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The Moon is important to us. It has played a major role in the evolution of our planet, most obviously by causing a reduction of the rotation rate of the Earth through tidal friction. It is even possible that the Moon and hence the tides could have provided one mechanism for the origin of life on Earth through the repeated flooding and drying out under the Sun of primitive organisms in inter-tidal pools [1], [2]. In addition, the Moon has been an important factor in the religions and cultures of many societies.

The determination of Jupiter’s even gravitational moments by the Juno spacecraft reveals that more than three thousand kilometres below the cloud tops, differential rotation is suppressed and the gas giant’s interior rotates as a solid body. Probing the depths of Jupiter The Juno mission set out to probe the hidden properties of Jupiter, such as its gravitational field, the depth of its atmospheric jets and its composition beneath the clouds. A collection of papers in this week's issue report some of the mission's key findings. Jupiter's gravitational field varies from pole to pole, but the cause of this asymmetry is unknown. Rotating planets that are squashed at the poles like Jupiter can have a gravity field that is characterized by a solid-body component, plus components that arise from motions in the atmosphere. Luciano Iess and colleagues use Juno's Doppler tracking data to determine Jupiter's gravity harmonics. They find that the north–south asymmetry arises from atmospheric and interior wind flows. To determine the depths of these flows, Yohai Kaspi and colleagues analyse the odd gravitational harmonics and find that the J 3 , J 5 , J 7 and J 9 harmonics are consistent with the jets extending deep into the atmosphere, perhaps as far as 3,000 kilometres. They conclude that the mass of Jupiter's dynamical atmosphere is about one per cent of Jupiter's total mass. The composition of Jupiter beneath its turbulent atmosphere remains a mystery. If different parts of a spinning object rotate at different rates, then the object probably has a fluid composition. Tristan Guillot and colleagues study the even gravitational harmonics and find that, below a depth of about 3,000 kilometres, Jupiter is rotating almost as a solid body. The atmospheric zonal flows extend downwards by more than 2,000 kilometres, but not beyond 3,500 kilometres, as is also the case with the jets. Jupiter’s atmosphere is rotating differentially, with zones and belts rotating at speeds that differ by up to 100 metres per second. Whether this is also true of the gas giant’s interior has been unknown 1 , 2 , limiting our ability to probe the structure and composition of the planet 3 , 4 . The discovery by the Juno spacecraft that Jupiter’s gravity field is north–south asymmetric 5 and the determination of its non-zero odd gravitational harmonics J 3 , J 5 , J 7 and J 9 demonstrates that the observed zonal cloud flow must persist to a depth of about 3,000 kilometres from the cloud tops 6 . Here we report an analysis of Jupiter’s even gravitational harmonics J 4 , J 6 , J 8 and J 10 as observed by Juno 5 and compared to the predictions of interior models. We find that the deep interior of the planet rotates nearly as a rigid body, with differential rotation decreasing by at least an order of magnitude compared to the atmosphere. Moreover, we find that the atmospheric zonal flow extends to more than 2,000 kilometres and to less than 3,500 kilometres, making it fully consistent with the constraints obtained independently from the odd gravitational harmonics. This depth corresponds to the point at which the electric conductivity becomes large and magnetic drag should suppress differential rotation 7 . Given that electric conductivity is dependent on planetary mass, we expect the outer, differentially rotating region to be at least three times deeper in Saturn and to be shallower in massive giant planets and brown dwarfs.

Improving the spatial resolution of remote sensing satellites has long been a challenge in the field of optical designing. Although the use of large-aperture reflective mirrors significantly improves the resolution of optical systems, controlling the film thickness uniformity remains an issue. The planetary rotation system (PRS) has received significant attention owing to the excellent uniformity of the coating applied to the large-aperture reflective mirror. However, the development of the PRS remains hindered by a lack of research on its properties and the design method of the shadow mask. To address this, we performed a theoretical analysis of the distribution of film thickness and uniformity in the PRS, which is impacted by parameters of geometric configuration in the vacuum chamber. We present a film thickness expression based on Knudsen’s law and the geometric configuration of the vacuum chamber that incorporates an additional shading function. Moreover, the variation of uniformity in the standard and counter PRSs was elucidated by changing the location of the evaporation source. Finally, a fixed-position shadow mask, which was obtained by theoretical design, allows the nonuniformity of the concave reflective mirror (with a 700 mm aperture) to reduce from 2.43% to 0.7%, highlighting the importance of initial shape design.

