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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. The 33 minute change in the orbital period of Dimorphos after the DART kinetic impact suggests that ejecta contributed a substantial amount of momentum to the asteroid compared with the DART spacecraft alone.

The discovery 1 of 1I/2017 U1 (1I/‘Oumuamua) has provided the first glimpse of a planetesimal born in another planetary system. This interloper exhibits a variable colour within a range that is broadly consistent with local small bodies, such as the P- and D-type asteroids, Jupiter Trojans and dynamically excited Kuiper belt objects 2 – 7 . 1I/‘Oumuamua appears unusually elongated in shape, with an axial ratio exceeding 5:1 (refs 1 , 4 , 5 , 8 ). Rotation period estimates are inconsistent and varied, with reported values between 6.9 and 8.3 h (refs 4 – 6 , 9 ). Here, we analyse all the available optical photometry data reported to date. No single rotation period can explain the exhibited brightness variations. Rather, 1I/‘Oumuamua appears to be in an excited rotational state undergoing non-principal axis rotation, or tumbling. A satisfactory solution has apparent lightcurve frequencies of 0.135 and 0.126 h −1 and implies a longest-to-shortest axis ratio of ≳5:1, although the available data are insufficient to uniquely constrain the true frequencies and shape. Assuming a body that responds to non-principal axis rotation in a similar manner to Solar System asteroids and comets, the timescale to damp 1I/‘Oumuamua’s tumbling is at least one billion years. 1I/‘Oumuamua was probably set tumbling within its parent planetary system and will remain tumbling well after it has left ours. The brightness variations of the interstellar object 1I/’Oumuamua observed during six nights are incompatible with a unique rotation rate, indicating that the body is tumbling. Colour measurements suggest a heterogeneous surface, with a large red region.

High-resolution radar images reveal near-Earth asteroid (66391) 1999 KW4 to be a binary system. The ~1.5-kilometer-diameter primary (Alpha) is an unconsolidated gravitational aggregate with a spin period ~2.8 hours, bulk density ~2 grams per cubic centimeter, porosity ~50%, and an oblate shape dominated by an equatorial ridge at the object's potential-energy minimum. The ~0.5-kilometer secondary (Beta) is elongated and probably is denser than Alpha. Its average orbit about Alpha is circular with a radius ~2.5 kilometers and period ~17.4 hours, and its average rotation is synchronous with the long axis pointed toward Alpha, but librational departures from that orientation are evident. Exotic physical and dynamical properties may be common among near-Earth binaries.

The Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect is believed to alter the spin states of small bodies in the solar system. However, evidence for the effect has so far been indirect. We report precise optical photometric observations of a small near-Earth asteroid, (54509) 2000 PH5, acquired over 4 years. We found that the asteroid has been continuously increasing its rotation rate ω over this period by dω/dt = 2.0 (±0.2) x 10⁻⁴ degrees per day squared. We simulated the asteroid's close Earth approaches from 2001 to 2005, showing that gravitational torques cannot explain the observed spin rate increase. Dynamical simulations suggest that 2000 PH5 may reach a rotation period of ~20 seconds toward the end of its expected lifetime.

Radar and optical observations reveal that the continuous increase in the spin rate of near-Earth asteroid (54509) 2000 PH5 can be attributed to the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, a torque due to sunlight. The change in spin rate is in reasonable agreement with theoretical predictions for the YORP acceleration of a body with the radar-determined size, shape, and spin state of 2000 PH5. The detection of asteroid spin-up supports the YORP effect as an explanation for the anomalous distribution of spin rates for asteroids under 10 kilometers in diameter and as a binary formation mechanism.

Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation 1 , 2 . Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid 1 – 3 . A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation 1 . NASA’s Double Asteroid Redirection Test (DART) mission is a full-scale test of kinetic impact technology. The mission’s target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the DART spacecraft 4 . Although past missions have utilized impactors to investigate the properties of small bodies 5 , 6 , those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft’s autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in the orbit of Dimorphos 7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary. The impact of the DART spacecraft on the asteroid Dimorphos is reported and reconstructed, demonstrating that kinetic impactor technology is a viable technique to potentially defend Earth from asteroids.

