The Mystery of Sedna’s Orbit

Jan 7

Quite far away, a lonely, red rock has something imprinted upon its mysterious orbit.
What secrets might it hold?

CORRECTIONS

The diagram at 4:00 mistakenly swaps the labels for sedna's periapsis and apoapsis.
(noticed by youtube viewer CatKhakis)

— Citations —

Info.

"Sunrise is cold and brief here. There's a new one every 10 hours."
timecode 00:14

on the rotation period of (90377) Sedna
2018, Gaudi et al.
§ abstract

https://arxiv.org/pdf/astro-ph/0503673.pdf

assumption: observer is 5' 9" tall
"a short horizon, never further than a mile away."
timecode 00:23

distance to horizon on Sedna
2022, WolframAlpha
§ results

https://www.wolframalpha.com/input?i=distance+to+horizon&assumption=%7B%22FS%22%7D+-%3E+%7B%7B%22HorizonDistance%22%2C+%22d%22%7D%7D&assumption=%7B%22F%22%2C+%22HorizonDistance%22%2C+%22h%22%7D+-%3E%225+ft+9+in%22&assumption=%7B%22F%22%2C+%22HorizonDistance%22%2C+%22r%22%7D+-%3E%22sedna%22

"Sedna was discovered in the year 2003."
timecode 00:55

"There are a few theories about Sedna's orbit and how it became so eccentric."
timecode 04:04

discovery of a candidate inner Oort cloud planetoid
2004, Brown et al.
A: publish date
B: § 4. Origin

https://web.gps.caltech.edu/~mbrown/papers/ps/sedna.pdf

... "advancements in astronomy started revealing exoplanets that defy expectations and distant local bodies roughly the size of Pluto, calling into question what exactly earns the title of planet. Sedna's discovery was one among them" ...
timecode 01:03

Planetesimals to Brown Dwarfs: What is a Planet?
2006, Basri & Brown
§ introduction

https://web.gps.caltech.edu/~mbrown/papers/ps/basribrown.pdf

"In 2015, Leleākūhonua was discovered, an even more distant object orbiting the Sun." ...
timecode 01:24

wiki: Leleākūhonua
Wikipedia
accessed 2022
§ summary

https://en.wikipedia.org/wiki/541132_Lele%C4%81k%C5%ABhonua

"These objects collectively motived the 2006 redefinition of planets." ...
timecode 01:28

Results of the 2006 IAU Resolution votes
2006, IAU
¶ 4

https://web.archive.org/web/20061107022302/http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html

"And so it was deemed that planets are a more exclusive club. Pluto was shut out."
timecode 01:45

Breaking News– Pluto not a planet!
2006, Phil Plait
Slate
¶ 1

https://slate.com/technology/2006/08/breaking-news-pluto-not-a-planet.html

"It measures about a thousand kilometers in diamater across each dimension."
timecode 02:01

... "that's only one percent of Earth's orbital speed."
timecode 03:12

wiki: Sedna
Wikipedia
accessed 2022
A: § infobox ¶ physical characteristics
B: § orbit and rotation

https://en.wikipedia.org/wiki/90377_Sedna#Orbit_and_rotation

"It can be found at 76 astronomical units."
timecode 02:34

sedna ephemerides for July 2076
2022, AstDyS
R value where "RA*cosDE" flips from negative to positive

https://newton.spacedys.com/astdys/index.php?pc=1.1.3.1&n=90377&oc=500&y0=2076&m0=1&d0=1&y1=2076&m1=12&d1=1&ti=18&tiu=days

"It accelerates to a speed of 4.6 kilometers every second" ...
timecode 02:53

sedna orbital speed at perihelion
WolframAlpha
accessed 2022
§ unit conversions

https://www.wolframalpha.com/input?key=&i=sedna+orbital+speed+at+perihelion

Sedna "gradually slows to 0.37 kilometers per second at apoapsis."
timecode 03:03

sedna instantaneous heliocentric velocity at apoapsis
WolframAlpha
accessed 2022
§ results

https://www.wolframalpha.com/input?key=&i=90377+sedna+instantaneous+heliocentric+velocity+at+previous+apoapsis+time+in+km%2Fs

"This [apoapsis] is past the termination shock; past the heliopause; past Voyager 1; through interstellar space; and right on the cusp of the theorized Oort cloud's inner edge."
timecode 03:28

voyager goes interstellar
2013, NASA/JPL-Caltech
§ image

https://photojournal.jpl.nasa.gov/catalog/PIA17046

... Sedna's "orbit takes a long time. 11,000 Earth years" ...
timecode 05:10

horizons: barycentric osculating orbital elements for sedna
JPL/HORIZONS
accessed 2022
PR values (measured in days)

https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Sedna%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271900-01-01%27&STOP_TIME=%272500-01-01%27&STEP_SIZE=%2750%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27

"The last time it reached perihelion, Earth was in an ice age."
timecode 05:24

scientists find an icy world beyond pluto, and the solar system suddenly seems bigger
2004, John Noble Wilford
The New York Times
accessed 2022
last line of article

http://www.nytimes.com/2004/03/16/us/scientists-find-icy-world-beyond-pluto-solar-system-suddenly-seems-bigger.html

