Of Particular Significance

How Far We Have Come(t)

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 11/12/2014

It wasn’t that long ago, especially by cometary standards, that humans viewed the unpredictable and spectacular arrival of a comet, its tail spread across the sky unlike any star or planet, as an obviously unnatural event. How could an object flying so dramatically and briefly through the heavens be anything other than a message from a divine force? Even a few hundred years ago…

Today a human-engineered spacecraft descended out of the starry blackness and touched one.

We have known for quite some time that our ancestors widely maligned these icy rocks, often thinking them messengers of death and destruction.  Yes, a comet is, at some level, not much more than an icy rock. Yet, heated by the sun, it can create one of our sky’s most bewitching spectacles. Actually two, because not only can a comet itself be a fabulous sight, the dust it leaves behind can give us meteor showers for many years afterward.

But it doesn’t stop there.  For comets, believed to be frozen relics of the ancient past, born in the early days of the Sun and its planets, may have in fact been messengers not of death but of life.   When they pummeled our poor planet in its early years, far more often than they do today, their blows may have delivered the water for the Earth’s oceans and the chemical building blocks for its biology.   They may also hold secrets to understanding the Earth’s history, and perhaps insights into the more general questions of what happens when stars and their planets form.  Indeed, as scientific exploration of these objects moves forward, they may teach us the answers to questions that we have not yet even thought to ask.

Will the Philae lander maintain its perch or lose its grip? Will it function as long as hoped? No matter what, today’s landing was as momentous as the first spacecraft touchdowns on the Moon, Venus, Mars, Titan (Saturn’s largest moon), and a small asteroid — and also, the first descent of a spacecraft into Jupiter’s atmosphere. Congratulations to those who worked so hard and so long to get this far! Now let’s all hope that they, and their spacecraft, can hang on a little longer.

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32 Responses

  1. Electrostatics may well help initiation of objects, thus the melt-fusion I propose (like building a snowball) presumably will not work if all the material is micron sized. Getting the first “fist-sized” object to act as a seed is an obvious difficulty, but I am far from convinced that electrostatic forces will get an object to a size in the gas stream of the accretion disk where it can act gravitationally. However, if someone can show that it is possible, of course i revise my opinion.

    Gas giants moving is simply through gravitational attraction. If you can get to a Jupiter and Saturn in about 1 MY, given that some disks last up to 30 MY, much more gas can be accreted, and of course, the smaller the star, the more tightly packed the planetary system because with less gas flow and less central field, corresponding temperatures are reached closer to the star. Effectively, if they grow big enough the planets play gravitational billiards, until you get some that will throw one (or more) out of the system leaving highly eccentric orbits to those remaining. The hot Jupiters arise through such highly eccentric orbits getting circularised by tidal interactions with the star. (That possibility is published theory, not mine.)

    To illustrate the possibility, the system closest to ours that we know about is HR 8799, with a stellar mass 1.5 +/- 0.3 times sol’s mass. If I assume the outer planet is where sit should be, then I predict the four giants to be at 68 A.U, 43 A.U., 20.9 A.U. and 11.8 A.U. They are actually at 68 A.U., 38 A.U, 24 A.U. and 14.5 A.U. Whether that is good or bad agreement I leave to you. The spacings are actually determined here by gravitational resonance, and if the planets were any larger, they would almost certainly be in unstable orbits. The basic problem with comparing observation with prediction, of course, is the prediction depends on several variables defined by the accretion disk, and by the time we observe the planets, the nature of the disk has long gone.

      1. Indeed, good news. Yes, I have seen this image and it is spectacular. Early planets are no surprise for me, but it will be the spacings of the gaps that will be of primary interest. Some have to be resonance gaps, but we shall have to wait and see what eventuates. Needless to say, I am awaiting the full paper.

