Where is the edge of space?

for quite a long time the sort of adopted agreed definition for the edge of space has been something called the Carmen line which is located at 100 kilometers above the Earth's surface it is not a legal definition but it's a definition that's been adopted by the fédération internationale aéronautique which is the world air sports federation but it's it's a largely unsatisfying definition because of course the atmosphere doesn't have an edge it's a continuous fluid body it has lots of different properties and lots of different regions but none of them have rigidly defined edges and in fact the properties change as a function of time and solar activity and lots of other things a hundred seems almost too perfect doesn't it it does so recently a paper has been published called the edge of space revisiting the Carlmont line and this was work done by an astrophysicist named Jonathan McDowell at the harvard-smithsonian Center for Astrophysics and he takes a closer look into whether there is a real scientific definition for the Karman line the original Karman line definition was roughly associated with the idea that there's a boundary between where aeronautical forces stop and you no longer get lift in the atmosphere aeronautical lift is a mechanical force it's generated by contact with a fluid the fluid obviously being the atmosphere and if you run out of fluid you run out of force and so the Karman line is you're you're sort of wearing our aircraft would have to travel at a speed that's greater than the orbital velocity in order to get enough lift from its wings to stay in the air so in this paper we looked at the orbits of 43000 satellites and tracked over the years and of course most of them are way above the Karman line but there were substantial numbers that throughout their orbits would pass below the hundred kilometer line getting even closer to 80 kilometers and not just on their last orbit before they disintegrated but they have multiple passages as well and so right away you can say okay well the 100 kilometer line doesn't make a lot of sense you can't have a satellite in orbit and then it comes in and Oh for a little bit it's not in space then it goes back into space and on and on and on and so right there is some evidence to at least support the idea of revisiting this definition so the second thing he did was actually use an atmospheric model and actually make the calculations of for a typical satellite where would the drag forces be enough to sort of cause it to fall back to earth for satellites that's exactly it so the conclusion he makes is that for a typical kind of space vehicle the gravity will exceed the aerodynamic forces for any object and steady flights at that altitude that altitude lies in about the 70 to 90 kilometer range so he factors in the time variation and all of this stuff and and finds a range for this limit but notes that it's always well below that 100 kilometer line this is just one argument other arguments would look at the structure of the atmosphere which is quite complicated but again it's divided into specific layers mostly based on where the gradient in temperature changes these are called pauses and so at about 85 kilometers we've got the Me's a pause which is the boundary between the mesosphere and the thermosphere and that marks the point which is the coldest point in the atmosphere below that point the chemical composition of the atmosphere is mostly steady and above that you've got different molecules moving in different ways and so from atmospheric physics there's also a boundary more towards the 80 kilometer line so what's really interesting about this argument is to actually appreciate how close space is because kilometers 100 kilometers that's not that far away you can easily drive that in an hour so I thought it might be fun to look on a map and actually appreciate to scale how how far away space is of course our map is centered on the centre of the universe which is here nottingham and the unit that we're going to use to mark scale on this map is the humble Lego block the height of this brick is 3.2 milimeters and so i printed this map so that five of these Lego bricks represent 100 kilometers on this map to put some things into scale first let's talk about airliners so when we're on a commercial airliner we're traveling at about an altitude of 10 to 12 kilometers so when we're traveling on a commercial airline we're not even traveling at the height of this brick above this map so the next skill I'm going to show you is the world record for how high a human being has jumped out of a balloon to skydive down to earth so this record was broken recently by Alan Eustace and he jumped from a height of 41 kilometres so that would record represent two bricks on this map and so now we want to go up to the Karman line and so the debate were discussing today is whether we define the edge of space at 80 kilometers which is here 400 kilometers which is here doesn't seem that high anyway does it so I think that's the amazing thing to appreciate so this height is a hundred kilometers what's really amazing is how small this number actually is how close we are to space so I tipped this on this the edge and I've got 100 kilometer marker here you can see that Nottingham is closer to space than it is to London and I can get that London in an hour and a half on the train all right so maybe Nottingham to London doesn't mean very much to you but if you knew you're in New York you're closer to space than you are to Philadelphia if you're in Los Angeles you're closer to space than you are to San Diego so let me do a Canadian one okay if you're in Montreal you're closer to space than you are to Ottawa I've got no idea where those places are I looked up Adelaide for you but nothing's in your answer didn't work when do you become an astronaut so NASA gives its astronaut wings to anyone who's trained and flown a successful mission that reaches above 50 miles which is 80 kilometers so that's actually the lower limit and there's a similar acknowledgement from the US FAA for civilians who have piloted a successful flight above is this important like is this just a bunch of people writing papers or does it matter where space starts and finishes so it matters from a scientific perspective because scientists like to study these sorts of things so it's perfectly understandable that people who are interested in atmospheric physics and the orbits of satellites would care but it it actually does have some wider issues that now touch on issues of economics and politics and defendants and things like that so I mentioned there is no International agreed legal definition of space there have been for some time moves to make a legal definition but that's always been opposed by the US and you can understand why because from a military point of view a government wouldn't want to be restricted by international space treaties when it's trying to launch high altitude ballistic missiles something like that and what about space tourism I guess they want it to be as low as possible so they can sell their space flights well that's the other issue so commercial space tourism is becoming a thing now as we film this Virgin Galactic has just managed to highlight a vehicle 282 kilometers in Turing space by the FAI definition it doesn't because it haven't reached the Karman line but it would matter very very much to a commercial enterprise to be able to say that they can take people into space now practically speaking you know I think what you would want from a space