Radar observations are a powerful technique to study near-Earth asteroids (NEAs). Goldstone's 3.75 m resolution capability is invaluable when attempting to image NEAs with diameters smaller than 140 m. The small NEAs are a very diverse population in which we continue to discover unusual objects.

Asteroid disk-integrated sparse-in-time photometry can be used for determination of shapes and spin states of asteroids by the lightcurve inversion method. To clearly distinguish the correct solution of the rotation period from other minima in the parameter space, data with good photometric accuracy are needed. We show that if the low-quality sparse photometry obtained from ground-based astrometric surveys is combined with data from the Wide-field Infrared Survey Explorer (WISE) satellite, the correct rotation period can be successfully derived. Although WISE observed in mid-IR wavelengths, we show that for the period and spin determination, these data can be modelled as reflected light. The absolute fluxes are not required since only relative variation of the flux over the rotation is sufficient to determine the period. We also discuss the potential of combining all WISE data with the Lowell photometric database to create physical models of thousands of asteroids.

For 40 years, the sizes and shapes of many dozens of asteroids have been determined from observations of asteroidal occultations, and over a thousand high-precision positions of the asteroids relative to stars have been measured. Some of the first evidence for satellites of asteroids was obtained from the early efforts; now, the orbits and sizes of some satellites discovered by other means have been refined from occultation observations. Also, several close binary stars have been discovered, and the angular diameters of some stars have been measured from analysis of these observations. The International Occultation Timing Association (IOTA) coordinates this activity worldwide, from predicting and publicizing the events, to accurately timing the occultations from as many stations as possible, and publishing and archiving the observations.

The formation and evolution of Solar System small bodies, in particular those in near-Earth orbits, is a complex problem which solution strongly depends on a better knowledge of their physical properties. To contribute to the international efforts in this direction the IMPACTON project (www.on.br/IMPACTON) set up a dedicated facility denominated Observatório Astronômico do Sertão de Itaparica (OASI). Using the 1-m telescope several dozens of NEAs were observed between March 2012 and October 2014. Here we will present the results obtained for 8 objects. Relative magnitudes were used to obtain lightcurves and derive rotational periods. Applying the inversion method developed by Kaasalainen and Torppa (2001) and Kaasalainen et al. (2001), along with lightcurves from literature, allowed to refine the rotational period of these asteroids as well as to derive their pole direction and shape. The obtained results confirm a lack of poles toward the ecliptic and with a majority of retrograde rotators. A more representative sample, however, is needed in order to drive robust conclusions.

Studies for spin parameters and shapes of asteroids provide us with important information about the interior structure of asteroids and the physical processes they have undergone. A large sample of basic physical parameters can help us also understand the evolution of asteroids. There is scarce information for slowly-rotating larger asteroids because more effort is required for observing them. Because of this, we have established an international collaboration to study slowly-rotating asteroids. As the first step of this project, we have observed asteroids (168) Sibylla and (346) Hermentaria in 2014 and 2015 using several telescopes located in China, Chile, and U.S.A. Combining previous photometric data with our new data, we have performed preliminary analyses and obtained spin parameters and shapes with their uncertainties for these two slowly-rotating asteroids for the first time, using the convex inversion method and the virtual photometry Monte Carlo method. A pair of pole solutions for (168) Sibylla are found around (4.3°, 53.5°) and (183.5°, 52.6°) with a period of 47.0000 h. We have found that the shape of Sibylla resembles an oblate spheroid. For (346) Hermentaria, we have also found a pair of pole solutions around (134.5°, 16.7°) and (321.5°, 14.5°) with comparable rms-values with a spin period of about 17.79000 h, and a shape resembling a prolate spheroid.

Boulders, rocks and regolith on fast rotating asteroids (<2.5 hours) are modeled to slide towards the equator due to a strong centrifugal force and a low cohesion force. As a result, regions of fresh subsurface material can be exposed. Therefore, we searched for color variation on small and fast rotating asteroids. We describe a novel technique in which the asteroid is simultaneously observed in the visible and near-IR wavelength range. In this technique, brightness changes due to atmospheric extinction effects can be calibrated across the visible and near-IR images. We use V- and J-band filters since the distinction in color between weathered and unweathered surfaces on ordinary chondrite-like bodies is most prominent at these wavelengths and can reach ~25%. To test our method, we observed 3 asteroids with Cerro Tololo's 1.3 m telescope. We find ~5% variation of the mean V-J color, but do not find any clearly repeating color signature through multiple rotations. This suggests that no landslides occurred within the timescale of space weathering, or that Landslides occurred but the exposed patches are too small for the measurements' uncertainty.

Space weathering affects reflectance spectra of the Moon and S-complex asteroids by spectral bluing (increasing reflectance with decreasing wavelength) of their surface materials at UV/blue (less than 400 nm) wavelengths. This spectral bluing is attributed to a degradation of the UV absorption feature seen in spectral reflectance of olivine as a result of the creation of nanophase (npFe0) iron. We have modeled the effect of the addition of small amounts of npFe0 intimately mixed with particles from a hypothetical material and a terrestrial basalt. The addition of 0.0001% npFe0 affects the reflectance at these UV/blue wavelengths, while the addition of 0.01% is required to see the visible/near infrared reddening and diminution of VNIR absorption features. Thus, the UV/blue spectral reflectance characteristics allow earlier detection of the onset of space weathering effects.

