Gravity Sucks


Recently, Jupiter was hit by a comet/asteroid that would have made the Chicxulub impact that wiped out the dinosaurs look like a pebble landing in a pond.

In talking about this with a colleague, the concept of gravitational wells came up, in particular the concept that Jupiter acts as a vacuum cleaner in our solar system, mopping up debris and protecting life on Earth from big impacts. In fact, a Jupiter-like planet may be a prerequisite for life elsewhere in the universe; think of Jupiter as a celestial bouncer making sure no one gate-crashes the party.

To help visualise this, I thought it would be fun to post a blog about what it would be like to wear a pair of “gravitational lenses” and see the solar system from a gravitational perspective.

If you think about Earth and what it looks like from space, you probably get a mind picture similar to the image above, but, from a gravitational perspective, the Earth isn’t quite so uniform and pretty, looking a bit more like something out of the Hunchback of Notre Dame.

The distortions in this image have been exaggerated, but they highlight the different gravitational variations found on Earth. These variations arise from differences in the thickness and composition of Earth’s crust, as well as how plates move relative to each other, subduction zones, the rise of mountains, depths of the sea, etc.

To complicate things further, the gravitational profile of Earth isn’t static as the Sun and Moon also play a part, flexing not only the tides in the sea, but the Earth’s crust as well. Remarkably, the gravitational attraction of the Moon causes the Earth’s crust to rise up to a foot along with high tides.

Space is unimaginably big, so much so we tend to underestimate just how vast distances are in space. We have no terrestrial basis for comparison, making the orders of magnitude difficult to comprehend when thinking about Earth, the Moon, Mars, our solar system, local stars, the Milky Way and the universe as a whole. Putting a man on Mars, as an example, seems easy. We put rovers there all the time. We put men on the Moon forty years ago. How hard can it be to get men and women to Mars? And the answer is, it is absurdly difficult. Getting to Mars isn’t just a matter of willpower, there are serious technical and logistical challenges in operating at that distance. NASA recently likened the Curiosity landing to hitting a golf ball from Los Angeles and achieving a hole in one in Scotland. Don’t underestimate just how incredible it is that Curiosity is driving around Gale Crater. It’s a technical feat beyond that of Stonehenge or the Pyramids.

Every pretty picture you’ve seen of the solar system is grossly distorted by non-linear scaling, and this one is no exception.

If we use a bowling ball to represent the Sun, then you’ll find the planets at the following distances from the bowling ball:

  • Mercury – a pin-head some 9 meters away
  • Venus – a peppercorn at 17 meters
  • Earth – another peppercorn at 24 meters
  • Mars – a pin-head at 36 meters
  • Jupiter – a golf ball or Macadamia nut in its shell set out at 120 meters
  • Saturn – a Macadamia kernel at 225 meters
  • Uranus – a coffee bean at 453 meters
  • Neptune – another coffee bean at just over 700 meters
  • Pluto – a full-stop at just over 900 meters

In between and all around there’s an awful lot of empty space. Well, “empty” is a misnomer, but there’s nothing of any substance beyond a wispy vacuum with highly energetic particles, electromagnetic radiation and the odd rock or stray clump of ice.

We tend to think of the solar system as flat because the planets orbit (mostly) on the same plane, being formed from an accretion disc billions of years ago, but, if we look at the gravitational distortion of the sun and planets we get a very different picture.

This representation of the gravitational wells surrounding the Sun and Jupiter gives us an entirely different view of space, dispelling the notion that space is flat. By the way, the spike in front of the Jupiter well is a Lagrange point, a gravitationally neutral point, where the strength of both gravity wells is effectively cancelled out.

It’s this gravity well surrounding our Macadamia-nut-Jupiter that vacuums up most of the debris that would devastate life on Earth.

XKCD put together the following infographic that highlights, among other things, why the Apollo mission to the moon required a huge Saturn V rocket one way, but only a small rocket for the return journey. (Click on the image to enlarge it and make it easier to read)

Dam “plugholes” are a good example of how a gravity well works, with the currents and the flow of water from all around a dam being influenced in one way or the other by the drain. Get too close and down you go.
In my novel Galactic Exploration the star ship Rift Valley encounters sinister aliens in a dense star cluster and uses the complex gravitational wells and Lagrange points to sail through the cluster as the crew try to escape their pursuers. From a gravitational perspective, the star cluster would have looked something like this, with each of the stars and super-jupiter planets being the long spikes reaching downward.
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25 thoughts on “Gravity Sucks

  1. Awesome post, interesting graphics. And hooray for amateur astronomers, we need as many eyes on the sky as possible, over 90% of what’s happening out there escapes our observation at any given time anyway.

