In order to determine the extent to which a global magnetic field is required for a planet to be habitable at its surface, expertise is required from diverse communities, some of which have diverged from each other over the past several decades. For example, modelers and observers of the terrestrial magnetosphere have limited overlap and interaction with modelers and observers of unmagnetized planets or the giant planets in our solar system. There is relatively limited interaction between any of the above communities and those who study exoplanets, though efforts are increasing to bridge the solar system and exoplanet communities. We describe a NASA Heliophysics DRIVE Science Center selected to answer the central question of this session: “Do Habitable Worlds Require Magnetic Fields”. This Center, named MACH (Magnetic Fields, Atmospheres, and the Connection to Habitability) includes scientists who study atmospheric escape from Earth, unmagnetized planets, and exoplanets. Over the next several years MACH will construct a framework that enables the evaluation of atmospheric loss from an arbitrary rocky planet, given information about the planet and its host star. The MACH Center hosted a community-wide workshop in June 2021 centered around this topic, and is seeking to grow their interactions with interested scientists from relevant disciplines.

Atmospheric escape occurs at planets everywhere, and influences the evolution of planetary atmospheres and surface habitability.We argue for developing a common understanding of atmospheric escape that accounts for different star and planet characteristics.This requires comprehensive measurements at multiple planets, new models that cover the entire parameter space, and interdisciplinary effort.

<p>Observations of clouds in planetary atmospheres can provide insight about atmospheric characteristics such as vertical temperature structure and dynamics. Clouds observed at the limb of a planet (from the perspective of the telescope or spacecraft observing them) can be particularly useful tools, in part because their height above the surface can be measured directly.</p> <p>The Emirates Mars Mission (EMM) has been recording visible light images of the Martian disk since early 2021, using the Emirates eXploration Imager (EXI). We present an analysis of limb clouds evident in EXI images taken using its red filter (centered on 635 nm) over the course of a Martian year. We present statistics on their height, thickness, spatial extent, and geographic and local time distribution – as well as correlations between these parameters. We place our results in context with previous work, and explore reasons for observed trends.</p>

Proton aurora at Mars are thought to form indirectly, as a result of solar wind proton charge exchange with planetary coronal hydrogen upstream of the bow shock. This charge exchange produces beamed energetic neutral atoms that bypass the induced magnetosphere and cause spatially uniform auroral emission when they collide with the thermosphere. Here we report multiple definitive observations of spatially localized "patchy" proton aurora at Mars using the Emirates Mars Ultraviolet Spectrometer on the Emirates Mars Mission, and characterize the plasma environment during these events using contemporaneous Mars Atmosphere and Volatile EvolutioN mission measurements. Multiple mechanisms are required to explain these observations, including at times the direct deposition of solar wind plasma into the thermosphere, particularly during radial interplanetary magnetic field conditions. Much future work will be needed to assess these mechanisms and understand the impact of these auroral events on Mars atmospheric evolution.

Motivation: Until recently, it had long been assumed that a global magnetic field will shield a planet’s atmosphere from being stripped away to space through interactions with the solar wind. Under this assumption, the shut-off of a global dynamo field at Mars contributed to the loss of significant atmosphere – enough to explain the evidence for liquid water on the surface long ago. Similarly, the lack of global magnetic field at Venus may have led to the loss of significant atmospheric oxygen over time. This assumption has been questioned in recent years, in part based on the similarity in ion escape rates between Venus, Earth, and Mars [1]. It has been instead proposed that the presence of a global magnetic field may even enhance atmospheric escape because the planet presents a larger electromagnetic cross-section to the solar wind than it would otherwise. Observational inter-planet comparisons, while valuable, are challenging to interpret because planets differ in many ways – Earth and Venus have different atmospheric compositions and rotation rates, for example. Global computer simulations using validated models can provide controlled experiments that isolate only the influence of a planetary magnetic field – but these models must be properly validated. Mars offers a unique opportunity to test the importance of a magnetic field in altering ion escape rates. This is because Mars possesses both magnetized and unmagnetized regions of the crust – allowing a relatively ‘controlled’ evaluation of the importance of magnetic fields in regulating ion escape in the limit of weak planetary magnetic fields. In this presentation we will review the evidence ‘for’ and ‘against’ magnetic fields playing an important role in atmospheric retention. We will then present results of observational and theoretical analyses ongoing in our group, with emphasis on global plasma modeling and on analysis of data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission.

