 2036.