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Earth's Minimoons (Orbiting Asteroids & Other Objects)

EnolaGaia

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Retrospective analysis of this 2016 fireball seen over Australia suggests it may have been a "minimoon" (a small asteroid or other space rock captured into an earth orbit before finally entering our atmosphere)
Fireball Spotted Over Australian Desert May Have Been Super-Rare 'Minimoon'

Fireballs explode in Earth's atmosphere all the time, usually unremarkably. And a fireball that exploded over the Australian desert in 2016 might have been mistaken for any other bolide, if not for a network of cameras monitoring the sky to search for just such events.

It was thanks to images taken by these cameras - called the Desert Fireball Network - that astronomers were able to ascertain the fireball was no ordinary exploding space rock.

Instead, velocity data revealed the rock had probably been in orbit around Earth before meeting its fiery end; a phenomenon known as a temporarily captured orbiter, or, colloquially, a minimoon. ...
FULL STORY: https://www.sciencealert.com/a-fire...t-could-have-been-a-rare-and-elusive-minimoon
 
Another rare minimoon has been identified. It's not projected to orbit earth for very long.

Earth Seems to Have Captured an Additional Moon, And We Didn't Notice For 3 Years

In the skies above Earth, astronomers with the Catalina Sky Survey have spotted what might be a new friend: an asteroid temporarily captured by our planet's gravity, what we call a minimoon.

It's named 2020 CD3, a small chunk of likely carbonaceous rock between 1.9 and 3.5 metres (6.2 and 11.5 feet) in diameter. And here's the kicker - the rock's trajectory indicates it's been in orbit for around three years already.

The near-Earth neighbourhood is a relatively busy place, with boatloads of asteroids zipping past. The precise numbers, however, are unclear; estimates put the number at millions, but as of February 25, the number discovered was only 22,211.

That's because asteroids are really small, we don't know where they are (so we don't know where to look), and they typically don't give off a lot of light, even when they're reflecting sunlight. ...

You'd think that, with so many rocks flying around, they'd get slurped up by Earth's gravity all the time. Well, they do; but most of them don't hang around long enough to become minimoons.

These briefly captured space rocks either head straight into the atmosphere, where they are burned up on entry, becoming spectacular fireballs; or they skim around for a partial orbit before their velocity carries them onwards and upwards.

It's only the smallest number of passing space rocks that are likely to become minimoons. According to a 2012 supercomputer simulation including 10 million virtual asteroids, only 18,000 got captured in Earth orbit.

So not only are they hard to spot, they are super-rare. There have been several candidates for minimoons, including two fireballs with slow velocities that implied an orbital origin, but only one confirmed - an asteroid called 2006 RH120 that orbited Earth for about a year from 2006 to 2007. ...
FULL STORY: https://www.sciencealert.com/earth-seems-to-have-captured-a-super-rare-mini-moon
 
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A new minimoon is about to be temporarily captured by earth's gravity well. There are growing suspicions this one may be a long lost rocket booster stage from the Sixties. Otherwise, its characteristics are odd for an asteroid.
Earth Is About to Capture a Minimoon, But There's Something Odd About This One

We all know and love our Moon. It's been Earth's constant companion for billions of years, a mainstay of the skies. But it's not our only companion.

Every now and again, a smaller object gets temporarily captured in our planet's orbit, hanging around for a short period of time - a few months or years - before being flung out back into space.

We call these objects minimoons, and while we have made a few tentative detections of such temporarily captured asteroids, only two have ever been confirmed - 2006 RH120, which visited in 2006 and 2007, and 2020 CD3, in Earth orbit from 2018 to 2020.

Now astronomers have spotted a new object, named 2020 SO, on an incoming trajectory that is likely to see it temporarily captured by Earth's gravity. Projections have an object arriving next month, in October 2020, and hanging around until May 2021, when it will depart for environs elsewhere. ...

2020 SO has been classified as an Apollo asteroid in the JPL Small-Body Database - a class of asteroids whose paths cross Earth's orbit. This class of asteroid often has near-Earth encounters. But there are a few clues that 2020 SO is not like the others.

The object is on an orbit that's just a smidge over a year, and on a very low inclination with respect to Earth's orbit; that is, it's not tilted, but on the same orbital path. Its eccentricity - the deviation of the shape of its orbit from a perfect circle - is just a little higher than Earth's. And its velocity is much, much lower than the velocity of an Apollo asteroid.

"The velocity seems to be a big one," space archaeologist Alice Gorman of Flinders University in Australia told ScienceAlert. "What I'm seeing is that it's just moving too slowly, which reflects its initial velocity. That's essentially a big giveaway."

Objects that have come from the Moon have a lower velocity than asteroids, too; but, Gorman noted, 2020 SO is even slower than Moon rocks.

All this points to the object potentially being space junk; specifically, according to Paul Chodas of JPL, the discarded Centaur stage of a rocket that launched an experimental payload called Surveyor 2 to the Moon in September 1966. ...

