The Solar System Doesn’t End At Neptune

A new day, a new obsession.

I was helping my daughter revise for her Science exams when we came across the astronomy chapter in her textbook. I realised that a lot of the material that she is learning is pretty much the same things that I was learning when I was in school, apart from the fact that we now have only eight planets in the solar system instead of nine (Sorry Pluto, you will always be a planet in my heart).


Truth of the matter is our solar system has way, way more celestial bodies in it than just the terrestrial planets, the asteroid belt, the gas giants and moons. To stop teaching about the Solar System at Neptune is a missed opportunity. #justsaying

I think that our Science syllabi in school can be more interesting and fascinating if we put in more chapters or topics to do with astronomy and the study of our Solar System. You know, make it less about which astronomer discovered which planet at which year (memory work) and make it more about how they did it, what were the consequences of their discoveries, what tools they used to explore the night skies and how far technologies have come in this modern world when it comes to finding very, very far and very, very small objects in the sky.

I’m no Science textbook author, but if I were, I would put into textbooks things I’m putting into this blog post now.

But first, let’s recap what is already in the textbooks.

Planets & Moons

We have our Sun, and orbiting it are the terrestrial planets Mercury, Venus, Earth and Mars. Then there’s the asteroid belt between the rocky planets and their gas giant neighbours, Jupiter, Saturn, Uranus and Neptune.

Image by Jonny Lindner from Pixabay

Now, moons. How many moons are there in the solar system? A staggering number of them. Apart from Mercury and Venus which have no moons, the rest of the planets have natural satellites orbiting them.

Earth has one, Mars has two, while the other planets have … a lot. At the time of this writing, Jupiter has 79, Saturn has 82, Uranus has 27 and Neptune has 14. You can see a pattern here, something along the lines of the larger the planet, the more moons they can hang on to.

That’s not how it works with Pluto.

Let’s talk about Pluto

Pluto has 5 moons. Five. There’s Charon, the largest of Pluto’s moon, pretty much half the size of Pluto. As you can see in the video below, they’re locked in this dance where they face each other; there’s a binary planet thing going on there.

Then you have the two larger ones, Nix and Hydra (the one that looks like it is drunk and spinning out of control). Between them is the smaller Kerberos and lastly, you have Styx which was found by New Horizons, the probe which travelled for 9 years just to check out Pluto. It has since moved on, and is en route to a Kuiper belt object, Ultima Thule. Read more about the New Horizons mission here.

I’m sure you know that Pluto is no longer a planet. I’m sure you know that it is a dwarf planet but did you know that it is a Kuiper belt object?

What Are Kuiper Belt Objects?

If you find asteroids in the asteroid belt then you will find Kuiper Belt Objects (KBO) in the Kuiper belt. Although Pluto was discovered in 1930, the Kuiper belt where it originated from was not found until the year 1992.

This is primarily because the belt is just so darn far away, beyond the orbit of Neptune. It’s a region that is cold and dark and full of small objects made of mostly rock, water ice, ammonia and methane.

That’s a pretty crowded neighbourhood beyond Neptune

The Kuiper belt starts at the edge of the orbit of Neptune, 30 AU from the Sun, and extends to around 50-55 AU from the Sun (reminder: 1 AU is the distance between the Earth and the Sun).

Sometimes KBOs are also known as trans-Neptunian objects (TNOs) although this definition covers pretty much everything that is found beyond Neptune.

Finding the Kuiper Belt

In 1943, long before we had the technology to locate the belt, astronomer Kenneth Edgeworth suggested the existence of objects beyond Neptune. Gerard Kuiper predicted a “belt of icy objects” near the edge of the solar system in 1951. This is why sometimes this region is known as the Edgeworth-Kuiper belt.

In 1992, after searching for 5 years, astronomer David Jewitt and graduate student Jane Luu, announced their discovery of the first Kuiper Belt object: 1992 QB1 also known as 15760 Albion.Since then there had been thousands more of such objects found.


We know that Pluto is a dwarf planet but it’s also a Kuiper Belt Object. In fact, it is the largest KBO in the group, with a diameter of 2377 KM, and technically it’s the first KBO every discovered.