Ultrahot giant exoplanets receive thousands of times Earth’s insolation 1 , 2 . Their high-temperature atmospheres (greater than 2,000 kelvin) are ideal laboratories for studying extreme planetary climates and chemistry 3 – 5 . Daysides are predicted to be cloud-free, dominated by atomic species 6 and much hotter than nightsides 5 , 7 , 8 . Atoms are expected to recombine into molecules over the nightside 9 , resulting in different day and night chemistries. Although metallic elements and a large temperature contrast have been observed 10 – 14 , no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night (‘evening’) and night-to-day (‘morning’) terminators could, however, be revealed as an asymmetric absorption signature during transit 4 , 7 , 15 . Here we report the detection of an asymmetric atmospheric signature in the ultrahot exoplanet WASP-76b. We spectrally and temporally resolve this signature using a combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by −11 ± 0.7 kilometres per second on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside 16 . In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. We conclude that iron must therefore condense during its journey across the nightside. Absorption lines of iron in the dayside atmosphere of an ultrahot giant exoplanet disappear after travelling across the nightside, showing that the iron has condensed during its travel.

Potentially habitable planets can orbit close enough to their host star that the differential gravity across their diameters can produce an elongated shape. Frictional forces inside the planet prevent the bulges from aligning perfectly with the host star and result in torques that alter the planet’s rotational angular momentum. Eventually the tidal torques fix the rotation rate at a specific frequency, a process called tidal locking. Tidally locked planets on circular orbits will rotate synchronously, but those on eccentric orbits will either librate or rotate super-synchronously. Although these features of tidal theory are well known, a systematic survey of the rotational evolution of potentially habitable exoplanets using classic equilibrium tide theories has not been undertaken. I calculate how habitable planets evolve under two commonly used models and find, for example, that one model predicts that the Earth’s rotation rate would have synchronized after 4.5 Gyr if its initial rotation period was 3 days, it had no satellites, and it always maintained the modern Earth’s tidal properties. Lower mass stellar hosts will induce stronger tidal effects on potentially habitable planets, and tidal locking is possible for most planets in the habitable zones of GKM dwarf stars. For fast-rotating planets, both models predict eccentricity growth and that circularization can only occur once the rotational frequency is similar to the orbital frequency. The orbits of potentially habitable planets of very late M dwarfs ( ) are very likely to be circularized within 1 Gyr, and hence, those planets will be synchronous rotators. Proxima b is almost assuredly tidally locked, but its orbit may not have circularized yet, so the planet could be rotating super-synchronously today. The evolution of the isolated and potentially habitable Kepler planet candidates is computed and about half could be tidally locked. Finally, projected TESS planets are simulated over a wide range of assumptions, and the vast majority of potentially habitable cases are found to tidally lock within 1 Gyr. These results suggest that the process of tidal locking is a major factor in the evolution of most of the potentially habitable exoplanets to be discovered in the near future.

Rossby waves are a pervasive feature of the large-scale motions of the Earth’s atmosphere and oceans. These waves (also known as planetary waves and r-modes) also play an important role in the large-scale dynamics of different astrophysical objects such as the solar atmosphere and interior, astrophysical discs, rapidly rotating stars, planetary and exoplanetary atmospheres. This paper provides a review of theoretical and observational aspects of Rossby waves on different spatial and temporal scales in various astrophysical settings. The physical role played by Rossby-type waves and associated instabilities is discussed in the context of solar and stellar magnetic activity, angular momentum transport in astrophysical discs, planet formation, and other astrophysical processes. Possible directions of future research in theoretical and observational aspects of astrophysical Rossby waves are outlined.

Precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter is used to determine the planet’s gravity harmonics, showing north–south asymmetry caused by atmospheric and interior flows. Probing the depths of Jupiter The Juno mission set out to probe the hidden properties of Jupiter, such as its gravitational field, the depth of its atmospheric jets and its composition beneath the clouds. A collection of papers in this week's issue report some of the mission's key findings. Jupiter's gravitational field varies from pole to pole, but the cause of this asymmetry is unknown. Rotating planets that are squashed at the poles like Jupiter can have a gravity field that is characterized by a solid-body component, plus components that arise from motions in the atmosphere. Luciano Iess and colleagues use Juno's Doppler tracking data to determine Jupiter's gravity harmonics. They find that the north–south asymmetry arises from atmospheric and interior wind flows. To determine the depths of these flows, Yohai Kaspi and colleagues analyse the odd gravitational harmonics and find that the J 3 , J 5 , J 7 and J 9 harmonics are consistent with the jets extending deep into the atmosphere, perhaps as far as 3,000 kilometres. They conclude that the mass of Jupiter's dynamical atmosphere is about one per cent of Jupiter's total mass. The composition of Jupiter beneath its turbulent atmosphere remains a mystery. If different parts of a spinning object rotate at different rates, then the object probably has a fluid composition. Tristan Guillot and colleagues study the even gravitational harmonics and find that, below a depth of about 3,000 kilometres, Jupiter is rotating almost as a solid body. The atmospheric zonal flows extend downwards by more than 2,000 kilometres, but not beyond 3,500 kilometres, as is also the case with the jets. The gravity harmonics of a fluid, rotating planet can be decomposed into static components arising from solid-body rotation and dynamic components arising from flows. In the absence of internal dynamics, the gravity field is axially and hemispherically symmetric and is dominated by even zonal gravity harmonics J 2 n that are approximately proportional to q n , where q is the ratio between centrifugal acceleration and gravity at the planet’s equator 1 . Any asymmetry in the gravity field is attributed to differential rotation and deep atmospheric flows. The odd harmonics, J 3 , J 5 , J 7 , J 9 and higher, are a measure of the depth of the winds in the different zones of the atmosphere 2 , 3 . Here we report measurements of Jupiter’s gravity harmonics (both even and odd) through precise Doppler tracking of the Juno spacecraft in its polar orbit around Jupiter. We find a north–south asymmetry, which is a signature of atmospheric and interior flows. Analysis of the harmonics, described in two accompanying papers 4 , 5 , provides the vertical profile of the winds and precise constraints for the depth of Jupiter’s dynamical atmosphere.

