I think “15 times further from the Sun than Pluto” is more meaningful for most readers than “700 times further from the Sun than Earth.” If it exists, it’s way way way out there.
It makes even less sense for Earth because Earth's orbit is near-circular, whereas Planet 9's hypothesized orbit is highly eccentric, more so than Pluto.
Most people don't know off-hand that Pluto is ~40-50AU from the sun, so 700AU is hard to conceptualize.
They're all horrible to conceptualize because people don't commonly deal with how far even something like the Earth to the Sun is, I don't think there is any winning answer here - at least an AU is consistently defined and maybe slightly more likely to be familiar, but it's still just about as crap to be honest.
Side note: Apart from AU already being defined as average distance and not current distance, the distance referenced is how far out the proposed object is now, not its general orbital parameters. At that orbital distance 23 years of motion isn't going to be much change in distance even if it's in a hyperbolic orbit.
My point was not about intuiting the distance, it's about what the solar system looks like qualitatively, as a cartoon with orbits drawn around the sun. Most people have no idea if 700AU is closer than Pluto, a little further than Pluto, or much further than Pluto. 15x the distance of Pluto is much more direct.
What's the benefit of communicating something is 15x the distance of Pluto if people are expected to have at least a ~15x error in how far away Pluto is supposed to be? At that point it's all nonsense, nothing is relevant anymore. Might as well say something useful for those who do have a clue about the solar system.
Hell, it's been nearly 2 decades since Pluto was itself planet 9. Just bringing the name up in a discussion about planets is going to cause more confusion.
15 time further than the furthest once-planet is fairly intuitive to say really freaking far; you don’t need to know how far pluto is, just that it’s the furthest.
> Might as well say something useful for those who do have a clue about the solar system.
The source we are discussing is space.com, a website which frequently mentions Star Wars and whose stated mission is to "transport our visitors across the solar system and beyond through accessible, comprehensive coverage of the latest news and discoveries." My comment was about communicating this research in a way that better fits "most readers" of space.com. If you think qualitative orrery models are beneath you and want to exclude those people, then you are not the target audience. Just go read the actual paper.
When you put it this way it depresses me (). It just illustrates just how unimaginably big space is, considering something that might be considered part of our own star's solar system can be four freaking light days away. We'll never get out of our solar system will we?
The most distant Voyager probe is about 167 AU out, or one light day, and it’s been travelling for 48 years.
If we are going to get anywhere in space it’s looking like we’re going to need some kind of technological leap. Would be wild to see that happen this lifetime.
I was just thinking of this XKCD comic specifically.
Most people won't even have the slightest idea what 1 AU is. Most people know less about most topics (including space) than the original ChatGPT (3.5) did — probably only people who at least started a degree with a space sciences module are likely to know more than 3.5, and I expect plenty of space.com readers to be enthusiastic amateurs rather than professionals.
That said, I do I expect the average reader of space.com to know what an astronomical unit is, but even so I don't expect them to know the average orbital distance of Pluto.
New horizons launched 9.5 years before it reached Pluto, and your average reader who has an interest in Planet 9 will likely know it took New Horizons about that long.
15x means no one alive today will see a mission that reaches the planet, and that's more accessible for most readers per above.
My favorite: Cody'sLab's "How far away are the nearest stars": https://youtube.com/watch?v=dCSIXLIzhzk
Also gives an intuition for how incredibly bright stars shine
I have a set of twelve books by an artist, titled "Astronomical" (one book for each letter). The first page shows the sun, then the rest of the books are almost all simply black pages, but with the planets and asteroid belt entities shown with accurate distance and size scale.
It communicates the scales really well, while only taking up a little over a foot of bookshelf space when not being "navigated". I have two heavy metallic retro looking rocket bookends for it.
Yeah, when the solar system was introduced to my class in grade school, we had an outdoor excursion where the teacher brought out a golfball and place it at one end, then brought out various tiny things (noting scale was very approximate) and paced off each to show the relative distances.
700 AU is way past heliopause, firmly in the interstellar space. Same, 15 times farther than Pluto is definitely away from the Solar system "proper". It's about 100 light-hours away from Sun.
I wonder how could this object be counted as a "planet" belonging to the Solar system, even if it were the size of Jupiter. But it's an object "estimated to be 2 to 4 times the radius, and about ten times the mass of the Earth". This must be another class of celestial bodies, some jumbo-sized Oort cloud object.
As long it is orbiting the sun, i.e bound by the solar gravitational field then it is in the solar system?
