Near-Earth asteroid (275677) 2000 RS11 was observed over 5 d in March 2014 with both the Arecibo (2380 MHz, 12.6 cm) and Goldstone (8560 MHz, 3.5 cm) planetary radar systems. The continuous-wave spectra and delay-Doppler images collected revealed a sub-km-sized object with a strongly bifurcated shape. We used these radar observations, in combination with seven optical light curves collected in 2014 and one light curve from 2023, to create a comprehensive shape and spin-state model for RS11. We find a rotation period of P = (4 . 445 +/- 0 . 001) h around a pole of lambda = (225 +/- 80) degrees and beta = (-80 +/- 9) degrees relative to the plane of the ecliptic. The shape of RS11 is unusual in that it does not resemble many of the other near-Earth asteroids modelled with ground-based radar. Whilst RS11 consists of a largely spherical, smaller lobe attached to an elongated, larger lobe via a narrow neck, the smaller lobe is not aligned with the long axis of the larger lobe, but is closer to the larger lobe's shortest principal axis. In combination with a large concavity observed on the outer face of the larger lobe, this may point to an unusual formation or event in the object's past. We estimate that RS11 has a geometric albedo of pv = (0 . 16 +/- 0 . 06) and a radar albedo 0 . 08 < r7OC < 0 . 16 . Analysis of its gravitational environment reveals that for standard S-type asteroid densities, we would not expect rotational instability and it is possible for RS11 to be a low tensile strength rubble-pile asteroid.

We detail the use of the University of Tasmania’s (UTAS) optical and radio telescopes to conduct observations of near-Earth asteroids from 2021 to 2024. The Canberra Deep Space Communication Complex transmitted a radio signal at 7159.45 MHz, with the radar echo detected by the UTAS radio telescopes. The method of accounting for the Doppler shift between the stations and the near-Earth object is described so that others can implement a similar program. We present our results, with confirmed detections of 1994 PC1 and 2003 UC20 asteroids using the Hobart and Katherine 12-m antennas, demonstrating the feasibility of using small radio telescopes for these observations. Additionally, the recently upgraded Ceduna 30 m antenna was used to detect 2024 MK. Data collected from other observatories, such as Tidbinbilla, as well as the UTAS radar tracking of the moon are also presented in the context of demonstrating the means of applying these Doppler corrections and the accuracy of each method. Optical observations conducted in this period are also detailed as they complement radar observations and aid in refining the orbit parameters.

Contact binaries are found throughout the Solar System. The recent discovery of Selam, the satellite of main-belt asteroid (152830) Dinkinesh, by the NASA Lucy mission has made it clear that the term 'contact binary' covers a variety of different types of bimodal mass distributions and formation mechanisms. Only by modelling more contact binaries can this population be properly understood. We determined a spin state and shape model for the Apollo group contact binary asteroid (388188) 2006 DP14 using ground-based optical and radar observations collected between 2014 and 2023. Radar delay-Doppler images and continuous-wave spectra were collected over 2 d in February 2014, while 16 light curves in the Cousins R and SDSS-r filters were collected in 2014, 2022, and 2023. We modelled the spin state using convex inversion before using the shape modelling software to include the radar observations in modelling concavities and the distinctive neck structure connecting the two lobes. We find a spin state with a period of (5.7860 +/- 0.0001) h and pole solution of lambda=(180 +/- 121)degrees and beta=(-80 +/- 7)degrees with morphology indicating a 520 m long bilobed shape. The model's asymmetrical bimodal mass distribution resembles other small near-Earth asteroid contact binaries such as (85990) 1999 JV6 or (8567) 1996 HW1, which also feature a smaller 'head' attached to a larger 'body'. The final model features a crater on the larger lobe, similar to several other modelled contact binaries. The model's resolution is 25 m, comparable to that of the radar images used

