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Forum » SpaceEngine » Science and Astronomy Discussions » Science and Astronomy Questions
Science and Astronomy Questions
steeljaw354Date: Sunday, 14.08.2016, 17:20 | Message # 736
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It probably can't clear it since it is to big.
 
WatsisnameDate: Sunday, 14.08.2016, 20:45 | Message # 737
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Quote steeljaw354 ()
What if we discovered a mars mass object in the kuiper belt that we somehow missed.


It would raise the immediate question of how we missed it. It should have easily been seen in surveys.

Quote anonymousgamer ()
I would think the real question is, what would happen to the Kuiper belt if there was a Mars mass object orbiting in it?


Margot's Π implies it would have an important role in the dynamics of the Kuiper belt -- it has just over 1 "orbit-clearing mass". Which means that even if it somehow evaded detection, the orbits of the other Kuiper belt objects would betray its existence.

This is another nice proof that the planetary definition does work. If an object gets massive enough to clear out its orbital region, then that region gets cleared out (mindblow), and the object becomes unique and what we call a planet. No such thing has happened in the Kuiper belt.





 
steeljaw354Date: Sunday, 14.08.2016, 21:00 | Message # 738
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What if it's orbit isn't clear though, would that mean they would have to re work the planet definition?
 
midtskogenDate: Monday, 15.08.2016, 04:58 | Message # 739
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Quote Watsisname ()
Margot's Π implies it would have an important role in the dynamics of the Kuiper belt -- it has just over 1 "orbit-clearing mass". Which means that even if it somehow evaded detection, the orbits of the other Kuiper belt objects would betray its existence.

The Kuiper belt is very large and can host different orbits. Have we really found many enough minor planets that would reveal the existence of larger bodies? What if one of the found bodies really is in the L4 or L5 point of a larger undetected (and extremely dark) object? I'm not saying it's likely, just speculating about what's possible.





NIL DIFFICILE VOLENTI
 
PlutonianEmpireDate: Monday, 15.08.2016, 05:01 | Message # 740
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What would it take for a Lifeterra to have this much real-time lightning in every single storm across the globe?






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WatsisnameDate: Monday, 15.08.2016, 06:39 | Message # 741
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Quote steeljaw354 ()
What if it's orbit isn't clear though, would that mean they would have to re work the planet definition?


It definitely would. We would also have to reconsider our understanding of celestial mechanics and solar system evolution.

midtskogen,
Yes, I think we have found enough objects in the Kuiper belt to know there is not a more massive body perturbing them.



Margot's Π also accounts for the size of the orbit -- the orbit-clearing mass scales with the orbital distance:



If a Mars-mass body were in the Kuiper belt, it would have just above the orbit-clearing mass. The mathematics shows that this would clear its region in about 10 billion years. This doesn't mean there wouldn't be other objects in that region today, but it does mean we would see obvious signs of the perturbing body.

Basically, the whole reason we have a Kuiper belt is because no object formed there with more than the orbit-clearing mass. If one did form there, there wouldn't be a Kuiper belt. The dynamics prevents bodies which approach the orbit-clearing threshold from existing within a population of bodies with comparable masses for solar-system timescales. This is why Soter's discriminant works. smile

PlutonianEmpire, wow! I have seen lightning of almost that intensity once before, in the Derecho that swept across the eastern US in 2012. Here's a 15-minute sample of the lightning recorded.



Mind, those are just the ground strikes -- not even counting the lightning within the cloud. To the eye it was continuous flashes.

Lightning in general depends on strong convection with water droplets or ice particles to produce charge separation. Convection requires unstable air, so high relative humidity. High amounts of CAPE (Convective Available Potential Energy) also helps, as it implies more rapid updrafts. The above derecho storm had CAPE of over 5000J/kg, which is huge for Virginia. That being said, it's possible to get a lot of lightning even with very low CAPE. Lightning frequency depends on the kind of storm and the region.

