The subject of this work is the physical characterization of asteroids, focusing on the thermal inertia of near-Earth asteroids (NEAs). Thermal inertia governs the Yarkovsky effect, a non-gravitational force which significantly alters the orbits of asteroids up to \sim 20 km in diameter. Yet, very little has previously been known about the thermal inertia of small asteroids including NEAs. Observational and theoretical work is reported. The thermal emission of asteroids has been observed in the mid-infrared (5-35 {\mu}m) wavelength range using the Spitzer Space Telescope and the 3.0m IRTF. A detailed thermophysical model (TPM) has been developed and extensively tested; this is the first detailed TPM shown to be applicable to NEA data. Our main result is the determination of the thermal inertia of 5 NEAs, increasing the total number of NEAs with measured thermal inertia to 6. For two of our targets, previously available estimates are refined. Our results allow the first determination of the typical thermal inertia of NEAs, which is around 300 J s^{-1/2} K^{-1} m^{-2}, larger than the typical thermal inertia of large main-belt asteroids (MBAs) by more than an order of magnitude. In particular, thermal inertia appears to increase with decreasing asteroid diameter. Our results have been used by colleagues to estimate the size dependence of the Yarkovsky effect, thus explaining the apparent difference in the size-frequency distribution of NEAs and similarly sized MBAs. Thermal inertia is a very sensitive indicator for the presence or absence of particulate material on the surface. Our results indicate that even sub-km asteroids are covered with coarse regolith.

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Surface Properties of Asteroids from Mid-Infrared Observations and Thermophysical Modeling

The NEAs (Near-Earth Asteroids) are good targets for spatial missions, since they periodically approach the orbit of the Earth. Recently, the NEA (153591) 2001 SN263 was chosen as the target of the ASTER MISSION- First Brazilian Deep Space Mission, planned to be launched in 2015. In February 2008, the radio astronomers from Arecibo-Puerto Rico concluded that (153591) 2001 SN263 is actually a triple system (Nolan et al., 2008). The announcement of the ASTER MISSION has motivated the development of the present work, whose goal is to characterize regions of stability and instability of the triple system (153591) 2001 SN263. The method adopted consisted in dividing the region around the system into four distinct regions. We have performed numerical integrations of systems composed by seven bodies: Sun, Earth, Mars, Jupiter and the three components of the system, and by thousands of particles randomly distributed within the demarcated regions, for the planar and inclined prograde cases. The results are diagrams of semi-major axis versus eccentricity, where it is shown the percentage of particles that survive for each set of initial conditions. The regions where 100% of the particles survive is defined as stable regions. We found that the stable regions are in the neighborhood of Alpha and Beta, and in the external region. It was identified resonant motion of the particles with Beta and Gamma in the internal regions, which lead to instability. For particles with I>45° in the internal region, where I is the inclination with respect to Alpha's equator, there is no stable region, except for the particles placed really close to Alpha. The stability in the external region is not affected by the variation of inclination. We also present a discussion on the long-term stability in the internal region, for the planar and circular cases, with comparisons with the short-term stability.

Stability Regions Around the Components of the Triple System 2001 SN263

Capabilities of GOSSAMER-1 derived Small Spacecraft Solar Sails carrying MASCOT-derived Nanolanders for In-Situ Surveying of NEAs

The NEA 2001 SN263 is a triple system of asteroids and it is the target of the ASTER MISSION - First Brazilian Deep Space Mission. The announcement of this mission has motivated a study aimed to characterize regions of stability of the system. Araujo et al., (2012), characterized the stable regions around the components of the triple system for the planar and prograde cases. Through numerical integrations they found that the stable regions are in two tiny internal zones, one of them placed very close to Alpha and another close to Beta, and in the external region. For a space mission aimed to place the probe in the internal region of the system those results do not seem to be very interesting. Therefore, knowing that the retrograde orbits are expected to be more stable, here we present a complementary study. We now considered particles orbiting the components of the system, in the internal and external regions, with relative inclinations between 90 < I 6 180 , i.e., particles with retrograde orbits. Our goal is to characterize the stable regions of the system for retrograde orbits, and then detach a preferred region to place the space probe. For a space mission, the most interesting regions would be those that are unstable for the prograde cases, but stable for the retrograde cases. Such configuration provide a stable region to place the mission probe with a relative retrograde orbit, and, at the same time, guarantees a region free of debris since they are expected to have prograde orbits. We found that in fact the internal and external stable regions significantly increase when compared to the prograde case. For particles with e = 0 and I = 180 , we found that nearly the whole region around Alpha and Beta remain stable. We then identified three internal regions and one external region that are very interesting to place the space probe. We present the stable regions found for the retrograde case and a discussion on those preferred regions. We also discuss the effects of resonances of the particles with Beta and Gamma, and the role of the Kozai mechanism in this scenario. These results help us understand and characterize the stability of the triple system 2001 SN263 when retrograde orbits are considered, and provide important parameters to the design of the ASTER mission.

Stable retrograde orbits around the triple system 2001 SN263

In late 2018, the asteroid Ryugu was in the Sun’s shadow during the superior solar conjunction phase. As the Sun-Earth-Ryugu angle decreased to below 3°, the Hayabusa2 spacecraft experienced 21 days of planned blackout in the Earth-probe communication link. This was the first time a spacecraft had experienced solar conjunction while hovering around a minor body. For the safety of the spacecraft, a low energy transfer trajectory named Ayu was designed in the Hill reference frame to increase its altitude from 20 to 110 km. The trajectory was planned with the newly developed optNEAR tool and validated with real time data. This article shows the results of the conjunction operation, from planning to flight data.

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Hayabusa2’s superior solar conjunction mission operations: planning and post-operation results

On the Trojan asteroid sample and return mission via solar-power sail -- an innovative engineering demonstration

HAYABUSA MISSION M Yoshikawa 1 , H Yano 2 , J Kawaguchi 2 , A Fujiwara 2 , M Abe 2 , T Iwata 2 , Y Kawakatsu 2 , S Tanaka 2 , O Mori 2 , T Yoshimitsu 2 , Y Takagi 3 , H Demura 4 , T Noguchi 5 , H Miyamoto 6 , 1 Japan Aerospace Exploration Agency (3-1-1, Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan, makoto@isasjaxajp), 2 Japan Aerospace Exploration Agency, 3 Toho Gakuen University, 4 The University of Aizu, 5 Ibaraki University, 6 The University of Tokyo

Technologies for Future Asteroid Exploration: What We Learned from Hayabusa Mission

Together with plasma instruments on board JEO and JGO, JMO will investigate the fast and huge rotating magnetosphere to clarify the energy procurement from Jovian rotation to the magnetosphere, to clarify the interaction between the solar wind the magnetosphere. JMO will clarify the characteristics of the strongest accelerator in the solar system. JMO will investigate the role of Io as a source of heavy ions in the magnetosphere. Proposed instruments on board JMO are magnetometers, low-energy plasma spectrometers, medium energy particle detectors, energetic particle detectors, electric field / plasma wave instruments, a dust detector, an ENA imager, and EUV spectrometer.

http://meetingorganizer.copernicus.org/EGU2009/EGU2009-8108.pdf

O. Mori

Papers

On the Trojan asteroid sample and return mission via solar-power sail -- an innovative engineering demonstration

Technologies for Future Asteroid Exploration: What We Learned from Hayabusa Mission

Exploration of Jovian Magnetosphere and Trojan Asteroids by a Solar Power Sail Mission