Planetary Defense Missions: Protecting Earth from Asteroids
Complete guide to planetary defense — how we detect, track, and deflect asteroids that could threaten Earth. From DART's impact to NEO Surveyor and Hera.
Planetary defense is humanity's effort to find, track, and if necessary deflect asteroids and comets that could impact Earth. The 2022 DART mission proved we can change an asteroid's orbit. This page covers every major planetary defense mission, detection program, and future plans.
| Mission | Agency | Year | Type | Status |
|---|---|---|---|---|
| Spaceguard Survey | 🇺🇸 NASA / International | 1998–2010 | Detection program | Goal achieved — found 90%+ of 1km+ NEOs |
| Catalina Sky Survey | 🇺🇸 NASA / University of Arizona | 2004 | Detection program | Active — leading NEO discovery program |
| Pan-STARRS | 🇺🇸 NASA / University of Hawaii | 2010 | Detection program | Active — wide-field survey telescope |
| ATLAS (Asteroid Terrestrial-impact Last Alert System) | 🇺🇸 NASA / University of Hawaii | 2015 | Detection program | Active — 4 telescopes worldwide, early warning system |
| NEAR Shoemaker | 🇺🇸 NASA | 1996–2001 | Orbiter / Lander | Success — first to orbit and land on an asteroid |
| Hayabusa | 🇯🇵 JAXA | 2003–2010 | Sample return | Success — first asteroid sample return |
| Hayabusa2 | 🇯🇵 JAXA | 2014–2020 | Sample return | Success — returned 5.4g from C-type asteroid |
| OSIRIS-REx / OSIRIS-APEX | 🇺🇸 NASA | 2016 | Sample return (extended: rendezvous) | Samples delivered 2023; spacecraft redirected to Apophis as OSIRIS-APEX |
| DART (Double Asteroid Redirection Test) | 🇺🇸 NASA | 2021–2022 | Kinetic impactor | Success — first asteroid deflection demonstration |
| Hera | 🇪🇺 ESA | 2024 | Investigation / Follow-up | Launched Oct 2024 — en route to Didymos/Dimorphos |
| Psyche | 🇺🇸 NASA | 2023 | Orbiter | En route — arriving at asteroid 16 Psyche in 2029 |
| Lucy | 🇺🇸 NASA | 2021 | Flyby mission | Active — first Trojan asteroid flyby completed (Dinkinesh, 2023) |
| NEO Surveyor | 🇺🇸 NASA | 2028 (planned) | Detection (space telescope) | In development — space-based infrared survey |
| Rapid Apophis Mission for Security (RAMSES) | 🇪🇺 ESA | 2028 (planned) | Rendezvous / Observation | Approved — fast-track mission to observe Apophis close approach |
Mission Details
Spaceguard Survey
Past🇺🇸 NASA / International
Detection program · 1998–2010 · Ground-based survey
- •Congressional mandate to find 90% of NEOs larger than 1 km
- •Goal achieved by 2010 — no civilization-ending asteroid found
- •Led to expanded mandate for 140m+ objects
Catalina Sky Survey
Active🇺🇸 NASA / University of Arizona
Detection program · 2004 · Ground-based survey (Mt. Lemmon, Arizona)
- •Discovered more NEOs than any other survey
- •Found over 10,000 near-Earth objects
- •Detected 2008 TC3 — first asteroid discovered before impact
Pan-STARRS
Active🇺🇸 NASA / University of Hawaii
Detection program · 2010 · Ground-based survey (Haleakala, Hawaii)
- •Discovered 'Oumuamua — first confirmed interstellar object (2017)
- •Contributes significant NEO discoveries annually
- •Surveys the entire visible sky monthly
ATLAS (Asteroid Terrestrial-impact Last Alert System)
Active🇺🇸 NASA / University of Hawaii
Detection program · 2015 · Ground-based (Hawaii, Chile, South Africa, Canary Islands)
- •Designed as a 'last line of defense' for short-warning impacts
- •Can detect 20m asteroid 1 day before impact, 100m asteroid 1 week before
- •4 telescopes provide near-complete sky coverage
- •Detected 2024 BX1 asteroid before Earth impact (Jan 2024)
NEAR Shoemaker
Past🇺🇸 NASA
Orbiter / Lander · 1996–2001 · Asteroid 433 Eros
- •First spacecraft to orbit an asteroid
- •First to soft-land on an asteroid (February 12, 2001)
- •Collected detailed data on Eros composition and structure
Hayabusa
Past🇯🇵 JAXA
Sample return · 2003–2010 · Asteroid 25143 Itokawa
- •First mission to return asteroid samples to Earth
- •Overcame multiple failures (ion engine, reaction wheels, fuel leak)
- •Returned ~1,500 particles from Itokawa surface
Hayabusa2
Past🇯🇵 JAXA
Sample return · 2014–2020 · Asteroid 162173 Ryugu
- •Returned 5.4 grams of pristine asteroid material
- •Created artificial crater on Ryugu with kinetic impactor
- •Found amino acids and other organic molecules in samples
- •Spacecraft now en route to asteroid 1998 KY26 (extended mission)
OSIRIS-REx / OSIRIS-APEX
Active🇺🇸 NASA
Sample return (extended: rendezvous) · 2016 · Asteroid 101955 Bennu → Asteroid 99942 Apophis
- •Returned 121.6 grams of asteroid Bennu samples (Sep 24, 2023)
- •Largest asteroid sample ever collected
- •Found amino acids and water-bearing minerals in samples
- •Now heading to Apophis — will arrive during 2029 close approach
DART (Double Asteroid Redirection Test)
Past🇺🇸 NASA
Kinetic impactor · 2021–2022 · Asteroid Dimorphos (moon of Didymos)
