Dance of the Planets

My friend Padi Boyd is an astronomer at NASA’s Goddard Spaceflight Center. She’s also a  singer, songwriter, and founding member of The Chromatics, an A Capella group who sing about, among other things, astronomy. So I was happy to hear their latest number, Dance of the Planets, got made into a nice little video. Check it out:

Dance of the Planets by The Chromatics

It’s a lovely song and a reminder of how much of our perception has  changed in such a short amount of time. Just 25 years ago, there was not a single known exoplanet – instead, we could only speculate about them and take a guess as to how what percentage of stars have planets, their number, and whether or not any of them might even have potentially habitable worlds.

Today, it’s a completely different story. We now know of more than 1800 worlds orbiting other stars, with thousands more waiting to be confirmed. We can confidently state that every star, regardless of its type, likely has at least one planet orbiting it.  The Kepler Space Telescope showed us that planets do in fact orbit other suns in their host star’s habitable zone, can have stable orbits in binary star systems, and come in a variety of sizes around stars very different than our Sun. The upcoming Transiting Exoplanet Survey Satellite will identify even more interesting targets for future telescopes, and get us started down the path of understanding what their atmospheres are made of.

It’s an exciting time to be discovering new worlds beyond our solar system, and Padi sums it up best with these lyrics:

At the dawn of the twenty-first century,
The dream has become a reality
We’re not quite as alone as we used to be,
There are planets around the stars


Many of us look at images of the planets of our solar system and see magnificent landscapes and stunning views of other worlds. But filmmaker Erik Wernquist sees humans living there. Go to full screen, HD, and turn up the sound:

Wanderers – a short film by Erik Wernquist from Erik Wernquist

I’ve watched this film about a dozen times now and I still cannot get over how incredibly amazingly cool this is! Wernquist takes us on a journey through time from nomads wandering the desert 10,000 BCE (underneath a sky filled with planets, no less) to future humans hiking on Europa, receiving shipments on Mars, to domed cities on Iapetus, and finally to clouds lit by ringshine as seen from a dirigible in Saturn’s upper atmosphere. All set to a heart jumping soundtrack, and narrated by Carl Sagan reading from Pale Blue Dot.


Best of all, the imagery Wernquist chooses are not only sourced from actual NASA and ESA spacecraft, but he accurately imagines the realities of living elsewhere in the solar system. For example, with a surface gravity of just 0.14g, you would be light enough on Titan to strap on some wings and fly through the methane atmosphere. And sure enough, that’s exactly what we see:

Flying over Legia Mare, Titan. Credit: Erik Wernquist

Or how about base jumping off the tallest cliffs in the solar system, which happen to be  on Uranus’ moon Miranda? With a surface gravity of just 0.018g, you’d have plenty of time to enjoy the view and could safely land on your feet with some simple retro rockets.

Base jumping off Verona Rupes, Miranda with Uranus in the background. Credit: Erik Werrnquist

Or just enjoying a pleasant day inside a pressurized rotating asteroid lit by an artificial sun.

A hollowed out asteroid is pressurized with air and filled with water to create lakes. It rotates about its long axis to create 1g acceleration via centripetal force. Credit: Erik Wernquist

Wernquist takes us on a journey that, for now, exists only in our dreams and speculations. But he manages to make these scenes seem so real that maybe, one day, they will be. Nothing that is depicted in this film is outright impossible, we only have to have the will to make this happen.

Update: I was initially going to offer a scene-by-scene breakdown to help explain what’s being depicted in each scene, but Erik has already done that here so by all means check it out!

Interstellar Review

Interstellar set a high bar – a blockbuster science fiction film that is based on real science. With physicist Kip Thorne providing accurate, no-kidding-this-is-how-it-would-really-be physics and Christopher Nolan as writer & director, what could go wrong?

Well, um… plenty. But I liked it anyway.

My issues with Interstellar were less science-oriented so much as plot, characterization, and dialog. To be fair, Gravity suffered from many of the same problems, and yet I loved it anyway. Why? Because it made a solid effort to get most of the science right and create a stunning visual experience that, for lack of a better word, educates the viewer about the challenges of spaceflight.

I felt that Interstellar does the same with general relativity but, like Gravity, does so at the cost of a contrived plot, cringe-worthy dialog, and a love theme that felt shoehorned in because movie. Oh, and it left some really bad science errors in its wake.

NOTE: From here on, it’s going to get spoiler-ific so be warned…

I could spend days writing up a detailed synopsis and critique of this film, but to be honest I really don’t have the time to plumb the depths. Besides, like many of Nolan’s films, the plot for Interstellar is rather involved and difficult to sum up in a short form. There’s a pretty good synopsis already up on Wikipedia, so I’ll just make some observations about the film here.