The estimated size of 2020 SO matches the properties of a 1960s-era Centaur stage. According to NASA's CNEOS database, the object is between 6.4 and 14 metres (21 and 46 feet) long; a Centaur stage measures 12.68 metres (41.6 feet). ...

FULL STORY: https://www.sciencealert.com/earth-might-be-about-to-get-a-temporary-minimoon-but-what-is-it

See Also:

Earth's new minimoon might be a rocket humans launched into space in the 1960s
FULL STORY: https://www.livescience.com/minimoon-human-made.html
 
A Mysterious Object Is Hurtling Towards Earth, and Scientists Don't Know What It Is

A mysterious object will fly past the Earth tomorrow and scientists still aren't quite sure what it is.

The object, dubbed 2020 SO by astronomers, will come within "just" 31,605 miles of our planet at 3:50 a.m. ET on December 1, according to NASA's Center for Near Earth Object Studies

The object, which is estimated to measure between 15-33 feet across, was discovered by the Pan-STARRS survey based in Maui, Hawaii, on September 17, 2020. This find was confirmed two days later by the Minor Planet Center, which is responsible for the designation of minor bodies in the solar system.

Initial observations suggested that the object was an asteroid. But scientists at CNEOS soon began to suspect that 2020 SO was not a normal asteroid.

"We are not sure it is an asteroid—that is, a natural body," Masi wrote on the Virtual Telescope Project website.

CNEOS director Paul Chodas subsequently suggested that 2020 SO may not be an asteroid at all, tentatively identifying it as the Centaur rocket booster from NASA's failed Surveyor 2 lunar mission, which launched on September 20, 1966.

270px-Centaur_upper_stage_being_lifted.jpg


He came to this conclusion after turning back the clock and running the object's orbit backwards using a computer model to work out its past trajectory through space.

Chodas found that the object had already passed relatively close to Earth several times over the past decades, including one moment that indicated it could have actually launched from Earth, according to NASA.

"One of the possible paths for 2020 SO brought the object very close to Earth and the Moon in late September 1966," Chodas said in a statement. "It was like a eureka moment when a quick check of launch dates for lunar missions showed a match with the Surveyor 2 mission."

The object's low relative velocity and orbital plane also supported the argument that the object was potentially not of natural origin.

2020 SO was captured by Earth's gravity on November 8, and calculations show it will remain in orbit around our planet as a temporary satellite until March 2021 before it escapes back into a new orbit around the sun.

https://www.newsweek.com/mysterious-object-earth-nasa-asteroid-1551202

maximus otter
 
A Mysterious Object Is Hurtling Towards Earth, and Scientists Don't Know What It Is
Initial observations suggested that the object was an asteroid. But scientists at CNEOS soon began to suspect that 2020 SO was not a normal asteroid. ...
CNEOS director Paul Chodas subsequently suggested that 2020 SO may not be an asteroid at all, tentatively identifying it as the Centaur rocket booster from NASA's failed Surveyor 2 lunar mission, which launched on September 20, 1966.

Based on telescopic observations NASA has now confirmed the mystery object is indeed a Centaur rocket booster.
NASA: Mystery object is 54-year-old rocket, not asteroid

A mysterious object temporarily orbiting Earth is a 54-year-old rocket, not an asteroid after all, astronomers confirmed Wednesday.

Observations by a telescope in Hawaii clinched its identity, according to NASA’s Jet Propulsion Laboratory in Pasadena, California. ...

Chodas was proven right after a team led by the University of Arizona’s Vishnu Reddy used an infrared telescope in Hawaii to observe not only the mystery object, but — just on Tuesday — a Centaur from 1971 still orbiting Earth. The data from the images matched. ...

FULL STORY: https://apnews.com/article/asteroids-hawaii-dc318b7880005a32f7829afc05a55c12
 
Object 2020 SO (the minimoon that turned out to be a Sixties-era rocker booster) will soon exit earth orbit and start orbiting the sun.
Earth is about to lose its second moon, forever

Earth's second moon will make a close approach to the planet next week before drifting off into space, never to be seen again.

"What second moon," you ask? Astronomers call it 2020 SO — a small object that dropped into Earth's orbit about halfway between our planet and the moon in September 2020. Temporary satellites like these are known as minimoons, though calling it a moon is a bit deceptive in this case; in December 2020, NASA researchers learned that the object isn't a space rock at all, but rather the remains of a 1960s rocket booster involved in the American Surveyor moon missions.

This non-moon minimoon made its closest approach to Earth on Dec. 1 (the day before NASA identified it as the long-lost booster), but it's coming back for one more victory lap ... Minimoon 2020 SO will make a final close approach to Earth on Tuesday (Feb. 2) at roughly 140,000 miles (220,000 kilometers) from Earth, or 58% of the way between Earth and the moon. ...

FULL STORY (With Animation Illustrating the Encounter):
https://www.livescience.com/farewell-minimoon-so-2020.html
 
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