Space medicine: The hurdle between Earth and Mars

Space medicine has moved from a niche specialty to a central consideration as agencies and private actors outline plans for crewed missions to Mars in the coming decades. While Mars is the most Earth-like world in the solar system, a long-term human presence there would demand resilience to radiation, microgravity, isolation, and the logistical demands of a multi-year round trip. The medical question is not merely whether we can build habitats; it’s whether the human body can tolerate the journey and stay healthy enough to function at needed levels for years away from Earth.

Astronaut selection today emphasizes health and robustness, and a medical screening gate keeps many people out. Tobacco use, autoimmune disorders, temporomandibular joint disorders, sleep apnea, asthma, hypertension, migraines, and anxiety or depression are among the conditions that can disqualify someone from spaceflight. Shawna Pandya, a research astronaut with the International Institute for Astronautical Sciences and director of its Space Medicine Group, notes that in earlier eras a diabetes diagnosis could end a child’s dream of becoming an astronaut. “Nothing that humanity has done that has been worthwhile has been easy,” she says, underscoring the need for advances in medical selection and management before deep-space missions.

After the gatekeeping, the remaining puzzle is physiology: under sustained microgravity, astronauts face accelerated bone and muscle loss, insulin resistance, and immune-system shifts. Haig Aintablian, director of the UCLA Space Medicine Program, compares spaceflight to pregnancy in terms of triggering distinct physiologic changes. Space medicine has its own specialty because the body must be understood in a context very different from Earth.

NASA still aims to push beyond low Earth orbit, with a Mars mission on the horizon for the 2030s. Mars is the closest approximate home anyone has yet contemplated for long-term human life on another world. The planet’s environment—dust that is toxic to inhale, a thin, unbreathable atmosphere, and roughly 40 percent of Earth’s gravity—poses unique challenges. More daunting is the distance: Mars can be about 140 million miles away, with round-trip communications that create hour- or even day-long delays. In a medical emergency, telemedicine guidance from Earth would not arrive quickly enough, and a return option is not readily available. The combination of long duration, radiation exposure beyond Earth’s magnetosphere, and limited resupply options makes a Mars mission a rigorous test of human physiology and medical systems.

Mars has limited protective magnetic shielding and a radiation environment that is not yet replicable on Earth. The long journey also means extended exposure to isolation and confinement, which can impact mental health. The first-class problem facing space medicine is not just damage control but prevention and resilience, so crews can operate autonomously for months or years at a time. As the field evolves, researchers are exploring ways to keep people healthy long before a mission begins, including telemetry-based monitoring, on-board diagnostics, and AI-assisted clinical support.

The history of human spaceflight adds urgency to the question. From Yuri Gagarin’s 1961 milestone to today’s more than 600 astronauts, the cohort remains limited, and women make up only a fraction of those flown. NASA researchers have identified several actionable health effects of spaceflight: radiation exposure, isolation, Earth distance, altered gravity, and immune-system changes. The 2019 NASA Twins Study, which compared identical twin brothers Scott and Mark Kelly over a year, showed how space can alter gene expression and physiology in ways that are not fully predictable from Earth. Scott Kelly’s telomeres lengthened during his time in space and mostly returned to baseline after his return; he also experienced cardiovascular changes and transient cognitive shifts. The study demonstrated both survivability and the depth of space’s effect on the body, underscoring how much remains unknown when the sample size is small.

The growth of civilian spaceflight in the last few years has expanded the pool of people who could provide medical data for space medicine, but it has also highlighted gaps. Private trips give scientists access to larger datasets, yet short suborbital hops do not replicate long-duration exposure to microgravity or deep-space radiation. Aintablian argues that the evolution of space medicine will require advances in countermeasures and perhaps new models for care that can function without constant Earth-based support.

To that end, researchers are pursuing both incremental and transformative goals. In the near term, NASA and partners are planning more robust on-site medical capabilities, including flight surgeons who can supervise care in flight and who could be accompanied by non-physician clinicians. A future scenario envisions health professionals joining crews on exploration missions, with AI assisting in diagnostics and decision support. Google has collaborated with NASA to develop an AI system that could guide astronauts in diagnosing and treating medical conditions in flight, especially when telemedicine from Earth is delayed. But as Pandya notes, the data requirements are substantial: models trained on current travelers may not generalize well to a broader, more diverse spacefaring population.

The research also highlights a gender gap in space-health data. Researchers emphasize the need to study reproductive health in space, noting that no human has yet experienced pregnancy in space and that there is little knowledge about space birth. Understanding how conception, pregnancy, and childbirth unfold in microgravity is viewed as essential groundwork for any long-term settlement plan.

NASA’s plans include a second Crew Health and Performance Exploration Analog experiment, scheduled to begin this October at the Johnson Space Center in Houston. The analog will involve a year-long simulated Mars mission in a 3D-printed habitat to study behavioral health, isolation, and crew dynamics. Bed-rest studies continue to simulate the physiological effects of altered gravity, helping scientists develop countermeasures without sending people into space.

Advances in broader health science are also driving momentum in space medicine. The concept of using space-derived insights to benefit Earth health has already borne fruit: imaging advances from early Moon missions later influenced CT and MRI development, and remote patient monitoring tools created for astronauts are now common in hospitals. Several researchers envision a future in which “avatars” of astronauts—stem-cell–derived organoids that mimic brain, heart, liver, and other tissues—can be studied and countermeasures tailored to individuals before they ever board a spacecraft. If realized, this could enable personalized medicine tailored to each astronaut’s unique physiology, potentially reducing the cost and risk of deep-space travel.

The field also faces practical constraints. Space medicine remains an expensive enterprise, and only a small minority of people ever travel to space. Yet its benefits may extend beyond the stars. In the near term, investments in radiation protection, autonomous medical care, and telemedicine-ready systems could improve health outcomes on Earth as well, particularly for patients with diabetes, cancer, and chronic diseases who rely on remote monitoring and timely medical interventions. In the long run, the pursuit of durable life-support for Mars—production of essential supplies, habitation systems, and reliable medical care—depends on advances in space medicine that can operate in the most extreme environments.

As researchers like Pandya and Aintablian stress, space medicine is not a luxury but a catalyst for resilience. Progress depends on disciplined science, robust data, and deliberate inclusion of diverse populations in research so that countermeasures are effective for all potential space travelers. The ultimate aim is not merely to visit Mars, but to live there safely, maintain health across decades, and perhaps eventually enable generations of humans to inhabit multiple worlds. If the lessons learned in space translate to better care on Earth, the investment will have broad and lasting impact on human health, well beyond the red horizon.