We compute the spherical albedo for a Lommel-Seeliger scattering ellipsoidal asteroid with a realistic disk-integrated phase function. The spherical (or Bond) albedo gives the ratio of the fluxes incident on and scattered by an asteroid. Thus, it plays a key role in the determination of the flux absorbed and afterwards thermally emitted by the asteroid at longer wavelengths. We provide extensive computations for the spherical albedo of low-albedo and moderate-albedo asteroids by utilizing the analytical disk-integrated brightness of a Lommel-Seeliger ellipsoid. In doing so, we utilize realistic triaxial models of known asteroids as well as idealistic prolate or oblate models of substantial elongation or flatness, respectively. We show that the spherical albedos can vary significantly as a function of the rotational pole orientation, rotational phase, and the triaxial ellipsoidal shape: variations of the order of 5-10% are realistic, with a tendency to grow with increasing elongation or flatness of the shape.

An estimation of the mass of the main asteroid belt was made on the basis of the new version of EPM2014 ephemerides of the Institute of Applied Astronomy of Russian Academy of Sciences using about 800000 positional observations of planets and spacecraft. We obtained the individual estimations of masses of large asteroids from radar data, as well as estimates of the masses of asteroids by using known diameters and estimated average densities for the three taxonomic types (C, S, M), and used the known mass values of binary asteroids and asteroids to which spacecraft approached. A two-dimensional homogeneous annulus with dimensions corresponding observed width of the main asteroid belt (2.06 au and 3.27 au) was used instead of a previous massive one-dimensional ring for modeling total perturbations from small asteroids. The obtained value of the total mass of the main asteroid belt is (12.25 ± 0.19)10−10M⊙.

In this work, we investigate the thermophysical properties, including thermal inertia, roughness fraction and surface grain size of OSIRIS-REx target asteroid (101955) Bennu by using a thermophysical model with the recently updated 3D radar-derived shape model (Nolan et al., 2013) and mid-infrared observations (Müller et al. 2012, Emery et al., 2014). We find that the asteroid bears an effective diameter of 510+6−40 m, a geometric albedo of 0.047+0.0083−0.0011, a roughness fraction of 0.04+0.26−0.04, and thermal inertia of 240+440−60 Jm−2s−0.5K−1 for our best-fit solution. The best-estimate thermal inertia suggests that fine-grained regolith may cover a large portion of Bennu's surface, where a grain size may vary from 1.3 to 31 mm. Our outcome suggests that Bennu is suitable for the OSIRIS-REx mission to return samples to Earth.

We review the most standard impact monitoring techniques. Linear methods are the fastest approach but their applicability regime is limited because of the chaotic dynamics of near-Earth asteroids. Among nonlinear methods, Monte Carlo algorithms are the most reliable ones but also most computationally intensive and so unpractical for routine impact monitoring. In the last 15 years, the Line of Variations method has been the most successful technique thanks to its computational efficiency and capability of detecting low probability events deep in the nonlinear regime. We also present some more recent techniques developed to deal with the new challenges arising in the impact hazard assessment problem. In particular, we describe keyhole maps as a tool to go beyond strongly scattering encounters and how to account for nongravitational perturbations, especially the Yarkovsky effect, when their contribution is the main source of prediction uncertainty. Finally, we discuss systematic ranging to deal with the short-term hazard assessment problem for newly discovered asteroids, when only a short observed arc is available thus leading to severe degeneracies in the orbit estimation process.

Deflection missions to near-Earth asteroids will encounter non-negligible uncertainties in the physical and orbital parameters of the target object. In order to reliably assess future impact threat mitigation operations such uncertainties have to be quantified and incorporated into the mission design. The implementation of deflection demonstration missions offers the great opportunity to test our current understanding of deflection relevant uncertainties and their consequences, e.g., regarding kinetic impacts on asteroid surfaces. In this contribution, we discuss the role of uncertainties in the NEOTωIST asteroid deflection demonstration concept, a low-cost kinetic impactor design elaborated in the framework of the NEOShield project. The aim of NEOTωIST is to change the spin state of a known and well characterized near-Earth object, in this case the asteroid (25143) Itokawa. Fast events such as the production of the impact crater and ejecta are studied via cube-sat chasers and a flyby vehicle. Long term changes, for instance, in the asteroid's spin and orbit, can be assessed using ground based observations. We find that such a mission can indeed provide valuable constraints on mitigation relevant parameters. Furthermore, the here proposed kinetic impact scenarios can be implemented within the next two decades without threatening Earth's safety.

Recent investigations on small asteroids, initiated by the Chelyabinsk event, are reviewed. New estimates of the terrestrial impact rate, importance of Sun-grazing conditions in the evolution of near-Earth objects, and problems associated with dangerous objects approaching the Earth from the Sun direction are discussed.