Pluto, together with Makemake (1430 KM), the second brightest KBO after Pluto, and oblong-shaped Haumea (1595 KM), are the only Kuiper Belt Objects that are also dwarf planets.

Read more about Kuiper Belt Objects here, here and here.

Eris, the Dwarf Planet from Beyond

At this point we know that the Kuiper Belt is very far away from the centre of our Solar System. And yet, beyond that we have a region called the scattered disk which extends up to 1000 AU from the Sun!

Now from this region, scientists found Eris. It was initially thought to be bigger than Pluto but eventually we discovered that it has a moon, and that in fact, it’s only about the same size as Pluto (2326 KM).

Eris and her moon Dysnomia, far beyond Pluto’s orbit

At its closest to the Sun, it’s 38 AU away; at its furthest, 96 AU! Remember that Neptune is at 30 AU – sunlight takes more than 4 hours to get to Neptune. Eris’ orbit is tilted by 45 degrees and it takes around 557 years to go once around the Sun.

Eris plays an important part in our understanding of the solar system because its discovery was one of the reasons Pluto got demoted to dwarf planet status. Had they decided to keep Pluto as a planet, Eris would have been the tenth planet in the solar system.

So based on the IAU definition of a planet released in 2006, our solar system now has 8 planets and 5 dwarf planets: Pluto, Makemake, Haumea and Eris. Wait, that’s four. What’s the fifth dwarf planet?

Ceres, King of the Asteroids

Ceres is the largest object in the asteroid belt, a region between Mars and Jupiter. It only has a diameter of 945 KM but because of its proximity to Earth, it was a lot easier to find than say, Pluto or Eris.

In fact, Ceres was discovered back in 1801 by Giuseppe Piazzi, and like Pluto, it was declared a planet. At the time, the Solar System had only 7 planets; Neptune had not been found yet. Ceres would become the fifth planet from the Sun for about 50 years before the discovery of more objects like it force astronomers to reclassify Ceres as an asteroid instead of a planet.


After Pluto was demoted to dwarf planet status, Ceres was once again reclassified as a dwarf planet. Amongst the 5 dwarf planets, Ceres is the only one within the inner Solar System. It’s also the first dwarf planet to have been visited by a dedicated space probe, Dawn back in 2015.

See pictures sent back from Dawn and read more about Ceres here.

Sedna, A World of Possibilities

Reading about Sedna fills me with frustration and with a new appreciation for the work astronomers do. You see, Sedna is widely considered a dwarf planet but it isn’t officially one, mainly because it is just too far to observe.

To be a dwarf planet you need to meet two requirements: you need to orbit the Sun, and you need to be big enough for your own gravity to give yourself a round shape. Unlike the definition for a planet, a dwarf planet need not have cleared the neighbourhood around its orbit.

Sedna is big enough to see, but is it big enough to have its own self-rounding gravity? The short answer is, we don’t know. That’s because Sedna has an incredibly elongated orbit.

Pluto orbits the Sun once every 248 years; Eris, once every 557 years. Sedna takes 11,400 years for one trip around the Sun. At its farthest from the Sun, Sedna would be 937 AU away. When it was found in 2015, it was 86 AU away, still a great distance from us. While it is big enough for us to sit up and take notice, but we just can’t see enough of it to be sure that it is a dwarf planet.

What we can study however is its orbital path, which many believe alludes to the existence of another giant planet beyond the Kuiper belt. It is believed that this trans-Neptunian planet would be able to explain the eccentric orbits of Sedna and other objects like it in the Kuiper belt. But until we find it, this is just a theory. Fingers crossed, we will one day find out why Sedna travels the way it does.

So, are we done? Nope.

Trojan Asteroids

In October 2021, NASA is launching Lucy, a space probe mission that will head for Jupiter trojans. #saywhatnow?

See it in action here

Jupiter trojans are a type of trojan asteroid (depicted in green in this pic above). There are two groups of asteroids that flank Jupiter on both sides while orbiting the Sun. They are found in stable orbits, at two Lagrangian points 60 degrees ahead (L4) and behind (L5) of Jupiter. Jupiter has millions of trojans larger than 1 KM across.

