• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

James Webb Telescope

Ziggurat said:
Why? It's a strange requirement which doesn't really correspond to what's important about being a planet.
Click to expand...

What is important about being a planet? (genuinely want to know as it's all a little abrirary and the only thing that I can think distinguishes the big, historic things we call planets from the other stuff out there is that they have cleared (or mostly cleared) their own orbit.

Either everything that's orbiting the sun (and not orbiting another body that's orbiting the sun and therefore a moon) then becomes a planet. Which is fine if you want all the detritus in the Kuiper belt, all the asteroids and, possibly the entire Ooort coud to count.

I freely admit I could be woefully wrong about all of this or have my facts completely base-over-apex. I just always thought it was odd to feel sorry for a space rock that's had its classification changed.
 
Last edited:
3point14 said:
What is important about being a planet? (genuinely want to know as it's all a little abrirary and the only thing that I can think distinguishes the big, historic things we call planets from the other stuff out there is that they have cleared (or mostly cleared) their own orbit.
Click to expand...

The historic planets are the blueprint, because that's where the name comes from. So we should use a definition which is connected to them, even though it doesn't have to include only them. The fundamental properties are orbiting around a sun, and being large. If it's too small, it shouldn't be a planet, because all the historic planets are large. We can't see even nearby stuff if it's small. Likewise, until recently we had no way of determining if orbits were cleared (and even that requires making an arbitrary choice about how cleared it needs to be), so that doesn't really connect with the properties of planets important to their original classification.

But we need something more objective than "large", so we have to pick a way to determine what counts as large enough. There is more than one way we could have done that. For example, you could do that based on minimum mass or radius. But hydrostatic equilibrium is more appealing to many people, because it connects better to our intuition, and I believe the astronomical community has mostly congregated around the hydrostatic equilibrium criteria.
 
Darat said:
That's why I was wondering if the Webb could be used once we think we know where it should be with more certainty then we currently have. It was seeing the images from Jupiter and Mars that made me think about it. I don't know why but I had thought the local planets would have been "too bright" i.e. too hot for the Webb to get good images.
Click to expand...

I think it would likely be astronomers a few years down the road analyzing the data for the purpose of finding any object that is suggested by Webb’s findings. Probably to be searched for, if anything suggests a large object, by future telescopes, or existing ones designed for solar system inquiries
 
What's considered a planet should be entirely dependent on the resulting mnemonic...

Mary Very Eagerly Miscalculates Just Such Ugly Naked Patooties

...can't be improved upon. Don't mess with it.
 
To be a planet a body has to: orbit its star; not orbit another body; not be made entirely of imagination, antimatter, or dairy products; identify as a planet; be gravitationally stabilized into the shape of a sphere, cylinder, or balloon animal; not be delinquent on its student loans; have women; not be too remote to make an effective demonstration; have accessible rest rooms; be at least 17% natural ingredients; have a lively party atmosphere or an atmosphere of foreboding; not be too small for the both of us; have a Queen; and be worth saving even if you've just about given up hope.

There are five of these in the Solar System, but their names and locations are closely guarded secrets.
 
Myriad said:
To be a planet a body has to: orbit its star; not orbit another body; not be made entirely of imagination, antimatter, or dairy products; identify as a planet; be gravitationally stabilized into the shape of a sphere, cylinder, or balloon animal; not be delinquent on its student loans; have women; not be too remote to make an effective demonstration; have accessible rest rooms; be at least 17% natural ingredients; have a lively party atmosphere or an atmosphere of foreboding; not be too small for the both of us; have a Queen; and be worth saving even if you've just about given up hope.

There are five of these in the Solar System, but their names and locations are closely guarded secrets.
Click to expand...

Freddie Mercury is a planet!
 
Myriad said:
To be a planet a body has to: orbit its star; not orbit another body; not be made entirely of imagination, antimatter, or dairy products; identify as a planet; be gravitationally stabilized into the shape of a sphere, cylinder, or balloon animal; not be delinquent on its student loans; have women; not be too remote to make an effective demonstration; have accessible rest rooms; be at least 17% natural ingredients; have a lively party atmosphere or an atmosphere of foreboding; not be too small for the both of us; have a Queen; and be worth saving even if you've just about given up hope.