Heliophysics is the system science of the physical connections between the Sun and the solar system. As the physics of the local cosmos, it embraces space weather and planetary habitability. The wider view of comparative heliophysics forms a template for conditions in exoplanetary systems and provides a view over time of the aging Sun and its magnetic activity, of the heliosphere in different settings of the interstellar medium and subject to stellar impacts, of the space physics over evolving planetary dynamos, and of the long-term influence on planetary atmospheres by stellar radiation and wind. Based on a series of NASA-funded summer schools for early-career researchers, this textbook is intended for students in physical sciences in later years of their university training and for beginning graduate students in fields of solar, stellar, (exo-)planetary, and planetary-system sciences. The book emphasizes universal processes from a perspective that draws attention to what provides Earth (and similar (exo-)planets) with a relatively stable setting in which life as we know it could thrive. The text includes 200 "Activities" in the form of exercises, explorations, literature readings, "what if" challenges, and group discussion topics; many of the Activities provide additional information complementing the main text. Solutions and discussions are included in an Appendix for a selection of the exercises.

The search for life on planets outside our solar system has largely been the province of the astrophysics community until recently. A major development since the NASA Astrobiology Strategy 2015 document (AS15) has been the integration of other NASA science disciplines (planetary science, heliophysics, Earth science) with ongoing exoplanet research in astrophysics. The NASA Nexus for Exoplanet System Science (NExSS) provides a forum for scientists to collaborate across disciplines to accelerate progress in the search for life elsewhere. Here we describe recent developments in these other disciplines, with a focus on exoplanet properties and environments, and the prospects for future progress that will be achieved by integrating emerging knowledge from astrophysics with insights from these fields.

The crustal remnant field on Mars rotates with the planet at a period of 24 h 37 min, constantly varying the magnetic field configuration interacting with the solar wind. Until now, there has been no self-consistent modeling investigation on how this varying magnetic field affects the solar wind plasma interaction. Here we include the rotation of this localized crustal field in a multispecies single-fluid MHD model of Mars and simulate an entire day of solar wind interaction under normal solar wind conditions. The MHD model results are compared with Mars Global Surveyor (MGS) magnetic field observations and show very close agreement, especially for the field strength along almost all of the 12 orbits on the day simulated. Model results also show that the ion escape rates slowly vary with rotation, generally anticorrelating with the strength of subsolar magnetic crustal sources, with some time delay. In addition, it is found that in the intense crustal field regions, the densities of heavy ion components enhance significantly along the MGS orbit, implying strong influence of the crustal field on the ionospheric structures.

The magnetic fields of the large terrestrial planets, Venus, Earth, and Mars, are all vastly different from each other. These differences can tell us a lot about the interior structure, interior history, and they can even give us clues to the atmospheric history of these planets. This paper highlights a classroom presentation and accompanying activity that focuses on the differences between the magnetic fields of Venus, Earth, and Mars, what these differences mean, and how we measure these differences. During the activity, students make magnetic field measurements and draw magnetic field lines of "mystery planets" using orbiting "spacecraft" (small compasses). Based on their observations, the students then determine whether they are orbiting Venus-like, Earth-like, or Mars-like planets. This activity is targeted to middle and high school audiences. However, we have also used a scaled-down version with elementary school audiences.

Since they are invisible to our eyes, planetary magnetic fields are difficult to visualize. However, we can learn much about a planet, its interior, and its history from studying its magnetic field. A challenge, then, is how can we effectively communicate the structure of planetary magnetic fields to the public, i.e., how can we help the public visualize planetary magnetic fields. An additional challenge is how can we effectively communicate the importance of studying planetary magnetic fields to the public, or why should they care. We address these challenges by developing a series of presentations about magnetic fields and their importance given on visually engaging spherical displays. We are also creating scientifically accurate three-dimensional models of planetary magnetic fields.

We have developed a presentation that investigates the differences in the atmospheres of Venus, Earth, and Mars, and how these differences arose. The target audience is elementary school age children. The presentation is a combination of planetary images displayed on engaging spherical displays and visual demonstrations. We recently tested and evaluated our preliminary presentation on the Lawrence Hall of Science's six-foot diameter Science on a Sphere.(TM) Our future plans include transferring this presentation onto a portable, table-top spherical display system to take into classrooms. We also plan to develop additional presentations targeting older age groups.