A speedy asteroid suddenly appeared and flew past Earth in just 30 minutes

Astronomers now know its orbit for the next 100 years.
Ameya Paleja

On July 25, 2019, astronomer Luisa Fernanda Zambrano-Marin and her team at the Aricebo Observatory in Puerto Rico spotted a fast-traveling asteroid headed toward Earth. Flying in from a blindspot, the asteroid gave the astronomers a window of barely 30 minutes to learn as much about it as they could, SciTech Daily reported. And then it was gone. 

Near-earth objects (NEOs) are comets or asteroids that come within a distance of 1.3 astronomical units (au) or the distance between the Earth and the Sun. According to the estimates of the Center for Near Earth Object Studies (CNEOS), there are nearly 30,000 asteroids that are known to us, while any such object that is wider than 460 feet (140 m) across is considered a potentially hazardous object (PHO). 

This is why astronomers try to keep a close eye in the skies for asteroids that might be heading toward the Earth and telescopes such as one in Puerto Rico have been designed to aid them in their search. 

What happened in 2019?

Zambrano-Marin and her team work at the University of Central Florida (UCF) that manages the Arecibo Observatory on behalf of the National Science Foundation (NSF). In July 2019, the team's radar scientists received an alert about an incoming asteroid. 

The team knew nothing about it since it had not been spotted before and it was coming from a blind spot for Earth, the solar opposition. The team sprang into action to collect as much data about the asteroid as they could. However, traveling at a relative velocity of over 14 miles (23 km) a second, the astronomers had very little time on their hands to record their data. 

In the end, the team barely got 30 minutes' worth of observation time with the asteroid but that was sufficient to provide details about its size, type, and what keeps it together. 

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Asteroid 2019 OK

The researchers found out that the asteroid was relatively small between 229 feet (70 m) to 422 feet (130 m) in diameter, which is just below the threshold for calling it potentially hazardous. 

Apart from the high speeds, the asteroid was also rotating very fast, at about 3-5 minutes, which puts it in the category of very fast-rotating asteroids that we rather know little about. 

Asteroid 2019 OK is also a C-type asteroid, a rather common type of asteroid found in our solar system. These are likely made up of clay and silicate rocks and given its fast rotation rate, it needs a minimum cohesion rate of 350 Pa to not fall apart. This is much lesser than the internal strength of fractured rocks on Earth, the researchers wrote in their paper that was published in The Planetary Science Journal last month.

The Arecibo Observatory's telescope collapsed in 2020 and the researchers are currently scanning through the troves of data collected over four decades to carry out their research. Based on the data they collected in 2019, the team has mapped out the orbit of Asteroid 2019 OK for 100 years, the research paper said.  

Just last week, China announced that it was building a radar system for planetary defense

If you would like to see some airplane-sized asteroids zip past within a few million miles from the Earth, you can do that this very week. Two of them, one relatively smaller will come close to under five million miles from Earth on July 24, while another asteroid, 2022 OA, discovered only this year swoop past us just 1.2 million miles away on July 25th. 

These may not be the fastest but definitely worth your time. 


We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical observations the apparent diameter is between 70 and 130 m. Combined with an absolute magnitude of H = 23.3 ± 0.3, the optical albedo of 2019 OK is likely between 0.05 and 0.17. Our measured radar circular polarization ratio of μC = 0.33 ± 0.03 indicates 2019 OK is likely not a V- or E-type asteroid and is most likely a C- or S-type. The measured radar echo bandwidth of 39 ± 2 Hz restricts the apparent rotation period to be approximately between 3 minutes (0.049 hr, D = 70 m) and 5 minutes (0.091 h, D = 130 m). Together, the apparent diameter and rotation period suggest that 2019 OK is likely not a rubble-pile body bound only by gravity. 2019 OK is one of a growing number of fast-rotating near-Earth asteroids that require some internal strength to keep them from breaking apart.

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