- •First test of planetary defense technology — impacted Dimorphos Sep 26, 2022
- •Changed Dimorphos' orbital period by 33 minutes (goal was 7+ minutes)
- •Proved kinetic impact can meaningfully alter asteroid orbits
- •LICIACube (ASI) captured impact imagery
Hera
Active🇪🇺 ESA
Investigation / Follow-up · 2024 · Asteroid Dimorphos (moon of Didymos)
- •Follow-up mission to study DART impact results in detail
- •Will measure Dimorphos mass, crater, and internal structure
- •Carries two CubeSats: Milani and Juventas
- •Arriving at Dimorphos in late 2026
Psyche
Active🇺🇸 NASA
Orbiter · 2023 · Asteroid 16 Psyche
- •First mission to a metal-rich asteroid
- •16 Psyche may be an exposed planetary core
- •Will study what planetary interiors look like
- •Testing deep-space optical communication (DSOC)
Lucy
Active🇺🇸 NASA
Flyby mission · 2021 · Jupiter Trojan asteroids (8 targets)
- •First mission to visit Jupiter's Trojan asteroids
- •Discovered Dinkinesh has a contact-binary moon (Selam)
- •Will visit 8 asteroids over 12 years (2021–2033)
- •Studying 'fossils' of solar system formation
NEO Surveyor
Future🇺🇸 NASA
Detection (space telescope) · 2028 (planned) · Sun-Earth L1 point
- •First space telescope dedicated to finding hazardous asteroids
- •Will find 90%+ of NEOs larger than 140 meters within 10 years
- •Infrared detection finds dark asteroids invisible to ground telescopes
- •Key to fulfilling Congressional mandate for NEO detection
Rapid Apophis Mission for Security (RAMSES)
Future🇪🇺 ESA
Rendezvous / Observation · 2028 (planned) · Asteroid 99942 Apophis
- •Will observe Apophis during historic April 13, 2029 Earth close approach
- •Apophis will pass within 31,000 km of Earth — closer than geostationary satellites
- •First time a large (370m) asteroid has been observed this close
- •Will study tidal effects of Earth flyby on asteroid
Frequently Asked Questions
Can we deflect an asteroid heading for Earth?▾
Yes — NASA's DART mission proved it in 2022. DART impacted the asteroid Dimorphos and changed its orbital period by 33 minutes (far exceeding the 7-minute goal). This demonstrated that kinetic impact is a viable deflection method for asteroids we detect years in advance. ESA's Hera mission is currently en route to study the impact results in detail.
How many potentially hazardous asteroids are there?▾
As of 2026, over 2,300 Potentially Hazardous Asteroids (PHAs) have been cataloged — objects larger than 140 meters that pass within 7.5 million km of Earth's orbit. However, none currently known pose a significant threat in the next 100 years. NASA's NEO Surveyor (launching 2028) will find the estimated 60% of 140m+ NEOs that remain undiscovered.
What is the biggest asteroid threat to Earth?▾
Asteroid 99942 Apophis (370 meters wide) will pass within 31,000 km of Earth on April 13, 2029 — closer than geostationary satellites. While it will NOT impact Earth, it's the closest approach by an asteroid of this size in recorded history. Both NASA (OSIRIS-APEX) and ESA (RAMSES) are sending spacecraft to study it during this flyby.
What would happen if a large asteroid hit Earth?▾
Impact effects depend on size: a 50m asteroid could destroy a city (like the 1908 Tunguska event), a 140m asteroid could devastate a region, and a 1km+ asteroid could cause global climate effects and mass extinction. The Chicxulub impactor that killed the dinosaurs was ~10 km wide. This is why planetary defense focuses on early detection and deflection capability.
How do we detect asteroids?▾
Ground-based surveys (Catalina Sky Survey, Pan-STARRS, ATLAS) scan the sky nightly using optical telescopes. NASA's upcoming NEO Surveyor will be the first dedicated space-based infrared telescope for asteroid detection, capable of finding dark asteroids invisible from the ground. The Vera C. Rubin Observatory (opening 2025) will dramatically accelerate discovery rates.
What is planetary defense?▾
Planetary defense encompasses all efforts to detect, track, characterize, and mitigate the threat of asteroids and comets that could impact Earth. It includes: ground and space-based surveys to find near-Earth objects, missions to study asteroid composition (OSIRIS-REx, Hayabusa2), deflection tests (DART), and future technologies like gravity tractors and ion beam deflection.
What samples have been returned from asteroids?▾
Three missions have returned asteroid samples: JAXA's Hayabusa returned ~1,500 particles from Itokawa (2010), JAXA's Hayabusa2 returned 5.4 grams from Ryugu (2020), and NASA's OSIRIS-REx returned 121.6 grams from Bennu (2023) — the largest asteroid sample ever. All samples contained organic molecules, advancing our understanding of solar system origins.
Last updated: 2026-03-27. Data sourced from NASA, ESA, JAXA, ISRO, CNSA, and official agency publications.
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