These trojans are the fossils left over from failed planet formations, remnants from when the Solar System was in its planet-forming phase. Lucy will be aiming for multiple Jupiter trojans during its 12-year mission to study and send back data that can help scientists understand more about planet formation.

Apart from Jupiter, at the moment of this writing, Neptune has 22 trojans, Mars has nine, Uranus has two, Earth has one, and Venus had one temporary trojan. Two of Saturn’s moons have trojan moons also known as co-orbital moons. Just to be clear, these aren’t moons that go around moons, they are just moons that orbit in a locked pattern (60 degrees ahead and 60 degrees behind) a fellow moon. Tethys has Calypso and Telesto, while Dione has Helene and Polydeuces. #betyoudidn’tknowthat


So far, all the objects that we have previously discussed, dwarf planets, asteroids, trojans, Kuiper belt objects and trans-Neptunian objects, are grouped under the category “minor planets”. The only one that has not been discussed is Centaurs. And that’s because centaurs are complicated.

Centaurs are small bodies in the outer solar system region, found between Jupiter and Neptune. They behave like, and thus are sometimes categorised as, comets and asteroids on top of being centaurs. It’s believed that they are strays that have escaped the Kuiper belt object inward towards the outer Solar System area.

They have chaotic orbits that are often eccentric (like stretched out ellipses) and unstable. Let’s talk about what those two things mean:

  • Eccentric orbit: Earth has a near circular orbit, so it has an orbital eccentricity of near zero. On the other hand, Halley’s comet has an orbital eccentricity of 0.97, a highly elliptical orbit. Because of the perturbations from the gas giants, many centaurs (though not all) are found to have eccentric orbits. So far, the centaur with the most eccentric orbit is Asbolus at 0.62.
  • Unstable orbit: Centaurs have dynamical lifetimes. This means their orbits will change over time. Some centaurs may move into different orbits after a period of time. If they get flung into the inner Solar System, the end up as Jupiter family comets (short-period comets). If they get flung outward, they may leave the Solar System entirely.

Below is a great image of what is in our outer Solar System (you can check out the source here). You have Jupiter (J), Saturn (S), Uranus (U) and Neptune (N) and the yellow Sun right in the middle. The blue flecks are Kuiper Belt Objects while the yellow ones are objects in the scattered disk region. The green flecks that are inside the orbits of the gas giants are the centaurs.

By User: Eurocommuter – Plotted by a program written by the author, CC BY-SA 3.0 (link)

Yes, the Solar System isn’t as empty as we thought. It’s just really big.

Gravitational Perturbations

Why are the orbits of centaurs so unstable? Well, as the orbits of centaurs cross the orbits of the four gas giants, centaurs are subject to the gravitational pull of the much larger planets. This extra force exerted by the planets is called gravitational perturbation and in the long run, it is this force that will cause the orbits of centaurs to change.

One wonderful story that illustrates the significance of perturbation is the discovery of Neptune.


Neptune was discovered in the mid-1800s and was the only planet in our solar system that wasn’t discovered from direct observation. It was simply too far and too small to be observed. But astronomers know that mathematically, it’s there.

Neptune’s position in the sky was calculated based on the understanding that something large, possibly a planet, had been causing irregularities in the orbit of Uranus. French astronomer Urbain Le Verrier did the math then sent the calculations to the Berlin Observatory for confirmation. Based on his calculations, Neptune was subsequently discovered in under an hour, and only a degree from the predicted location. #mathisgreat

If Neptune can exert such an influence on a fellow gas giant, imagine the chaos Neptune and the other gas giants can cause when it comes to smaller bodies like 2060 Chiron, a centaur that’s only 206 KM across. Chiron’s orbit crosses between Saturn and Uranus and lasts around 50 years. It also exhibits comet-like activities, such as having a coma when its orbit is near the Sun (at its perihelion).

If you look up info about other centaurs and check out their orbits, it will probably look something like this.

And if you look further, say at Chariklo, you might find more interesting information, like how this centaur has not one, but two rings around it.