So, it's hard to say exactly what a planet would have to be like to have lightning like that video in storms everywhere, but the general idea is it should be a generally unstable atmosphere, with high humidity, low condensation level, and a lot of cloud condensation nuclei.

Another way to get high lightning frequency is with turbulent ash clouds, like in volcanic eruptions, which make for some of the coolest images: happy

volcanic lightning gallery





 
PlutonianEmpireDate: Monday, 15.08.2016, 07:57 | Message # 742
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Cloud condensation nuclei, would those be ambient dust particles by any chance?

As for the high humidity, I keep thinking dew points in the lower 80's with temps in the upper 80's would do the trick. Might they?

The article on CAPE mentioned some adiabatic info. If my installation of Space Engine became omnipotent ( lol ) for example, would changing the Adiabat factor for Earth in either direction (up or down) influence CAPE activity on Earth? Cool pic btw! biggrin

And wow at the volcano pics! surprised





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midtskogenDate: Monday, 15.08.2016, 09:42 | Message # 743
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Quote Watsisname ()
This is why Soter's discriminant works.

But how to distinguish between proto-planets and dwarf planets?

Quote Watsisname ()
it does mean we would see obvious signs of the perturbing body

If we did see it, how should the planet be classified?

Quote PlutonianEmpire ()
Cloud condensation nuclei, would those be ambient dust particles by any chance?

As for the high humidity, I keep thinking dew points in the lower 80's with temps in the upper 80's would do the trick. Might they?

The most important factor is rapid upward winds. Warm, humid air alone will do nothing, but if such air moves upwards, the more humid, the better fuel for thunder. But you can have thunderstorms even if the dewpoint is well below freezing.

A dewpoint near 30 °C is terrible. I arrived in Mumbai at midnight once. The temperature was 31 °C and it was heavy fog. Very uncomfortable to breathe that air. Where I usually live we rarely have dewpoints above 15 °C.





NIL DIFFICILE VOLENTI


Edited by midtskogen - Monday, 15.08.2016, 09:46
 
FastFourierTransformDate: Monday, 15.08.2016, 10:18 | Message # 744
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I normally don't like this kind of continuous debate around the planethood issue. It's quite etymological in nature I think. Important for taxonomy but not really something to bother in terms of scientific understandig. But your answer, Watsisname, it's very very interesting, I can see now much better the fact that the criterions are aproached in a quantitive way to make this taxonomy at least non totally arbitrary.

WoW!! the graph is on logarithmic scale!! Pluto is far from been a planet. Much farther than it seems. Now I know that if Eris orbited at the distance of the Earth it would be considered a planet. Funny thing.
 
steeljaw354Date: Monday, 15.08.2016, 12:50 | Message # 745
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If you want to discuss the planethood stuff it'd be better to do it in the dedicated thread, I'm not convinced Pluto isn't a planet due to some orbital mechanics, physical mechanics applies better.

1) Orbits one or more stars or stellar remnants
2) Is in hydrostatic equilibrium
3) Doesn't undergo fusion currently or in the past
4) Doesn't orbit another object that applies to this set of rules. Or else it's a moon.

Non arbitrary definition without orbital clearing. It doesn't matter how many there are, as that is just an excuse.


Edited by steeljaw354 - Monday, 15.08.2016, 12:56
 
WatsisnameDate: Monday, 15.08.2016, 13:00 | Message # 746
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Quote PlutonianEmpire ()
Cloud condensation nuclei, would those be ambient dust particles by any chance?


Oh, they can be tons of things. Wikipedia has a good article on them. It'd be very hard for a terra with an atmosphere to have no CCNs at all.

CCN are important for cloud formation, because thermodynamically, water molecules don't like forming cloud droplets. A few molecules may randomly bump together, but they will come apart again instead of growing to a drop. When this was first being studied, a researcher basically came at the absurd conclusion that rain is impossible! And by the physics, he was right! It's the CCNs that do it. Without them, the relative humidity must be much higher.