With the improvements of the observational technology for the new surveys the number of asteroid detections is rapidly increasing. For this reason we must use very efficient methods to compute orbits with these data. We have to identify observations taken in different nights as belonging to the same asteroid. If we do not have an efficient algorithm for that, the unidentified observation database can increase without control, and we risk to detect the same objects multiple times.

The problem of binary asteroids orbit determination is of particular interest, given knowledge of the orbit is the best way to derive the mass of the system. Orbit determination from observed points is a classic problem of celestial mechanics. However, in the case of binary asteroids, particularly with a small number of observations, the solution is not evident to derive. In the case of resolved binaries the problem consists in the determination of the relative orbit from observed relative positions of a secondary asteroid with respect to the primary. In this work, the problem is investigated as a statistical inverse problem. Within this context, we propose a method based on Bayesian modelling together with a global optimisation procedure that is based on the simulated annealing algorithm.

We report the current results on a comprehensive scan of the near-Earth asteroid catalog for evidence of the Yarkovsky effect in the orbital motion of these bodies. While most objects do not have sufficient observational data to reveal such slight acceleration, we do identify 42 asteroids with a “valid” detection of the Yarkovsky effect, i.e., those with a signal at least 3 times greater than the formal uncertainty and a value compatible with the Yarkovsky mechanism.

We also identify a special category of non-detection, which we refer to as “weak signal,” where the objects are of a size that would permit a clear detection if the Yarkovsky effect is maximized, and yet the orbit is clearly incompatible with such accelerations. The implication is that the Yarkovsky effect is reduced in these cases, presumably due to mid-range obliquity, but possibly also due to size, bulk density, thermal inertia, albedo, or spin rate markedly different from assumptions.

Finally, there are a number of asteroids showing a significant signal for nongravitational acceleration, and yet with a magnitude too great to be attributed to the Yarkovsky effect. We term these “spurious detections” because most are due to erroneous optical astrometry, often involving a single isolated night from precovery observations. Some cases may be due to other nongravitational accelerations, such as outgassing, mass loss, or micro-meteoroid flux.

Due to the close distance to the Sun, solar radiation pressure (SRP) plays an important role in the dynamics of satellites around near-Earth asteroids (NEAs). In this paper, we focus on the equilibrium points of a satellite orbiting around an asteroid in presence of SRP in the asteroid rotating frame. The asteroid is modelled as a uniformly rotating triaxial ellipsoid. When SRP comes into play, the equilibrium points transformed into periodic orbits termed as``dynamical substitutes". We obtain the analytical approximate solutions of the dynamical substitutes from the linearised equations of motion. The analytical solutions are then used as initial guesses and are numerically corrected to compute the accurate orbits of the dynamical substitutes. The stability of the dynamical substitutes is analysed and the stability maps are obtained by varying parameters of the ellipsoid model as well as the magnitude of SRP.

The Minor Planet Center receives up to several million astrometric observations of minor planets and comets each month. Given the volume of observations, the sheer number of known objects against which to possibly match, the shortness of the time interval over which each object was likely observed, and the uncertainties in the positions, and occasionally possible errors in times, reported, a number of data processing challenges present themselves. These include: Identifying observations of objects reported as new with already known objects; linking together sets of observations from different nights which may belong to the same object; determining if a set of observations has been assigned to the wrong object; determining if an object with a very short arc is possibly a Near-Earth object; prioritizing newly discovered objects in order of need of follow up; and, efficiently matching one or more observations with known objects.

While regular astronomical image archive searches can find images at a fixed location, they cannot find images of moving targets such as asteroids or comets. The Solar System Object Image Search (SSOIS) at the Canadian Astronomy Data Centre allows users to search for images of moving objects, allowing precoveries. SSOIS accepts as input either an object designation, a list of observations, a set of orbital elements, or a user-generated ephemeris for an object. It then searches for observations of that object over a range of dates. The user is then presented with a list of images containing that object from a variety of archives. Initially created to search the CFHT MegaCam archive, SSOIS has been extended to other telescopes including Gemini, Subaru/SuprimeCam, WISE, HST, the SDSS, AAT, the ING telescopes, the ESO telescopes, and the NOAO telescopes (KPNO/CTIO/WIYN), for a total of 24.5 million images. As the Pan-STARRS and Hyper Suprime-Cam archives become available, they will be incorporated as well. The SSOIS tool is located on the web at http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/ssois/.

The NEO Coordination Centre (NEOCC) has been established within the framework of the ESA Space Situational Awareness (SSA) Programme. Among its tasks are the coordination of observational activities and the distribution of up-to-date information on NEOs through its web portal.

The Centre is directly involved in observational campaigns with various telescopes, including ESO's VLT and ESA's OGS telescope. We are also developing a network of collaborating observatories, with a variety of capabilities, which are alerted when an important observational opportunity arises.

From a service perspective, the system hosted at the NEOCC collects information on NEOs produced by European services and makes it available to users, with a focus on objects with possible collisions with the Earth. Among the tools provided via our portal are the Risk List of all known NEOs with impact solutions, and the Priority List, which allows observers to identify NEOs in most urgent need of observations.