Gaia is a satellite mission of the European Space Agency which is creating a catalogue of extremely accurate positions, distances and space motions of two billion stars in our Galaxy, along with more than one hundred thousand solar system asteroids, and several million distant quasars, all on the same extragalactic reference system. Complementary information on each object's multi-epoch photometry and spectra provides a vast and unprecedented data base of (model-dependent) fundamental physical quantities, such as each star's mass, age, and chemical composition. I outline the field's historical context, and explain the key principles involved in these space measurements. This is followed by a broad review of the many areas of solar system science, stellar structure and evolution, and topics in Galactic structure, evolution, and dynamics, that are being derived from these data.

I provide a synopsis of many of the scientific advances made by Gaia, through to the end of 2023,

Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency. JASMINE has two main science goals. One is the Galactic archaeology with Galactic Center Survey, which aims to reveal the Milky Way's central core structure and formation history from Gaia-level (~25 $\mu$as) astrometry in the Near-Infrared (NIR) Hw-band (1.0-1.6 $\mu$m). The other is the Exoplanet Survey, which aims to discover transiting Earth-like exoplanets in the habitable zone from NIR time-series photometry of M dwarfs when the Galactic center is not accessible. We introduce the mission, review many science objectives, and present the instrument concept. JASMINE will be the first dedicated NIR astrometry space mission and provide precise astrometric information of the stars in the Galactic center, taking advantage of the significantly lower extinction in the NIR. The precise astrometry is obtained by taking many short-exposure images. Hence, the JASMINE Galactic center survey data will be valuable for studies of exoplanet transits, asteroseismology, variable stars and microlensing studies, including discovery of (intermediate mass) black holes. We highlight a swath of such potential science, and also describe synergies with other missions.

Astrometry, the measurement of accurate star positions and motions, was first carried out from space by the European Space Agency's Hipparcos mission in the 1990s. Today, it is undergoing a particularly dramatic advance with ESA's ongoing Gaia mission, launched in 2013. I explain why star positions are of such importance in astronomy, and outline the 2000-year history of the field. This illustrates the profound scientific insights that have been gained over the past centuries as measurement accuracies have advanced, as well as the technical and computational challenges involved. I explain the reasons why measurements from space became necessary in order to advance the field, and outline the measurement principles underpinning these two space mission. I conclude with a summary of the contents of the latest Gaia catalogue release, list some of the scientific highlights that have been revealed by Gaia so far and, in the process, demonstrate how these measurements are revolutionising our understanding of the origin, structure, and evolution of our Galaxy.

The Gaia space astrometry mission is measuring accurate distances and space motions of more than two billion stars throughout our galaxy and beyond. This is a first look at how Gaia is contributing to fundamental physics, and in particular to our understanding of dark matter, for which a few examples are given from the current literature. One of our goals is to illustrate how deep and often surprising insight into very diverse areas of fundamental physics can be extracted from this new and enormous high-accuracy stellar data set. In this spirit, we finish by suggesting a search for a connection between stellar activity, dark matter streams, and planetary configuration in nearby exoplanetary systems, as has been tentatively proposed in the case of the solar system. Dark matter candidates that could be probed by such a test include anti-quark nuggets, which have also been postulated as a possible explanation of the anomalous heating of the solar corona, and of the matter–antimatter asymmetry in the universe.

Context. Teegarden's Star is the brightest and one of the nearest ultra-cool dwarfs in the solar neighbourhood. For its late spectral type (M7.0 V), the star shows relatively little activity and is a prime target for near-infrared radial velocity surveys such as CARMENES. Aims. As part of the CARMENES search for exoplanets around M dwarfs, we obtained more than 200 radial-velocity measurements of Teegarden's Star and analysed them for planetary signals. Methods. We find periodic variability in the radial velocities of Teegarden's Star. We also studied photometric measurements to rule out stellar brightness variations mimicking planetary signals. Results. We find evidence for two planet candidates, each with 1.1 M-circle plus minimum mass, orbiting at periods of 4.91 and 11.4 d, respectively. No evidence for planetary transits could be found in archival and follow-up photometry. Small photometric variability is suggestive of slow rotation and old age. Conclusions. The two planets are among the lowest-mass planets discovered so far, and they are the first Earth-mass planets around an ultra-cool dwarf for which the masses have been determined using radial velocities.

Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.

The CARMENES radial velocity (RV) survey is observing 324 M dwarfs to search for any orbiting planets. In this paper, we present the survey sample by publishing one CARMENES spectrum for each M dwarf. These spectra cover the wavelength range 520--1710nm at a resolution of at least $R > 80,000$, and we measure its RV, H$\alpha$ emission, and projected rotation velocity. We present an atlas of high-resolution M-dwarf spectra and compare the spectra to atmospheric models. To quantify the RV precision that can be achieved in low-mass stars over the CARMENES wavelength range, we analyze our empirical information on the RV precision from more than 6500 observations. We compare our high-resolution M-dwarf spectra to atmospheric models where we determine the spectroscopic RV information content, $Q$, and signal-to-noise ratio. We find that for all M-type dwarfs, the highest RV precision can be reached in the wavelength range 700--900nm. Observations at longer wavelengths are equally precise only at the very latest spectral types (M8 and M9). We demonstrate that in this spectroscopic range, the large amount of absorption features compensates for the intrinsic faintness of an M7 star. To reach an RV precision of 1ms$^{-1}$ in very low mass M dwarfs at longer wavelengths likely requires the use of a 10m class telescope. For spectral types M6 and earlier, the combination of a red visual and a near-infrared spectrograph is ideal to search for low-mass planets and to distinguish between planets and stellar variability. At a 4m class telescope, an instrument like CARMENES has the potential to push the RV precision well below the typical jitter level of 3-4ms$^{-1}$.

ASIGNIFICANT ADVANCE IN THE KNOWLEDGE of exoplanet interiors and atmospheres was made possible with the discovery of transiting exoplanets. Densities derived from their masses and radii are providing some indications of their interior structure and composition, while optical and infrared transit and eclipse spectroscopy are yielding the first insights into the atmospheric composition, atmospheric dynamics, and thermal transport processes of hot Jupiters. All of this has been substantially facilitated by the knowledge of interiors and atmospheres of the solar system planets and satellites acquired over the last half century. The insights that can be expected from improved photometric or spectroscopic measurements, for example, with JWST due for launch in 2020, are substantial. For planets inferred to be in the ‘habitable zone’ of their host star, where liquid water is expected to be supported, diagnostics can hope to identify detailed atmospheric compositions, including signatures that may be attributable to primitive or more advanced life forms. These advances are providing a new impetus to searches for life, and even for intelligent life, and the grand question of whether life is extremely common, or extremely rare, elsewhere in the Universe. Introduction Physical models of exoplanets span two extreme classes of object, and potentially much in between: the lowmass high-density ‘solid’ planets dominated by metallic cores and silicate-rich and/or ice-rich mantles, and the high-mass low-density gas giants dominated by their massive accreted H/He envelopes. For the gas-rich giants, models of their interiors and models of their atmospheres are closely connected, and the most recent atmospheric models couple their emergent flux with their assembly by core accretion. Models of their interiors predict bulk properties such as the pressure–temperature relation, and their radii as a function of mass. For close-in, highly irradiated gas giants, the additional external heat source has a significant effect on the pressure–temperature structure of the outer atmosphere. Combined with inferences on their probable bulk chemical composition, atmospheric models also predict colours and spectral features arising from specific atomic and molecular species.

This paper presents the specification, design, and development of the Radial Velocity Spectrometer (RVS) on the European Space Agency’s Gaia mission. Starting with the rationale for the full six dimensions of phase space in the dynamical modelling of the Galaxy, the scientific goals and derived top-level instrument requirements are discussed, leading to a brief description of the initial concepts for the instrument. The main part of the paper is a description of the flight RVS, considering the optical design, the focal plane, the detection and acquisition chain, and the as-built performance drivers and critical technical areas. After presenting the pre-launch performance predictions, the paper concludes with the post-launch developments and mitigation strategies, together with a summary of the in-flight performance at the end of commissioning.

1. Introduction 2. Radial velocities 3. Astrometry 4. Timing 5. Microlensing 6. Transits 7. Imaging 8. Host stars 9. Brown dwarfs and free-floating planets 10. Formation and evolution 11. Interiors and atmospheres 12. The Solar System Appendixes References Index.