See NASA images of the 2 large asteroids that passed Earth

Radar imagery in black and white showing a larger object and a tiny white blip below in 7 frames.
When the 2 large asteroids passed Earth in late June, 1 was hiding a secret. NASA images revealed that asteroid 2011 UL21 (top circle) has a tiny moon (bottom circle) as a companion. Image via NASA/ JPL-Caltech.

NASA images the 2 large asteroids that passed Earth

NASA’s Goldstone radar in California observed the two large asteroids that passed Earth in late June. The radar targeted the larger asteroid, 2011 UL21, for nine days and the somewhat smaller asteroid, 2024 MK, for three days. On July 3, 2024, NASA shared the images it obtained. It said 2011 UL21 was harboring a tiny moon, and 2024 MK had its orbit changed due to its close pass by Earth.

Earlier observations showed asteroid 2011 UL21 to have an impressive diameter of about 1 mile (1.5 km). Because about 2/3 of large near-Earth asteroids are binary systems, scientists suspected 2011 UL21 might have a companion. And, indeed, they found a little moonlet in their imaging. The images showed a moonlet about 1.9 miles (3 km) from its parent asteroid.

NASA said:

Radar observations taken during these two close approaches will provide valuable practice for planetary defense, as well as information about their sizes, orbits, rotation, surface details and clues as to their composition and formation.

2 large asteroids passed near Earth

In an astronomical coincidence, the asteroids appeared best on the same night, June 28. Asteroid 2011 UL21 is one of the largest near-Earth asteroids visible in amateur telescopes this year, at 1 mile (1.5 km) wide. Asteroid 2011 UL21 is larger than 99% of all known near-Earth objects. However, it passed at a safe distance of 4,122,350 miles (6,634,279 km) from Earth’s surface – or about 17 times farther than the moon – on June 27.

The other asteroid, newly discovered 2024 MK, is a bit smaller. Estimates vary, but NASA says it is 500 feet (150 m) wide. But it passed closer to us than the moon on June 29.

The Minor Planet Center classified both 2011 UL21 and 2024 MK as a Potentially Hazardous Asteroids due to their large sizes and nearness to Earth. But, to be clear, there is absolutely no danger from any of the asteroids, or from any known space rock so far.

Imaging 2024 MK

At around 500 feet (150 meters) wide, asteroid 2024 MK passed only about 3/4 the moon’s distance from Earth. NASA said:

Close approaches of near-Earth objects the size of 2024 MK are relatively rare, occurring about every couple of decades, on average, so the JPL team sought to gather as much data about the object as possible.

Its orbit was changed by Earth’s gravity as it passed by, reducing its 3.3-year orbital period around the sun by about 24 days. Although it is classified as a potentially hazardous asteroid, calculations of its future motion show that it does not pose a threat to our planet for the foreseeable future.

Large asteroids: A rock in space shown from different angles as it tumbles.
This is the view of the asteroid 2024 MK as it tumbled past Earth. The Goldstone Solar System Radar in California captured these images of the 500-foot-wide asteroid. Image via NASA/ JPL-Caltech.

Asteroid 2011 UL21

Asteroid 2011 UL21 is a huge space rock. As you might have guessed from its name, we’ve known about it since 2011. Scientists discovered it in October 2011 from the Catalina Sky Survey in Tucson, Arizona. However, this was its closest approach in its orbit since its discovery. Asteroid 2011 UL21 passed closest to our planet on June 27 around 4:16 p.m. EDT (20:16 UTC).

However, asteroid 2011 UL21 was easily observable in small telescopes until June 30. It appeared brightest on Friday, June 28. Then, in 65 years, the large space rock will return even closer to Earth on June 25, 2089.

In fact, due to its large size and amazing speed of 57,937 miles per hour (or 93,240 km per hour) relative to Earth, observers could easily detect the asteroid’s motion against the stars in telescopes of 6-to-8 inches (15-20 cm) and larger.

Watch asteroid 2011 UL21 pass background stars in this video from Steven Bellavia and the Custer Institute and Observatory.

Asteroid 2024 MK

While it’s taken years from asteroid 2011 UL21’s discovery to its closest flyby, asteroid 2024 MK is another story. Scientists discovered 2024 MK on June 16, 2024, with ATLAS-Sutherland in South Africa. And just a couple weeks later it made its closest pass to Earth. Asteroid 2024 MK passed Earth at about 77% the Earth-moon distance. And while it is much smaller than 2011 UL21, a rock this size would still do considerable damage if it struck Earth. For comparison, the space rock that disintegrated over Chelyabinsk in Russia in 2013 was about 1/5 to 1/10 of the size of 2024 MK.

Closest approach of asteroid 2024 MK was on June 29, 2024, at 9:50 am EDT (13:50 UTC). However, the asteroid appeared brightest on Friday, June 28. Coincidentally, it was the same night as 2011 UL21 appeared brightest.

Bottom line: When two large asteroids passed our planet in late June, NASA captured images of these near-Earth space rocks. And one was hiding a tiny moon.


July 4, 2024

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