    Not only gravity makes traveling in space difficult (ignoring particle projectiles), electromagnetic distortions also become relevant for a larger metallic object with a non-orbital trajectory, like a ship or a rocket. Comets with metal cores are similarly affected, and drawn toward gas giants when they approach their orbit around the sun, their field of action, so to speak.

    I love speculations about inter-stellar travel, no matter which scientific theory they are founded on. :)

    • Yeah, there was another strike last year. No one saw it, but an amateur astronomer picked up a dark black smudge, larger than Earth, low in the southern hemisphere.

      As Jupiter takes 12 years for one orbit of the sun, it’s surprising how much it soaks up. You’d think more debris would slip through.

      • It’s the EM attraction of it’s entire orbit around the sun, the pull it generates as it moves through the sun’s electro-magnetic field. Gravity wells are only relevant within the immediate proximity of a planet, but electro-magnetism is wide-ranged. And since space is far from empty, but rather like a dispersed soup of swarf, the planets carve something similar to trenches in their orbits, and comets rarely cross Jupiter’s. :D

      • I don’t know enough about that to comment. Certainly, there’s plenty of electromagnetic energy produced by the sun and planets, but how that effects other objects I’m not sure. It would be interesting to see what research NASA has done along these lines.

  2. Great post and thanks so much for the Gravity Wells illustration.
    Still can’t get my head wrapped around the concept of gravity tho although I know that mass does play a part in it. Jupiter is a massive looking planet although it IS a gas giant, right? Is it determined if it has a solid core, and just how massive is it really?

    • Gas giants are big… Remember how Pluto got relegated to the status of “dwarf planet?” Well, there’s an argument to say we Earthlings have a bias in our own favour in calling Pluto a dwarf for convenience. Line the planets up next to each other and it’s pretty clear Earth, Venus, Mars, Mercury and Pluto are all dwarfs in comparison to the gas planets.

      Solar System

      Crunch all the other planets up together, including the other gas giants, and they wouldn’t equate to half of the mass of Jupiter! Earth would fit into Jupiter over a thousand times.

      Here’s some interesting links you might enjoy

      http://io9.com/5900093/a-breathtaking-reminder-of-just-how-gigantic-jupiter-really-is

      http://www.universetoday.com/46055/jupiter-our-silent-guardian/

      Thanks for dropping by

      • Thanks for the reply and the links.
        Just sometimes, the idea that the gases around Jupiter would constitute its mass simply escapes me because I tend to view mass as something solid. I understand that IF there is a solid under all that gas, it would be liquid as the pressure would turn the gasses into liquid state, but no one really knows for sure, right?
        Thanks again, anyway.

      • It’s hard to think that a gas giant could be so massive because we tend to think of gas as wispy and light. Jupiter, however, is unimaginably big. Look at this photo of the moon Io passing in front of Jupiter. Io is roughly the same distance from Jupiter as our Moon is from Earth. There’s no similar photos of the Moon and Earth from the same distance, but this one taken by the NASA Near spaceprobe is pretty close and gives you a good idea of just how big Jupiter is by comparison.

        Io and Jupiter
        Near image of Moon and Earth

        All that hydrogen gas compresses under gravitational pressure into a liquid and then a metal as gravity slowly overcomes the various other nuclear forces keeping the atoms separate. If the pressure continues to increase (as more mass is added), you’d eventually get fusion and a gas giant would become a star (Jupiter would need to be about 80 times its current mass for that to occur). And this raises an interesting point, stars ARE gas giants, just really, really big gas giants that are undergoing gravity-induced fusion. Wild, huh.

        So, although we don’t know what’s at the heart of Jupiter by direct observation, we’ve got a fair idea as Jupiter fits into the model that leads us to stars, etc.

      • Never really thought of the sun as a gas giant actually, because never thought of the sun in relation to a planet! at least from a composition point of view. Yeah – wild!
        Thanks for the feedback tho. I did link to your page in my current post. Hope you don’t mind.

  3. bck If I understood it right, gravity is generated when the Higgs Boson colides and reacts with a particle giving that particle an amount of mass and releasing particles of gravitons and each amount of mass releases a different amount of gravitons (that’s the theory at least, IF I understood it right).

    Hey Peter, in your discussion about inter-stellar travel, gravity wells can affect ships in their trajectories and even in sensor arrays for navigation systems due to EM fields. So, my question is, if theoretically possible, entering hyperspace wouldn’t avoid such troubles? The theory appears to point out that gravity doesn’t affect other dimensions. Am I over-thinking this?

    • Tough question… not sure I can answer it fully, but I’ll have a crack.

      All quantum fields have particles associated with them, but the particles and fields are different. The Higgs Boson is the particle associated with the Higgs field, and it’s the field that is thought to give particles mass. I did a post about Higgs called the God Damn Particle, that has a NASA video that explains all this better than I can. Best I understand it, the Higgs field is like your swimming pool. Photons are like a boogy board or a lump of Styrofoam that can skim along the surface easily, while quarks are like us trying to run from one side of the pool to another. We get slowed down by the water and so have “mass.” But that’s probably a gross oversimplification.

