A Multi‐Purpose Heliophysics L4 Mission

Abstract

The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 au from the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of the solar photosphere centered on W60, the Earth's nominal magnetic field connection to the Sun. Such a mission on its own would serve as a solar remote sensing observatory that would oversee the entire solar radiation hemisphere with significant relevance for protecting Moon and Mars explorers from radiation exposure. In combination with appropriately planned observatories at L1 and L5, the three spacecraft would provide 300° longitude coverage of photospheric magnetic field structure, and allow continuous viewing of both solar poles, with >3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun with a 7.2° inclination out of the heliographic equator, 14.5° out of the ecliptic plane. We discuss the impact of extending solar magnetic field observations in both longitude and latitude to improve global solar wind modeling and, with the development of local helioseismology, the potential for long-term solar activity forecasting. Such a mission would provide a unique opportunity for interplanetary and interstellar dust science. It would significantly add to reliability of operational observations on fast coronal mass ejections directed at Earth and for human Mars explorers on their round-trip journey. The L4 mission concept is technically feasible, and is scientifically compelling. Section 1: IntroductionSpace weather (SWx) forecasting is a complex problem, spanning vastly different regions of space and involving several scientific disciplines within and beyond Heliophysics. The main pillar that all SWx forecasts rely on is rapid availability of sets of observations of the Sun and inner heliosphere measured on the ground and on space platforms. Budgetary realism dictates the locations of observatories and their instrumentation to be chosen carefully so they address short-term needs and lead to long-term improvements.It is important to note that much of the underlying physics of space weather is not yet understood. This includes, to name just a subset of phenomena, the initiation of flares and coronal mass ejections, the acceleration of the solar wind and that of particles to high energies. At the time of writing, the Parker Accepted ArticleThis article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Solar Polar Flux Redistribution based on Observed Coronal Holes

“…Consequently, the polar field distributions in the models are determined entirely by the advection of lowlatitude fields towards the poles by (primarily) meridional circulation combined with the random emergence and motion of flux in the polar regions. This process yields average flux densities and evolution consistent with observations (see Figure 11 of Posner et al 2021), but the polar field distribution is unconstrained at any given time. This is particularly problematic because the prominent dipole field component, especially during solar minimum, is driven largely by the polar fields (Wang et al 2009).…”

“…A number of methods have been developed to fill the polar magnetic field directly from lower-latitude observations (e.g., Sun et al 2011;Linker et al 2013Linker et al , 2017Sun 2018;Mikić et al 2018) and it is also possible to estimate the polar magnetic fields with flux transport models (Worden & Harvey 2000;Schrijver & Derosa 2003;Upton & Hathaway 2014). In particular, the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model (Arge et al 2010(Arge et al , 2011Hickmann et al 2015) creates an ensemble of realizations of the photospheric field, each with a unique representation of the polar fields, estimating the uncertainty due to the lack of direct observations (e.g., see Figure 11 in Posner et al 2021).…”

Understanding the Origins of Problem Geomagnetic Storms Associated with “Stealth” Coronal Mass Ejections

“…In addition, these are science missions not dedicated to space weather operations, and most data are made available only with significant delays. For space weather monitoring, a solution would be to develop a network of observatories, starting with missions to the L5 or L4 Lagrange points (Vourlidas 2015;Posner et al 2021;Bemporad 2021) that could monitor CMEs travelling towards Earth. More ambitious plans to improve space weather predictions might include placing satellites at L3 to monitor the far side of the Sun, and placement in high-inclination (polar) orbits to monitor CMEs emitted from all solar longitudes-the benefits of solar observations from "unconventional" viewpoints were reviewed by Gibson et al (2018).…”

CMEs and SEPs During November–December 2020: A Challenge for Real‐Time Space Weather Forecasting

“…By then, the advantages of remote‐sensing observations of the Sun from two well‐separated viewpoints will be lost at least for a while (we note that SolO is equipped with a coronagraph and a heliospheric imager, but its rapidly changing heliocentric distance and longitudinal separation with Earth may not be optimal for forecasting purposes). Dedicated missions to the Lagrange L4 and/or L5 points (e.g., Bemporad, 2021; Posner et al., 2021; Vourlidas, 2015) may prove beneficial in this regard. This includes the European Space Agency's (ESA) Vigil (Pulkkinen et al., 2019) mission, which is currently in development to place a spacecraft equipped with remote‐sensing and in situ instruments at L5.…”