Planetary Protection for 

Mars Science Laboratory 

National Aeronautics and Space Administration

NASA takes strict precautions to avoid the possible 

introduction of microbes from Earth when sending 

robotic spacecraft to any solar system body with 

the potential for past or current biological activity. 

For the Mars Science Laboratory mission’s Curiosity 

rover, this includes requirements for the cleanliness 

of flight hardware before launch and specific criteria 

for its landing site and areas it will explore.

What is planetary protection?

“Planetary protection” is the term given to the 

practice of protecting solar system bodies from 

contamination by Earth life, and protecting Earth 

from possible life forms that may be returned from 

other solar system bodies. NASA has a planetary 

protection officer responsible for establishing 

and enforcing planetary protection requirements 

consistent with agency policy and the obligations 

of the United States under the 1967 Outer Space 

Treaty. Article IX of that treaty stipulates that the 

exploration of space be conducted in a manner 

that preserves the pristine biological conditions of 

celestial bodies.

NASA requires that each spacecraft project be 

responsible for implementing measures to comply 

with the agency’s planetary protection requirements 

for the project. In general, this results in specific 

planetary protection considerations during the 

design, assembly, test and transport of mission 

hardware to keep it biologically clean before flight.

How is planetary protection being 

handled with Mars Science Laboratory?

For Curiosity, compliance with NASA planetary 

protection requirements was accomplished mainly 

through the careful maintenance of clean room 

protocols, periodic cleaning of spacecraft surfaces 

with alcohol wipes, and dry heat treatment of some 

spacecraft parts.

Technicians and engineers assembling the 

components of the rover and preparing it for launch 

routinely cleaned surfaces by wiping them with 

alcohol. In addition, rover components tolerant 

of high temperature were treated using dry heat 

techniques to reduce the number of bacterial spores. 

Selected components were heated to temperatures 

ranging from 110 to 146 degrees Celsius (230 to 

295 degrees Fahrenheit) for durations up to 144 

hours. Tools and other equipment that could come 

into contact with rover hardware were also cleaned 

routinely with alcohol wipes. 

Spore-forming bacteria have been the focus of 

planetary protection standards because these 

bacteria can survive harsh conditions for many years 

as inactive spores. Planetary protection requirements 

called for the entire Mars Science Laboratory flight 

system to launch with no more than 500,000 

bacterial spores — about one tenth as many as in a 

typical teaspoon of seawater. 

In addition, the exposed interior and exterior 

surfaces of the landed system, including the rover, 

parachute and back shell, were limited to carrying no 

In a clean room at NASA’s Kennedy Space Center, Mars Science 

Laboratory personnel sample the inboard side of the spacecraft’s heat 

shield to confirm its cleanliness before final assembly for launch.
NASA Facts

Jet Propulsion Laboratory

California Institute of Technology 

www.nasa.gov

For more information on the Mars Science Laboratory mission and 

the Curiosity rover, visit mars.jpl.nasa.gov

more than 300,000 spores, with the average spore density not 

exceeding 300 spores per square meter (about 11 square feet). 

This ensures that any biological load is not concentrated in one 

place. 

The heat shield and descent stage will hit the ground hard 

enough that hardware could break open. The number of spores 

inside this hardware that could be exposed was included in the 

final spore count.

The NASA planetary protection team carefully sampled the 

surfaces of Mars Science Laboratory flight hardware and 

performed microbiological tests to demonstrate that the 

spacecraft meets these requirements. The team found Mars 

Science Laboratory to be extremely clean: the final bioassays 

found a total of 278,000 spores on the entire flight system, with 

56,400 spores on the surfaces of rover hardware.

What could happen now that Curiosity has been 

launched?

It is unavoidable that portions of the flight hardware will 

impact the surface of Mars as part of a normal landing event. 

This impact may cause the hardware to split open and 

potentially release spores trapped inside the hardware during 

manufacturing processes. To ensure Mars Science Laboratory 

does not exceed the spore allocation, studies were conducted 

on various materials, including paint, propellants and adhesives, 

to determine the number of spores in a given volume. 

In many cases, the parts of the spacecraft containing these and 

other materials were treated with dry heat to reduce the number 

of spores. For hardware expected to impact Mars, such as the 

cruise stage after its separation from the aeroshell, a detailed 

thermal analysis was conducted to make sure that plunging 

through the Mars atmosphere gets the hardware sufficiently hot 

that few spores survive.

Curiosity uses heat from a Multi-Mission Radioisotope 

Thermoelectric Generator (MMRTG) to produce electricity 

and keep the rover’s internal systems at proper operating 

temperatures. Because of heat produced by the generator, 

the Mars Science Laboratory project is also complying with a 

planetary protection requirement to avoid going to any site on 

Mars known to have water or water ice within 1 meter (about 

3 feet) of the surface. 

This is a precaution against any landing-day accident that could 

introduce unsterilized hardware into an environment where heat 

from the mission’s MMRTG and a source of Martian ice or water 

could provide conditions favorable for terrestrial microbes to 

grow on Mars.

The MMRTG is expressly designed to contain its fuel in 

accident environments that could occur on Earth, including its 

atmosphere. While atmospheric conditions at Mars would have 

different effects on the MMRTG in a failed entry/descent, the 

construction of the generator still affords significant capability to 

contain the fuel in several potential contingency scenarios.

It is possible, but not likely, that any microbes that remained on 

the flight hardware could come to rest near a warm element of 

the power source. However, given Mars’ intense environmental 

conditions—including sterilizing radiation from the sun and 

extremely cold temperatures—it is highly unlikely that Earthbased life could survive for any significant length of time.

Another way of helping make sure the Mars Science Laboratory 

mission does not transport Earth life to Mars is to ensure that 

any hardware that was not cleaned for planetary protection 

purposes, such as the upper-stage propulsion system, does 

not encounter Mars accidentally. When Curiosity lifted off on 

November 26, 2011, the initial flight path for the spacecraft 

and the Centaur upper stage of its Atlas V launch vehicle was 

selected so that the flight system’s trajectory would miss Mars 

without further spacecraft maneuvers during cruise to the red 

planet. 

This trajectory correction strategy occurred as planned, thus 

confirming that the spacecraft was put on target for landing but 

the Atlas upper stage will not impact on Mars.

JPL 400-1484 8/12