Launch me

Staging – that’s the way you do it

Having our heroes launch from Earth to Endurance atop a Saturn V-style launch vehicle made perfect sense – to get into Earth orbit without staging, your rocket would have to be 95% fuel, your ship would have to be 95% gas can, and that’s a lot of extra weight you now have to launch. Staging is the only way to get around this problem today.

But later in the film, we see our heroes making multiple planet-to space trips in completely reusable Single Stage to Orbit (SSTO) vehicles, at least one of which is from a planet with a surface gravity 30% greater than Earth’s. Somehow, these smaller ships have energy to spare?

But even later in the film, the staging requirement suddenly comes back in order for our heroes to escape their slingshot trajectory around a black hole.

Now, I get that it’s all in service to the story, but it bothers me to introduce a crucial bit of physics at the beginning, ignore it for most of the rest of the film, and then suddenly require it again to move the story along.

The wormhole


This was one of my favorite bits of the film and was unquestionably gorgeous in its execution. A three-dimensional mouth of a wormhole would certainly look like a sphere full of the stars on the other side.

But why would “They” place a wormhole at Saturn, of all places? I can appreciate having it some distance away so that tidal forces from the wormhole don’t cause even bigger problems for Earth, but shouldn’t you at least place it elsewhere in Saturn’s orbit so as not to tidally disrupt Saturn’s outer moons and create a possible debris field for travelers?

My guess is that the wormhole is at Saturn because it looks cool on film and serves as a visual foreshadowing of the scene around the black hole. Oh well, at least it took the crew two years to get there.

Update 11 November 2014: It was pointed out to me that this was a nod to Arthur C. Clarke’s novelization of 2001: A Space Odyssey. In the novel, the monolith was placed at Saturn. Duh, of course! But why would “They” place the monolith at Saturn? Don’t they know Saturn is hard for humans to get to? Ok, ok, ok…

Speaking of which, it’s also unclear to me how Endurance decelerates once it emerges from the other side. After all, if you’re going fast enough to get to Saturn in just two years, you now have a hell of a lot of kinetic energy you need to get rid of. I’m guessing “They” must have set up the wormhole to act as a gravitational brake or something at the other end, but this is never explained. Oh well.

Water world, extreme tides, and time dilation

The crew returns from a 2-hour excursion on Miller’s planet to discover to their horror that 23 years have elapsed on Earth. It was great seeing time dilation depicted like this, albeit under just the right circumstances.

First, the planet lies close to Gargantua, a black hole with 100 million times our Sun’s mass. By comparison, the black hole at the center of the Milky Way is only 4 million solar masses – now we know why they’re 10 billion light-years away – Gargantua is in a whole other galaxy!

Gargantua is also rotating at 99.8% the speed of light. Under these conditions, tidal forces from the black hole are low enough that a planet can orbit at a “safe” distance without being torn apart (I’m going to trust that Kip Thorne’s calculations are right about this and save myself some work). That’s important because Miller’s planet is in Gargantua’s habitable zone – that is, is at that critical distance where liquid water can exist on the surface.

But if Gargantua is a black hole, how is there any warmth or light? It turns out it’s all coming from around the black hole – some from its accretion disk, which is heated to millions of degrees, and some from the distant starlight that’s being bent and refracted around the black hole. That’s very cool.

However…the accretion disk would be flooding the entire system with x-rays. It isn’t clear to me that any of those planets’ magnetospheres would be able to withstand that much bomboardment. I wonder if this was factored into the calculation? I’m guessing not.

(Incidentally, physicist Kip Thorne has a companion book – which I’ve thoughtfully added to my wish list – that explains the science in the film. He’s forgotten more about black holes in the last five minutes than I’ll ever know in my entire lifetime – that is, not very much.)

A "ranger" spacecraft at Miller's planet
A ranger spacecraft at Miller’s planet

What’s less clear is how Miller’s planet can have shallow oceans and yet have tidal waves kilometers high? Certainly, the waves are due to the extreme tidal pull of Gargantua, but wouldn’t those same tidal forces cause Miller’s planet to be tidally locked? If so, then there wouldn’t be any waves in the first place. Granted, the tidal wave served as a plot device to delay their departure and confront the effects of time dilation, but this had my spider senses tingling.

Love transcends space and time and… give me a break

FL-23327Due to the loss of time and fuel (hey, fuel is now a limited resource again!), the crew must now decide which of the remaining two planets to visit before returning home. It’s at this point that we learn that Amelia Brand (Anne Hathaway) is in love with Dr. Edmunds, the scientist who went to Edmunds’ planet. In pleading her case, she states that love, like gravity, is capable of transcending dimensions and possibly time. This is the part that bugs me the most and strikes me as being kind of sexist to be honest. Does Brand have to be in love with Edmunds? Was this intended to be a tear-jerker? Ugh.

I know, it’s a reason to create dramatic tension but this felt like the most contrived plot twist in a film that had plenty of contrived twists in it already.

