
Asteroid that cohabits an orbit with Jupiter came from outside the solar system - digital55
https://www.nytimes.com/2018/05/21/science/asteroid-interstellar-jupiter.html
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roryisok
Three space stories on the front page today. Makes me happy

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flukus
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?

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SideburnsOfDoom
> 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.

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slavik81
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.

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richmarr
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.

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bediger4000
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.

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Scaevolus
"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](http://sci-hub.tw/10.1038/nature01622)

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

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jcims
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)](https://en.wikipedia.org/wiki/Biomass_\(ecology\))

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

3\.
[https://www.saylor.org/content/BIO_Kimball/users.rcn.com/jki...](https://www.saylor.org/content/BIO_Kimball/users.rcn.com/jkimball.ma.ultranet/BiologyPages/G/GenomeSizes.html)

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auntienomen
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.

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jcims
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.

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auntienomen
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.)

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

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zeristor
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...

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

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

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Sir_Cmpwn
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.

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gene-h
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...](https://www.nasa.gov/mission_pages/stardust/mission/index-aerogel-
rd.html)

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tomatotomato37
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

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

