We have analyzed MAVEN observations of fields and plasma signatures associated with an encounter of fully-developed Kelvin-Helmholtz (K-H) vortices at the northern polar terminator along the martian induced magnetosphere boundary. The signatures of the K-H vortices event are: (i) quasi-periodic, “bipolar-like” sawtooth magnetic field perturbations, (ii) corresponding density decrease, (iii) tailward enhancement of plasma velocity for both protons and heavy ions, (iv) co-existence of magnetosheath and planetary plasma in the region prior to the sawtooth magnetic field signature (i.e. mixing region of the vortex structure), and (v) pressure enhancement (minimum) at the edge (center) of the sawtooth magnetic field signature. Our results strongly support the scenario for the non-linear growth of K-H instability along Mars’ induced magnetosphere boundary, where a plasma flow difference between the magnetosheath and induced-magnetospheric plasma is expected. Our findings are also in good agreement with 3-dimensional magnetohydrodynamics (MHD) simulation results. MAVEN observations of protons with energies greater than 10 keV and results from the Walén analyses suggests the possibility of particle energization within the mixing region of the K-H vortex structure via magnetic reconnection, secondary instabilities or other turbulent processes. We estimated the lower limit on the K-H instability linear growth rate to be ~5.84 x 10^-3 s^-1. For these vortices, we estimated the instantaneous atmospheric ion escape flux due to the detachment of plasma clouds during the late non-linear stage of K-H instability to be ~5.90 x 10²⁶ particles/s. Extrapolation of loss rates integrated across time and space will require further work.

Using Mars Atmosphere and Volatile EvolutioN (MAVEN) observations from 2014-2019, we characterize how the structure and composition of the nightside ionosphere varies on solar cycle and seasonal timescales. At fixed altitudes between 150-200 km, plasma densities vary substantially on these timescales in response to variations in fixed thermospheric pressure levels, which cause the ionosphere to rise and fall in altitude. Additionally, solar cycle and seasonal trends in the electron impact ionization (EII) rate affects nightside densities; higher densities are observed near solar maximum and Mars perihelion (when EII rates are largest), and lower densities are observed near solar minimum and Mars aphelion (when EII rates are smallest). Lastly, densities in the high-altitude (>200 km) nightside ionosphere vary significantly over the solar cycle: topside O⁺ densities vary by a factor of 50 and topside O₂⁺ densities vary by a factor of 40. Topside ion densities were relatively stable throughout the solar minimum of 2018-2019

Measurements of Energetic Neutral Atoms (ENAs) provide information about both the plasma and neutral environments along the line-of-sight for any ENA instrument, though the individual influences of the plasma and neutral components are convoluted due to the nature of the charge-exchange ENA generation process. We combine ion flux and magnetic field measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter at Mars with models for the Martian exospheric components to estimate the average observable oxygen and hydrogen ENA distribution from various vantage points in the near-Mars space environment. By constraining the plasma environment in this manner, the neutral component can be deconvoluted from past or future ENA measurements, enabling suitably equipped orbiters to probe the Martian exosphere.

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 will host a community-wide workshop in June 2021 centered around this topic, and is seeking to grow their interactions with interested scientists from relevant disciplines.

While the two unmagnetized planets Venus and Mars have many similarities regarding the solar wind-atmosphere interactions, they vary in mass, size, and atmosphere density and temperature. In addition, Mars has localized crustal magnetic fields. Venus is closer to the Sun, where the solar radiation, solar wind, and interplanetary magnetic field (IMF) are all stronger. It is not well understood yet how the different upstream conditions and the different intrinsic characteristics separately affect the two planets' respective induced magnetospheres. To answer this question, we analyze the ion and magnetic field data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission and the ESA Venus Express (VEX) mission to study the plasma environments and ion escape at Mars and Venus. We first examine the upstream solar wind and IMF measurements from MAVEN and VEX to select data under similar upstream conditions at the two planets. With these selected data, we will examine the spatial distributions of magnetic field, solar wind plasma, and planetary ions, and identity the plasma boundaries at the two planets. The induced magnetosphere morphology, different ion escape channels, and ion loss rates will be compared between the two planets under similar solar wind conditions. These comparisons will help us to better distinguish between the effects of external drivers and planets’ intrinsic characteristics on the formation of induced magnetospheres and ion loss from unmagnetized planets.