There a way to get water to form droplets without condensation nuclei, but it doesn't usually happen in atmospheres. You can observe it every time you open a soda or beer bottle, as the sudden fog that appears at the top. (I love this article, by the way.) The sudden expansion of the air cools it very severely (well below freezing!) and allows the water molecules to stick together and form droplets. The interesting thing about this is that all the droplets are basically identical -- the same size. This is "homogeneous nucleation". A very different kind of cloud than what we see in the sky.

Anyway, that's all getting way tangential -- I just get really excited about cloud microphysics because I think it's so cool.

Quote midtskogen ()
The most important factor is rapid upward winds.


Yeah, high humidity alone does nothing, because you need the air to convect. Rapid upward moving air allows the charge separation. However, the relative humidity (or mixing ratio) does correlate to lightning activity, because it provides the instability and energy for updrafts.

Another factor beyond humidity and CAPE is a lifting mechanism -- something to get the air moving upwards to start the convection. Fronts, convergence, or low pressure systems can act to lift the air (cold fronts especially force air upwards rapidly). But some of the most powerful storms in the US plains states occur when the lower atmosphere is extremely humid, but capped under a stable layer of warmer air. This is like putting a lid on a pressure cooker, building up lots of energy as daylight heats the surface, and eventually, if the capping inversion is broken, the convection starts vigorously. Violent supercell storms can pop up in literally minutes.

And, because it's beautiful and appropriate, here's an epic timelapse of lightning storms:


Quote midtskogen ()

But how to distinguish between proto-planets and dwarf planets?


I think this would be a matter of timescale. We're pretty biased in our definitions because we live in a ~5 billion year old system. But how about 2 billion? 10 billion?

There could be a useful approach in that the accretion phase of planet growth doesn't last very long relative to the age of the system -- but then again that also depends on the mass of the star. What if we're dealing with high mass stars? So... it's more complicated than we might like. It works well for our system and we think other sun-like and low-mass systems.

Quote midtskogen ()

If we did see it, how should the planet be classified?


That, I think, would be a matter of a lot of debate within the scientific community. I'd certainly need to think about it a lot, myself. This would be a big wrench in the gears of what we think we understand so far. Sort of like finding a star with the mass of Jupiter. (Not that crazy, but a similar idea.)

These are really good questions!

FastFourierTransform, I feel the same way. The debate is seemingly endless and emotionally charged. But it's exciting to me to see the quantitative approaches, because they seem to support the intuitive categorization methods we had started with. In studying them we learn a lot about how systems work, and I think that is much more interesting than the name we slap on an inanimate object.

It's like people who memorize the value of the speed of light or other physical quantities to huge numbers of digits. Cool, but does it really help you understand it better?

I think at this point let's put any further discussion of planet definitions in the dedicated thread. I was going to do that earlier but we have multiple subjects going on at once.





 
midtskogenDate: Monday, 15.08.2016, 16:40 | Message # 747
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This video which turned up as suggestions after watching the one above, has some amazing lightnings.





NIL DIFFICILE VOLENTI
 
WatsisnameDate: Tuesday, 16.08.2016, 13:03 | Message # 748
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"If you're gonna go out chasing lightning, remember, that if you can hear lightning, you're close enough to be struck. So always bring a good set of ear plugs."

I love this guy. biggrin And his storm chasing, photography, and narrative style are masterful.





 
steeljaw354Date: Tuesday, 16.08.2016, 13:32 | Message # 749
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Can this happen?
 
WatsisnameDate: Tuesday, 16.08.2016, 14:45 | Message # 750
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Rather than give a full answer, I'd like to see if you can reason it out. smile

Hint: Think about gravity. If you throw something upwards, what speed does it have when it hits the ground again (ignore air). What if you throw it faster? How fast do you have to throw it to make sure it escapes the planet altogether? What does this imply about the speed an asteroid or comet will have when it hits a planet?





 
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