Understanding the physical characteristics of small bodies in the Solar System is crucial for refining models of their formation and evolution. Although several kilometre-sized asteroids have already been visited by spacecraft, 1998 KY26 will be the first asteroid in the decametre range to be explored in situ. Its diameter and spin period place it above the spin barrier, suggesting that its formation and properties may differ from those of previously visited bodies. However, the key physical characteristics of 1998 KY26 remain poorly understood. We conducted a photometric observing campaign during 1998 KY26’s close approach to Earth in 2024. Our observations revealed that 1998 KY26 has a high optical albedo and colours consistent with an E-type taxonomy. We also determined its spin period to be (5.3516 ± 0.0001) minutes—twice as fast as previously reported. Using lightcurve inversion methods, we derived a retrograde pole solution and constructed convex and non-convex shape models. By integrating these models with Goldstone radar data from 1998, we estimated 1998 KY26’s diameter to be (11 ± 2) m. The most likely structure for 1998 KY26 is monolithic, yet a fine grained rubble-pile structure is theoretically possible given its required small strength level. We found that it will be possible to validate these results with future JWST observations. Our comprehensive characterisation of 1998 KY26 can inform the planning of the Hayabusa2# spacecraft’s rendezvous encounter, scheduled for July 2031. Additionally, it provides valuable insights into the non-gravitational forces acting on small Solar System bodies, enhancing our understanding of their orbital evolution which could shed light on the nature of dark comets.

Janus is a NASA SIMPLEx mission currently in Phase B. The SIMPLEx program is designed around the idea of using secondary launch opportunities to explore interplanetary destinations. The Janus mission concept plans to take advantage of the NASA Psyche launch to send two spacecraft to fly by Near Earth Objects of interest. A specific point design has been developed that sends two spacecraft to two binary asteroid systems, (175706) 1996 FG3 and (35107) 1991 VH, both of which have been observed repeatedly with photometry, spectrometry and radar. The Janus mission sends light-weight, low-cost spacecraft built by Lockheed Martin to encounter these high-science value small body targets. The science instruments are a visible and IR imager, from Malin Space Science Systems. The spacecraft will perform a rigorous remote sensing campaign when the object is a point source, and when resolved. The spacecraft will track the binary asteroid systems through closest approach, allowing for a combination of absolute surface resolution, relative resolution across the target asteroids and phase angle coverage unparalleled in previous asteroid flyby missions. Janus science will combine flyby observations of the target binary asteroids with ground-based observations, enabling the high resolution imaging and thermal data to be placed into a global context and leveraging all available data to construct an accurate topographical and morphological model of these bodies. Based on these measurements, the formation and evolutionary implications for small rubble pile asteroids will be studied. The science team members all have experience on asteroid missions or have made extensive ground based observations of NEAs. The industry team has extensive experience in the design, fabrication and operation of interplanetary spacecraft and instrumentation.Acknowledgements: The Janus mission is supported by NASA under a contract from the SIMPLEx Program Office. Part of this research was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

We report radar, photometric, and visible-wavelength spectrophotometry observations of NEA 2018 EB obtained in 2018. The radar campaign started at Goldstone (8560 MHz, 3.5 cm) on April 7, and it was followed by more extensive observations from October 5 to 9 by both Arecibo (2380 MHz, 12.6 cm) and Goldstone. 2018 EB was observed optically on April 5, 8, and 9 and again on October 18. Spectrophotometry was obtained on October 19 with the SOAR telescope, and the data suggest that 2018 EB is an Xk-class object. The echo power spectra and delay-Doppler radar images revealed that 2018 EB is a binary system. Radar images constrained the satellite's diameter to 0.15 - 0.05 + 0.02 km, but the data were not sufficient for shape modeling. Shape modeling of lightcurves and radar data yielded an oblate primary with an effective diameter D = 0.30 +/- 0.04 km and a sidereal rotation period of 4.3 - 0.5 + 0.6 hr. Measurements of delay-Doppler separations between the centers of mass of the primary and the satellite, along with the timing of a radar eclipse observed on October 9, resulted in an orbit fit for the satellite with a semimajor axis of 0.50 - 0.01 + 0.04 km, an eccentricity of 0.15 +/- 0.04, a period of 16.85 - 0.26 + 0.33 hr, and an orbit pole constrained to the ecliptic longitudes and latitudes of lambda = 93 - 43 degrees + 27 degrees and beta = 48 - 18 degrees + 7 degrees . The system mass was estimated to be 2.03 - 0.08 + 0.52 x 10 10 kg, which yielded a bulk density of 1.4 - 0.5 + 0.6 g cm-3. Our analysis suggests that 2018 EB has a low optical albedo of p V = 0.028 +/- 0.016 and a relatively high radar albedo of eta OC = 0.29 +/- 0.11 at Arecibo and eta = 0.22 +/- 0.10 at Goldstone.