Chariklo is a centaur slash asteroid that has an orbit between Saturn and Uranus. It looks something like this. #iknowitdoesntlooklikemuch #waitforit

Chariklo via the Hubble Space Telescope in 2015

Discovered in 1997, Chariklo is the largest known centaur so far, with a diameter of around 300 KM. In 2014, a group of scientists found evidence of rings on Chariklo by observing it during an occultation. An occultation occurs when the object you want to study crosses in front of a star, thereby blocking its light from reaching you. The longer the period of the block, the larger the object.

During the stellar occultation of Chariklo, the light magnitude from the start dipped not once, but 5 times, indicating 2 distinct ring systems (and outer and an inner) around Chariklo.

Read more about this process here.

I’ve gotten to this point in my post when I discovered that scientists are still at odds on how to define centaurs. I mean, if you think about it, they’re everywhere and then millions of years down the road, they’re just not where they were anymore. They’re not doing that to annoy you, that’s just how they roll. But you got to admit, centaurs are just too cool to leave out of this post.

Finally Wrapping Up

The thing with astronomy is that the objects we find inside our Solar System don’t have to fall neatly into boxes for us. Try as we might to classify this object or that, we will constantly be making new and surprising discoveries that will push the boundaries of our definitions and force us to rethink and recategorise and reboot our understanding of the cosmos for as long as we are willing.

This is precisely why No. 1, astronomy is a must-learn topic in Science class. And No. 2, we need to and should update our textbooks to give our children the opportunity to learn about all these “new” discoveries beyond Neptune.

If you want the next generation to be fascinated with Science, keep astronomy in Science class and it will do the rest.

HDIM Reviews: Love, Death + Robots (2019)

Love, Death + Robots is an anthology of 18 stories, ranging from 6 minutes to 16 minutes long. There’s sex, nudity, profanity, violence and gore sprinkled all over them. Each episode is made with digital animation, each in turn with its own signature, theme and flair. The animation is as nice to enjoy as the storylines themselves. That said, not every episode is for everyone.

Love, Death, Robot

This series is sooooooo not for kids. There’s no two ways about it. So many of them could have worked fine with a PG-rating but for some reason, they just want to throw some genitalia in, some nudity in, some cussing or a gunshot to the head, just for the heck of it.

Netflix just wants to get it out of the way that this is a purely NSFW watch. Doesn’t mean you cannot work around it. If you’re pressed for time, I suggest you check out the following 9 episodes first:

Suits – 17 Min (Monster Warfare)

Easily my favourite in the whole series, this episode features in stunning graphics a community of farmers that have to fight off swarming alien pests with mech robots, missiles and cannons like it’s just one of their everyday farming chores. There’s slight cussing and a ton of alien-killing. Fun watch you can enjoy with older kids.

Lucky 13 – 14 Min (Warfare)

Pilots are a superstitious bunch, says Colby the protagonist in the show. But as she was the rookie, she had no choice but to fly the “coffin with wings”. This is a good one. One of my favourites. I forget that this is purely digital animation when I watch Colby and the soldiers in action. At least until she is out of the plane. The storyline is simple but it takes the cake. Nice one.

Zima Blue – 10 Min (Safe)

A young reporter heads to an exclusive interview with art extraordinaire Zima as she breaks down Zima’s artform. Upon meeting him, he asks her to tell the world his story: why most of his work features a special type of blue and what he found at the end of his search for truth and his origin. This is based on a short story by Alastair Reynolds who is also the author for Beyond the Aquila Rift.

Fish Night – 10 Min (1 Quick Strip)

A father-and-son salesman team suffers a car breakdown on a deserted stretch of road. The father ponders upon the concept of ghosts from an older world. That night, they get visitors, but not the kind you’d expect. One of the more visually stunning episode in the whole anthology and great storytelling.

Three Robots – 11 Mins (language)

Three tourist robots visit a post-apocalyptic Earth planet. It’s a funny, intelligent episode that pokes fun at the apocalypse, not something you see every day. This episode is based on a short story by John Scalzi who also wrote the Yogurt story and Alternate Histories.

Helping Hand – 10 Min

A lone astronaut works at a space station with no backup. After a mishap she found herself set adrift, running low on oxygen, with no way to get back to the station. Because the title of the story is Helping Hand, of course she got back safe and sound. The how though, is what makes this a great story that will haunt you long after you’re done with them. I can’t label the genre without giving the spoiler away.

