Asteroid that cohabits an orbit with Jupiter came from outside the solar system | Hacker News Reader

Asteroid that cohabits an orbit with Jupiter came from outside the solar system

nytimes.com

67 pointsdigital5539 comments

Three space stories on the front page today. Makes me happy

Why is originating outside the solar system the only explanation for a retrograde orbit? Couldn't a close encounter or several with other bodies reverse it's direction around the sun?

I imagine the probability of that happening would be less than capturing a wandering body.

> Why is originating outside the solar system the only explanation for a retrograde orbit?

From TFA:

> “But at the beginning of this investigation, we did not suspect BZ to be of interstellar origin,” he explained. “We developed a new method that allows us to follow the asteroid back in time to see which part of the solar system it came from.”

> But as far back as they could trace the jigsaw parts of the solar system — rocks and planets swirling and mixing — all the way to its birth, 4.5 billion years ago, BZ kept going around the same wrong way. Which meant the asteroid could not have been part of the swirling cloud of dust and gas from which the sun and planets originally condensed so long ago.

In other words: in simulation runs, extrasolar was the only explanation for this retrograde orbit.

That sounds a bit like starting with a smoothie and running the blender in reverse until the starberries put themselves back together. The n-body problem is chaotic and 4.5By is a long time. It's incredible.

edit: The actual paper is very readable and very interesting. Props to the NYT for linking it.

It's more like putting berries into the blender and running it to see how often a berry hits you in the eye. They found that coplanar planets and coplanar debris statistically won't produce this specific type of (high inclination) orbit.

Jupiter's orbit is fairly circular (eccentricity about 0.05). How does an extrasolar obeject get captured into such an orbit?

I read somewhere that in-system asteroids could be captured into circular orbits (Phobos, Demos at Mars, lots of moons of Saturn and Jupiter) if they're originally half of a binary asteroid. The other half gets kicked away to circularize the remaining half's orbit. That doesn't seem like something that could happen to put an object into retrograde orbit around the Sun.

"Here we show that irregular satellites are captured in a thin spatial region where orbits are chaotic , and that the resulting orbit is either prograde or retrograde depending on the initial energy. Dissipation then switches these long-lived chaotic orbits into nearby regular (non-chaotic) zones from which escape is impossible. The chaotic layer therefore dictates the final inclinations of the captured moons" http://sci-hub.tw/10.1038/nature01622

I found this: http://www2.esm.vt.edu/~sdross/papers/borum-et-al-2012-repor...

It reads as I remember, but the diagrams are better than I recall. Maybe there is another paper out there with less cool diagrams on this topic.

Does the fact we can find objects from others systems increases the likelihood of panspermia ?

Can't find a sound source right now[1] but reportedly some mushroom spores are able to make it into space and withstand its conditions.

Edit: thus the more extraterrestrial material makes it to earth the higher the chances that biological material able to withstand the transport conditions makes it here as well.

[1] https://www.dopemagazine.com/spores-in-space/

Tardigrades have been demonstrated capable of surviving in space for extended periods and withstanding extreme conditions.

http://www.bbc.co.uk/nature/12855775

Then there is the whole recent "Octopus RNA too weird for Earth" thing, which is setting alight the panspermia theses .. myself, personally, I'm tending to think its more and more likely.

In my head, in 10 years time, we'll all have this gigantic "there is life in space, and its just like here on Earth only .. hardier .." discussion again and again. Or, maybe we'll still be wondering .. either way, my mind is made up: Octopus are galaxy-wide species, tardigrades too, and we monkeys better be careful we don't join the rest of whatever bipedal species are out there, and step on too many of our little tardigrade/octopus buddies. And, so on.

(BTW, don't eat octopus! If the aliens invade, they'll probably massacre you eaters first!)

I think so. Four billion years doesn't seem like enough time to evolve the the sophisticated encoding mechanism of DNA and the level of complexity in individual organisms and the interdependencies they have on each other.