Also depending how elliptical the orbit, is the perigee might be much closer than 700AU, while still being further than Pluto's orbit. For all we know 700 AU is the apogee and say the perigee is 70 AU (1.4x Pluto's apogee ).
The body must also be large enough to clear other bodies in the same orbit, except at the Trojan positions (L4 and L5), to be considered as a planet. Otherwise it would just be a Trans-Neptunian Object (TNO) or a Kuiper Belt Object (KBO) at these distances.
It obviously does in this case. But this pedantic detail is rather important. It was used to demote Pluto a few years back.
Does it? Would we actually know if there was another slightly more sparse belt at 700AU? If we can't track a large planet in that area, why would we be certain about the belt?
Alternatively, if it's an external object captured by the Sun, how would we even classify it as clearing or not if there's nothing to clear?
Well, apparently the object causes bunching of other bodies in the Kuiper belt. And it would have got enough time to complete a few orbits. I assume that at some point, the other objects on its orbit would have been thrown off course or consumed by the planet.
> how would we even classify it as clearing or not if there's nothing to clear?
I assume that it's based on mathematical modeling.
I wanted to get a sense of what that MEANS relative to the rest of the gas giants. Apparently it’d be roughly the size of Uranus or Neptune.
I guess I’d always put all the gas giants in the same “very, unimaginably big” bucket. I knew Jupiter was the biggest, then Saturn, but I didn’t realize just HOW big they were compared to the rest. At the risk of stating the very, very obvious, Jupiter is huge!!!
Masses of gas giants are: Jupiter, 317.8 earth mass; Saturn, 95.2 earth mass; Neptune, 17.1 earth mass; Uranus, 14.5 earth mass
The rest of the planets are theorized to have condensed from the protoplanetary disk that formed the same molecular cloud the Sun did. I. e. they have formed at approximately same time as the sun and from same material, sans gravitational separation.
Would likely be older than the solar system itself. Probably not first gen star old, but likely would have formed before the sun did. Don't know how different it would be though. Would have formed out of maybe different ratios of elements than what was in the molecular cloud we formed from, but otherwise a large body like this would have undergone similar geological processes as our own planets.
The other planets formed from material in the same nebula (cloud of gas and dust) that collapsed to form the sun. The idea here is this planet would have been moving through the interstellar medium and just happened to pass close enough to the sun’s gravity well to get captured in a (very distant) orbit.
Capture would be like a reverse gravitational slingshot? This planet happened to meet the sun at an angle where it lost enough energy to fall into orbit instead of slinging back out like those comets that come around on long cycles?
It would be like a reverse gravitational slingshot, in a different way.
There is no way to capture with just 2 bodies - it would have to leave on gthe same hyperbolic orbit that it arrived on. However if it drove by and had a close enough interaction with a third body, like Jupiter, it could lose angular momentum to the planet, resulting in entering an orbit around the Sun. Further gravitational interactions with planets could then smooth that orbit out over time.
Alternately this could be the more straightforward scenario of interstellar object hits planetoid, they merge, and the new combined object is now in orbit.
AFAIK, it could be in a 2 bodies slingshot, multi-body interaction with some other stuff on the Oort cloud, or tidal interaction (what could happen way more easily with a nebula).
But a ball needs to lose energy to not roll right back up a hill to the same height it came from. And if that "ball" is a mass from outside our solar system, it will roll right back out of the solar system just as easily as it rolled in unless there is enough forces to slow it down enough to capture it.
Not true. An obit is not an infinite "plain" with a finite "hill" on but rather a finite "valley". The ball will exit the valley on the other side unless it loses excess kinetic energy somewhere in the valley.
Anything that approaches the sun will do so with faster than escape velocity because the gravitational potential energy gets converted into kinetic during the approach. Newtonian mechanics is time-reversible - just like it's impossible for an object in orbit to spontaneously escape without gaining energy from somewhere first, it's impossible to enter orbit without losing energy to another body.
Small nit: this is for objects approaching from infinity in a two body system. Otherwise the object can be in orbit and already be “captured” there. For example, the moon also approaches earth slightly over the month while speeding up, then slows down while moving away. Or it could just be a 3 body system, which is chaotic and can’t be modeled accurately and can have objects spontaneously eject from the stable system (even though the physics is indeed reversible)
Your first nitpick only makes sense with a weird definition of "approaches" for the context, so I think it just adds confusion. They're pretty clearly talking about something that is headed in the direction of the sun and not already in orbit.
And the comment you're responding to already mentioned that other bodies can make a capture happen. Nobody was saying capture is impossible.
