In mid-July, nearly 600 “martians” from more than 20 countries gathered at the Ninth International Conference on Mars (aka 9th Mars) to discuss the status and future of our exploration of the Red Planet. As in the past, the aim of this conference was to pull together the breadth of current Mars knowledge in order to identify current paradigms in our understanding of Mars evolution. Then, based on current understandings of Mars’ history, state, and processes, conference attendees were asked to look to the future and identify top science questions for the next decade of Mars exploration. 9th Mars was held at a particularly relevant time for gathering the international Mars community, as the 2020s will begin with multiple Mars missions from multiple space agencies, and yet few subsequent missions have been confirmed. This period will be considered by the next U.S. Planetary Science Decadal Survey, which will be a key input for NASA’s planetary science priorities in 2023–2032.

In the 9th Mars conference program, approximately 100 oral presentations were scheduled in two parallel sessions organized according to high-level science questions, and approximately 300 posters were divided into four poster sessions. Plenary presentations and panel discussions about the state of Mars science understanding and forward-looking plans such as Mars Sample Return and Human Exploration served as focal points for pulling the attendees back together into one group. Additionally, four integration teams (focused on Climate, Geology, Life, and Preparation for Human Exploration) were tasked with listening to all presentations in their respective topic areas to seek out high-priority, repeated, or connecting concepts. These designated “Integrators,” drawn from across disciplines and career levels, presented their results on the final day of the conference and gathered final input from attendees. Their Integration Reports, available on the conference website, will serve as inputs to discussions within the Mars Exploration Program Analysis Group (MEPAG) and, in particular, the ongoing MEPAG Goals revisions.

Key perspectives that emerged at the conference included the growing diversity and number of possibly habitable environments on Mars. Key elements for life have been detected in situ, and remote sensing shows increasing numbers of sites with evidence of past hydrothermal and other hydrologic activity. One sobering note was that surface dust and mineral properties can obscure the true abundance and distribution of key minerals (i.e., if seen from orbit, there is something there, but a lot is hidden), leading to the question, “How can the true diversity of Mars mineralogy be sampled at reasonable cost?”

Growing evidence of active processes shows that modern Mars remains a dynamic planet that is still changing today. When seeking to understand the present-day environment, measurement of winds and water vapor within the planetary boundary layer, including their diurnal behavior, remain high-priority knowledge gaps. The volatility of H₂O and CO₂ play important roles in modifying the surface. Understanding the role of dust remains an ongoing challenge, especially the chain of events that leads to episodic planet-scale dust events, such as the planet encircling dust event observed in detail during summer 2018, when the local opacity was high enough to starve a solar-powered rover. Continued investigation of how such high-level dust activity has altered both atmospheric and surface processes is needed. While recurring slope lineae (RSL) were a key topic of debate at 8th Mars, at 9th Mars the accumulating evidence seemed to indicate that these landforms are more dry than wet.

One of the top areas of discussion at 9th Mars concerned methane, and a spirited panel discussion focused around potential explanations for why different missions are measuring some or none of this trace gas. Given general agreement that the differing measurements are correct, the discussion turned to what is the source of methane that was detected by MSL (including perhaps from the rover?) and how the gas could be so rapidly destroyed that it was detected at the surface but not at higher altitudes. The methane discussion was part of a much broader discussion about where to look for possible extant life. That led to discussion of ideas and measurement approaches about where and how to search the subsurface, which is thought to be more habitable than the surface.

Understanding the nature and evolution of the ancient environment(s) continues to challenge us, and new data and modeling efforts are needed to advance our knowledge. The debate about the existence of an ancient ocean continues (and if it was there, how long was it there?). Attempts to simulate an ancient greenhouse atmosphere able to support an early hydrological cycle were much debated, particularly about the role of reducing gases (H₂, CH₄). However, isotopic measurements and credible extrapolations of measured current-day atmospheric loss rates show that most of the early Mars atmosphere has been lost to space. The timing of elements of that atmospheric evolution (solar forcing, water availability, etc.) and its nature (episodic, punctuated, trending) remain challenging targets for future measurement and research.

There was also continued progress in understanding the climate and climate shifts of Amazonian Mars, including evidence of prolonged, if episodic, water activity early on; the abundance of mid-latitude ground ice (exposed in craters, cliffs, and surface/near-surface properties); and models connecting the radar-revealed internal layers of the polar caps with layering at the edges and shifts in accumulation/ablation due to obliquity cycles.

In addition to the vigorous, broad, and illuminating science discussion, it was wonderful to see the diversity in countries, disciplines, institutions, and people who are involved in Mars exploration. For example, many presentations and attendees were from the United Arab Emirates, who join the Mars mission community with the Emirates Mars Mission Hope orbiter, launching in 2020. This community expansion bodes well for continued tremendous advancement as we move into the next decade and define what future Mars exploration may look like.

9th Mars was convened by the Jet Propulsion Laboratory, California Institute of Technology, and NASA, with funding provided by NASA and assistance by the Lunar and Planetary Institute. The 9th Mars plenary conference presentations, all abstracts, the integrator reports, and many e-posters are available at the conference website.

— Text provided by Serina Diniega (Jet Propulsion Laboratory/Mars Program Office), Rich Zurek (Jet Propulsion Laboratory/Mars Program Office),
Michael Meyer (NASA Mars Exploration Program), Bethany Ehlmann (California Institute of Technology), Brandi Carrier (Jet Propulsion Laboratory/Mars Program Office),
and David Beaty (Jet Propulsion Laboratory/Mars Program Office)