What if?

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This topic contains 85 replies, has 15 voices, and was last updated by  Strega 5 years, 8 months ago.

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  • #718

    SteveInCO
    Participant

    Hmmm… I’ll start with something that may seem irrelevant to that question.

    There is popular confusion over the term “orbit” I think. Technically even a flyby is an “orbit”, it’s a hyperbolic one. That’s the trajectory something follows when it is moving at greater than escape velocity, and it’s symmetrical, something coming “inbound” is moving with the same energy as it will when outbound (and when it’s a given distance away on the inbound leg, it’s moving at the same speed, relative to the primary, as it will be on the way out, at that distance). A hyperbolic orbit, however, doesn’t repeat, it goes off to infinity in either time and space. But usually “orbit” is used to mean something going around and around the other object in a repeating pattern, which is some sort of an ellipse (a perfect circle being a very special case of an ellipse). If you are just below escape velocity, it will be a very large ellipse. Of course that’s the “two body” treatment of the matter; there are more than two objects in our universe, and if the other objects are close and/or large enough, you can see things like objects moving at greater than escape velocity being “captured” into (elliptical) orbits and the like.

    Satellites are objects that are in an (elliptical) orbit about another body, and New Horizons was never in such an orbit about Pluto, so I have to say that part of Davis’s statement is wrong.

    By the way, when I mentioned hyperbolic (flyby) orbits, I described them in such a way that makes it seem like you can’t get a “gravitational boost” or “slingshot” from a planet (such as New Horizons got from Jupiter) but that’s not true. You don’t gain speed with respect to the planet, but you *can* gain it with respect to the Sun. You have to fly “behind” the planet in its orbit about the sun, and your trajectory ends up bent in the direction of the planet’s motion, your speed plus the planet’s orbital speed added together. If you cross the planet’s orbit in front of it, you will end up slowing down. Here’s Wikipedia on the subject: https://en.wikipedia.org/wiki/Gravity_assist and this animation http://www.theplanetstoday.com/voyager_flight_path.html shows what happened to Voyagers 1 and 2. (There doesn’t seem to be any way to pause, zoom, or restart other than to reload the page, and the planets are drawn too large to make it clear which side of the planet the flyby is.) Slingshots can only be understood by being willing to think in terms of multiple frames of reference. (I tried finding a satisfactory youtube video to *show* this rather than describe it in words, but gave up after three tries.)

    • This reply was modified 5 years, 9 months ago by  SteveInCO.
    #721

    Davis
    Moderator

    @steveinco by orbit I meant when it was first launched and was in orbit around the Earth for some time before it headed for Pluto…but maybe this is incorrect as well.

    #725

    Unseen
    Participant

    Technically even a flyby is an “orbit”, it’s a hyperbolic one.

    Even though I’m guilty of being technical often enough, I think many people roll their eyes as soon as they see a sentence start with “Technically…” LOL

    #745

    Davis
    Moderator

    How is this for incredible beautiful detail? Mountain ranges similar (at least in appearance) to those on Earth.

    • This reply was modified 5 years, 9 months ago by  Davis.
    • This reply was modified 5 years, 9 months ago by  Davis.
    #746

    Davis
    Moderator

    A gorgeous shot of Charon.

    #749

    Unseen
    Participant

    The scientists are saying that the strangest thing so far is that they see no impact craters. Well, I see features that resemble impact craters, but apparently they are not.

    #753

    SteveInCO
    Participant

    @steveinco by orbit I meant when it was first launched and was in orbit around the Earth for some time before it headed for Pluto…but maybe this is incorrect as well.

    That sort of thing does happen, but according to Wiki, it was launched directly onto its trajectory. Various technical and weather snafus almost caused it to miss this window, in which case it would have to have gone out there without the velocity boost from the Jupiter flyby… and if that had happened, we’d still have two to four years to wait.

    I find it astounding that we could even THINK of a direct launch to Pluto. That is one hell of a lot of rocket power.

    #754

    SteveInCO
    Participant

    Lack of impact craters implies a source of heat making the surface a bit “plastic”, at least while the bombardments were happening. Or perhaps there’s another explanation.

    As far as the mountains looking earthlike…well, it will certainly blow peoples mind if they turn out to have been eroded by fluids! I don’t get quite that sense though; I’m reminded (somewhat) of some pictures of the lunar highlands. Still, 11,000 foot peaks are a surprise. How did they form?

    #778

    Davis
    Moderator

    Still waiting for that stunning high resolution image of one side of Pluto. In the mean time…here is a nifty little feature…a mountain with a moat around it…though I think they are using some poetic astronomer license on this description. It’s at the top left if you aren’t good at finding Waldo.

    They have also discovered some cañons that are up to 10km deep (6miles). Imagine bungee jumping down one of those mega deep canyons. I don’t even know how different the experience would be with less gravity/pressure. I assume you’ll fall more slowly and bounce back less dramatically? Maybe a sciency person here can help with that one? I suppose with temperatures below -200ºC that the bungee cord would snap?

    • This reply was modified 5 years, 9 months ago by  Davis.
    #780

    Davis
    Moderator

    @steveinco A direct launch! It just makes everything even more outrageously shizzle-nizzle! This is one of those…off by a centimetre at the start…off by thousands of kilometers at the target?

