The Top 3 Weirdest Asteroids We’ve Ever Visited

Asteroids float silently in our solar system, holding clues to how planets formed billions of years ago. These rocky bodies, leftovers from the early chaos, have been targets for daring space missions that bring back stunning discoveries. In recent years, spacecraft from NASA and JAXA have landed on or orbited some of the strangest ones, revealing shapes and materials that surprise scientists. For example, the OSIRIS-REx mission collected dust from Bennu in 2020 and returned it to Earth in 2023, with 2025 studies showing the asteroid carries carbon-based compounds and phosphates that could link to life’s building blocks on Earth. This primitive rock, about 490 meters across, formed around 4.6 billion years ago and later broke apart from a larger body. Missions like these help us understand impacts and water in space history.

Japan’s Hayabusa2 spacecraft visited Ryugu in 2018, touching down twice to grab samples rich in organics and salts, returned in 2020. New analysis in 2024 found salt crystals up to 400 micrometers wide, suggesting the asteroid once had liquid water deep inside its parent body tens of kilometers across. These finds paint Ryugu as a watery relic from the outer solar system. Meanwhile, the original Hayabusa mission in 2005 sampled Itokawa, proving it is not a solid chunk but a jumbled pile of debris held by weak gravity. What could these odd visitors tell us about threats from space or even the origins of life?

What Makes Ryugu Look Like a Spinning Top?

Ryugu stands out with its diamond or spinning top shape, measuring about 900 meters across at its widest point and 800 meters tall, like a lopsided pyramid floating in space. This unusual form came from fast rotation that flattened the poles and bulged the equator, a process driven by the asteroid’s spin rate of one rotation every 7.6 hours. Scientists confirmed this shape during the Hayabusa2 mission, which arrived at Ryugu on June 27, 2018, and orbited for over a year, mapping the surface with cameras and spectrometers. The asteroid’s rough, boulder-covered terrain has few smooth areas, making landings tricky, but the spacecraft succeeded in collecting 5.4 grams of material from two sites.

What adds to Ryugu’s weirdness is its low density of just 1.19 grams per cubic centimeter, about half that of water ice, showing it is a rubble pile (a loose stack of rocks and dust with up to 50 percent empty space inside). This structure likely formed when a larger asteroid shattered in a collision and pieces reassembled under gravity. Samples returned on December 5, 2020, revealed hydrous minerals like phyllosilicates (clay-like substances that hold water molecules) and carbonates covering up to 5 percent of some grains, pointing to ancient chemical reactions with water at temperatures around 0 to 100 degrees Celsius. Fun fact: These organics, including long-chain hydrocarbons, match those in meteorites that have fallen on Earth, hinting Ryugu delivered similar ingredients early in our planet’s history. Imagine a cosmic delivery service from 4.6 billion years ago!

Compared to solid asteroids like Vesta, Ryugu’s porous build means it absorbs impacts differently, with seismic waves (vibrations from hits traveling at speeds around 50 meters per second) shaking the whole pile rather than cracking a hard shell. For visualization, NASA’s artists often depict Ryugu’s shape in diagrams showing the equatorial ridge, like a spinning pizza dough that puffed up unevenly. Recent 2024 studies of the samples found nitrogen-rich compounds like ammonium silicates, which are rare and suggest Ryugu drifted from the outer solar system where colder conditions preserved them. This makes Ryugu not just weird in looks but a key to tracing solar system migration.

Why Is Bennu Ejecting Particles and Spinning Faster?

Bennu surprises with its dynamic behavior, as NASA’s OSIRIS-REx spacecraft watched particles as large as 1 meter shoot off its surface at speeds up to 3 meters per second, some escaping into space while others fall back like gentle rain. This ejection happens about every 16 days from bright spots near the equator, possibly from thermal cracking (heat from sunlight breaking rocks) or static electricity buildup. The mission, launched September 8, 2016, arrived December 3, 2018, and observed this for two years, capturing over 2,000 images showing the asteroid’s diamond-like shape, 490 meters in diameter, with a rotation period of 4.3 hours. Bennu’s surface is covered in boulders up to 50 meters tall, making it look like a pile of jagged gravel rather than a smooth rock.

The asteroid’s spin is speeding up due to the YORP effect (a torque from sunlight absorbing and re-emitting heat unevenly, pushing the rotation like a tiny propeller), which could double its speed in 1.5 million years and risk breaking it apart. As a rubble pile with density around 1.26 grams per cubic centimeter, Bennu holds together loosely, formed from fragments of a larger body destroyed by impacts billions of years ago. Samples collected October 20, 2020, totaled 121.6 grams of dark, carbon-rich dust and rocks, analyzed in labs showing magnesium carbonate and sodium phosphate minerals that formed in watery environments at low temperatures, about 0 to 50 degrees Celsius. These phosphates, essential for DNA and bones, suggest Bennu carried life’s precursors, exciting astrobiologists.