We present the results of a fourth planetary defense exercise, focused this time on the small near-Earth asteroid (NEA) 2023 DZ2 and conducted during its close approach to the Earth in 2023 March. The International Asteroid Warning Network (IAWN), with support from NASA's Planetary Defense Coordination Office (PDCO), has been coordinating planetary defense observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. The last campaign focused on the NEA Apophis, and an outcome of that exercise was the need for a short burst campaign to replicate a real-life near-Earth object impact hazard scenario. The goal of the 2023 DZ2 campaign was to characterize the small NEA as a potential impactor and exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication with a short notice of just 24 hr. The entire campaign lasted about 10 days. The campaign team was divided into several working groups based on the characterization method: photometry, spectroscopy, thermal IR photometry and optical polarimetry, radar, and risk assessment. Science results from the campaign show that 2023 DZ2 has a rotation period of 6.2745 ± 0.0030 minutes; visible wavelength color photometry/spectroscopy/polarimetry and near-IR spectroscopy all point to an E-type taxonomic classification with surface composition analogous to aubrite meteorites; and radar observations show that the object has a diameter of 30 ± 10 m, consistent with the high albedo (0.49) derived from polarimetric and thermal IR observations.

The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos, on 2022 September 26 UTC. We estimate the changes in the orbital and physical properties of the system due to the impact using ground-based photometric and radar observations, as well as DART camera observations. Under the assumption that Didymos is an oblate spheroid, we estimate that its equatorial and polar radii are 394 +/- 11 m and 290 +/- 16 m, respectively. We estimate that the DART impact instantaneously changed the along-track velocity of Dimorphos by -2.63 +/- 0.06 mm s-1. Initially, after the impact, Dimorphos's orbital period had changed by -32.7 minutes +/- 16 s to 11.377 +/- 0.004 hr. We find that over the subsequent several weeks the orbital period changed by an additional 34 +/- 15 s, eventually stabilizing at 11.3674 +/- 0.0004 hr. The total change in the orbital period was -33.25 minutes +/- 1.5 s. The postimpact orbit exhibits an apsidal precession rate of 6.7 +/- 0.degrees 2 day-1. Under our model, this rate is driven by the oblateness parameter of Didymos, J 2, as well as the spherical harmonics coefficients, C 20 and C 22, of Dimorphos's gravity. Under the assumption that Dimorphos is a triaxial ellipsoid with a uniform density, its C 20 and C 22 estimates imply axial ratios, a/b and a/c, of about 1.3 and 1.6, respectively. Preimpact images from DART indicate Dimorphos's shape was close to that of an oblate spheroid, and thus our results indicate that the DART impact significantly altered the shape of Dimorphos.

