Cassini and I: a love story #GrandFinale

Dear the Internet,

Let me tell you about a somewhat one sided love story between an Australian writer and an interplanetary Flagship-class unmanned spacecraft.

I’ve written before about the way that the Cosmos series was pivotal for me and loomed large in the relationship between my father and I, how it became tangled up in my grief when he passed away in 1987, and how it ended up with Voyager-themed ink being permanently applied to my left arm.

See, by the time Cosmos was being made the Voyager spacecraft were only half way through their grand tour of the four giant planets of our solar system: they’d taken the first close up shots of Jupiter and then of Saturn, with Uranus and Neptune to come.

And those pictures of Saturn were mesmerising. Aside from being scientifically fascinating and the mission a triumph of human ingenuity, Saturn’s also just stunningly beautiful.

For me, like so many other people, Voyager 1 and 2 became symbolic of the finest human impulses. The thought of these two robotic emissaries rushing toward interstellar space, bearing a fragile message of hope (and music) seemed like the actions of an optimistic, inquisitive species to me. And, as I have previously written, there was also that resonance with my father – “a recognition that Voyager and Dad exist a long way away from where I am – one in space, the other in time – and that neither are ever coming back.”

But one spinoff was that it whet my interest in space probes more generally, and due partially because of the Saturn connection and mostly because it was a few months after the tenth anniversary of my father having lost his battle with leukemia, I poured a lot of grief-energy into learning about the Cassini-Huygens mission that was taking humanity back to Saturn.

It would take four years for Cassini to get from Earth to the ringed planet. Once there it would drop the Huygens lander on Titan (which was in itself astonishing: the one and only lander humans have successfully deployed beyond Mars) and then dedicate itself to sweeping through the Saturnian system to, among other things, take a whole bunch of photos. And god, how I wished that my father would be there to see them, which was to be something of a theme for the next few decades.

A very well-loved Voyager shot of Saturn, complete with blutack stains.

I logged every infrequent update in those early-internet times, wept at the gorgeous Van Gogh swirls of the Jupiter in the photographs it shot in 2000 during its slingshot path out of to Saturn, and rejoiced with completely indefensible joy when Cassini successfully carried out the Huygens landing and began taking the first close up pictures of Saturn’s moons and rings.

And it just didn’t stop: Cassini would finish one phase of its mission, still be completely operational, and then have its mission extended: when it got to the end of the Prime Mission in 2008, it was extended for another two years. And then another seven.

And during that period it was discovering more and more things about the marvellously dynamic Saturnian system (including seven new moons!), and thereby giving insights into how the solar system – and by extension we – might have formed out of the gas and dust surrounding the Sun five billion years ago.

And I very much appreciated the fact that when it took the heart-burstingly beautiful photograph of Earth through the rings – known as “the day the Earth smiled” – it just so happened to be my 41st birthday. You know, just in case I wasn’t already emotionally invested enough in this damn mission.

Yep. Annotated. ANNOTATED.

And this September Cassini ends almost 20 year odyssey by plunging into the atmosphere of Saturn to be vaporized, lest it collide with one of Saturn’s moons that might potentially harbour some form of life and really not need any Earthly contamination. And because of the way that the Earth is aligned, the mighty dish at the Canberra Deep Space Communication Complex will be picking up the final radio signals it ever sends*.

In other words, this mission I’ve been following since the beginning officially ends within driving distance of where I’m living.

So: it would mean a ridiculous amount to me to be there at the end to say goodbye to a friend that’s brought me so much joy and fascination for so very, very long.

And if you want to see me get overly emotional on Twitter live from the CDSCC, then here’s hoping I convince the good people there that I should be one of the invitees to cover the #GrandFinale live. And this is my case for inclusion.

Yours in Cassini-related hope,


*Well, technically that final radio signal will arrive about one hour and ten minutes after Cassini’s been silenced, since Saturn will be about 8.5 AU away from Earth at the time. But you know what I mean.

Pluto’s not a planet, and that’s honestly OK

It’s no reflection on the awesomeness of Pluto to say it’s a different thing, honest. 



As New Horizons proves once again that humans are freakin’ amazing and brilliant when we work together and use our mighty brains to solve interesting problems (and as we all pore over the photos that have been released and get excited about the ones yet to come – what are those impact crater-looking things? Is that a volcanic mare, or a mighty series of dunes? Why is it a different colour to its main moon Charon? EVERYTHING IS THE MOST INTERESTING THING!), the debate over whether Pluto should or shouldn’t be a “planet” has threatened to flare up again.

You might recall that in 2006 it was determined that Pluto was no longer considered to be a planet on par with the now-limited-to-eight main bodies in the solar system.

The reason for this was that bodies had been discovered further out in the Kuiper Belt (the region of icy rubble beyond the orbit of Neptune) and it was thought likely by the International Astronomical Union that as our technology improved we’d be discovering more and more of these things – which turned out to be correct.