I really wish I could find a sort of statistical breakdown of the odds of this all working purely by chance (I'm definitely a fan of evolution and i'm not necessarily invoking woo or God here, just thinking that there are mechanisms at play we don't understand, and a head start would explain a lot for me)

This is how my hopelessly naive mind thinks about the problem:

Let's round up to say there is 10^15kg of biomass on the planet[1], and there are 10^12 cells per kg[2]. Let's assume that those cells have reproduced every hour for the last 4 billion years (or 35x10^12 hours). That's ~35x10^39 opportunities to pass evolved genetic material to the next generation of cell.

One of the organisms with the simplest known genome is mycoplasma genitalium[3], with ~588 genes expressed over 580,070 base pairs. Each base pair has four possible configurations (A,C,G or T).

I don't know much of anything, and I definitely don't know the rules around how the base pairs come together. I'm going to naively assume that these base pairs can come together any way they like, and that mutations in DNA express themselves as changes in these sequences. This leaves the DNA of mycoplasma gentalium with 4^580070 or 8.7*10^349236 possible configurations of their DNA.

Obviously only a small portion of those are viable. But how do you get from nothing to something of the complexity required to reproduce, and then how do you get from something of that level of simplicity to the genetic diversity that we have on the planet. How many generations from the first living organism are there to current people. Let's say it's a trillion generations. How does random mutation bring you from say a half a million base pairs at the beginning to 3 billion finely tuned base pairs[3] at the end? It just doesn't seem like enough time to me.

1. https://en.wikipedia.org/wiki/Biomass_(ecology)

2. https://en.wikipedia.org/wiki/Cell_(biology)

3. https://www.saylor.org/content/BIO_Kimball/users.rcn.com/jki...

Nature doesn't use arbitrary random sequences of base pairs, any more than we use random sequences of English letters. We can make them, of course, but that's as meaningful as 'bthdkekd'.

I am not sure we know enough about the correlation structure of the DNA code to do the calculation you propose.

In a way it is arbitrary, because anything else would imply meaning or intent. Mutations are, as far as we know, arbitrary.

Your last point is the thing that has stymied me to date. What is the range of mutation that would allow for a successful offspring and convey (mal)adaptive changes.

I use 'arbitrary' in the sense of uniformly random. The point is it's not uniformly random. You can think of reproduction as a random walk in the space of DNA combinations, but it's not a uniform random walk. It has a structure that comes from the biochemical processes which perform the recombinations of DNA. Focusing on mutations ignores this point. (Also, as an aside, it's not settled that mutations occur at random positions. That may be a reasonable starting point, but it's likely that the way DNA folds into nucleosomes/chromatine/chromosomes biases the location of mutations.)

I'm not a biologist, but I'd be surprised that genetic reproduction would be as stable 3 billion years ago than now. I would not be surprised that monocellular beings, which don't need DNA replication to survive, had a more defective cloning system, thus more subject to whichever DNA replication bug.

Plus, life took about 1 billion years to emerge. This is huge. The solar system took about the same time to form. Also, life may be extremely slow to appear, but once it's there, progression is quicker. Since the beginning of phanerozoic eon (and Cambrian explosion), a geologic period (Pleistocene, Jurassic, Cambrian...) only lasts a few tens of millions years. I find it very plausible that at the beginning of Cambrian era, a critical step in evolution was reached, allowing a better and faster evolution.

4 billion years, but also massively parallel. Trillions of simultaneous random walking hill-climbers.

This is one heck of a hillclimb:

https://www.youtube.com/watch?v=aoCzZHcwKxI

Pulling this completely out of my ass, lets say the ability to camoflage is 30 genes, ones to modify skin color, signalling to do it on command, mapping to specific parts of the body to create a specific pattern, all of the above for skin morphology, mental ability to map this to prey avoidance, all of the above for ink synthesis (glands, storage, ability to express on command). Let's further assume that those genes are expressed over 500 base pairs (woefully short) for better or worse.

Somehow those genes need to be introduced into the genome to create a ninja octopus out of whatever its predecessor was. To date, all i've heard is that mutation is the source of this new genetic material. So somehow we need to mutate our way to these 500 base pairs. Let's divide that by ten as some kind of poor man's compensation for the flexibility of dna to handle noise and whatnot.