Space debris are composed of both natural and human made objects, some in near Earth orbits while others are passing through deep space. Asteroids may represent one form of near Earth and deep space debris. In this article we report on a set of asteroid observations from the southern hemisphere. We indicate that Apollo and Aten class asteroids represent another form of deep space debris of a potentially hazardous nature to orbiting spacecraft and/or Earth based locations. We also show some of the operational challenges, types of facilities and the importance of geographic diversity, that is, necessary for detecting, observing and characterising asteroids, especially PHA’s. For many years, space agencies and institutions have observed and monitored near Earth asteroids and objects (NEO’s) using high gain radio frequency antennas and optical telescopes in the northern hemisphere (GSSR, Arecibo, Catalina, Pan-STARRS, Atlas and Linear) 1) However a regular operational system to monitor the southern skies does not have the same level of maturity and is where a percentage of asteroids and various human made objects are not detected until they pass into northern skies. To fill that gap the Southern Hemisphere Asteroid Radar Program (SHARP) 2) located in Australia uses available antenna time on either a 70 or 34 m beam waveguide antenna located at the Canberra Deep Space Communication Complex (CDSCC) to transmit a Doppler compensated continuous radio wave at 2.114 GHz (14.2 cm) and 7.15945 GHz (4.2 cm) toward the NEO and receive its echoes at the 64 m Parkes or 6 m × 22 m Australia Telescope Compact Array (ATCA) antennas at Narrabri in Australia. This mode of NEO observation is termed a deep space bistatic radar. The southern hemisphere program has also recently been joined by the 12 m University of Tasmania antennas at Hobart (Tasmania) and Katherine (Northern Territory). Combining SHARPS bistatic radar with small optical apertures located at the University of New South Wales (UNSW) and University of Western Australia (UWA) allows combined optical/RF NEO detections. Whilst sub-metre class optical instruments have contributed independently to asteroid detection over decades, the use of coordinated small 0.3–0.5 m instruments synchronized to large asteroid radars offers an observational flexibility and adaptability when larger optical systems 3) are dedicated to other forms of professional optical astronomy. Since 2015, SHARP has illuminated and tracked over 30 NEO’s ranging in diameter from 7 to 5000 m at ranges of 0.1–18 lunar distances (LD) from Australia.

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 min was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision 1 , but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement ( β ) was possible 2 , 3 . In the years before impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos 4 – 6 . Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be −33.0 ± 1.0 (3 σ ) min. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a substantial amount of momentum to the asteroid beyond what the DART spacecraft carried.

We describe three HF(9.6MHz) bistatic radar experiments that were conducted in 2022 with the High-frequency Active Auroral Research Program (HAARP) facility and the University of New Mexico Long Wavelength Array (UNM-LWA) and the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The purpose of these experiments was to understand the potential for using these facilities in a bistatic radar mode for planetary science investigations, specifically, near-Earth asteroid interior sensing (cislunar and Apophis 2029 flyby). We conducted two Moon-bounce experiments as well as the first asteroid detection experiment at 9.6 MHz using ~1.25 GW EIRP transmissions of FMCW radar chirps. We attempted to detect asteroid 2010 XC15 at 2 Lunar distances for which several hours of coherent processing are required for a positive signal to noise ratio. Data are still under analysis but future experiments at these wavelengths may have to target asteroids that approach closer than 2 Lunar distances. In addition, the processing of received waveforms revealed ionosphere effects that suggest the potential for using these facilities for future ionospheric research.

We describe results of a planetary defense exercise conducted during the close approach to Earth by the near-Earth asteroid (99942) Apophis during 2020 December–2021 March. The planetary defense community has been conducting observational campaigns since 2017 to test the operational readiness of the global planetary defense capabilities. These community-led global exercises were carried out with the support of NASA’s Planetary Defense Coordination Office and the International Asteroid Warning Network. The Apophis campaign is the third in our series of planetary defense exercises. The goal of this campaign was to recover, track, and characterize Apophis as a potential impactor to exercise the planetary defense system including observations, hypothetical risk assessment and risk prediction, and hazard communication. Based on the campaign results, we present lessons learned about our ability to observe and model a potential impactor. Data products derived from astrometric observations were available for inclusion in our risk assessment model almost immediately, allowing real-time updates to the impact probability calculation and possible impact locations. An early NEOWISE diameter measurement provided a significant improvement in the uncertainty on the range of hypothetical impact outcomes. The availability of different characterization methods such as photometry, spectroscopy, and radar provided robustness to our ability to assess the potential impact risk.