From its pole-to-pole orbit, the Juno spacecraft discovered arrays of cyclonic vortices in polygonal patterns around the poles of Jupiter. In the north, there are eight vortices around a central vortex, and in the south there are five. The patterns and the individual vortices that define them have been stable since August 2016. The azimuthal velocity profile vs. radius has been measured, but vertical structure is unknown. Here, we ask, what repulsive mechanism prevents the vortices from merging, given that cyclones drift poleward in atmospheres of rotating planets like Earth? What atmospheric properties distinguish Jupiter from Saturn, which has only one cyclone at each pole? We model the vortices using the shallow water equations, which describe a single layer of fluid that moves horizontally and has a free surface that moves up and down in response to fluid convergence and divergence. We find that the stability of the pattern depends mostly on shielding—an anticyclonic ring around each cyclone, but also on the depth. Too little shielding and small depth lead to merging and loss of the polygonal pattern. Too much shielding causes the cyclonic and anticyclonic parts of the vortices to fly apart. The stable polygons exist in between. Why Jupiter’s vortices occupy this middle range is unknown. The budget—how the vortices appear and disappear—is also unknown, since no changes, except for an intruder that visited the south pole briefly, have occurred at either pole since Juno arrived at Jupiter in 2016.

In the manufacture of small-sized parts, the finishing of the internal channels of a complex cross-section with a coating is particularly difficult. To solve this problem, it is proposed to use centrifugal processing with steel balls in containers with planetary rotation. The paper presents the results of computer simulation of the contact interaction of balls with the surface of the part channel. These data made it possible to establish that at certain velocities and directions of the flight vector at the moment of contact, the balls allow you to remove the micro-roughness of the coating without violating the integrity of the part base. The simulation results formed the basis for the design of an industrial installation and the assignment of centrifugal-planetary processing modes. The proven technology of finishing the internal channels of small-sized details provided a reduction in the proportion of damaged parts by 4...4.3 times relative to the basic technological process.

The Martian magnetotail is largely controlled by the solar wind (SW) and is modulated by variations in the upstream drivers. However, due to the limitations of single‐spacecraft observations, the effects of SW variations on the Martian magnetotail have not been fully understood so far. Here, using Tianwen‐1 and MAVEN data, we report for the first time the rapid response of Martian magnetotail to the SW disturbance. In our study, Tianwen‐1 detected the flapping of Martian magnetotail, while MAVEN monitored disturbances in the upstream SW. The results indicate that a 20% increase (or decrease) in SW dynamic pressure and a 30° (or 50°) rotation of interplanetary magnetic field clock angle could cause the Martian magnetotail to swing rapidly. These two SW disturbances could lead to oscillations of the Martian magnetotail. This study reveals the importance of joint observations for studying the interaction between the SW and Mars. Plain Language Summary Mars lacks an intrinsic global magnetic field and as a result solar wind (SW) interacts directly with its ionosphere and atmosphere, leading to a high dependence of the Martian induced magnetosphere on SW conditions. Understanding the interaction between the SW and Mars can provide critical information for studies of planetary evolution, especially the effect of the SW on the Martian magnetotail. In previous studies, using single satellite observations, we limit ourselves to studying some local physical processes or statistical properties. Here, based on the joint measurements by Tianwen‐1 and MAVEN, we observed the rapid response of Martian magnetotail to the SW disturbance, finding that a 20% increase (or decrease) in SW dynamic pressure and a 30° (or 50°) rotation of IMF clock angle could cause the Martian magnetotail to swing rapidly. These two SW disturbances could lead to oscillations of the Martian magnetotail. These results can help us understand the SW interaction with the Martian induced magnetosphere. Key Points We report for the first time the rapid response of Martian magnetotail to the solar wind (SW) disturbance by using Tianwen‐1 and MAVEN data A 20% increase (or decrease) in PSW and a 30° (or 50°) rotation of interplanetary magnetic field clock angle could cause the Martian magnetotail to swing These two SW disturbances could lead to oscillations of the Martian magnetotail