There are five of these in the Solar System, but their names and locations are closely guarded secrets.
Click to expand...


Hmm, browsing at random through this thread, and glancing at some of the posts about Pluto, I got to wondering what exactly it is that actually sets apart a planet from a ...not planet. Was idly wondering if I should click around a bit --- or whether, as happens far more frequently, I should open a search page with the search terms "how is a planet defined", then bookmark it, and then forget all about it. Clearly now I need to do neither: a better more exhaustive list of things a planet is, or should be, I don't think I'm likely to find anywhere else. Nice!
 
Chanakya said:
Hmm, browsing at random through this thread, and glancing at some of the posts about Pluto, I got to wondering what exactly it is that actually sets apart a planet from a ...not planet. Was idly wondering if I should click around a bit --- or whether, as happens far more frequently, I should open a search page with the search terms "how is a planet defined", then bookmark it, and then forget all about it. Clearly now I need to do neither: a better more exhaustive list of things a planet is, or should be, I don't think I'm likely to find anywhere else. Nice!
Click to expand...

For those that do not know much about the subject here is the official definition of a planet

1. It must orbit a star (in our cosmic neighborhood, the Sun).
2. It must be big enough to have enough gravity to force it into a spherical shape.
3. It must be big enough that its gravity cleared away any other objects of a similar size near its orbit around the Sun
Click to expand...
.

https://solarsystem.nasa.gov/planets/in-depth/

The last one made Pluto not a planet. Though one could argue that the Earth is not a planet as it orbits the centre of gravity of the Earth-Moon system, rather than the sun. Or if you disagree how much bigger does the moon have to be before that is a planet or the earth is not a planet?
 
rjh01 said:
Though one could argue that the Earth is not a planet as it orbits the centre of gravity of the Earth-Moon system, rather than the sun. Or if you disagree how much bigger does the moon have to be before that is a planet or the earth is not a planet?
Click to expand...

Nah. The centre of gravity of the Earth-Moon system lies within the earth. Sure, the moon has a tidal influence on the earth, making it wobble a bit, but it's much more massive than the moon.

Earth mass: 5.972 × 10^24 kg

Moon mass: 7.348 × 10^22 kg

The earth weighs 81 moons. Pluto only weighs about 8 Charons, and the centre of gravity of that system lies between the two bodies.

And "clearing the orbit" includes capturing other bodies as a satellite.
 
3point14 said:
The currently used definition of planet seems to me to be extremely logical and appropriate. I really don't get why some have so much of an issue with it.
Click to expand...

Logical? Fascinating.

1) Criterion two of the definition is that an object "has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape".

2) Mercury is not in hydrostatic equilibrium.

https://www.cambridge.org/core/book...nd-mechanics/F983F6077F81832582CD3FC47D1E136A

"We show that, like those of the Moon, Mercury's ellipsoidal shape and geoid are far from hydrostatic equilibrium, possibly the result of Mercury's peculiar surface temperature distribution and associated buoyancy anomalies and thermoelastic stresses in the interior."

3) The IAU consider Mercury to be a planet.

Can you explain the logic there?


One of my issues with the definition is that it doesn't acheive anything. A proper scientific definition would allow us to categorise objects in space (including those around other stars) by their intrinsic properties, not their locational properties (orbiting the Sun) nor their transient properties (other objects in their orbits).

Another issue is that I want science to be honest and reliable. But this makes me feel that astronomy isn't either. This definition was formulated to arbitrarily declare these eight objects (no more no less) to be planets and it doesn't even achieve that, so they ignore it.
 
Strikes me that deciding what criteria do and don't qualify a body for the label "planet" isn't actually science, so the matter of science's honesty doesn't arise.

On the other hand it sounds like the definition quoted needs a bit of a massage in its wording, as it appears Mercury has the requisite gravity but does not quite take the defined shape due to other factors which act on it.
 
Dr. Becky had a terrifying idea in this video that planet nine might be a black hole.




Too close, too close. Push it away.
 
Solitaire said:
Dr. Becky had a terrifying idea in this video that planet nine might be a black hole.

Too close, too close. Push it away.
Click to expand...

That's not too terrifying.

Thanks for the video. It confirms what I suspected about the exoplanet image earlier in the thread.
 
You must log in or register to reply here.

Back
Top Bottom