      There’s two schools of thought on gravity. (1) that it’s a consequence of mass distorting space/time as described by Einstein’s relativity and (2) that it’s a force carried by gravitons. Really, they’re two different ways of describing the same phenomenon. In Quantum mechanics, fields and particles have opposites, anti-particles (like anti-matter). That there’s no anti-graviton has me leaning toward (1) that gravity is a consequence rather than a force, but current thinking is that the answer is (2) and we simply have more to learn and discover.

      Now, to your question, would gravity effect a ship in hyperspace? Hmmm…. The concept of hyperspace is purely a fictional notion. hyperspace as we think of it in science fiction is another dimension beyond space (although it’s very vaguely defined and still includes the four dimensions – time transpires while in hyperspace and things have shape, etc). If there was such a higher dimension, would it be influenced by normal space/time? My guess would be yes, as you need to enter and exit at certain points so it would have to be an overlay on top of normal space/time. So fly too close to a star and I suspect you’ll find yourself flung in another direction.

      There is the scientific notion of a wormhole which would also allow for faster-than-light travel, but if these exist travel would be instantaneous, like stepping through a doorway in New York and stepping out into Tokyo. Draw two dots at either end of a piece of paper, imagine one’s in the Milky Way, the other’s somewhere in Andromeda. Then fold the paper over without creasing it and you can touch the two dots together, that’s essentially how a wormhole would link two distant points in space. In this scenario, then, there would be no influence from the intervening gravity wells, EM, etc, between the two points as those aspects of space would never be travelled through.

      I’m not a physicist, so this is all back-of-the-envelope thinking, but I hope it helps.

      Thanks for dropping by the blog.

      • Dude, I was simplifying the explanation for bck1402.

        Odd, I’m pretty sure I read somewhere that even though it was a sci-fi creation, thanks to advances in the “braneverse” theory that the other dimensions of the universe could be explored and even used. Wormhole, love it, but it rubs me the wrong way on the massive amount of energy to open one and the instability (I don’t like the idea of blowing up mid way). I think we’ll have to uncover the secrets of sub-particles and dark energy and dark matter before we especulate how to violate, circumvent or even use the laws of physics at our favor for star travel. For now I’ll wait for Star Trek Into Darkness, because particles take an average of thousands of colisions to get something useful.

      • Wormholes, travelling between branes, hyperspace, it’s all pretty wild… Stephen Hawking once noted that the best evidence against time travel was the absence of time travellers dropping in from the future. I wonder if the same is true in regards to FTL. Perhaps the best evidence that the speed of light is an unavoidable limitation on physical travel is the fact we don’t have the neighbours dropping by for tea and biscuits.

        Life exists in outer space, of that there’s no doubt, as we are living proof of life in outer space. How prolific is life? How prolific is intelligent life? That’s unknown. But that we’ve not been visited by something like Arthur C. Clarke’s monolith, silently waiting for intelligent life to arise, could very well be because of the restraint on travel faster than light limiting an alien civilization’s ability to detect life and drop by for a chat in any reasonable amount of time.

        As discussed in the novel Galactic Exploration, life is THE most precious commodity in the universe. Forget about gold and diamonds, the evolution of life forms is priceless. In that regard, Arthur C. Clarke’s monolith is an entirely plausible, logical response to finding life elsewhere in the universe, to sit back and watch what Natural Selection can concoct within a particular environ, waiting for intelligence to arise. That we don’t see that (in our limited sample of one) could/might confirmation/suggest that there’s no FTL so this type of exploration is not practical. But given time, Von Neumann monolith-like probes could spread within a galaxy without the need for FTL, but they’d probably outlive the civilizations that sent them forth. Ah… it’s fun to think about the possibilities.

        Thanks for dropping by the blog

        Cheers
        Peter

      • Hey, I thought you’d like this… Dam “plugholes” are a good example of how a gravity well works, with the currents and the flow of water from all around a dam being influenced in one way or the other by the drain. Get too close and down you go.
        plug hole

      • Hey, that’s a great news article, thanks for the heads up. I’d heard about the Alcubierre drive, but not these more recent developments. And yes, such a ship, distorting space/time would be effected by gravity wells. Stars and planets, though, are few and far between, but at warp 10 could be a very real problem.

  4. Nice post. I love the graphic showing the Sol-Jovian Lagrange point. If you could climb to the top of that point, you could tip yourself off with the gentlest of nudges and, if your aim is good, end up anywhere you want in the inner solar system, and possibly out to Saturn or beyond.

    But if you’re heading toward Mars, you might have to ride a gravitational ridge that would take you through the Trojan asteroids, and that could lead to things getting all smashy.

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