Weird 'Trojan in Retreat" asteroid may be an ancient alien
Tuesday, May 22, 2018, 9:02 PM - The vast majority of asteroids are 'citizens' of our solar system, as they formed here billions of years ago. We've seen at least one 'tourist', when asteroid 'Oumuamua passed through last year. Now, we may have found our first known 'permanent resident' asteroid, here from distant alien star.
Last year, astronomers revealed Asteroid 2015 BZ509, or 'BZ' for short, which was already remarkable due to its retrograde orbit. Unlike the vast majority of objects in our solar system, which orbit around the Sun in a counter-clockwise direction (when you view the system from above the Sun's north pole), asteroid BZ orbits the other way around.
What's more, this "Trojan in Retreat", as the researchers called it, has a close relationship with Jupiter. There are massive clusters of asteroids that both precede and follow Jupiter in its orbit - collectively known as 'Trojan' asteroids - and all of the ones we know about, except BZ, orbit in the same direction as Jupiter. BZ avoids impacting with Jupiter by having a tilted orbit, so that every time the two would meet, the asteroid is either above Jupiter or below it.
According to new research, published in the Monthly Notices of the Royal Astronomical Society, BZ's orbit is super-stable.
In their study, astronomers Fathi Namouni, of Observatoire de la Côte d'Azur in France, and Dr Helena Morais, of the Universidade Estadual Paulista in Brazil, plotted BZ's orbit and ran their model backwards, to discover that its orbit is so stable that it may even pre-date the formation of our solar system!
"It is a strong candidate for the oldest object in the solar system," Dr. Namouni told Reuters.
How is this possible?
Although Jupiter is the biggest planet in the solar system, which can easily fling any asteroid that dares to play chicken with it into the Sun, or even completely out of the solar system, it seems that BZ's orbit is just right to prevent either of those things from happening.
Phil Plait, of SyFy's Bad Astronomy, explains it very well:
Also weirdly, it gets close enough to Jupiter twice every orbit to get a bit of a tug from the giant planet's huge gravity. Over time, you'd think that should disturb the orbit enough to send BZ off its path, either plunging it into the Sun or ejecting it from the solar system. But that's not the case; last year it was found that, because of its unusual orbit, when it passes Jupiter one time it gets tugged first one way, and then the next pass it gets tugged the other way (think of it as left and right if that helps). The two forces balance out, and BZ's orbit is stable.
So, what does this mean?
It could mean that BZ is not a native of our solar system, but instead, arrived here, whole and intact, from some distant alien star.
"If 2015 BZ509 were a native of our system, it should have had the same original direction as all of the other planets and asteroids, inherited from the cloud of gas and dust that formed them," Dr. Namouni said, according to the Royal Astronomical Society.
So, this asteroid, already one of the strangest denizens of our solar system, may not even be from here!
Now, this isn't the ONLY explanation for BZ's strange and super-stable orbit.
According to Phil Plait:
First, just because their simulations show it could have been in its orbit for 4.5 billion years doesn't mean it has been. Maybe it had a planetary encounter a few thousand years ago and got lucky. In general (as they point out in their paper) many objects in this part of the solar system don't last long in their orbits before being nudged away by gravitational perturbations. But that doesn't mean there can't be exceptions. Again, I'm not saying this is one, but the onus is on them to show it isn't.
Also, it's possible we're just seeing the biggest object in a population of smaller ones in similar orbits. A good example of this is Pluto. It's also on a special orbit that brings it closer to the Sun than Neptune, but they can't interact because Pluto's orbit is shaped in such a way that every time it crosses Neptune's orbit, the big planet is one-fourth of the way around its orbit, so it's too far away to affect Pluto. There are lots of smaller objects on similar orbits just recently discovered, too. If this is the case, then it's less likely BZ is an outlier.
Still, if BZ is a permanent resident asteroid, arrived here from some distant star to make this its new home, it could be an important factor in the discussion of how life developed on Earth.
"This discovery tells us that the solar system is likely to be home to more extra-solar asteroids and comets captured early in its history," Dr. Morais told Reuters. "Some of these objects may have collided with the Earth in the past possibly carrying water, biomolecules or even organic material."