Hello Space Fans and welcome to another edition
of Space Fan News.
In this episode the story this week comes
from my alma mater, the University of Colorado
at Boulder with a story that has many good
and interesting things about it: it’s from
CU, there may not actually be a Planet 9 that’s
causing the strange outer solar system orbits,
and the major work behind this study was done
by a CU undergrad - that’s right, and undergraduate
student is shedding light on a difficult problem.
OK, most of have know for a while about the
theory that what might be causing the observed
orbits of these strange objects in the outer
solar system called ‘detached objects’.
The orbits were so strange that normal planetary
motions and theories of solar system formation
could not explain why they orbited the Sun
the way they did.
So, astronomers Konstanin Batygin and Mike
Brown proposed, after trying to rule out every
other possible explanation, proposed that
maybe there is an as yet unseen planet affecting
the orbital dynamics of these bodies.
This idea made a lot of sense, we found the
planet Neptune this way, we saw the effects
this planet had on the other planets, namely
Uranus, in our solar system and was able to
figure out that there must be a planet there
and sure enough, after lots of observing and
looking for it, Neptune was found in 1846.
So doing the same kind of math, Batygin and
Brown determined that if the orbits observed
by these strange objects, among them the minor
planet known as Sedna, then the planet must
be really far out, around 800 astronomical
units or so, be really big, about 2-4 times
the radius of Earth and about 10 times more
massive, and orbit the Sun once every 10 to
20 thousand years or so.
OK, so this was a big news and everybody has
been trying to find it ever since.
And no one has found it yet.
As I said, Batygin and Brown (whom I’ve
had in hangouts before) have said that they
knew this claim would require extraordinary
evidence so they worked really hard to eliminate
every other possible explanation before saying
this might be due to a planet.
Well they didn’t work hard enough because
last week at the summer meeting of the American
Astronomical Society, the CU Boulder team
announced another possibility.
The collective gravity of all the strange
little objects floating around past the orbit
of Neptune, when you add them all up, could
explain the strange orbits seen by Sedna and
the other objects plotted by astronomers.
The outer solar system is a really strange
place gravitationally, there a lots of orbits
of lots of things that when you plot them
accurately, don’t make any sense.
Sedna for example, a little smaller than Pluto,
takes 11 thousand years to go around the Sun
once.
It’s orbit is also circle-shaped and doesn’t
go anywhere near big planets like Jupiter
of Neptune.
So, how did Sedna get there?
It remains a mystery and hence the name: detached
objects, the closest they ever get to the
Sun is so far away that they aren’t affected
by the gravity of the larger planets, the
appear detached from the solar system.
So the outer solar system has lots of things
circling the Sun in really strange orbits
that can’t easily be explained, not even
with another planet out there.
But if you add up all the gravitational effects
of all the detached objects out there, some
really interesting things happen that appear
to explain these orbits.
An undergradate student working in the Dept
of Planetary and Atmospheric Sciences at CU,
a place I spent way too much time in, wrote
some code that calculated the orbits of of
the minor planets, such as Pluto, icy moons
and a variety of space debris.
According to the simulations, the orbits of
the icy objects beyond Neptune circle like
the hands of a clock, in a very Copernican
way.
Some of those orbits, like asteroids moved
faster and in tandem, flying in formation.
Other objects, big ones like Sedna, move much
more slowly.
So what happens when the fast ones, overtake
the slow ones?
It’s a very interesting gravitational problem,
one that hasn’t been really considered before.
When this happens, the smaller objects begin
to pile up on one side of the sun.
These orbits crash into some of the bigger
bodies causing a minor planet like Sedna,
which once had a normal, ellipsoidal orbit,
into a detached, circular one.
This simulation was confirmed by predicting
another strange thing about detached objects,
the bigger a detached object is, the further
away its orbit becomes from the sun.
Another interesting idea that came out of
this: as space debris interacts in the outer
solar system, their orbits tighten up and
widen in a repeating way.
This cycle could have the effect of altering
comet orbits towards the inner solar system
including the Earth, on a predictable timescale.
So let this story be an example to all of
you looking for a career in science.
Many people ask if you need a PhD to do astronomy
and the answer is a resound NO!
It may come to pass that we will ultimately
find Planet 9, but given how hard everyone
is looking, it really should have been found
by now, it was not hypothesized to be a small
thing after all.
This research provides another explanation
for observations and I’d love to hear what
Batygin and Brown have to say, but they haven’t
responded to my emails yet.
I’m sure they are quite busy now but I will
try to keep you posted.
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