Phobos and Deimos: a bridge between scientific investigations and human exploration at NASA Forum

(Article by Dr Sarah Crites, International Top Young Fellow at ISAS)

The moons of Mars, whose origin will be probed by the Martian Moons eXploration (MMX) mission, are intriguing to scientists for many reasons–but at the 2017 NASA Exploration Science Forum, held on 18-20 July, 2017 at NASA’s Ames Research Center, their potential to enable human exploration of the Solar System was brought to the forefront as well.  The purpose of the forum, hosted by the NASA Solar System Exploration Research Virtual Institute (SSERVI), is to enable scientific discussions about human exploration targets of interest, and for many at the forum, the moons of Mars fall perfectly at this intersection of scientific curiosity and exploration potential.

Dr. Pascal Lee of SETI started the conversation about the moons of Mars on the first day of the conference, highlighting the importance of Phobos and Deimos for future human exploration of the solar system and describing their potential value for in-situ resource utilization, Mars sample storage and caching, and teleoperation of robots on Mars.  Lee also emphasized the fact that, in addition to their many advantages as stepping stones for future human exploration, Phobos and Deimos are inherently scientifically exciting to explore.  It was these scientific attractions that Professor Masaki Fujimoto, Director of the ISAS Department of Solar System Sciences, focused on in his presentation updating those gathered about current plans and motivations for the Martian Moons eXploration (MMX) mission.

The Martian moon, Phobos.

On the second day of the forum, volatiles in the Solar System were the main topic of discussion, and once again, Phobos and Deimos emerged as bodies of particular interest for this field of study.  If the moons of Mars are captured asteroids, they are direct relics of the delivery process of organics and water into the inner Solar System–an exciting prospect for both scientists interested in the early Solar System, and human explorers who may need a water or fuel supply as they move beyond Earth.  However, billions of years of sunshine and heating at the orbit of Mars could have dried out the uppermost layers of the moons, regardless of how water-rich they were when they formed.  Dr. Timothy Stubbs of NASA’s Goddard Space Flight Center addressed this topic, describing ongoing efforts to create detailed illumination and temperature maps of Phobos’ surface, and to model the stability of subsurface water ice on Phobos.

On the third and final day of the forum, the conversation turned to the major motivation for the Martian Moons eXploration (MMX) mission: did Phobos and Deimos form through a giant impact, or are they captured asteroids?  Dr. Robin Canup of the Southwest Research Institute described simulations of the formation of Phobos and Deimos from an impact-generated disk, focusing on the challenge of keeping tiny Deimos from being destroyed in the process.  The simulations suggest that if they formed from a giant impact, Phobos and Deimos would mostly be made up of Mars material thrown into orbit by the impact, and that because of the hot, energetic process, the moons would contain very little water.  These predictions provide important context for understanding the samples that the Martian Moons eXploration (MMX) mission will bring back, and Canup ended her talk by highlighting this point.  “It’s an extremely exciting development,” Canup said of the JAXA mission.  “[It] should allow a definitive conclusion on how these objects formed.”

Canup’s presentation clearly demonstrated how theoretical modeling efforts can provide outputs that are directly relevant to space missions.  This is the philosophy behind the work of Dr. Hidenori Genda and Dr. Ryuki Hyodo of the Tokyo Institute of Technology’s Earth-Life Science Institute (ELSI), whose recent activities have focused on modeling possible Phobos and Deimos-forming impacts.  Genda and Hyodo hope to establish a new style of mission-driven theoretical research in Japan, which would focus on obtaining simulation results that can directly constrain properties observable by space missions.  This goal of maximizing flight outcomes through enhancing communication and collaboration between space mission planners and scientific researchers is one shared by SSERVI, whose mission includes “enabling cross-disciplinary partnerships throughout the science and exploration communities.”

An artist’s impression of the Martian Moon eXploration spacecraft.

An additional goal of SSERVI is to bring together researchers from many nations to study scientific questions related to human exploration, and throughout the forum, the value and importance of these international collaborations was highlighted.  In addition to ISAS Professor Fujimoto’s invited presentation about the Martian Moons eXploration (MMX) mission, representatives from the Mexican and Korean space agencies also attended the meeting to describe their plans for scientific exploration of Earth’s moon.  During a town hall meeting, Dr. Jim Green, NASA Planetary Science Division Director, reminded attendees that NASA will be developing a key instrument onboard MMX.  “We’re really delighted to partner with JAXA,” Green said.  “They’ve asked us to provide a gamma ray and neutron spectrometer for the Martian Moons eXploration mission.”

The forum closed with keynote talks by Dr. Alan Stern, Principal Investigator for NASA’s New Horizons mission, who described the history of solar system missions leading up to the exploration of Pluto and the Kuiper Belt, and Dr. Jack Burns, Principal Investigator of the SSERVI Network for Exploration and Space Science, who invited attendees to consider why we explore space.  “Planetary science is becoming more international,” Stern said, referencing JAXA’s small bodies missions and the Akatsuki Venus Climate Orbiter as examples.  He painted a picture of a bright future for space science and exploration: “There is a growing awareness in capitals around the world that the 21st century is the century for humans to begin exploring all of our solar system.”  Burns left the meeting attendees with a simple reminder of the shared motivation behind international space exploration: “Humans are meant to explore…We explore to gain knowledge and to satisfy our curiosity.”  After the forum, it was clear that Phobos and Deimos will be important stepping stones to satisfy that curiosity as humanity ventures beyond Earth orbit and out into the solar system.