Moon found orbiting near-Earth asteroid

Two side-by-side images of a space rock with a small white dot at two different positions near it.
Astronomers used radar to obtain images of asteroid 2020 BX12. They found a smaller object orbiting it. Note the smaller object’s change in position from the February 4, 2020, image to the February 5 image. That shift is due to the little moon’s motion in orbit around the larger asteroid. Image via Arecibo Observatory.

Scientists at the Arecibo Observatory in Puerto Rico announced on February 10, 2020, that they’ve discovered a moon orbiting the near-Earth asteroid 2020 BX12. Near-Earth means the asteroid comes into Earth’s neighborhood. 2020 BX12 is also defined as a potentially hazardous asteroid, meaning it’s big enough to cause regional damage if it were to strike us. But this asteroid – and its newly found moon – pose no danger at this time. This double asteroid is currently moving away from Earth.

The discovery of the asteroid moon came not long after the Arecibo Observatory had resumed telescope operations after a temporary suspension following a series of earthquakes striking the southern part of the island. Shortly after resuming operations this month – on February 4 and 5 – astronomers using Arecibo’s planetary radar system discovered the moon orbiting 2020 BX12.

Huge dish embedded in the ground with towers around it and cables holding up a receiver high above it.
A wide view of the Arecibo Observatory’s big radio dish. This iconic observatory in Puerto Rico has appeared in films, games and TV shows. Image via Arecibo Observatory.

The new radar images from Arecibo indicate that the moon is about 230 feet (70 meters) wide. That’s in contrast to the asteroid itself, which is about 540 feet (165 meters) wide. Notice the name of this asteroid: 2020 BX12. Its name is a clue that the asteroid itself was found earlier this year. Astronomers found it via the ATLAS near-Earth asteroid survey being conducted from the Mauna Loa Observatory in Hawaii.

From the changes in position of the moon during the radar observations, the scientists were able to determine that while the larger asteroid rotates about once every 2.8 hours, the moon likely rotates at the same speed as it orbits the bigger asteroid – approximately every 50 hours or less. The Earth’s moon is similarly “tidally locked,” meaning it completes one rotation and one orbit over the same amount of time (one month).

Luisa Fernanda Zambrano-Marin, a science operations associate at Arecibo and graduate student from the University of Granada in Spain, said she was excited about the team coming together to continue observations despite the ongoing caution about strong earthquakes. She was running the observation that took the images of 2020 BX12 on February 4 and 5, 2020, and worked with the team to derive the estimates for the properties of what was found to be two asteroids.

In a statement, Anne Virkki, the head of the planetary radar group at the Arecibo Observatory, said:

We are more than glad to be able to resume observations, especially when we get to observe asteroids as interesting as 2020 BX12.

She continued:

Only a few asteroids of more than 150 meters across come as close to the Earth as 2020 BX12 does, and even fewer of them are binary asteroids, which can provide us with valuable information on asteroids’ sizes, shapes, masses and densities. Combining the radar data with optical observations can help to reveal the objects’ compositions, and how binary asteroids form and change with time.

For more about the newly found moon, visit NAIC’s Planetary Radar Science Group page.

Orbiting moons have been detected in fewer than 15% of all near-Earth asteroids.

In addition to the discovery of the asteroid’s moon, the radar data revealed that the asteroid is likely round, possibly similar in shape to the asteroid 101955 Bennu. NASA’s OSIRIS-REx spacecraft is visiting Bennu right now for a first-of-its-kind American mission to collect samples and return them to Earth.

Animated GIF image of 2020 BX12 and its satellite.
Series of range-Doppler radar images of 2020 BX12 observed on February 4, 2020. Image via Arecibo Observatory.
A view from the ground of the Arecibo Observatory dish, surrounded by thick forest, and receiver suspended above it.
Another view of Arecibo via University of Central Florida, which currently operates the observatory.

Bottom line: Near-Earth asteroid 2020 BX12 has a satellite in orbit around it. This discovery was made by scientists at the Arecibo Observatory in Puerto Rico while observing the asteroid on February 4 and 5, 2020.

Via University of Central Florida

Via Arecibo Observatory

February 18, 2020

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