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The transit method of exoplanet discovery and characterization has enabled numerous breakthroughs in exoplanetary science. These include measurements of planetary radii, mass-radius relationships, stellar obliquities, bulk density constraints on interior models, and transmission spectroscopy as a means to study planetary atmospheres. The Transiting Exoplanet Survey Satellite (TESS) has added to the exoplanet inventory by observing a significant fraction of the celestial sphere, including many stars already known to host exoplanets. Here we describe the science extraction from TESS observations of known exoplanet hosts during the primary mission. These include transit detection of known exoplanets, discovery of additional exoplanets, detection of phase signatures and secondary eclipses, transit ephemeris refinement, and asteroseismology as a means to improve stellar and planetary parameters. We provide the statistics of TESS known host observations during Cycle 1 and 2, and present several examples of TESS photometry for known host stars observed with a long baseline. We outline the major discoveries from observations of known hosts during the primary mission. Finally, we describe the case for further observations of known exoplanet hosts during the TESS extended mission and the expected science yield.

Venus is Earth’s twin in size and radiogenic heat budget, yet it remains unclear how Venus loses its heat absent plate tectonics. Most Venusian stagnant-lid models predict a thick lithosphere with heat flow about half that of Earth’s mobile-lid regime. Here we estimate elastic lithospheric thickness at 75 locations on Venus using topographic flexure at 65 coronae—quasi-circular volcano-tectonic features—determined from Magellan altimetry data. We find an average thickness at coronae of 11 ± 7 km. This implies an average heat flow of 78 ± 69 mW m−2, higher than Earth’ s average but similar to terrestrial values in actively extending areas. For some locations, such as the Parga Chasma rift zone, we estimate average heat flow exceeding 75 mW m−2. Combined with a low-resolution map of global elastic thickness, this suggests that coronae typically form on thin lithosphere, instead of locally thinning the lithosphere via plume heating, and that most regions of low elastic thickness are best explained by high heat flow rather than crustal compensation. Our analysis identifies likely areas of active extension and suggests that Venus has Earth-like lithospheric thickness and global heat flow ranges. Together with the planet’s geologic history, our findings support a squishy-lid convective regime that relies on plumes, intrusive magmatism and delamination to increase heat flow.An analysis of elastic lithospheric thickness suggests most coronae on Venus form on thin lithosphere with heat flow similar to that of rift zones on Earth, supporting a planet with active rifting and a squishy-lid convective regime.

Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins.

Venus is the most physically similar planet to Earth in the solar system as it is only 5% smaller than Earth, while having 20% less mass. The current surface conditions on Venus are dramatically different than Earth, however climate simulations have shown that Venus may have been able to sustain a temperate climate and surface ocean in its past. While the possibility of an extended habitable period in Venus' history is exciting, it is also alarming since the science community has been unable to reach a consensus on the factors which may have led to Venus' fall from grace. In hopes to uncover the mysteries of Venus' past, an international fleet of orbiters and descent probes will be sent to Venus in the coming decades. These missions will work to constrain Venus' history of water loss and understand the level of past and present geological activity on its surface. In addition to in-situ measurements, we can attempt to learn about the commonality of Venus-like evolutions by studying the plethora of exoplanets discovered in the last few decades. The work presented within this dissertation lays out the groundwork for future observations of exoVenuses with JWST and HWO by documenting known terrestrial planets within the VZ, highlighting those which are optimal targets for JWST, investigating pathways for confidently identifying exoVenuses, and predicting the efficiency at which JWST and HWO can make spectroscopic observations. These topics are discussed throughout the four chapters of this dissertation which are as follows. Chapter 1 is a preliminary study that was conducted in the early phases of the TESS mission to estimate the number of exoVenuses that TESS would discover throughout its primary mission. Chapter 2 is a follow-up study of Chapter 1 which catalogs all of the known exoVenuses and conducts a demographic analysis of known exoVenuses which includes distributions of various planetary, orbital, and stellar parameters. The exoVenuses which should be prioritized for JWST observations are highlighted based on their observability and similarity to Venus. We also evaluate the exoVenuses which do not transit their host star and discuss the potential of directly imaging exoVenuses in the future. Chapter 3 investigates the similarities between exoVenus and exoEarth transmission spectra and identifies pathways by which the two planet types can be differentiated. In addition, JWST observations are simulated for both exoVenuses and exoEarths in order to estimate the observation time needed to detect atmospheric species which can be used to discern the two planets. Lastly, Chapter 4 is focused on identifying ways of determining that an exoEarth is volcanically active through HWO direct imaging observations, and predicting the ability of HWO to detect molecular features in an exoEarth reflectance spectrum. Although this study is not particularly focused on exoVenuses, knowing how to identify active volcanism on exoplanets is applicable to exoVenuses as Venus is predicted to have an abundance of volcanic activity in its history. The main conclusions of the dissertation and potential future work are summarized in Chapter 6.

In this work we discuss various selected mission concepts addressing Venus evolution through time. More specifically, we address investigations and payload instrument concepts supporting scientific goals and open questions presented in the companion articles of this volume. Also included are their related investigations (observations & modeling) and discussion of which measurements and future data products are needed to better constrain Venus’ atmosphere, climate, surface, interior and habitability evolution through time. A new fleet of Venus missions has been selected, and new mission concepts will continue to be considered for future selections. Missions under development include radar-equipped ESA-led EnVision M5 orbiter mission (European Space Agency 2021 ), NASA-JPL’s VERITAS orbiter mission (Smrekar et al. 2022a ), NASA-GSFC’s DAVINCI entry probe/flyby mission (Garvin et al. 2022a ). The data acquired with the VERITAS, DAVINCI, and EnVision from the end of this decade will fundamentally improve our understanding of the planet’s long term history, current activity and evolutionary path. We further describe future mission concepts and measurements beyond the current framework of selected missions, as well as the synergies between these mission concepts, ground-based and space-based observatories and facilities, laboratory measurements, and future algorithmic or modeling activities that pave the way for the development of a Venus program that extends into the 2040s (Wilson et al. 2022 ).

Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins.

Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins.

The transit method is biased toward short orbital period planets that are interior to their host star's Habitable Zone (HZ). These planets are particularly interesting from the perspective of exploring runaway greenhouse scenarios and the possibility of potential Venus analogs. Here, we conduct an analysis of predicted TESS planet yield estimates produced by Huang et al. (2018), as well as the TESS Object of Interest (TOI) list resulting from the observations of sectors 1 - 13 during Cycle 1 of the TESS primary mission. In our analysis we consider potential terrestrial planets that lie within their host star's Venus Zone (Kane et al. 2014). These requirements are then applied to a predicted planetary yield from the TESS primary mission (Huang et al. 2018) and the TOI list, which results in an estimated 259 Venus analogs by the end of the TESS primary mission, and 46 Venus analogs in the TOI list for sectors 1 - 13. We also calculate the estimated transmission spectroscopy signal-to-noise ratio (S/N) for Venus analogs from the predicted yield and TOI list if they were to be observed by the Near-Infrared Imager and Slitless Spectrograph (NIRISS) on the James Webb Space Telescope (JWST), as well as update the S/N cutoff values determined by Kempton et al. (2018). Our findings show that the best estimated Venus analogs and TOI Venus analogs with \\(R_{p} < 1.5 \\, R_\\odot\\) have an estimated transmission spectroscopy S/N \\(> 40\\) while planets with radii \\(2 \\, R_\\oplus < R_p < 4 \\, R_\\oplus\\) can achieve S/N \\(> 100\\)