Asteroids two-by-two The increased interest in the observation of main-belt asteroids in recent years has led to the identification of tens of asteroid pairs, which follow near-identical orbits around the Sun even though they are not physically bound together. Rotational fission of larger bodies has been hypothesized as a mechanism for their formation, an idea that gains support with some new observations. Theory predicts that the mass ratios of two asteroids in a pair will be than about 0.2 and that as the mass ratio approaches this upper limit, the spin period of the larger body is extended. Accordingly, photometric observations of 35 asteroid pairs reveal none with mass ratios greater than 0.2, and as mass ratios approach 0.2, primary periods grow longer. This suggests that asteroid pairs form by rotational fusion of a parent asteroid into a short-lived proto-binary system. Rotational fission may explain the formation of pairs of asteroids that have similar heliocentric orbits but are not bound together. These authors report photometric observations of a sample of asteroid pairs revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. In agreement with crucial predictions, they do not find asteroid pairs with mass ratios larger than 0.2, and as the mass ratio approaches 0.2 the primary period grows long. Pairs of asteroids sharing similar heliocentric orbits, but not bound together, were found recently 1 , 2 , 3 . Backward integrations of their orbits indicated that they separated gently with low relative velocities, but did not provide additional insight into their formation mechanism. A previously hypothesized rotational fission process 4 may explain their formation—critical predictions are that the mass ratios are less than about 0.2 and, as the mass ratio approaches this upper limit, the spin period of the larger body becomes long. Here we report photometric observations of a sample of asteroid pairs, revealing that the primaries of pairs with mass ratios much less than 0.2 rotate rapidly, near their critical fission frequency. As the mass ratio approaches 0.2, the primary period grows long. This occurs as the total energy of the system approaches zero, requiring the asteroid pair to extract an increasing fraction of energy from the primary's spin in order to escape. We do not find asteroid pairs with mass ratios larger than 0.2. Rotationally fissioned systems beyond this limit have insufficient energy to disrupt. We conclude that asteroid pairs are formed by the rotational fission of a parent asteroid into a proto-binary system, which subsequently disrupts under its own internal system dynamics soon after formation.

Multiple-asteroid systems are important because they represent a sizable fraction of the asteroid population and because they enable investigations of a number of properties and processes that are often difficult to probe by other means. The binaries, triples, and pairs inform us about a great variety of asteroid attributes, including physical, mechanical, and thermal properties, composition, interior structure, formation processes, and evolutionary processes. Observations of binaries and triples provide the most powerful way of deriving reliable masses and densities for a large number of objects. The density measurements help us understand the composition and internal structure of minor planets. Binary

Observations of near-Earth asteroid 1998 KY26 shortly after its discovery reveal a slightly elongated spheroid with a diameter of about 30 meters, a composition analogous to carbonaceous chondritic meteorites, and a rotation period of 10.7 minutes, which is an order of magnitude shorter than that measured for any other solar system object. The rotation is too rapid for 1998 KY26 to consist of multiple components bound together just by their mutual gravitational attraction. This monolithic object probably is a fragment derived from cratering or collisional destruction of a much larger asteroid.

The following paper examines planetary defense from the perspective of astronomy, which describe scientifically the global nature of the asteroid threat through direct sky observations, technology, which offers concrete solutions of asteroid deflections, international law, which studies within what legal frames planetary defense and asteroid mining is a feasible effort, and finally political science that explores the normative perception of the whole planetary defense endeavor. The aim of this article is to describe the dynamic between an overtly positivist threat formulation and normative implications of different ways of addressing the threat. Beside planetary defense efforts, it is crucial to focus on industrial capacities useful for asteroid mining because that would lead to a loud voice on international level in discussing future space mining regime. From the theoretical point of view, the topics are interlinked via the cosmopolitan theory of international politics and Welsh School of Critical Security Studies. All these theoretical perspectives accentuate positive security, therefore, potential scientific and industrial capacities of the Czech Republic in the field of asteroid mining and planetary defense are portrayed as humanistic and globally responsible solutions to the asteroid threat. Finally, we argue that proper identification of local research and industrial capacities are not necessarily only useful for scientific and economical interests of a small state but can be used as a foreign policy leverage to prevent super power from usurping the global debate.