The Space-Based Time-Domain Revolution in Astrophysics

TL;DR

Space-based time-domain photometry from Kepler/K2 and TESS has unlocked uninterrupted, high-precision light curves for millions of stars, transforming fields from asteroseismology and convection studies to exoplanet demographics, galactic archaeology, and extragalactic transients. By detailing fundamental mission parameters, target-selection strategies, and the broad physics enabled by continuous monitoring, the paper highlights breakthroughs in stellar interiors, rotation and activity, flare statistics, and binary evolution, as well as the demographics of dark compact objects. It also emphasizes the synergistic gains from open data and citizen science, and surveys the upcoming missions (PLATO, Roman, Earth 2.0) that will extend baselines, broaden wavelength coverage, and further empower global participation. The work argues that open, time-domain space missions offer unparalleled scientific productivity per cost and should remain central to the future of astronomy, given their transformative impact across multiple domains.

Abstract

Space-based time-domain telescopes such as CoRoT, Kepler/K2 and TESS have profoundly impacted astrophysics over the past two decades. Continuous light curves with high cadence and high photometric precision are now available for millions of sources within our galaxy and beyond. In addition to revolutionizing exoplanet science, the data have enabled breakthroughs ranging from the solar system to stellar interiors, the transient universe, and active galaxies. The key summary points of this review are: (1) Stellar astrophysics has been transformed by the ability to probe the internal structures of stars, test the physics of stellar convection, connect stellar rotation and magnetic activity, and reveal complex variability in young stars. (2) Ages of stellar populations probe the formation history of our Milky Way, and binary star variability enables the detection of "dark" galactic populations such as solar-mass black holes and neutron stars. (3) Early-time observations of explosive transients provide new insights into the progenitors of supernovae, while the quasi-periodic variability of galaxies probes the physics of accretion processes onto supermassive black holes and the tidal disruption of stars. (4) Observations of solar system objects reveal asteroid compositions through their rotation periods and amplitudes, constrain the cloud structure of ice giants, and allow the discovery of new objects in the outer solar system. (5) Open data policies and software have contributed to remarkable scientific productivity and enabled discoveries by citizen scientists, including new exoplanets and exotic variability in mature Sun-like stars.

Figures (11)

• Figure 1: The number of stars with precise, continuous space-based light curves has increased by four orders of magnitude in the past 20 years. Approximate number of stars observed with precisions of $<$1 mmag per hour as a function of year of launch of space-based missions. Symbol areas scale with the typical time baseline of continuous observations. Dashed circles for TESS and PLATO denote the typical longest continuous observations. Color coding shows the wavelength of the central bandpass. BRITE Constellation is the only mission which observed with multiple bandpasses (CoRoT used a prism to obtain spectral information for exoplanet targets). See Table \ref{['tab:space_telescopes']} for details on yield estimates.
• Figure 3: The evolution of target selection for space-based photometry missions. Gaia color versus absolute magnitude for stars observed by space-based time-domain mission. Color-coding shows the logarithmic number density in each bin. WIRE, MOST and BRITE distributions are approximated by stars with $G < 6$, and TESS distribution with $G < 12$. The Kepler and K2 panels use actual target lists. Values are not corrected for reddening.
• Figure 4: Stars with detected solar-like oscillations as a function of distance. Following ground-based RV campaigns ($\approx$ 20 stars), CoRoT yielded the first high-quality detections from space ($\approx$ 10 stars). Kepler enabled $\approx$ 700 detections, but mostly in faint and distant stars. The K2 ($\approx$ 200 detections) and TESS ($\approx$ 900 detections) missions have bridged the gap to nearby stars, for which asteroseismology can be combined with complementary methods. Catalog detections are taken from sayeed_homogeneous_2025 (Kepler), lund_k2_2024 (K2), hatt_catalogue_2023 and lund_luminaries_2025 (TESS).
• Figure 5: Space-based telescopes revealed that the time-domain variability due to stellar granulation and oscillations are closely linked. Correlation between surface gravities measured through asteroseismology and the autocorrelation of light curves for stars observed by Kepler. Figure reproduced from kallinger_precise_2016.
• Figure 6: Space-based time-domain photometry has revolutionized our understanding of stellar flares. Left, reproduced from maehara_statistical_2015: Kepler light curve of a main-sequence G-type star showing a superflare. The bottom panel shows a zoom-in on the flare. Right, reproduced from feinstein_testing_2022: Flare rates across the H-R diagram derived from TESS light curves.