What is Planetary Defense ?

Planetary Defense entails the protection of our planet from Near-Earth Objects. Near-Earth Objects (NEOs) are small bodies in our Solar System, like comets or asteroids. They also orbit the Sun,  but can enter our planet’s neighborhood by passing within 45 million kilometers of Earth’s orbit. Planetary Defense involves preventing and mitigating the impact of NEOs, which Citizen Astronomers can support by observing these objects to help space scientists understand their movement and watch for danger.

community map

Credits: NASA/JPL-Caltech

Potentially Hazardous Objects

The first Solar System object to be dubbed a NEO was the asteroid Eros , and over 29,000 more have been identified since.  When a NEO comes too close to our planet and is large enough to cause significant damage to us, it is classified as a Potentially Hazardous Object (PHOs). As of 2022, more than 2,000 PHOs are known and monitored. Luckily, there are lots of telescope organizations watching our close neighbors, like NEO-WISE, ATLAS, PAN-STARRS, and CSS — and of course, you with the Unistellar network!

Asteroid Impacts

NEOs do hit Earth in real life, not just in the movies. Hundreds of meteorites are falling to the surface of Earth everyday. Most of these are insignificant, but some have seriously damaged our planet. 

The Chelyabinsk event in Russia, which occurred in 2013, is an example of a recent, destructive encounter. In this case, a 19m-wide asteroid entered Earth’s atmosphere and exploded with nearly 30 times the energy of an atomic bomb. Planetary Defense aims to prevent events like these so that we do not end up like the dinosaurs! For example, NASA has launched the DART mission to alter the orbit of a Near-Earth asteroid. With advances like these, and your help, we can help defend the Earth.

Your Contribution

NEOs are fast-moving targets in the sky, which makes successful observations of them indispensable to Planetary Defense research. Your observations of NEOs help scientists refine their orbits and measure their rotation and shape.

To join as a Planetary Guardian, visit our new missions page to find an event visible to you. Head to the Tutorial page for guidance on how to master your Unistellar telescope. The exciting results from Citizen Astronomers’ observations of NEOs are posted on the Results page, so you can see what kind of discoveries you will be making!

Getting started


Discover how to use your telescope as a scientific tool for Planetary Defense.


Find a mission you can contribute to.


Discover the exiting results the Unistellar community produced.

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