In the giant impact theory, the Moon formed from debris ejected into an Earth-orbiting disk by the collision of a large planet with the early Earth. Prior impact simulations predict that much of the disk material originates from the colliding planet. However, Earth and the Moon have essentially identical oxygen isotope compositions. This has been a challenge for the impact theory, because the impactor’s composition would have likely differed from that of Earth. We simulated impacts involving larger impactors than previously considered. We show that these can produce a disk with the same composition as the planet’s mantle, consistent with Earth-Moon compositional similarities. Such impacts require subsequent removal of angular momentum from the Earth-Moon system through a resonance with the Sun as recently proposed.

Forming a Moon with an Earth-like composition via a Giant Impact

We obtained estimates of the Johnson V absolute magnitudes ( H ) and slope parameters ( G ) for 583 main-belt and near-Earth asteroids observed at Ondřejov and Table Mountain Observatory from 1978 to 2011. Uncertainties of the absolute magnitudes in our sample are H data with absolute magnitude values given in the MPCORB, Pisa AstDyS and JPL Horizons orbit catalogs. We found that while the catalog absolute magnitudes for large asteroids are relatively good on average, showing only little biases smaller than 0.1 mag, there is a systematic offset of the catalog values for smaller asteroids that becomes prominent in a range of H greater than ∼10 and is particularly big above H  ∼ 12. The mean ( H catalog  −  H ) value is negative, i.e., the catalog H values are systematically too bright. This systematic negative offset of the catalog values reaches a maximum around H  = 14 where the mean ( H catalog  −  H ) is −0.4 to −0.5. We found also smaller correlations of the offset of the catalog H values with taxonomic types and with lightcurve amplitude, up to ∼0.1 mag or less. We discuss a few possible observational causes for the observed correlations, but the reason for the large bias of the catalog absolute magnitudes peaking around H  = 14 is unknown; we suspect that the problem lies in the magnitude estimates reported by asteroid surveys. With our photometric H and G data, we revised the preliminary WISE albedo estimates made by Masiero et al. ( Masired, J.R. et al. [2011] . Astrophys. J. 741, 68–89) and Mainzer et al. ( Mainzer, A. et al. [2011b] . Astrophys. J. 743, 156–172) for asteroids in our sample. We found that the mean geometric albedo of Tholen/Bus/DeMeo C/G/B/F/P/D types with sizes of 25–300 km is p V  = 0.057 with the standard deviation (dispersion) of the sample of 0.013 and the mean albedo of S/A/L types with sizes 0.6–200 km is 0.197 with the standard deviation of the sample of 0.051. The standard errors of the mean albedos are 0.002 and 0.006, respectively; systematic observational or modeling errors can predominate over the quoted formal errors. There is apparent only a small, marginally significant difference of 0.031 ± 0.011 between the mean albedos of sub-samples of large and small (divided at diameter 25 km) S/A/L asteroids, with the smaller ones having a higher albedo. The difference will have to be confirmed and explained; we speculate that it may be either a real size dependence of surface properties of S type asteroids or a small size-dependent bias in the data (e.g., a bias towards higher albedos in the optically-selected sample of asteroids). A trend of the mean of the preliminary WISE albedo estimates increasing with asteroid size decreasing from D  ∼ 30 down to ∼5 km (for S types) showed in Mainzer et al. ( Mainzer, A. et al. [2011a] . Astrophys. J. 741, 90–114) appears to be mainly due to the systematic bias in the MPCORB absolute magnitudes that progressively increases with H in the corresponding range H  = 10–14.