So we need to introduce 50 essential base pairs. There are 4^50 possible combinations of these base pairs, or 10^29 in more recognizable numbers. Do we have 10^29 generations to introduce those? That's a lot of octopus.

> Somehow those genes need to be introduced into the genome to create a ninja octopus out of whatever its predecessor was.

Well no one is saying that a ninja octopus just appeared one day by chance.

> lets say the ability to camoflage is 30 genes, ones to modify skin color, signalling to do it on command, mapping to specific parts of the body to create a specific pattern, all of the above for skin morphology, mental ability to map this to prey avoidance, all of the above for ink synthesis (glands, storage, ability to express on command). Let's further assume that those genes are expressed over 500 base pairs (woefully short) for better or worse.

Think about the things that you said above.

If one octopus out of the hundreds of millions of generations had one of the 30 gene changes that did one thing to its skin that was beneficial, then in short order (say a few thousand generations) that would be the dominant type of octopus. Then one-by-one the items that you listed could easily do the same. Some individually, others maybe at the same time.

I mean there have only been a little over 100k generations since humans split from apes. So a lot can happen in the time spans you are talking about.

Octopuses as a species are supposedly 296 million years old, hatch by the thousands, and only live 3-5 years, so 100 million generations of thousands of octopuses or so to get to where they are today.

The other issue is that usually seemingly useful and complex systems are not "suddenly" created - i.e. they don't just appear. In living organisms almost every feature is an extremized or repurposed variant of some other system.

Something like a bacterial flagellum for example is actually a special-case configuration of proteins which allow the bacteria to secrete compounds. (see: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4632597/ and other resources - it's really interesting)

So all the individual systems in the octopus camoflage system didn't just have to suddenly appear - they all would trace their function to other systems the octopus already had - i.e. its not "chance of this exact thing appearing" its "chance a mutation doesn't make the old system totally useless, while maybe providing a slight benefit".

It's definitely not "totally random". DNA (and more importantly, RNA since that's probably where replication started) have their own chemistry and physics - i.e. it's not like toggling bits in a computer, particular combinations act very different to others. In the case of RNA this is notable because RNA sequences can fold and work as enzymes (ribozymes) on their own.

This means you're definitely not throwing random combinations together until something works - there are favored paths all the way down to the base-pair level.

It's worth reading about the RNA world hypothesis (https://en.wikipedia.org/wiki/RNA_world) to get a feel for this idea. It's unproven (and hell, panspermia still might speed everything up since dumping a truckload of ribozymes from the dessicated remnants of another planets biosphere would be a hell of a kickstart) but it's based on different observed properties of these compounds today.

Ok, ok , it's going to be hard to get used to but maybe, over time I can accept them and find rest again.

Wouldn’t there be as many alien asteroids orbiting in the same direction as against it?

I imagine there should be a few alien asteroids amongst the current contingent.

I take it isotopic Analysis can only be done with a sample. There are energy level differences in isotopes though...

what sort of delta V would a probe need to shadow it?

Perhaps a Jupiter, solar transfer orbit could help...

From what I can tell from the animation in the article, it shouldn't be that far out.

I'm not an astronomer or anything, but from my point of view, it would be quite interesting to find out more about that asteroid's composition etc.

It's not about how far out they are, but how fast they are going relative to Earth. When you're trying to get to something in space, you need to roughly match both positions and velocities between you and your target.

I did a quick googling, the earth's orbital speed is 29.78 km/second, so you'd need to cancel that out first, then speed up again to match the speed of the asteroid. For comparison, you need 9.4 km/s of delta-V to bring something in low earth object (7.8 km/s for orbit, plus 1.3-1.8 km/s for atmospheric and gravity drag). To put something in counter-rotating low earth orbit, you probably also need to add the rotation speed of the earth (at the location of launch), but, I don't know the figures there (not a three second googling away).