  2. Some of the comments above relate to “Why do this?” I believe there is a chance we may gain some quite important information about how solar systems are formed, BUT there are two reasons why we may not. The first problem is, the underpinning theory I hope will be supported does not depend solely on mathematics, but rather on initial conditions. The second one is, as I noted above, the surface may not be sufficiently primordial, however since Philae is digging, there is a chance. What I hope Philae will detect is neon trapped in the ice, or in the emissions, if they are detectable by Philae when they come.

    There is a basic problem with planetary formation that is generally swept under the carpet. The standard theory assumes gravitational attraction of a distribution of planetesimals, but after fifty years of trying, there is no reasonable theory as to how the planetesimals form. Assume you get the planetesimals, the most aggressive (i.e., the most favourable values of variables) resultant modelling indicates it takes about 3 – 4 MY for a core to form big enough to get Saturn going at 10 A.U., and cores are very difficult to get going further out. It then takes several MY to get from core to something big enough to get runaway gas accretion. The problem then is, the star LkCa 15 is about 2 MY old, and appears to have a giant of about 5 Jupiter masses with a semi-major axis of 15.7 +/- 2.1 A.U.

    Note these models also suffer from a self-consistency problem. How can a core for Saturn take that time, when the same sort of modelling originally required 100 MY to form Earth?

    Anyway, my theory of planetary formation involves (for the giants) the cores to form by melt-fusion of ice, the fusing agent being entrapped ices in the cores of water ice (except for Jupiter, which had to rely on water ice). The mechanism is essentially similar to the way a snowball forms. This predicts the chemistry of the systems and the relative distances of the giants in our solar system reasonably well, but there is one potential ice not accounted for: neon. If there were neon trapped in ices in the accretion disk, then a further planet is possible at some distance in the order of 100 A.U. out. But this is where this sort of theory runs into trouble: we do not know the initial conditions. If the accretion disk material had a temperature roughly > 15 degrees K, neon could not accrete anything by this mechanism, and would not be in the ice. Second, because Jupiter is only about a 5th the size of the giant around LkCa 15, then our solar system had to have ejected its accretion disk within about 1 MY. (According to the information I have, a little under half the stars do that, so it is not an unreasonable requirement.) Growth at such a distance would be correspondingly slower, and any planet may not have had time to get big enough. (It is possible that bodies like Sedna may have arisen this way.)

    So, that is why I am very interested in what Philae has to say. In my view, it is not a waste of time, because it may answer an important question (important in my opinion, anyway). Of course the big disappointment would be if Philae has no means of detecting neon.

    1. You may want to look into the idea of electrostatic forces helping bind dust grains together to form planetesimals. It’s an interesting idea we’re only just beginning to explore.

      I am also interested in what your theory says about the gas giants moving and so-called ‘hot Jupiters’.

  3. Newton’s bucket shows that true (rotational) motion is anti-correlated with, and so not identical with, proper motion . So according to Newton, the rate of true rotation of the bucket (and water) is the rate at which it rotates relative to absolute space. But the general idea is that although a spatial distance is well-defined between any two simultaneous points of this spacetime, only the temporal interval is well-defined between non-simultaneous points.
    This allowed the measurable “speed of light c” to replace absolute space(or ether) with spacetime – all of this formulation and definition has been given in terms of the geometry of spacetime. Mach said, In absolute space’s place we need only substitute the frame of the fixed stars, as is the practice in astronomy or sea navigation.
    According to Gottfried Wilhelm Leibniz, space, which is after all constructed from ideal places, is itself ideal: ‘a certain order (Einstein’s speed of light ?), wherein the mind conceives the application of relations’.
    For a massive particle we can always find a rest frame, but for a massless particle there is no rest frame and therefore it is impossible to find a spin eigenfunction about any axis other than along the direction of travel. Another way to see it is to look at how we quantize the photon. we start with a vector field, which actually has 4 degrees of freedom. but gauge invariance forces 2 of these degrees of freedom to be unphysical. gauge invariance again relies on the photon being massless (here comes the Spontaneous symmetry breaking).

