Solar System Exploration
Our solar system has one star, eight planets, five dwarf planets, hundreds of moons, thousands of comets, and asteroids - LOTS of asteroids. Join us as we mark International Asteroid Day to call attention to the importance of detecting and tracking asteroids that could potentially impact our planet, and the role of asteroids in the formation of the solar system.
current count
Total Asteroids
Near-Earth Asteroids
Finding Them Before They Find Us
Asteroids – along with comets, and meteors – are chunks of rock, ice, and metal left over from the formation of our solar system 4.6 billion years ago. There are currently about 1.4 million known asteroids, and more than 3,900 known comets (including comet fragments).
Most asteroids orbit our Sun between Mars and Jupiter in the main asteroid belt. Sometimes, asteroids and comets are nudged into Earth's neighborhood by the gravity of nearby planets. These objects are called Near-Earth Objects, or NEOs. NEOs come within 30 million miles of Earth’s orbit.
Although there are no known significant asteroid impact threats for the foreseeable future, studying NEOs helps identify Potentially Hazardous Asteroids (PHAs) – asteroids that could someday impact our planet.
NASA sends spacecraft to study asteroids up close. Space telescopes and ground-based telescopes also track and identify asteroids. In 2016, NASA established the Planetary Defense Coordination Office (PDCO) to manage the agency’s efforts in planetary defense.
For International Asteroid Day, here are some resources to help you learn about asteroids and planetary defense.
All About Asteroids
Asteroids, sometimes called minor planets, are rocky remnants left over from the formation of our solar system about 4.6 billion years ago.
Learn More About Asteroids
“A large asteroid impact is potentially the only natural disaster humanity has the technology to predict years in advance and take action to prevent.”
Lindley Johnson
NASA Planetary Defense Officer Emeritus
Planetary Defense at NASA
In 2016, NASA established the Planetary Defense Coordination Office (PDCO) to manage the agency's ongoing mission of finding, tracking, and better understanding asteroids and comets that could pose an impact hazard to Earth.
Learn More About the PDCO
Featured NASA Asteroid Missions
NEO Surveyor
Near-Earth Object (NEO) Surveyor is the first space telescope specifically designed to hunt asteroids and comets that may be potential hazards to Earth. As it scans the solar system, NEO Surveyor's sensitive infrared detectors will let it track the most elusive near-Earth objects. Dark asteroids and comets don't reflect much visible light, for example, but they will glow in the infrared spectrum as they're heated by sunlight. The project is managed by NASA's Jet Propulsion Laboratory (JPL) in Southern California.
WISE/NEOWISE
After its primary mission ended, the WISE space telescope started it’s second act as NEOWISE. In late 2013, the spacecraft was assigned a new mission by NASA’s Planetary Science Division to help NASA identify and describe near-Earth objects (NEOs).
OSIRIS-REx/OSIRIS-APEX
Launched on Sept. 8, 2016, NASA's OSIRIS-REx arrived at near-Earth asteroid Bennu in 2018, and collected a sample of dust and rocks. On Sept. 24, 2023, the spacecraft flew by Earth and dropped off the asteroid sample capsule. It didn't land, and has a new assignment and a new name: It's now called OSIRIS-APEX and will explore asteroid Apophis.
Psyche
The Psyche spacecraft is on its way to a unique metal-rich asteroid with the same name, orbiting the Sun between Mars and Jupiter. By August 2029 the spacecraft will begin exploring asteroid Psyche, which scientists think may be the partial core of a planetesimal, a building block of an early planet.
Lucy
NASA's Lucy mission will explore a record-breaking number of asteroids in the solar system’s main asteroid belt, and Trojan asteroids that share an orbit around the Sun with Jupiter. Launched on Oct. 16, 2021, Lucy has already made discoveries. On Nov. 1, 2023, Lucy made its first asteroid encounter - an asteroid with a contact binary asteroid as its moonlet.
DART
NASA's Double Asteroid Redirection Test (DART) – the world’s first planetary defense technology demonstration – successfully impacted asteroid Dimorphos on Sept. 27, 2022, in the agency’s first attempt to move an asteroid in space. Dimorphos is a moonlet to asteroid Didymos.
Dawn
NASA's Dawn spacecraft was launched in 2007 to explore asteroid Vesta, the second most massive body in the main asteroid belt. Dawn arrived at Vesta in 2011, then orbited and explored Vesta for over a year before leaving in September 2012 to explore dwarf planet Ceres.
Galileo
NASA's Galileo mission was the first spacecraft to fly past an asteroid. It flew past asteroid Gaspra in 1991, and asteroid Ida in 1993.
NEAR Shoemaker
NASA's NEAR was the first spacecraft to orbit an asteroid, and also was the first spacecraft to land on one. Launched on Feb. 17, 1996, NEAR flew by asteroid Mathilde on June 27, 1997. Then on Feb. 14, 2000, NEAR began orbiting asteroid Eros. On Feb. 12, 2001, NEAR touched down on Eros – the first time a U.S. spacecraft was the first to land on a celestial body.
Deep Space 1
Deep Space 1 (DS1) was designed to test new technologies for future deep space and interplanetary missions. As a bonus, the spacecraft also flew by asteroid 9969 Braille on July 29, 1999, at a range of about 16 miles (26 kilometers).
Stardust/Stardust NExT
NASA's Stardust was the first spacecraft to bring samples from a comet to Earth. Launched on Feb. 7, 1999, the spacecraft flew within 155 miles (250 kilometers) of comet P/Wild 2 and collected samples of dust and volatiles from the comet's coma. On Nov. 2, 2002, it flew by and imaged asteroid 5535 Annefrank. The spacecraft was given an extended mission known as New Exploration of Tempel 1 (NExT) that included a flyby of Comet Tempel 1.
Featured Asteroids
NASA has sent several robotic spacecraft to encounter asteroids up close to learn more about their composition, size, and to better understanding these space rocks.
What’s That Space Rock?
Asteroids, comets, meteors, and meteorites. What are they, and how can we tell them apart?
Learn More
10 THINGS about our solar system
1. Many Worlds
Our solar system has eight planets, and five dwarf planets.
2. Small Worlds, Too
More than 1.3 million asteroids, and about 3,900 comets are in our solar system.
3. Lots of Moons
Our solar system has more than 200 moons.
4. Meet Me in the Milky Way
Our solar system is in one of the Milky Way galaxy’s four spiral arms.
5. A Long Way Around
Our solar system takes about 230 million years to orbit the galactic center.
6. Spiraling Through Space
The Milky Way is a spiral galaxy.
7. Room to Breathe
Our solar system has many worlds with many types of atmospheres.
8. Ring Worlds
The four giant planets – and at least one asteroid – have rings.
9. Getting Out There
More than 300 robotic spacecraft have left Earth's orbit, and 24 U.S. astronauts have traveled to the Moon.
10. Life as We Know It
So far, Earth is the only place we've found life in our solar system.
