EarthSky | $5-billion asteroid Nereus flies by tomorrow


Graphic comparing size of Nereus to Eiffel Tower.
Nereus is approximately 330 meters (yards) wide. Its size is often compared to the Eiffel Tower. Image via NASA.

A 1,083-foot (330-meter) asteroid has created a buzz on social media this week. It’ll pass Earth on Saturday, December 11, 2021. Closest approach will happen at 13:51 UTC (10:51 a.m. EST; translate UTC to your time) on December 11. It will not strike Earth. At its closest, Nereus will pass about 2.4 million miles (3.9 million km) away. That’s close on a cosmic distance scale. But it’s still about 10 times the moon’s distance. Yet this close pass and others has caused 4660 Nereus to be classified as a Potentially Hazardous Asteroid. It makes close approaches several times each century. And – in part because it comes close and in part because it’s “slow” – space entrepreneurs have cast their gaze toward Nereus as well. By some reports, the space rock is worth an estimated $5 billion in precious metals.

Nereus completes an orbit around the sun every 661 days (1.81 Earth-years). Saturday’s close pass of 10 lunar-distances will be its closest until 2060, when Nereus will pass at only three lunar-distances.

Will you see it?

This object will not be visible to eye alone. Asteroid 4660 Nereus will reach a visual magnitude around 12. That’s far too faint to see with the eye. To see Nereus, you would need at least an 8-inch (20-cm) telescope, or larger.

An amateur astronomer pointing a telescope at the correct location and time, can carefully observe the stars in the field of view, and then compare the view 15 or 20 minutes later to try to detect an apparent star that has changed position. The moving “star” will be asteroid Nereus. A long-exposure image would be an easier way to detect the space rock, since it will appear as a streak or line, because of its motion.

On December 9, 2021 at 9:00 p.m. CT, asteroid Nereus will be located close to star HIP 52064. Illustration by Eddie Irizarry / Stellarium

Video of asteroid Nereus

Astronomer Alessandro Marchini emailed EarthSky to say that his group at the University of Siena spent some time this week observing asteroid 4660 Nereus. He called it “a very interesting object” and said:

Asteroids are one of the research fields of our observatory: analyzing their changes in brightness over time, we can estimate their shape and their rotation period.

I made a time-lapse video with the images collected with our telescope in more than 3 hours on December 7, with the rush among the stars of the asteroid Nereus.

You can see Alessandro’s video below:

Space entrepreneurs are eyeing it

Asteroid Nereus is an elongated rock that travels at 14,719 miles per hour (23,688 km/h). While this may sound like a huge speed, Nereus is in fact a “slow” space rock compared to many other asteroids. That relatively low speed is an advantage for those who want send a robotic spacecraft in the future to study it. That is, its slow speed means a spacecraft can rendezvous with the asteroid more easily. In 2009, space scientists considered Nereus “a strong candidate for a rendezvous mission.” It would take about a year for a robotic spacecraft to enter orbit around Nereus.

And space entrepreneurs are eyeing Nereus as well, for the same reason, because of its slow speed relative to other asteroids. The Hill reported on December 1:

Asterank, a database that monitors more than 600,000 asteroids, estimates that Nereus’ value is at $4.71 billion, making it one of the most cost-effective asteroids to leverage for mineral resources. The asteroid is thought to contain billions worth of nickel, iron and cobalt.

Asteroid mining is a concept that began to gain popularity in the early 2010s, but now as the commercial space industry has taken off with big players like Blue Origin and SpaceX, it could pick back up again starting with Nereus.

Chart showing relative value of various asteroids.
View larger. | Lots of asteroids – indeed, perhaps most of the millions of asteroids in our solar system – are valuable because of the metals they contain. But Nereus’ slow speed makes it a logical first target. Chart via Asterank

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Astronomers are studying it, too

In 2002, the space rock made a similar approach to Earth which enabled scientists to study its shape and size using radar. Using the Arecibo Observatory and the Goldstone Antenna at California, astronomers sent radio signals that allowed them to obtain very good radar images. However, since this week’s approach is slightly closer than the previous ones, scientists might detect some surface features that were not visible in 2002.

This closer approach might also reveal if the asteroid has a “moon” orbiting around it, as many asteroids do. Bad luck, though. Astronomers say the iconic Arecibo Observatory in Puerto Rico was the best tool for detecting a “moon” or secondary space rock. And, as you might have heard, Arecibo collapse and was decommissioned last year.

But astronomers are already studying asteroid Nereus during this flyby, with other earthly observing tools. Radar observations from Goldstone started on December 5. They’re expected to continue for about two weeks.

Asteroid Nereus: Radar image of space rock.
This is a radar image of asteroid 4660 Nereus. If you saw the asteroid through a small telescope it would look, true to its name, “star-like.” Image via NASA/NSF/Arecibo Observatory.
Five circles of different colors indicate the orbit of Asteroid 4660 Nereus
Orbit of Asteroid 4660 Nereus via NASA/JPL.

Bottom line: Asteroid Nereus will pass Earth at about 10 lunar distances (2.4 million miles, 3.9 million km) on Saturday, December 11, 2021.



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