Although both Planetary Protection and Planetary Defense programs at NASA include the word “planetary” and aim to protect the planet, that’s where similarities end. These two vital efforts oversee very different aspects of the agency’s role in protecting Earth, and in some cases, other planets. 

“These similar sounding efforts are often confused in the media and in casual conversation,” said Nick Benardini, NASA Planetary Protection Officer. “Both seek to protect Earth from potentially hazardous space threats, but otherwise they could not be farther apart from one another.”

So, what are Planetary Protection and Planetary Defense? Planetary Protection is 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. It focuses on sustainable and responsible exploration of the solar system in response to the Outer Space Treaty. Planetary Defense deals with Near-Earth Objects (NEOs) — i.e., asteroids and comets — that orbit the sun like the planets, but whose orbits can bring them into Earth’s neighborhood (within 30 million miles of Earth’s orbit). It’s an “applied planetary science” to track and catalogue potentially hazardous NEOs.

“For Planetary Protection, it’s all about protecting the Earth’s biosphere from harmful contamination (microbial life) brought back from target bodies, like Mars, that have the potential to harbor life, whereas for Planetary Defense, the concern is protecting the Earth from Near-Earth Objects that could cause a potential impact event,” explained Benardini. 

“Planetary Protection is about the small, squishy stuff,” added Lindley Johnson, Planetary Defense Officer. “Planetary Defense deals with the big, hard stuff!”

Another way of comparing the two disciplines is in orders of magnitude. Planetary Protection focuses on microorganisms on the micrometer to nanometer scales and organic contamination measured at the atomic level. Planetary Defense focuses on extremely large objects on the kilometer to meter scales. Both require very different measurement tools as well: Planetary Protection needs a microscope to observe these objects, while Planetary Defense needs a telescope. 

The disciplines also manage very different impact timeframes. In the world of Planetary Protection, if a contamination event occurred, it would take time to fully actualize as the organisms would have to replicate and transfer from host to host. For comparison, with Planetary Defense, an event’s impact would be instantaneous. 

While both Planetary Protection and Planetary Defense ultimately have the shared goal of protecting the planet, understanding the differences can be helpful as NASA explores farther into the solar system and universe and completes more missions to near-Earth targets. Questions can be directed to Benardini or Johnson.