mission is the experience of weightlessness and the experience of looking out the window and seen the earth as a as a ball you would get that from 80 kilometers as well as you would from 100 kilometers but like I look at that and I look at how low that is and I imagine go how come you can see the curvature of the earth from such a that doesn't seem that high I think partly that's because I've printed a map out on a flat piece of paper so in reality this is a curved surface that I'm showing you here you might not see it as a complete ball but you would definitely see the curvature of the earth you would experience the earth as a sphere it becomes quite clear that for a commercial enterprise you're not going to want to waste money and fuel and an increase risk by taking people up to 100 kilometers if they can get the same experience going to 80 kilometers but part of that experience for people will be able will be being able to say I have officially been to space where would you be drawing the line well I'm pretty convinced by this paper I mean it has some pretty sound arguments from a number of different directions so I think if there was a move to redefine the 80 kilometer line is the McDowell line I think that should go down very well but the but McDowell says 70 to 90 that's like super vague well that's just because scientists you you know scientists you've talked to enough of us over the years and we like our error bars and we like our confidence intervals but if you want to define a line you might as well put it in the middle of a region that is well bounded this paper has revisited the numbers and the back of the envelope calculations that gave a hundred are now refined and they might not give a more precise number but they at least show us that it's not a hundred and so it's very unsatisfying to keep it at that level I thought it would be fun to actually build up perspective on the altitude that other objects in space yes part of this was motivated by the fact that just last week I went outside as I was coming home from work and happened to see the International Space Station go overhead it was really bright was beautiful passage and as always I was struck by looking up and thinking oh my god there's human beings flying above my head in orbit around the earth that's pretty amazing how far away are they actually up there the Space Shuttle now no longer in existence but I couldn't resist getting my Lego out used to take astronauts up to the International Space Station like May Jamison and that's at 400 kilometers above the surface of the earth so in our LEGO bricks if this is a hundred we need four times that amount so that's do this 13 14 16 I feel like I'm on Lego masters 20 excellent right so this is the orbit at which human beings continuously inhabit a space station orbiting the Earth and even that is not that high I'm slightly less impressed I think one of the values of human spaceflight one of the real values is cultural not scientific and it's putting human beings high enough to give them that's perspective on space and if they only have to go that high to be able to look out in one direction and see nothing but the infinity of space and then turn around and look down and see the earth in enough scope to see not borders and not resources to be exploited but to appreciate this is the one and only place where life in the universe exists and to look out to the horizon and appreciate how razor thin that precious atmosphere that keeps us safe is then I think I think it's quite amazing that you don't have to get that high up to find a perspective where you realize just how precarious and how delicate the ecosystem and the Geo system on earth is what else you want to show him you got Hubble there or okay so I've got Nancy Roman and the Hubble Space Telescope one of my favorites and this orbits an altitude of 540 kilometers it used to be higher but it's slowly even at the altitude it suffers from a cumulative atmospheric drag over time so it's going lower and lower and that represents Preem it's the highest altitude that the Space Shuttle could reach because it was Hubble was designed to be put into Earth orbit at an altitude where the Space Shuttle could repeatedly go and service it and it's a good thing it did because we benefited from those servicing missions quite a lot and so I've got 20 bricks now and I need to put eight more to get up to the height of the Hubble Space Telescope so one two three five now we've run out of thin bricks so we're gonna put three more on top and so that's how how high the Hubble Space Telescope is all right so there's the Hubble Space Telescope yeah there you go see that not to scale of course the whole Space Telescope is about the size of the bus not about the width of the United Kingdom well there's lots of satellites up there in orbits GPS Global Positioning satellites orbit at an altitude of 20,000 kilometers above the surface of the earth that would require a thousand Lego bricks and I'm not going to build that today but I would just note that that would take us 3.2 meters above this map okay so right through the ceiling okay and these are satellites they're in geosynchronous orbits so they orbit the Earth twice a day but there are satellites that are even further up there called geostationary orbit their orbital period is matched with the rotation of the earth so they orbit once a day which means that they are effectively always above the same location above the equator and these are the satellites that give us our weather meet readings and our actives are communications relays on this scale you need 1789 bricks which would take you five point seven meters above the table way up way up we're looking here down at the UK and Europe how many bricks down is the other side of the earth so I said that the GPS satellites are at a thousand bricks above the earth but the other side of the earth would only be 640 bricks so that's less than the height of the GPS satellites about what if I wanted to go to the moon of course you want to go to the moon well you would need to travel 19,000 220 Lego bricks away which on this scale would be 60 meters there's been enough recent attention to this idea that the Karman line needs to be redefined that the organizations that deal with aeronautical things and the organization that deals with astronautical things are proposing to get together in the coming year to have a symposium to look at the scientific and the political and whatever other arguments go into this to see if we need to actually have a definition of where is space and what that might be we made a video a couple years ago saying that Voyager has left the solar system and just left the solar system again so most things in space don't have a hard edge and that means that different definitions can apply and you can argue too til the cows come home about whether Pluto's a planet or where the solar system ends or how big is the Milky Way and to some extent you will never get a satisfying answer because science often comes with caveats that say it depends what you mean I can tilt it but you'll notice that the access of the spin keeps pointing the same direction it explains things but the main thing it does is creates a huge problem because if you're a theoretical physicist you can do a calculation that says okay so I'm creating all these virtual particles

Channel: Sixty Symbols

Views: 202,124

Rating: 4.9166894 out of 5

Keywords: sixtysymbols, space, karman line, atmosphere, edge

Id: nILOHp79njQ

Length: 16min 6sec (966 seconds)

Published: Wed Jan 16 2019