"Sedna will reach its nearest approach by the year 2076."
timecode 05:38

horizons: sedna july 2076 batch
JPL/HORIZONS
accessed 2022
where "rdot" flips from negative to positive values

https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%27Sedna%27&START_TIME=%272076-Jul-10%27&STOP_TIME=%272076-Jul-25%27&STEP_SIZE=%274%20hours%27&QUANTITIES=%2719%27

Media

m1 - timecode 04:34

sedna as seen by hubble
2004, NASA, ESA, and M. Brown (Caltech)

https://hubblesite.org/contents/media/images/2004/14/1518-Image.html

CREDITS

Brandt Hughes
research, writer, host, editor,
music production, sound design

MUSIC

"Cold Sunrise"

"In the Wrong Place"

"Suspended Ink"

"Still Too Far"

all produced by Brandt Hughes

available to download on
patreon bandcamp

Transcript

>> Query preempted.

>> Sunrise is cold and brief here.

There's a new one every 10 hours.

Hills of rich red soil and sparse outbreaks of ice sprawl out toward a short horizon, never further than a mile away.

This is 903777 Sedna.

Sedna coasts through the inky, black night; as an outcast in its own home.

It stares back at us from just at the edge of our perception.

And the thing is, nobody's quite sure how it got there.

Sedna was discovered in the year 2003.

At the time, Pluto was still widely considered to be a planet but advancements in astronomy started revealing planets in other solar systems that defy expectations and distant bodies in our own solar system roughly the size of Pluto.

All of which called into question, what exactly earns the title of planet?

Sedna's discovery was one among them.

It wasn't the largest local body found, but it was the most distant at the time.

The discovery of these objects collectively motivated the 2006 redefinition of planets, which was a two year process carried out by an organization called the International Astronomical Union, or the IAU.

And so it was deemed that planets are a more exclusive club.

Pluto was shut out and Sedna found itself belonging elsewhere.

However, it begets acceptance as a dwarf planet, a trans-neptunian object, or TNO, and as an eponymous sednoid.

It measures about a thousand kilometers in diameter across each dimension.

About the same size as Ceres, and just over a quarter the size of our moon.

Its mass is unknown.

Usually we would calculate that by observing it interacting with its satellites, but we haven't detected any.

Sedna exists in anxious isolation.

It's an extraordinary isolation at that.

It's a big part of what makes Sedna so notable.

It can be found at 76 astronomical units, or AU, which is two and a half times Neptune's distance from the Sun.

But that's at its perihelion, the point in its orbit where it's closest to the Sun.

As it approaches the Sun, it accelerates to a speed of 4.6 kilometers every second until it is flung out to drag through that vast darkness.

It gradually slows to 0.37 kilometers per second at apoapsis.

This is fairly slow.

For context, that's only 1% of Earth's orbital speed.

To find Sedna when it's furthest from the Sun, you would have to investigate an area about a thousand times beyond the Earth's distance from the Sun.

This is past the termination shock; past the heliopause; past Voyager One; through interstellar space; and right on the cusp of the theorized Oort cloud's inner edge.

This orbit is unusual.

The solar system likes to make objects that are in fairly concentric orbits, but this one is all over the place.

This indicates that something happened to it after it had already formed.

But what?

It doesn't seem like there's a definitive consensus yet, but there are a few theories about Sedna's eccentricity, which, if determined, might unveil a piece of our solar system's history.

Our solar system may have been born in a dense, stellar cluster wherein many nearby stars may have gradually displaced Sedna's orbit before the cluster dispersed.

This was the leading theory at the time of discovery.

Or...

maybe it's possible that eons ago, a single star may have grazed by our system in an impressive near-miss that displaced Sedna's orbit.

Or...

there may be a large but distant planet in the far reaches of our solar system that we haven't discovered yet.

And maybe it influences the orbits of Sedna and many other distant bodies.

Or...

Sedna may have originated in another solar system entirely.

Then it was ejected in exile, only to stumble upon our own safe haven.

And of course, it could always be the result of something we haven't thought of.

But what we do know is that its orbit takes a long time.

11,000 Earth years.

But Sedna will bask in its next frigid summer a lot sooner than that.

The last time it reached perihelion Earth was in an ice age.

Next time, however...

Earth will be in— -well, I'll let you find out.

Sedna will reach its nearest approach by the year 2076.

But I should note that when Sedna gets as close as it's going to get, you still can't see it with the unaided human eye from Earth.

But if you were to look at it with a powerful telescope or a probe of some sort, you might see one of the reddest bodies in the solar system just behind Mars.

In the meantime, you can find me online at cohost.org/brandt, and you can chat with other viewers of the channel at discord.emergentbeacon.com and you can support the channel at patreon.com/emergentbeacon where you can get updates about upcoming videos, as I work on them, and just help fund and support videos just like this.

For those of you still watching, thanks for your time.