    This quantization of Geometry, made Leonhard Euler, to swing from geometry towards algebra – the rubber sheet topological geometry – through observing the motion of the Moon. Euler’s moment of inertia, developed upto GEODESIC – which made possible to track and land on unshaped objects like comets ?

    But this constancy also depends on Spontaneous symmetry breaking ?

    1. Communicating at quantum mechanical ground state ?
      “Humans may have no free will”

      Now Bob, Alice and Charlie shared informations at QM ground state. At quantum computing, the rule will try to eliminate the human will.
      The information will be shared either with two or alone as virtual – without mass or gravity (if we say mass and gravity are two sides of a coin).
      But reality have three sides of a coin ?.

      1. But what IS free will? It cannot be something you just do because of ‘clockwork physics’ because there is no choice there. But if it is random, is that free will? A leaf blows random in he wind, but it does not have free will. So what is it?

        1. Thank you Mr. Kudzu for answers,
          I go basically Cartesian – the Body-Mind dualism. It may be a primitive thinking, may be wrong. Science speak about empiricism rather than idealism now. But dualism came out of science. In Decartes’s Meditation VI, “Concerning the existence of Material things, and the real Distinction between Mind and Body”,
          “In sofar as they are the subject of pure Mathematics”,
          “I now know at least that they can exist, because I grasp them clearly and distinctly” – So material things exist and contain the properties essential to them (Mathematics).
          If one is DISTINCT (body), another one associated with it must also distinct (Mind or FREE WILL) – I understand like this !

          He further said, “Mind of man is sufficient to discover more perfect (immortal) than myself”. Free will constitutes intuition (contrasting unconsciousness and intention) – A fragmented expression of insights.
          So Descartes in 1619, connected Geometry (properties essential to them) with Algebra (reunion of broken parts).

          This is different from Kantian “Immortality of soul (Transcendental)”.
          Descartes concentrated in CORRELATION of Body&Mind.

          But development of science shows, reality (Naturalness) is more Transcendental ?
          I understand Gravity, to maintain mass proportionality, based on, “Matter consists mostly of empty space”.
          The energy conservation maintains ‘clockwork physics’ – and also the Randomness of spontaneous symmetry breaking. Immortality means, not long living – but to detach from energy conservation (distinct) ?

          1. MATTER to exist, there must be CP ( Charge conjugation Parity symmetry ) VIOLATION.
            Richard Feynman says, CP violation is Relative !
            Quantum mechanics allows, and indeed requires, temporary violations of conservation of energy – so one particle can become a pair of heavier particles (the so-called virtual particles), which quickly rejoin into the original particle as if they had never been there. If that were all that occurred we would still be confident that it was a real effect because it is an intrinsic part of quantum mechanics, which is extremely well tested, and is a complete and tightly woven theory–if any part of it were wrong the whole structure would collapse.

            MORTALITY, creation of Matter and Violation of Conservation of Energy are interconnected !
            IMMORTALITY means – to DETACH (distinct) from (violation of) Energy conservation ?

  4. “… When they pummeled our poor planet in its early years, far more often than they do today, their blows may have delivered the water for the Earth’s oceans and the chemical building blocks for its biology. ”

    ” … far more often than they do today … ”

    Great observation Professor, could you explain this to the folks at NASA?

  5. @veeramohan: In re. reaching and rendezvousing with P67: This spacecraft has had to alter its original trajectory probably more than any other spacecraft: first, it had to get accelerated sufficiently to get way past Mars’ orbit, then turn around and accelerate back toward the comet, catching and matching its orbital velocity inward toward the Sun. That alone is quite a feat. “Gravity assist” has become an almost standard way of gaining velocity by using the gravitational energy of a large body to accelerate a much, much smaller body: the Earth and Mars were “slowed” (decelerated) by an incredibly tiny amount as Rosetta was accelerated and flung past them, farther out from the Sun. Simple conservation of momentum. Then, once Rosetta arrived at the comet, it couldn’t just “orbit” it the way one would orbit a larger body; P67 doesn’t have enough gravity, and its odd shape and rotation makes its gravitational field different from that of a symmetrical body. It took them weeks before Rosetta could maintain a Keplerian gravitationally-bound orbit, where Rosetta did not have to fire its thrusters to stay in the “orbit”.