So uh, yes. Needs a rocket with at least four times as much delta-V as what we currently use to put something in orbit. I'm reading the New Horizons project, which up until now was the fastest thing to leave Earth, was shooting away from us at 16.26 km/s - all from chemical thrust. The Voyager 1 is still going a bit faster thanks to gravity assists.

Probably a bunch. I'm not a rocket scientist, but Google tells me Jupiter's orbital velocity is about 13,000 m/s, with Earth's velocity being about 30,000 m/s.

If my KSP-taught understanding of orbital mechanics is correct, you'd first have escape earth's gravity(~13,000m/s), then reverse your orbital velocity(about 60,000m/s, also matching the orbital plane of the asteroid in the process), and then do a standard hohmann transfer to the asteroid orbit(looks like about another 5,000m/s) just to get to the asteroid, but then you have to cancel the closing speed. I don't know enough to know how to calculate the approach velocity but looks like it might be a bunch.

Chart showing d/v required to reach various objects in our solar system: https://i.imgur.com/WGOy3qT.png

I'd love to see Scott Manley do a video on what would be required.

I guess I could do it myself, I'd just need to install the solar system mod...

I bet he will.

I have RSS installed, but not far enough into the tech tree for ions yet, which is about the only way I could imagine it being remotely possible.

May be able to shave a few thousand DV off with some well-timed gravity assists.

Yeah, I'm nowhere near good enough at the game - I've never even landed on another planet. I absolutely don't know how to set up gravity assists.

It's orbiting the wrong way around, so you need to lose all of your orbital momentum and add it all back again. This is an extremely expensive maneuver to do in the inner solar system (i.e. from an Earth launch). The easiest way to do this is to achieve near escape velocity and adjust your orbit on the cheap at the edge of the solar system, but now you're talking about a mission which would span several decades.

Nah. Just do a slingshot around Jupiter to turn Around.

Not sure if your comment is sarcastic, but I'll humor it.

Jupiter is orbiting the sun at 13 km/s (very fast). If you slingshot around it, you can definitely be moving away from it at a decent clip. However, you'll still be going around the sun at a pace near 13 km/s (very fast). You still have to lose all of that orbital velocity before you can even think about going in the other direction. And even if you reduce your orbital velocity to zero, now you're just going to fall into the sun. You need to add the bulk of what you just lost back into your orbital energy, but going the other direction. All of this has to be precicely manuvered to put you in an orbit to meet up with the probe. On top of all of that, you still have to climb out of Earth's gravity well and spend a lot of fuel getting to Jupiter.

Also, once you start going the other direction, gravity assists become much more difficult to do with anything spinning normally. Inversely, if you don't turn around, you'll just wiz by the object when you meet up with it and have hardly any time for science.

Maybe we can take advantage of the fact it's orbiting the wrong way. Perhaps we can send an impactor and capture some of the ejecta. At the very least we can analyze the spectra of the impact flash to see what it's made of. Perhaps we can even fly through the ejecta plume and run it into a mass spectrometer to do isotopic analysis. If the time between the impactor and the probe is short enough, perhaps the ejecta will still be plasma which we can run straight through our mass spectrometer. It might even be possible to capture a small amount of ejecta if we use something like an aerogel particle collector like the Stardust mission used[0].

[0]https://www.nasa.gov/mission_pages/stardust/mission/index-ae...

Maybe, but that will still be very hard. After the collision a lot of the debris will still be moving at a speed and direction comparable to the asteroid's original trajectory. Because the asteroid will have the greater mass, you'll find it'll be the net exporter of inertia into the impact mass.

On top of that, making the rendezvous at such an extreme difference of speed will be very difficult.

Problem with an impactor (besides any trailing analytical probes being sandblasted by ejecta) is that its a permanent expirement that can screw up any future passive observational experiments

That being said, if we do eventually find another retrograde asteroid that is otherwise unremarkable, I would be all for an extreme speed impact experiment. If it's close enough to the sun we may even get some low grade relativistic effects being observed

TIL the euphamism "cigar shaped" when something clearly looks like a turd.

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