Exposing Microorganisms in the Stratosphere
NASA study exposing Bacillus pumilus spores to stratospheric Mars-like conditions.
NASA’s E-MIST project (Exposing Microorganisms in the Stratosphere) sent *Bacillus pumilus* bacteria and their spores into Earth’s stratosphere—about 31 km up—to see if they could handle conditions like those on Mars. The bacteria hitched a ride on a helium balloon, where they faced low pressure, dryness, cold, and ionizing radiation. A test flight launched from New Mexico on August 24, 2014, followed by a longer one on October 10, 2015.
Microbes from every major biological group have turned up in Earth’s upper atmosphere. If they can grow or reproduce up there, it would widen the search for habitable zones on other planets to include their atmospheres. The study also looked at spore-forming bacteria originally found in NASA spacecraft assembly facilities—if these tough spores can survive Mars-like conditions, it could improve planetary protection rules.
The stratosphere (10–50 km up) mimics Mars’ surface: extreme cold, low pressure, dryness, oxidation, and strong solar radiation. The test microbe, *Bacillus pumilus* strain SAFR-032, is a radiation-tolerant spore-former first isolated from a clean room in a NASA spacecraft facility.
The 80-pound gondola had four doors that rotated to expose up to ten samples for eight hours each. To end the flight, an explosive charge tore a hole in the balloon, and the payload—including E-MIST and other experiments—parachuted back to Earth. Researchers then recovered the samples. Key components included a lithium-ion battery, a UV radiometer, humidity and temperature sensors, and a flight computer.
After eight hours at 31 km, 99.9% of the bacteria were dead. Of the 40 million spores exposed, only 267 (0.0007%) survived. The researchers calculated that no spores would have survived if the flight had lasted 150 more minutes (630 minutes total). The survivors had three single-nucleotide changes compared to ground controls, in genes linked to sporulation and metabolism. Similar mutations showed up in SAFR-032 samples exposed outside the International Space Station.
Even after cleaning, spacecraft still carry microbes embedded in surfaces, instruments, and electronics—places sunlight can’t reach. The few survivors might evolve in worrying ways. The researchers suggest embedding UVC LED arrays in lander hardware to sterilize those hidden spots.
- field
- Astrobiology / Planetary Protection
- known_for
- Testing microbial survival in stratospheric conditions analogous to Mars
- microorganism_tested
- Bacillus pumilus strain SAFR-032
- altitude_of_exposure
- 31 km above sea level
- first_flight_date
- 24 August 2014
- second_flight_date
- 10 October 2015
- survival_rate
- 0.0007% (267 of 40 million spores viable)
Lore & Background
The E-MIST study used a helium-filled balloon to lift an 80-pound gondola to the stratosphere. The gondola had four doors that rotated to expose up to ten experimental samples each for eight hours. After exposure at 31 km altitude, 99.9% of the bacterial population was destroyed; only 267 spores out of 40 million remained viable. The researchers noted that most terrestrial bacteria would be inactivated within the first day on Mars if contaminated spacecraft surfaces receive direct sunlight.
Reader's Guide
E-MIST is significant because it directly tested whether spore-forming bacteria isolated from NASA spacecraft assembly facilities could survive Mars-like conditions in Earth's stratosphere. The study found that while the vast majority of spores were killed, a tiny fraction survived and showed three single nucleotide substitutions in genes associated with sporulation and metabolism. This suggests that even after cleaning, spacecraft may carry embedded microorganisms that could survive and potentially evolve under Martian conditions. The researchers proposed using ultraviolet-C lamps embedded in lander hardware to sterilize interior surfaces. The findings inform planetary protection protocols and broaden the search for habitable zones to include planetary atmospheres.
Did You Know?
- The E-MIST gondola carried a lithium-ion battery, UV radiometer, humidity and temperature sensors, and a flight computer.
- The flight was terminated by an explosive charge that tore a hole in the balloon, allowing the payload to return under parachute.
- Surviving spores showed three single nucleotide substitutions compared to unexposed controls kept on the ground.
- A similar observation was recorded on SAFR-032 samples exposed outside the International Space Station.
Frequently Asked Questions
What is Exposing Microorganisms in the Stratosphere (E-MIST)?
E-MIST is a NASA astrobiology project that carried bacteria aboard helium balloons into Earth's stratosphere to test whether microbial life can endure conditions that closely mirror those on the Martian surface.
Which microorganism did E-MIST test, and at what altitude?
The project exposed Bacillus pumilus strain SAFR-032, both as vegetative cells and as spores, at roughly 31 kilometers above sea level, where the samples faced low pressure, extreme dryness, freezing temperatures, and ionizing radiation.
When and where did the E-MIST test flights take place?
The first test flight launched from New Mexico on August 24, 2014, and a second, longer-duration flight followed on October 10, 2015, each using a helium balloon to deliver the bacterial payload into the stratosphere.
Why is E-MIST important for planetary protection and the search for life on Mars?
By revealing whether real Earth microbes can survive or even reproduce under stratospheric conditions analogous to Mars, E-MIST helps scientists calibrate both the outer limits of microbial resilience and the contamination risks that planetary-protection protocols must address.
What does E-MIST tell us about the possibility of life persisting in Earth's upper atmosphere?
The project builds on the observation that microbes from every major biological group have already been recovered from the upper atmosphere; if those organisms can grow or reproduce at 31 km, it widens the atmospheric window where life might persist and where astrobiologists should search for biosignatures.
More in Astrobiology space missions 1-24
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