    However, I would also caution against over-hyping what has just been accomplished and what we might learn. This is a Jovian comet, that has been around the Sun multiple times. As such, it has been subject to the environment of the inner solar system for a very long time. The head, neck, and body of the “rubber duck” shape appear to have different compositions, with lots of strange topology and maybe even geology. I had a discussion with one of the JPL leads on the mission who was speculating that it might not be “primordial” like we have always assumed comets to be. Just as the various moons around the outer planets each have very individual characteristics and histories, we need to be careful about generalizing from a sample of this one comet to comets in general, or to the ways that planetary systems originally form.

    We should also be aware that the survival of the lander — if it survives — is far from being a technological triumph. First, it was designed to land on a very different type of body than the one they found. Everyone assumed that comets are relatively smooth, oblong ice-and-dust balls, with relatively gently sloping terrain, and that is what Philae was designed to land on. (If Philae landed on a slope greater than 30 degrees to the local gravitational field, it would tip over.) P67 is anything but smooth, with scarps and gashes and slopes and “boulders” everywhere, tumbling head-over-ass (in rubber duck terms) through space. The batteries in the lander will only last a few days at most; the lander had to land in a location (and orientation) with sufficient sunlight to recharge those batteries. Even in the most favorable orientation, the lander is only expected to last a little over a month before it has to be put to sleep while its batteries recharge. No one knows if it will survive those sleep periods, with the comet beginning to outgas more and more as it approaches the Sun. This is nothing like a Mars rover.

    Once released, the descent of the lander was totally uncontrolled. It had no thrusters to control its trajectory or speed or even its orientation. It just slowly fell in free-fall, in the direction it was going when ejected from Rosetta. And almost none of the landing systems worked right. The jet nozzle that was supposed to fire downward upon surface contact, to push the lander onto the surface in such a low gravity environment, was inoperative; they could never get it armed. The harpoons that were supposed to fire into the surface and anchor the lander apparently never fired (despite early claims that they did, in which case they may have actually pushed the lander back up off the surface — hopefully to be clarified soon). The landing struts were supposed to absorb the shock of impact without causing the lander to bounce; they were apparently not effective. It appears that the lander bounced at least twice — also hopefully to be clarified soon. The “ice screws” that were designed to dig into subsurface ice and secure the lander failed to do so. So the fact that this thing is doing as well as it is, is basically just due to plane dumb luck, despite the technical prowess required to get it there and the sophistication of the instruments on board.

    1. Thank you Mr. WLM, science should be a modern superstition for laymen.
      Quantum physics is possible because, probability density is quantized. why it was not occurred in other ways, was the “spontaneous symmetry breaking”. ?
      In above situation, an orbital quantization should be a basic. Otherwise it will not come under computations.
      You have explained very neatly, this was the case. Of course the technological advancement is a great feat.
      Thanks to the Constancies of heavens.

      1. … many mistakes… main one… “science should not become modern superstition”. “Quantization out of vortex like orbits in general relativity as mass in the middle”.

    2. On the other hand if it is NOT primordial this will also be informative; for one thing it would then not be equally altered all over, boring into it would quite likely give us a less ‘contaminated’ sample. We’d also get information on just what a few billion years of photochemistry can do to a body and maybe even answers to questions we didn’t think to ask.

  6. In media, the distance traveled by Rosetta from earth, varies from 310 million Kms, 500 million Kms to some Billion Kms – Any problem in speed of light calculations ?

    /Getting from Earth to a comet that is travelling towards the Sun at 18 kilometres per second (11 miles per second) was a landmark in space engineering and celestial mathematics./ – Moon also travelling 3,683 kilometers per hour around the earth. Any diffrence in Comet landing from Moon landing – in context with Physics or Basic science (not technology) ?