Absolute Magnitudes of Asteroids and a Revision of Asteroid Albedo Estimates from WISE Thermal Observations

AIDA DART asteroid deflection test: Planetary defense and science objectives

https://hal-insu.archives-ouvertes.fr/insu-01667223/document

European component of the AIDA mission to a binary asteroid: Characterization and interpretation of the impact of the DART mission

https://www.astro.umd.edu/~dcr/reprints/cheng_pss121,27.pdf

Asteroid Impact & Deflection Assessment mission: Kinetic impactor

There is evidence of past Near-Earth-Objects (NEOs) impacts on Earth and several studies indicating that even relatively small objects are capable of causing
large local damage, either directly or in combination with other phenomena, e.g. tsunamis. This paper describes a space mission concept to demonstrate some of the
key technologies to rendezvous with an asteroid and accurately measure its trajectory during and after a deflection maneuver. The mission, called SIROCO, makes
use of the recently proposed ion beam shepherd (IBS) concept where a stream of accelerated plasma ions is directed against the surface of a small NEO resulting in
a net transmitted deflection force. We show that by carefully selecting the target NEO a measurable deflection can be obtained in a few weeks of continuous thrust
with a small spacecraft and state of the art electric propulsion hardware.

The SIROCO Asteroid Deflection Demonstrator

Mitigation-relevant science with Don Quijote - a European-led mission to a near-Earth asteroid

AIDA: Asteroid Impact & Deflection Assessment

The ̈AIDA ̈ cooperation was initiated in 2011 between ESA, DLR and Observatoire Côte d ́Azur (OCA) on one side and NASA and John Hopkins University Applied Physics Laboratory (JHU/APL) on the other, to assess concepts of mutual interest, with an initial focus on Planetary Defense. The US part, Double Asteroid Redirection Test (DART) would impact a high-velocity projectile into the smaller asteroid of the target binary system 65803 Didymos on October 2022 with the purpose of modifying the relative orbit. The mission goal for ESA’s Asteroid Impact Mission (AIM) study is to characterise the components of a binary asteroid, especially from the dynamical point of view. The mission concept focuses on the monitoring aspects i.e., the capability to determine, in-situ, the key physical properties of a binary asteroid playing a role in the system’s dynamic behaviour. For this purpose, even if not a must, choosing a target whose dynamics have already been well characterised from the ground (e.g., by means of radar and photometry observations). Current baseline targets are asteroids 65803 Didymos (planned reference cooperative mission with US) or 1996FG3. An AIM fly-by mission was also considered, however, due to a more limited return on the mission goals, and significant technical challenges and mission risks, this scenario has been abandoned in favour of an AIM rendezvous spacecraft. The main objectives of the AIM rendezvous spacecraft are: • Determine binary asteroid orbital and rotation state • Analyse size, mass and shape of both binary asteroid components • Analyse geology and surface properties • Observe the impact crater and derive collision and impact properties (requires the DART mission). Within the study all major design trade-offs have been carried out. Given the demanding mass envelope imposed by the use of the VEGA LV, the selection of the spacecraft propulsion technology (chemical or electrical) was of particular importance. The analysis considered mostly the reference interplanetary trajectory (direct transfer or including swing-bys) and the resulting mass at arrival. Due to the low values of the arrival mass at the asteroid, chemical propulsion was discarded. The resulting baseline trajectory involves an Earth swing-by and assumes a performance of a SNECMA PPS-1350 Hall-effect thruster, as the one demonstrated by ESA’s SMART-1 lunar mission. The AIM rendezvous mission is designed to be compatible with the VEGA launch vehicle, which would require an additional “kick motor” (e.g., STAR-48) to perform the Earth escape burn. On arrival, the spacecraft would perform continuous observations from a serious of “station points” fixed point relative to the asteroid inertial frame and at a safe distance, out of the sphere of influence of both Didymos components. It would also deploy cubesat-sized probes that would perform seismic experiments, in this way complementing remote sensing data and providing an insight into the level of internal cohesion. In order to be able to image the two bodies for precise measurements of the orbital state, distances of 13.5 to 17 km were considered for the 1st characterisation point. If the AIM spacecraft arrives at the target before the DART spacecraft, the impact of the DART spacecraft will be observed from a 2nd characterisation point of 100 km to avoid any damage by debris generated in the impact. AIM would then prospect the post-impact environment, and the associated change in the binary asteroid relative orbit (which could be compared with telescope and radar observations from ground) and resulting debris (which cannot). A strawman payload for the characterisation of the asteroid consists of a Narrow Angle Camera, a Micro laser Altimeter, a Thermal IR Imager and a NIR spectrometer. A Call for Experiment Ideas has been carried out in 2013, which has resulted in the identification of instrumentation concepts that will be explored in the frame of industrial activities in 2014. As part of ongoing analysis work technology demonstration options to be considered also include: lightweight high speed / high resolution camera, 3D camera, TriDAR for mapping and proximity operations, on-board autonomy (i.e. autonomous diagnostic and decision making), tone-base cruise health monitoring, housekeeping data compression, high performance DHS and GNC for proximity operations (incl. non-space spin-in e.g. parallel “voting” computer architectures, GNC software auto-coding), precise s/c tracking and vision-based orbit determination, lightweight seismometer, deployable monitoring nanosats, spacecraft impact vulnerability protection and recovery operations. The subject of this paper is in particular the additional mission analysis work to be carried out in early 2014 in order to assess options for missions involving Electric Propulsion and the VEGA LV on combination with an alternative upper stage, e.g. Lisa Pathfinder Propulsion Module. The analysis will also consider alternative and backup scenarios leading to an increased mission flexibility.