    I shouldn’t have skimped on reading about the launch. Time to read up on the entire mission…from planning to today. I wish I had a source other than a wikipedia page that was lengthy (in case anyone knows of one).

    • This reply was modified 5 years, 9 months ago by  Davis.
    • This reply was modified 5 years, 9 months ago by  Davis.
    • This reply was modified 5 years, 9 months ago by  Davis.
    #791

    SteveInCO
    Participant

    Midcourse corrections were possible and mandatory; we don’t have THAT kind of precision [The reason it’s incredible is the sheer amount of delta V it takes to get out there without any gravitational assists, which we could have done with that rocket and probe if we had to]. There are thrusters with a small supply of fuel for that purpose. Corrections of course are smaller the earlier they are made.

    Furthermore, we made corrections just before the flyby to steer through areas safer from debris. And there is the possibility *still* of making a course change to bring New Horizons past another Kuiper Belt Object.

    A lot of people are saying “well this will ensure Pluto gets reclassified as a planet again” but a look at another KBO would possibly provide the evidence that Pluto is quite typical for a KBO. So if Pluto were classed as a planet, a lot of other objects (Eris, Quaoar (sp?) and so on) would also have to be, and we’d suddenly be up in the teens for numbers of “planets” with more undoubtedly on the way.

    I was staring at those pictures (not the one you just posted, it wasn’t out yet) and having to remind myself we have good, solid pictures of PLUTO. All I saw as a kid for pictures of it was a dot in a starfield with an arrow pointing to it, because it looked like just another star (it’s both tiny and far away). We had a lot of knowledge of Jupiter, Saturn, etc. but Pluto was a big fat ZERO for knowledge. I feel a certain amount of awe.

    • This reply was modified 5 years, 9 months ago by  SteveInCO.
    #793

    Unseen
    Participant

    A lot of people are saying “well this will ensure Pluto gets reclassified as a planet again”

    One of the qualifications to be a full-blown planet is that it must have cleared its orbit. Pluto is pretty much part of the Kuiper Belt. In other words, it’s in a dirty orbit.

    #795

    SteveInCO
    Participant

    They have also discovered some cañons that are up to 10km deep (6miles). Imagine bungee jumping down one of those mega deep canyons. I don’t even know how different the experience would be with less gravity/pressure. I assume you’ll fall more slowly and bounce back less dramatically? Maybe a sciency person here can help with that one? I suppose with temperatures below -200ºC that the bungee cord would snap?

    I’m curious about that feature up by one o’clock on the disk of Charon, it looks like a deep groove along a polar line of latitude. Is it an image processing artifact or did something do this in the distant past?

    The gravity there is very low, a ten km fall would take a lot longer. There’s not enough atmosphere for there to be a meaningful terminal velocity. If you were there and jumped off, after a second your speed would be less than a foot per second. (On earth, you’d be falling at 32 feet per second after the first second). Charon’s gravity is 0.278 meters per second per second, while Earth’s is about 9.8 meters per second per second.

    Plugging into various formulae that come out of physics class, to fall ten kilometers on Charon would require 268 seconds (on earth it would require 45 seconds, and that’s if you aren’t slowed down by atmospheric drag). After 268 seconds, you’d be traveling at 268 * 0.278 = 74.5 meters per second, or 268 kilometers per hour. (Hmm, the number 268 shows up twice, but I think it’s coincidence). Impact would almost certainly be lethal. The speed on earth after a fall like that (again, without drag) would be 1588 kph, which is over the speed of sound (in our atmosphere), and that impact would definitely be lethal.

    The bungee cord would have to be specially made to withstand the cold. Anything we use here would almost certainly be brittle at those temperatures. I have no idea if we even know of a material that would behave like rubber at that temperature.

    #796

    SteveInCO
    Participant

    A lot of people are saying “well this will ensure Pluto gets reclassified as a planet again”

    One of the qualifications to be a full-blown planet is that it must have cleared its orbit. Pluto is pretty much part of the Kuiper Belt. In other words, it’s in a dirty orbit.

    Ironically, it could be argued that because Pluto is there, Neptune obviously hasn’t cleared its orbit (Pluto’s orbit is elliptical and it is sometimes closer to the sun than Neptune, the last such time was 1979-1999), and shouldn’t be considered a planet.

    I don’t think very many people are satisfied with the definition formulated in 2006.

    For what it’s worth, I don’t think it should be considered a planet myself. But really, it is what it is. Where we draw our dividing lines matters little in the end.

    • This reply was modified 5 years, 9 months ago by  SteveInCO.
    #845

    Davis
    Moderator

    I agree @steveinco. Earth has comets/meteorids trailing us and preceeding us in its trip around the Sun as well as weaving in and around our orbit. I know that these objects may seem trivial but given that those who coined the term “clearing the neighbourhood) haven’t provided any figures for just what is a dominant object (and reasoning behind the figures) its all ever so slightly silly-dilly.

    Plus Pluto is just simply awesome and for its awesomeness alone it should be a planet. Like…seriously bro!

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