    /Rosetta, carrying Philae, was hoisted into space in 2004, and took more than a decade to reach its target in August this year, having used the gravitational pull of Earth and Mars as slingshots to build up speed./ —
    Please explain this, both in Newtonian and General relativity.

    /We investigate the nucleation process for the possible types of vacuum bubbles. We classify false vacuum bubbles of a self-gravitating scalar field with compact geometries. We show that there exist numerical solutions representing the tunneling from the true vacuum state to the false vacuum state. The solutions are possible only gravity taken into account. We present the analytic computations for the radius and nucleation rate of a vacuum bubble using the thin-wall approximation. We discuss possible cosmological implications of our solutions./—-

    1. The media are… poor when it comes to facts and figures. When I was at university we were told to go online and find the melting point of Radium; various sources were out 500C.

      The moon landing was considerably easier for several reasons; first the moon is a lot bigger, a LOT. (It is easier to hit a barn with a rock than tin can.) Secondly the gravity is higher and gravity tends to help you land. Miss by 1% on the moon you land slightly off. Miss 1% on a comet and you can bounce off the surface like a ball and not come down again. (The rover bounced TWICE!) Thirdly the space is well… less vast near the moon. It’s a few million miles if you really stretch things out. For the comet, a million is a drop in the bucket.

      The gravity thing is a ‘gravitational slingshot’; http://en.wikipedia.org/wiki/Gravity_assist Basically one object gets kicked out faster and another object gets pushed in towards the sun. This happens because as you are pulled closer to a planet the planet is also pulled closer to *you*. If you approach a planet from the sun side it gets pulled toward the sun and you get pulled away from the sun. You can then ‘whizz by’ with that extra energy, going faster.

        1. Yes, but you have to be very VERY careful.

          Firstly, comets may be (we cannot yet say ‘are’) very fragile; the one discussed here could likely be split in two if you were to use a few sticks of dynamite at its middle. (It may be held together only by gravity and dust.) A big problem would be not shattering the comet to bits when the bomb went off.

          Secondly you could need a lot of bombs; comets are heavy, this we know. You can break it into bits but those bits wouldn’t be moving much different. Better would be some sort of nuclear powered rocket that could mine the comet, ‘burn’ it and eject the gas as exhaust. Or, if you had enough comets and computers you could find one that would get near Earth IF it were given a small nudge. But some scientists are saying that a way to do that would be simply to paint the comet (Or asteroid.) on one side with white paint.

          It’s a tricky and interesting area of research and conjecture.

  7. Indeed, as scientific exploration of these objects moves forward, they may teach us the answers to questions that we have not yet even thought to ask.

    Well, I certainly hope so. Because the kinds of questions that we can ask now are pretty boring. I’m sorry, I can’t get excited over this. We are constantly told that this research “may give us ideas as to the origin of the solar system.” [1] Since when has the nebular hypothesis been controversial? [2] Why is this interesting anyway? Sure, it makes great TV, but what exactly is being accomplished scientifically? As Ianmillerblog points out, there is zero reason to think that these chunks of rock remain as they were billions of years ago. But even if they were, so what?

    Send a probe to Titan and find plesiosaurs in the oceans there. Examine a rock sample from a comet and find a supersymmetric particle. Great! But don’t try to get me excited about “Oh, there’s a tiny amount of water on this thing, probably that means that it supported life a jillion years ago!”

    Face it folks, this expensive little jaunt is a monumental bore!

    1. There’s a lot to be said for monumental bores; like it or not the bulk of science is based upon solid, ‘dull’ research. Our failure to support such holds us back on many things, and not just in science.

      And the achievement itself is exciting. We’re (probably) not going to find little green men on this thing? Such a pity. But to sweep the whole thing aside? A waste of a good imagination. We’re a species that gets excited over mere calendar dates. (Both Y2K and 2012.) but when so many great minds come together to accomplish something like this we turn aside? Terrible.