I thought the context is orbital mechanics, for which the term approach is the common term for a portion of the trajectory where the bodies move towards each other. Take any Wikipedia article for an orbiting solar body and search approach eg: https://en.m.wikipedia.org/wiki/Halley%27s_Comet
That is not true. If it approaches with less than escape velocity it will gain all the velocity necessary to escape in the process of approaching the Sun.
You could think of it as speeding up as it falls toward the sun, it then slows down by the exact same amount as it leaves the Sun.
In order to stay near the sun it needs to lose some of that speed, and given that momentum is conserved, the only possible way is to either hit the Sun or send that momentum to a third object.
Would this be far enough out to use the sun's gravitational lensing to image distant planets?
It seems like the idea was to send a bunch of instruments way out and then take pictures in the brief time they were at a useful distance, but if there's a planet out there we can orbit and so stop the instruments at that distance it seems like we could make a permanent super telescope.
orbiting a planet in that case is no different than orbiting a sun on the same orbit as planet. Probably even more cumbersome, all that jiggling around. Or are you talking about making a gravity assist to turn the orbit of the probe into less eccentric?
Because more people know about Pluto than Eris or Sedna. And we know that Pluto is the furthest away planet (sue me). So 15x Pluto is much easier to visualize in context of the entire solar system than 700x Earth. My cosmological knowledge is above average, but I don't know off the top of my head if 700 AU is super-duper far away or still in the range of the gas giants.
> And we know that Pluto is the furthest away planet (sue me)
I don't need to sue you. It's just entirely incorrect by any sane definitions of a planet. It's not the further if you include similar bodies or not a planet. As I have no interest in saving American misplaced pride (because let's not kid ourself it's about anything else), I don't see the point of spreading misinformation.
> Because more people know about Pluto than Eris or Sedna
Only if you were born before it was retrograded which will be less and less likely as time goes on.
> My cosmological knowledge is above average, but I don't know off the top of my head if 700 AU is super-duper far away or still in the range of the gas giants.
I'm not convinced that giving it in multiple of the distance between Pluto and the sun is in any way more useful than distance between the Earth and the sun or that it helps conceptualise the distance relative to the gas giants.
Anyway, Pluto orbit is highly excentric so you have 20AU of wiggle room here when considering distance.
I know it's not a planet, hence my sarcastic "sue me". I suppose the self-irony didn't work too well over text. My point was that many people still know about Pluto as a body that's at the edge of many people's everyday conceptualizations of the solar system, and I argue that makes it a more useful tool for helping people intuitively understand the particular distances involved.
> Only if you were born before it was retrograded which will be less and less likely as time goes on.
I admit my age plays into it. Though I am curious about the role Pluto has in modern primary school, do you know? I understand that it now has the same technical status as Eris et al., but I think it's still a fantastic example of how scientific understanding develops and changes. Not on par with discarding heliocentricity, but a very practical example of ongoing changes still present in our own time.
> As I have no interest in saving American misplaced pride (because let's not kid ourself it's about anything else)
I don't understand how this ties into American pride (nor am I American), what did I miss?
> I don't understand how this ties into American pride (nor am I American), what did I miss?
Pluto was the only planet discovered by an American and most of the people who are extremely attached to it tend to feel that removing Pluto as a planet is somehow taking something away from the USA.
As far as I know, the topic barely exists at all in other countries.
Thanks for explaining, I've never heard about this. In my social circle, nobody would seriously try to argue that it should still count as a "real" planet, but we still refer to Pluto-as-planet in an affectionate, nostalgic way.
Most readers probably know Pluto is the... well... it's not the farthest dwarf planet. But they know it's far, but don't realize just how far it is. I certainly didn't until I watched a video about it.
700 further from the Sun than Earth is tangible as "really really far" though.
It's sort of amazing to me that the Sun can capture objects that far away. Like obviously even at that distance the Sun would be by far the closest massive thing, but it's hard to comprehend the effects of gravity being strong enough at that distance. From "Planet 9" the Sun probably wouldn't significantly stand out from all the other stars in the sky, yet you'd be orbiting it.
I think both work. The average reader doesn't need to conceptualize these distances. They just need to know they're reallllly far away and realllllllly realllllllly (9x) far away. You can use the earth or pluto distances as relative scales.
I think both comparisons together paint a good picture: 15 times further than Pluto, which itself has an orbit ranging from 30 to 49 AU (the distance between Earth and the sun.)
Most people have at least a vague sense of Pluto being the edge of the solar system, so hearing that Planet Nine could be way beyond that makes it feel almost interstellar