So we had a choice: either redefine planet to mean the eight things that we currently define them as – thereby eliminating Pluto – or adding dozens of new planets to the list every year. Thanks to technological advances like the Hubble telescope and better computer algorithms for automatically recognising odd orbits in data, there are almost 400 candidate planet-like objects out in the Kuiper Belt. That’s a lot of things for eight year olds to memorise.

Thus in 2006 the IAU settled on a definition for planet that had three main tenets: if you’re big enough to be round, you’re going around the sun and there’s no other significantly-sized body in your orbit, then guess what? You’re a planet.

Pluto ticks most of the boxes, but the definitions are a little bit arbitrary.

The first two seem OK. A planet has to be orbiting the Sun so moons and satellites, which orbit planets that orbit the Sun, therefore don’t count.

That might seem obvious, but it’s worth remembering that almost all of the moons around the planets are a) basically spheres and b) in two cases, larger than one of the planets (the Jupiter moon Ganymede and the Saturnian moon Titan are both larger than Mercury – although they’re not as dense and therefore don’t have as much mass. See? It’s complicated).

Second, the thing has to be big enough to undergo “hydrostatic equilibrium” under it’s own mass. Thus lumpy little asteroids don’t count (and technically the planets aren’t actually spherical – they’re slightly flattened at the poles and wider at the equator because of their rotation, making them “oblate spheroids”, but that’s nit-picking).

Thirdly – and this where Pluto fell down – they have to have “cleared their orbit” of other bodies. This is the most arbitrary distinction of all, but the argument goes like this: you need to be big enough that your gravity has either thrown everything else out of your orbit or it’s been attracted to you and collected it.

Pluto doesn’t count for two reasons. One, that there are other things in its wide orbit (“plutininos”) that its gravity is not powerful enough to disturb. It also, technically, crosses the orbit of Neptune although the two are in what’s called an orbital resonance, so they’re never in the same place at the same time – otherwise the utterly enormous Neptune would easily slingshot Pluto out of the Solar System entirely.

It’s been pointed out that most of the planets absolutely have significant things in their orbits – aside from Neptune, which hasn’t cleared Pluto from its orbit, the Earth, Mars and Jupiter all have bodies of asteroids scattered in our orbits and no-one appears to be arguing we’re not planets as a result. But this was a definition invented mainly to find a way to exclude Pluto and get things to a manageable system.

But to be honest, “planets” is a problematic term in any case.

It’s derived from the the Greek term for “wanderer” and were so-called because the the five close enough to be visible to humans before the invention of the telescope (Mercury, Venus, Mars, Jupiter and Saturn) were points of light that moved through the skies when viewed from Earth, unlike the apparently fixed stars.

The fact we invented the word to describe little points of light in the sky is why we have the same name for “little solid lumps of rock”, like Venus, as we do for “massively giant seething balls of gas”, like Jupiter.

You could make a very solid argument to call those types of things by different, less Earth-centric names, the way we do for other non-planet things in our solar system like asteroids and comets, but we’re kinda stuck with it.

So I rather like that we have a different name for the amazing objects out beyond the orbit of the last of the gas (well ice) giants.

Out past Neptune is Pluto and the other “trans-Neptunian” objects, including a load of amazing dwarf planets: in orbits wider than Pluto’s, there are Eris, Makemake, Haumea, Sedna, Orcus, Salacia and others that haven’t officially been given names yet.

They’re all smaller than our Moon and they’re – probably, we think – made of ice, mainly water and methane. In fact, they appear to be more like giant comets than they are like the four inner planets.

And that’s why, dumb as the term might be, I like that there’s a different word for them. “Dwarf planet” is a stupid name (and it’s not what astronomers use, incidentally: they call them “planetoids’) but it at least acknowledges that they’re different things*, an exciting group of different bodies about which we barely know anything and which we’re the first generation to be able to discover.

And if the fact that you’ve heard of Pluto means that you might be interested to learn more about Eris or Makemake, that’s a great thing in itself (their orbits are nuts, by the way). And hell, it makes more sense to celebrate Pluto as Amazing Gateway to the Glories of the Kuiper Belt rather than The Shitty Last Planet After The Proper Ones.

And in any case, New Horizons has made the distinction kinda moot. Look at that photo at the top of the page again: Pluto is now a place.

It’s a real, tangible world ten years and billions of kilometres away, with its own characteristics and mysteries and beauty. However we define it, we’re the first humans in history to see its face – and that’s the thing that fills me with hope and joy for our species.

Dammit, we’re an amazing species when we want to be.



* Of course, then you have the question of why tumbling balls of frozen methane are labelled the same as a solid sphere of rock in a diffuse belt of other rocks, since the major asteroid Ceres has also been deemed a dwarf planet, but that’s a different rant. Dammit, what’s wrong with just declaring Ceres The Mighty King Of The Asteroid Belt rather than confusing the issue by making people think it’s like Pluto, only closer?