Asteroid Investigation Mission: TheEuropean Contribution to the AIDA EU-US Cooperation

In the frame of NEO exploration and planetary defence, the two-part AIDA mission is currently studied by NASA and ESA. Being composed of a kinetic impactor, DART (NASA), and by an observing spacecraft, AIM (ESA), AIDA has been designed to deliver vital data to determine the momentum transfer efficiency of a kinetic impact onto a small body and the key physical properties of the target asteroid. This will enable derivation of the impact response of the object as a function of its physical properties, a crucial quantitative point besides the qualitative proof of the deflection. In the course of the AIM mission definition, a lander has been studied as an essential element of the overall mission architecture. It was meant to be deployed on Didymoon, the secondary body of the binary NEA system 65803 Didymos and it was supposed to significantly enhance the analysis of the body’s dynamical state, mass, geophysical properties, surface and subsurface structure. The mission profile and the design of the 13kg nano-lander have been derived from the MASCOT lander flying aboard Hayabusa2, differing from its predecessor by having an increased lifetime of more than three months, a surface mobility capability including directed movement, a sensor system for localization and attitude determination on the surface and a redesigned mechanical interface to the mother spacecraft. The MASCOT2 instrument suite consists of a bi-static, low frequency radar (LFR) as main instrument, supported by an accelerometer (DACC), a camera (MasCAM), a radiometer (MARA) and a magnetometer (MasMAG); the latter three already flying on MASCOT. Besides the radar measurements, the camera is meant to provide high-resolution images of the landing area, and accelerometers to record the bouncing dynamics by which the top surface mechanical properties can be determined. During the DART impact, MASCOT2 was expected to be able to detect the seismic shock, providing valuable information on the internal structure of the body. MASCOT2 was supposed also to serve as a technology demonstrator for very small asteroid landing and extended operations powered by a solar generator. In this paper, we describe the science concept, mission analysis of the separation, descent and landing phase, the operational timeline, and the latest status of the lander’s design. Despite the fact that AIM funding has not been fully confirmed during the ESA Ministerial conference in 2016, MASCOT2 is an instrument package of high maturity and major interest for planetary defense and NEO science. With appropriate tailoring and optimization, it can be considered and studied for future missions.

Andres Galvez

Papers

The SIROCO Asteroid Deflection Demonstrator

Mitigation-relevant science with Don Quijote - a European-led mission to a near-Earth asteroid

AIDA: Asteroid Impact & Deflection Assessment

Asteroid Investigation Mission: TheEuropean Contribution to the AIDA EU-US Cooperation

MASCOT2 - A small body lander to investigate the interior of 65803 Didymos' moon in the Frame of AIDA/AIM