In comparison, most asteroids stay static, but Bennu’s activity makes it like a mini-volcano in space, with particles forming a faint dust plume extending 100 meters. For better understanding, refer to OSIRIS-REx’s particle ejection charts, which plot events over time to show patterns tied to sunlight angles. 2025 updates from sample studies revealed Bennu originated beyond Saturn’s orbit before migrating inward, with unusually high magnetism from iron-nickel grains, stronger than expected for such a primitive body (NASA, 2025a). This migration explains its mix of outer solar system ices and inner heat-altered rocks, a weird blend not seen elsewhere.

How Did Itokawa Turn Out to Be a Loose Pile of Rubble?

Itokawa shocked scientists with its peanut shape, stretching 535 meters long, 294 meters wide, and 209 meters tall, like two boulders fused together, confirmed by Japan’s Hayabusa spacecraft during its 2005 rendezvous. Unlike expected craters, the surface has smooth areas called “seas” of fine gravel and a giant 49-meter boulder named Yoshinodai, too large for the asteroid’s gravity to launch from impacts. The mission arrived September 12, 2005, and collected 1,500 microscopic particles before returning them June 13, 2010, proving Itokawa’s density is only 1.9 grams per cubic centimeter, lower than concrete, indicating a rubble pile structure (loose rocks bound by mutual gravity, with no solid core). This setup formed when a 20-kilometer parent body shattered, and fragments gently collided to reform.

The lack of big craters stems from impacts causing material to flow and fill holes, like sand in a shaken box, with seismic speeds estimated at 20 to 50 meters per second across the pile. Samples showed S-type composition, matching ordinary chondrite meteorites, with olivine and pyroxene minerals (silicate rocks that cooled slowly at 800 degrees Celsius deep in the original body). Fun fact: Itokawa rotates every 12.13 hours, fast enough to flatten its shape but slow enough to hold the rubble stable. Compared to denser asteroids like Eros at 2.67 grams per cubic centimeter, Itokawa’s weakness means a close Earth flyby could shake it apart.

Visualize Itokawa’s structure with diagrams from Hayabusa images, showing the “head” and “body” divided by a narrow neck, suggesting two pieces merged after a hit. Analysis confirms no water alteration, unlike Ryugu, but traces of space weathering darkened its surface over millions of years. These discoveries from 2005 to 2011 papers reshaped models of asteroid evolution, showing rubble piles make up half of near-Earth objects (JAXA, 2011).

Conclusion

Visiting asteroids like Ryugu, Bennu, and Itokawa has uncovered their bizarre shapes, active behaviors, and ancient materials, teaching us about solar system violence and potential life seeds. From spinning tops of rubble to particle-spewing diamonds and peanut-shaped piles, these worlds prove space holds endless surprises backed by missions from NASA and JAXA. As we analyze fresh samples, the picture of our cosmic neighborhood grows clearer.

Sources

JAXA. (2011). Hayabusa sample analysis results. ISAS/JAXA. https://global.jaxa.jp/article/special/hayabusa/

JAXA. (2021, December 23). A first look at the composition of the sample from asteroid Ryugu. ISAS/JAXA. https://www.isas.jaxa.jp/en/topics/002895.html

JAXA. (2024, November 22). Salt Crystals in Samples from Asteroid Ryugu Sheds Light on Origin. ISAS/JAXA. https://www.isas.jaxa.jp/en/topics/003879.html

NASA. (2020, October 16). Ten Things to Know About Bennu. NASA. https://www.nasa.gov/solar-system/ten-things-to-know-about-bennu/

NASA. (2024, November 3). 25143 Itokawa. NASA Science. https://science.nasa.gov/solar-system/asteroids/25143-itokawa/

NASA. (2025a, January 29). NASA’s Asteroid Bennu Sample Reveals Mix of Life’s Ingredients. NASA. https://www.nasa.gov/news-release/nasas-asteroid-bennu-sample-reveals-mix-of-lifes-ingredients/

NASA. (2025b, March 11). The asteroid Bennu is even weirder than we thought. NASA (via New Scientist collaboration). https://www.newscientist.com/article/2471749-the-asteroid-bennu-is-even-weirder-than-we-thought/ (Note: Adapted from peer-reviewed summary; primary data from OSIRIS-REx team.)

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