Earth’s Temporary Moon

Earth has acquired a temporary moon. It has been tagging along with us for about 60 years and will continue to tag along until 2083. It is a small asteroid going by the name 2025 PN7.

Officially discovered by the University of Hawaii and confirmed this past week, it is what’s known as a “quasi-moon”—a rare celestial companion that travels almost exactly in sync with Earth. It’s not a true moon because it doesn’t orbit around the Earth. Right now, it is orbiting the sun, keeping pace with us so that it appears to shadow our planet.

2025 PN7 is estimated to be 18 to 36 meters wide, about the height of a small building, which is tiny by cosmic standards. That may be why it took so long to notice it.

Our real moon is held tight by gravity, but this asteroid isn’t bound to us. Think of it as a friendly jogger matching our stride on the same track—close enough to notice but never touching.

After 2083—if its current orbit holds that long—it will drift away into open space. At its closest approach to us, it gets within 4 million kilometers, which is roughly ten times the distance between Earth and the moon. At its most distant, it can swing out to 17 million kilometers. That changing distance is because of the competing gravity of the sun and various planets.

So far, astronomers have confirmed only eight quasi-moons. Each of them is a small but valuable clue in understanding how asteroids move and how Earth’s gravity shapes the space around us. These objects are more than curiosities. They help refine orbital models, improve predictions for near-Earth asteroids, and could serve as testing grounds for future missions. After all, they’re close, relatively stable, and reachable without traveling too far from home.

2025 PN7 will never outshine our real moon. But it’s there and worth knowing about.

 

https://www.msn.com/en-us/news/technology/nasa-confirms-earth-now-has-two-moons-until-2083/ar-AA1OQpRt?ocid=hpmsn&cvid=68f6da61133a4c1f869a4eb40f801f5c&ei=63

 

Wandering Jupiter

A few weeks ago, I explored the possibilities of what might happen if Neptune's orbit should get jiggled by a rogue sun wandering too close to our system. More recently, I read an article that explains that Jupiter has already done some wandering, in order to be in the orbit it's in.

Jupiter's current orbit averages 5.2 astronomical units (AU = the average distance between the sun and Earth). But researchers now say the gas giant started to form some 18 AU away, which is about twice as far out as present-day Saturn. Furthermore, Jupiter made that journey in about 700,000 years, which is the blink of an eye in astronomical terms.

The idea of a wandering Jupiter is not new; I've heard several theories about it. But this time there is some proof that Jupiter formed a long way from the sun and then migrated inward, and that proof came from the Trojan asteroids that share Jupiter's orbit.

Jupiter has 2 groups of Trojan asteroids that share its orbit around the sun. A large group is in front of the planet, and a smaller group follow it. Researchers ran numerous computer simulations that showed the early solar system through millions of years of evolution by 50-day increments.

The simulations showed that the inward migration of the giant planet always resulted in a larger swarm of Trojans in front of Jupiter than behind it. As Jupiter traveled inwards—propelled by gravitational interactions between the fledgling gas giant and the sun's protoplanetary disk—it created a wide zone of gravitational stability in front of it, leading to more asteroids being caught before it than behind it.

Other simulations that relied on Jupiter forming in its current position resulted in both groups of asteroids being the same size.

One more step to this becoming the solar system we know today.

I can't help but wonder what was happening to Venus, Earth and Mars during the 700,000 years that Jupiter came rolling so much closer.

 

"Trojan asteroids reveal Jupiter's great migration", Astronomy, July 2019