We report observations of the Apollo-class potentially hazardous asteroid 1981 Midas, which passed 0.090 au from Earth (35 lunar distances) on 2018 March 21. During this close approach, Midas was observed by radar both from the Arecibo Observatory on March 21 through 25 (five nights) and from NASA’s Goldstone Deep Space Communications Complex on March 19 and 21. Optical lightcurves were obtained by other observers during four apparitions (1987, 1992, 2004, and 2018), which showed a rotation period of 5.22 hr. By combining the lightcurves and radar data, we have constructed a shape model for Midas. This model shows that Midas has two lobes separated by a neck, which, at its thinnest point, is about 60% of the width of the largest lobe. We also confirm the lightcurve-derived rotation period and show that Midas has a pole direction within 6° of ecliptic longitude and latitude (λ, β) = (39°, −60°) and dimensions of (3.41 ± 9%) × (1.90 ± 11%) × (1.27 ± 29%) km. Analysis of gravitational slopes on Midas indicates that nearly all of the surface has a slope less than the typical angle of repose for granular materials, so it does not require cohesion to maintain its shape. In addition, we measured a circular polarization ratio of 0.83 ± 0.04 at Arecibo’s 13 cm wavelength, which is the highest seen to date for any near-Earth asteroid with visible and near-infrared spectral type V.

We report results of Canberra-ATCA Doppler-only continuous wave (CW) radar observations of near-Earth asteroid (163899) 2003 SD220 at a receiving frequency of 7159 MHz (4.19 cm) on 2018 December 20, 21, and 22 during its close approach within 0.019 au (7.4 lunar distances). Echo power spectra provide evidence that the shape is significantly elongated, asymmetric, and has at least one relatively large concavity. An average spectrum per track yields an OC (opposite sense of circular polarization) radar cross section of 0.39, 0.27, and 0.25 km(2), respectively, with an uncertainty of 35%. Variations by roughly a factor of two in the limb-to-limb bandwidth over the three days indicate rotation of an elongated object. We obtain a circular polarization ratio of 0.21 +/- 0.07 that is consistent with, but somewhat lower than, the average among other S-class near-Earth asteroids observed by radar.

Ground-based planetary radar systems are a crucial tool for post-discovery high-precision astrometry and physical characterization of near-Earth asteroids and comets.Radar ranging and imaging capabilities exceed those of any other ground-based instruments.As described in more detail in the Decadal white paper (henceforth WP) Mainzer et al. and WP Taylor et al., detection and characterization of potentially hazardous asteroids was mandated by the US Congress through George E. Brown, Jr. Near-Earth Object Survey Act in 2005.While optical telescopes survey for new asteroid detections, post-discovery characterization using planetary radar can secure the heliocentric orbit information, extending the interval of reliable orbit estimation by decades to centuries for most objects and preventing recently-discovered objects from being lost.Radar observations also provide constraints on the object's size, rotation state, morphology, satellites, and near-surface geology as well as regolith properties, making groundbased radar systems a powerful, low-cost complement to spacecraft destined for specific targets.Furthermore, they can be used for characterizing the nuclei of comets, which are typically obscured by the dust coma at optical wavelengths, and probe the decimeter-scale coma particle abundance, which is relevant especially for the study of disintegrating comets.These characteristics are invaluable information for understanding the formation and evolution of asteroids and comets, which are the building blocks of our Solar System, for evaluating impact risk and developing impact mitigation technologies, and for ensuring safe spacecraft encounters.In the next decade, in addition to continuing as a state-of-the-art astrometric tool for planetary defense, we expect ground-based radar observations to expand our knowledge of the physical characteristics of the near-Earth asteroid population in terms of their shape, binarity, and near-surface structure.We recommend that facilities with ground-based radar systems, planetary radar programs, and research and analysis of radar observations receive full support from NASA and NSF to ensure their availability to the planetary science community and as a resource for planetary defense initiatives through the next decade.