      Besides, you never know; I remember when there was a project o measure the decelerating expansion of the universe. They were looking at supernovas or something. Whatever, it’d be a nice refinement in the Big Bang theory but nothing to write home about.

      Only, it turned out the expansion was, or at least appeared to be, accelerating. Kinda the exact opposite of what we expected. We still have only the poorest idea of what that discovery means. What happens if we find an alien plesiosaur in a comet? Or heck even just incredibly complex organics? What if we find no organics at all? Or something that makes no sense? It’s happened before it will happen again, but you never know until you look.

  8. First, I congratulate ESA on what they’ve done. It is not sure at the time of writing this whether Philae has secured itself, but I wish ESA luck with that.

    On the other hand, I also caution against getting caught up with issues like, “comets brought our water”, or “we have found what delivered the biogenesis precursors”. Regarding the delivery of water to Earth, what we have to look at is the set of volatiles, and the atmospheres of the three rocky planets do not accommodate any common source (other than somehow arriving from the accretion disk). This really is a case of applying logic to the whole data set. Second, I also caution against drawing conclusions about the origin of the building blocks of life. Of course I have my own ideas on this (caution!) but the comet is either just dislodged or it has been around before. If it has been around before the surface has been heated before, and the volatiles may not remain where Philae landed, or alternatively what remains may have been chemically altered. Anything organic on the surface will have probably undergone chemical reactions. Yes, it is cold out there, but then material has also been there for about 4.5 GY, so cold or not, chemical reactions will have occurred. Further, most icy bodies out at Sedna’s range (100 A.U.) have had significant photochemistry take place on their surfaces (which is why they appear reddish). Accordingly, we should all be a little cautious about jumping to whatever conclusions we feel like when some data starts coming in.

  9. “How Far We Have Come(t)” … or maybe “How Far We have Cometh” ?

    You bring up are very interesting question, by say “how far we have come”. Our brain has evolved into a very complex physical structure composed of a complex neural network which gives us the ability to develop progressively complex thoughts, learning.

    My question Prof is, can physics be used to explain a) evolution and b) the consciousness that is inherent (seems to be, anyway) with such a complex neural network?

    I suppose another way of posing the question is, can physics be used to explain biology?

      1. Thank you for the link. As expected many generalities but one concept that is a definite eye catcher is;

        “In some interpretations of quantum mechanics, the perception of a deterministic reality, in which all objects have a definite position, momentum, and so forth, is actually an emergent phenomenon, with the true state of matter being described instead by a wavefunction which need not have a single position or momentum. Most of the laws of physics themselves as we experience them today appear to have emerged during the course of time making emergence the most fundamental principle in the universe and raising the question of what might be the most fundamental law of physics from which all others emerged.”

        This could explain consciousness. If everything is made of waves (at various frequencies) and somehow they are slowed down to create a structure of know momentum and position, mass, (via “gravity” and I place this in parenthesis because I don’t what gravity is or if it is real) then this structure could be influencing the emerging waveforms around it. So a thought could be waveforms of radiate energy created by the highly energetic structure (neuron network of our brain). And these thoughts dissipate in spacetime and regenerated with similar stimulus (firings).

        In other words, waveform being the fundamental can create emerging systems which in turn can create more “stable” waveforms i.e. fermions and bosons.

        So I ask based on this idea a single fundamental force in nature is possible, one which conglomerates even the fundamental waveforms. Example, interaction of fields create ripples (particles) and these particle inturn create higher ordered fields.

        Which bring me to one of my first questions I have asked on this site, are particles trapped vortices of spacetime?

  10. Matt,
    Speaking of comets bringing chemical building blocks, etc., could they have brought a whole lot more? I’m curious as to your view of the panspermia hypothesis. I’m referring mainly to Joseph Kirschvink’s talk at IAS (Dyson Freeman’s 90th Birthday Conference) which we both atended. Hope you’re enjoying yourself at CERN.

  11. Watched this live on TV. The emotions I had when they got the touchdown signal were similar to what I experienced when I watched the moon landing in 1969. What an incredible species we are!

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