Alternate Histories – 7 Min (Nudity)

Ask anyone what would they do if they could go back in time, and some might say something about Hitler. Well, there’s an app for that now. What would happen if Hitler had died? The demo version of Multiversity, the app shows you six alternate timelines. Hitler is depicted in a cute way in this app but don’t let that fool you, he dies quite horribly in every single one of them.

When The Yogurt Took Over – 6 mins (safe?)

This is a real short one. It’s only around 6 mins long. The design reminded me of Cloudy with a Chance of Meatballs and the narrator’s voice made me feel a bit of nostalgia. Turns out, the episode was narrated by Maurice LaMarche (the latter in Pinky and the Brain). This could be one you can watch with the kids if you don’t mind that one scene where there is a naked lady protesting, and a guy shooting himself in the head, point-blank.

*I read the short story this episode is based on. This is a story better savoured as a read than an animated episode.

The President speaks to Yogurt

Ice Age – 10 Min (Safe)

A couple who just moved in found a miniature lost civilisation in their old fridge. Tobey Maguire and Mary Elizabeth Winstead, the only two real life characters in the whole anthology star in this episode. It would have worked with just either one of them, really. You can watch this with the kids unless you have a problem with them seeing how a T-Rex feeds.

Let’s see what we got in the fridge

What about the Rest?

When you got time for the rest of the anthology, here’s what to expect. These will take you out of your comfort zone. For the general population anyways.

The Witness – 12 Min (Lots of Nudity)

A prostitute and nude cam dancer in a Hong-Kong’esque city witnesses a murder across the building. She is chased across town by the murderer. Due to the nature of her work, she is naked more than 60% of the episode, even as she runs in public trying to escape her pursuer. The graphics are extremely fluid and life-like, and the conclusion will blow your mind.

Shape-Shifter – 16 Min (Monster Warefare)

Two soldiers with unnatural powers sign up for a tour in Afghanistan. They face discrimination on camp but continues to serve out of the love for their country. For me, the discrimination is harder to watch than the gore. They have captured warfare wonderfully well. Not so much with the eyes and mouths.

Beyond the Aquila Rift – 16 Min (Sex)

Based on a short story by Alastair Reynolds, a space crew got lost while travelling through space. Waking up from cryogenic sleep, Thom is greeted by a friendly face who tells him they are thousands of light years off course from home. The truth however is far far worse. Greta is extremely lifelike compared to the rest of the cast. That’s all I have to say about this one.

This is Greta. Greta is animated.

Sonnie’s Edge – 17 Mins (So Not Safe)

If you are a fan of MMA, imagine that with two monsters battling it to the end in the ring. Expect extreme violence best savoured in HD. Oh and there’s a side story about why Sonnie would not throw the fight and where she got her edge. The graphics are better than the storyline. Take the wins.

Welcome to MMMA

The Secret War (Monster Warfare)

We follow a small Russian army in their deadly fight against an ancient evil. Unless you like battles with ugly, vicious monsters, you can give this one a skip. I wish I did. It wasn’t a pretty sight. This guy (below) looks incredible lifelike and natural compared to his peers. I applaud the team that made this possible.

Incredibly lifelike

Blindspot – 8 Min (Violence)

A group of 5 cybernetic robbers ambush a heavily guarded train to steal a microchip. Unbeknownst to them, something deadly awaits them on board. The animation feels like an upgrade of your 80s Saturday morning action cartoon. You know what else? This could work as a spinoff series.

Good Hunting – 17 Mins (Not Safe)

The huli jing is a spirit fox, a mythological creature in Chinese folklore. In this story a huli jing forges a friendship with the son of a spirit hunter who decapitated her mother. As ancient China evolves, the huli jing struggles to return to her true form and seeks the help of her old friend. A lot of nudity in this one, and the cruelty of mankind will make you sick to your stomach.

The Dump – 10 Min (Just downright urgh)

A City Inspector tries to evict a stubborn, dirty, old man who lives a home he built in the city dump. The old man tells the inspector the tale of Otto, which he had found in the same dump. I needed to wash my eyes after watching this one. It’s amazing how ugly and displeasing they can make everything look in this one. That in itself is an artform.