A villain? Really?


The crew goes to Mann’s planet where they find Dr. Mann (Matt Damon) alive in hibernation. The planet is cold and desolate with an ammonia atmosphere. It turns out that Mann has been sending false reports that the planet is suitable for human habitation in the hopes that Earth would send a crew to rescue him. But rather than come clean, Mann leads Cooper away from camp to show him the habitable region he claims is just “over there.”

You can see where this is going.

Mann tries to kill Cooper by cracking his helmet and leaves him to die of exposure to the ammonia atmosphere. He returns to base camp, steals a ship, and flies off to steal Endurance and return home.  The base camp is booby-trapped, killing the last remaining member of Endurance’s crew that isn’t Matthew McConaughey or Anne Hathaway.

To be honest, I’m just going to stop there because this whole segment just didn’t work for me. I think Interstellar missed a major opportunity to distinguish itself from typical science fiction films and instead decided to shoehorn in an action sequence complete with a villain that felt out of place in the story. You’re 10 billion light-years from Earth,  humanity’s very existence is at stake, and you want to muck about with an action sequence? You’re orbiting a frigging black hole for crying out loud!!!!!

Rendezvous at Gargantua


With Endurance crippled, Cooper and Brand decide their only option is to make a slingshot run around Gargantua to gather enough speed to make the trip to Edmunds’ planet. TARS, one of the service robots, will be jettisoned into the black hole inside one of the shuttles, relaying as much data as possible before crossing the event horizon.

This is in the hope that enough information can be transmitted through the wormhole back to Earth to help whomever is left to figure out a means for bringing the rest of humanity along with them. Due to time dilation, their journey around the black hole will take 68 years on Earth.

Let me pause for a moment and say that the whole business of mucking about a black hole is exactly what I loved about the film! The rendering is the result of a year of computational work based on Thorne’s equations. It’s gorgeous and I’m going to leave it at that…

…because Cooper jettisons himself into the black hole as well in order to shed more weight from Endurance so that Brand may live.

Update: 11 November: I basically rewrote the rest of this segment to clarify the whole bit on how you can survive crossing a black hole’s event horizon if the conditions are right. I hope this helps

Now, a lot of early reviews balked at this sequence, and it’s understandable. In “classic” black hole theory, we assume the simplest case where the black hole is about 5-10 solar masses and not rotating. In that case, the black hole’s tidal forces would be so strong as you cross its event horizon that even an astronaut’s body would be stretched and torn down to its individual atoms in a process affectionately known as spaghettification.

However, Gargantua is in fact a 100 million solar-mass black hole that is rotating at 99.8% the speed of light. These two qualities literally change the equation of such a black hole’s tidal forces in such a way that you can fall into the black hole without noticing anything – gentle tidal forces are absent, let alone the extreme spaghettifying ones.

What I don’t understand is how Cooper survives getting gamma-rayed to death from the intense radiation at the accretion disk. I think they entered from above the disk, but I’d think that the radiation environment is still pretty strong, though to be honest, I’m really not sure so I’m going to trust that this part is legit, but I’m not sure.

Anyway, the practical upshot is TARS and Cooper can pass through Gargantua’s event horizon and fall into the black hole in one piece. without being stretched out into a sting of atoms due to what would otherwise be extreme tidal forces.

Bootstrap Paradox

It’s been speculated that black holes of sufficient mass can be used as gateways to higher dimensions, but by definition, we ultimately cannot know for certain what happens beyond a black hole’s event horizon. After all, nothing, not even light, can escape from within this region so we have no way of knowing. But since this is a movie…

…It turns out that “They” were humanity’s descendents all along and that it was Cooper himself who sent TARS’ data on the black hole back through time to his adult daughter, now a physicist trying to find a way to save humanity. In other words, it’s self-consistent time travel made possible by the fact that Cooper was the one sending messages back through time to himself which set Cooper on his journey to the black hole. Meanwhile, Cooper’s daughter uses her father’s messages to save humanity, who are then able to leave Earth, survive, and eventually become pan-dimensional beings. Yay.

His mission complete, “They” send Cooper back through the wormhole (hey, they’re hyper-dimensional beings after all) where he is rescued near Saturn, taken aboard Cooper station – humanity’s new outpost made possible by Cooper’s daughter’s work.

Now 108 years old, Cooper’s daughter tells Cooper to go back through the wormhole to find Brand, now living on Edmunds’ planet, and bring her home. Cooper and a newly-repaired TARS steal a Ranger and the credits roll.

Summing up

Despite its story flaws, I liked Interstellar if for no other reason than we got to see the effects of general relativity portrayed in a major motion picture. Maybe it was because my expectations were lowered, but I enjoyed it and would like to see it again, story tropes and all. The visualizations were amazing and it’s nice to have a demonstrable proof that you can have a major blockbuster film that is grounded in physics. More like this, please.