The induced magnetosphere and magnetotails on Mars and Venus are considered to arise through the interplanetary magnetic field (IMF) draping around the planet and the solar wind deceleration due to the mass loading effect. Thus, the induced magnetosphere morphology should be controlled by the IMF’s direction. However, the large-scale magnetic fields observed over the north polar region on Venus have a bias in the dawnward direction and seemingly unresponsive to the IMF's direction. Based on the long-term observations of VEX and PVO, and a joint observation of VEX and Messenger, we show that the induced magnetosphere contains a second type of global magnetic field and the large-scale dawnward fields are only a part of it. This global field, referring to as a looping field, has a shape of a cylindrical shell around the magnetotail and a direction of counterclockwise looking from the tail toward the planet. The same global looping field has also been found on Mars with MAVEN observation; therefore, this type of global looping field is a common feature of unmagnetized planetary bodies with ionospheres and it should also exist on Titan and near-Sun comets. The comparison of the looping fields on Mars and Venus shows that the looping field is stronger on Mars. The solar wind azimuthal flows around the magnetotail towards the -E magnetotail polar region are observed by MAVEN. We illustrate that the looping field can be formed by bending the draped field lines with these azimuthal flows and that these azimuthal flows are associated with heavy ion plumes along the +E direction that are expected to be stronger on Mars than Venus. The current system associated with the looping field and its possible connection with the nightside ionosphere formations and ion escapes on Mars and Venus are discussed.

The ESA-JAXA joint mission BepiColombo is now on the track to Mercury. After the successful launch of the two spacecraft for BepiColombo, Mio (Mercury Magnetospheric Orbiter: MMO) and Mercury Planetary Orbiter (MPO), commissioning operations of the spacecraft and their science payloads were completed. BepiColombo will arrive at Mercury in the end of 2025 after 7-years cruise. The long cruise phase also includes 9 planetary flybys: once at the Earth, twice at Venus, and 6 times at Mercury. Even during the interplanetary cruise phase, the BepiColombo mission can contribute to the heliospheric physics and planetary space weather in the inner solar system. In addition, NASA’s Parker Solar Probe was launched in 2018 and it is orbiting around Sun (~0.05 AU at perihelion). ESA’s Solar Orbiter was launched in February 2020 and will have a highly elliptic orbit between 1.2 AU at aphelion and 0.28AU at perihelion. These multi spacecraft observations provide us great opportunities to investigate the inner heliosphere. The Earth flyby and the first Venus flyby were successfully completed on 10 April 2020 and on 15 October 2020, respectively. Planetary flybys are great opportunities not only for scientific motivation but also for instrument calibrations. Especially ion sensors onboard MPO (SERENA/MIPA and PICAM) and Mio (MPPE/MIA and MSA) can detect ions only during the planetary flybys because of constraints on spacecraft attitude and field of views. During the two flybys in 2020 science observations are performed and plasma instruments successfully measured both the Earth’s magnetosphere and Venus’s induced magnetosphere. The second Venus flyby and the first Mercury flyby will happen on 10 August 2021 and on 1 October 2021, respectively. Here we present the updated status of BepiColombo mission, initial results of the science observations during the interplanetary cruise and planetary flybys, and the upcoming observation plans.

We examine the effects of solar wind dynamic pressure and Alfven Mach number on the solar wind plasma interaction with the magnetosphere and surface of Mercury. We use the Amitis model, a three-dimensional GPU-based hybrid-kinetic model of plasma (particle ions and fluid electrons). We use a wide range of solar wind dynamic pressure (~5-50 nPa) and Alfven Mach numbers (~1-10) to investigate the effect of different plasma environment on the shape and structure of the magnetosphere. Our main objective is to characterize the plasma condition that results in disappearance of the dayside magnetopause. We also use our model to predict plasma and magnetic field observations by ESA's/JAXA's mission BepiColombo during its Mercury flybys.