Sucker of Souls – 13 MINS (Lots of Blood)

An extremely violent and bloody episode, Sucker of Souls features a mercenary-aided academician stumbling upon Dracula in its purest form. Expect a lot of blood, gun power, bombs, running and did I mention blood?

Before the chaos

This anthology idea is nice. You can come in, watch an episode 5-10 minutes long, ruminate on it, then come back for more. More short stories, please!

Pickering’s Harem: Sexism in the Study of Stars

TIL about Annie Jump Cannon and Cecilia Payne, two scientists I have never heard about, probably because of their gender.

At a time when women were expected in the kitchen instead of in a lab, these two scientists were part of an 80-women crew tasked by Edward Pickering to do the grueling work of cataloguing stars – by hand and magnifying glass – in 1896.

There were no computers back then. The women were the computers. Here’s a snapshot of part of the group dated possibly in 1911.

Harvard-Smithsonian Center for Astrophysics Back row (L to R): Margaret Harwood, Mollie O’Reilly, Edward C. Pickering, Edith Gill, Annie Jump Cannon, Evelyn Leland (behind Cannon), Florence Cushman, Marion Whyte (behind Cushman), Grace Brooks. Front row: Arville Walker, possibly Johanna Mackie, Alta Carpenter, Mabel Gill, Ida Woods.

Annie Jump Cannon developed a stellar classification system, and classified 350,000 stars in her lifetime. At the peak of her career, she could classify 200 stars an hour, down to the 9th magnitude, much fainter than what the human eye is accustomed to, with unbelievable accuracy. Her classification system, a merging of the systems developed by Williamina Fleming and Antonia Maury, is still in use in modern astronomy today, also known as the Harvard Spectral Classification.

Cannon was also deaf, by the way, a result of scarlet fever when she was much younger. But I digress.

Cannon did not understand the significance of her work, until Cecilia Payne joined the crew and figured out that the classifications pointed to how hot the stars were, a breakthrough discovery at the time. Payne explained this in her PhD thesis, Stellar Atmospheres, which she completed at the age of 25.

Alongside that discovery, she also explained and proved that hydrogen is the most abundant element in the universe and is pretty much what stars are made of. At the time, it was widely believed that stars share the same make up as the Earth.

Her dissertation proves this to be untrue but the top expert at the time convinced her to omit her conclusions from her thesis. Despite this, her dissertation is widely recognised as an important piece of work in our understanding of the Universe.

Pickering’s Computer Women worked 6 days a week, 7 hours a day and were paid no more than 25 cents an hour. Most would often not be credited or recognised for their work until much later in life and when women in Science became a less alien idea.

Here are some other names with their own contributions to the cause:

  • Mary Anna Draper (Mrs Draper) the wife of Henry Draper, who donated her husband’s equipment and her inheritance to the Harvard College Observatory, subsequently funding Pickering’s crew in their star classification efforts. Although she is not part of Pickering’s Crew, without her monetary involvement and influence, the crew would probably never come to be.
  • Williamina Fleming, was initially Edward Pickering’s maid, but eventually became a major contributor to the Henry Draper Catalog‘s first classification of 10,000 stars. She was also the uncredited discoverer of the Horsehead Nebula.
  • Henrietta Swan Leavitt discovered the relation between “the luminosity and the period of Cepheid variables” and contributed to the understanding of galactic distance indicators. Her work would help many other astronomers (such as Edwin Hubble) make other discoveries.
  • Antonia Maury conducted initial study of the spectroscopic binary orbit. Her work was eventually used by Danish astronomer Ejnar Hertzsprung in his efforts to identify giant and dwarf stars.

The work of these women are far more complex than my small brain can comprehend but the fact that they can get anything done under relatively hostile and demoralising workplace conditions is a miracle in itself.

Nowadays we can find more women doing well in Science even though sexism is still alive and thriving in many corners of the globe. But if sexism couldn’t stop the likes of women like Cannon and Payne, its not going to stop today’s women from making their name in Science either.

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