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The Astronomy Thread 
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Post Re: The Astronomy Thread
icekatze wrote:
hi hi

I'm not sure we know enough about the stellar winds from small stars to say just how problematic they are. If there are studies out there about stellar winds from red dwarf stars, I haven't been able to find them anyways. I've seen studies that show how massive, high temperature stars have higher velocity, more energetic stellar winds than our own; and I've seen studies where people assume Sun-like stellar winds for estimating the effect of red dwarfs on their planets. But it seems like actually measuring solar winds of stars the sun's size or smaller is difficult to do optically.

I guess that's just another uncertainty to deal with until we get better measurements.
Something about the output of red dwarfs was supposed to be less stable than sun-like stars: however, I imagine that (on average, at least) luminosity and stellar wind tend to vary in coordination with each other. I don't actually look for studies (I'm more inclined to engineering or technician interests than scientific), but if you're specifically looking for one, then I'd look at red dwarf variability and the relation between luminosity and stellar wind in red dwarfs.


Thu Aug 25, 2016 5:00 pm
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Post Re: The Astronomy Thread
hi hi

That's just it though, I have looked, and as far as I can tell, the relationship between luminosity and stellar wind is unclear due to lack of good data. We have information on ultra-massive stars because we can detect their significant rate of mass loss over time. (O and B stars lose around 10^-6 Solar masses each year, at velocities in excess of 1000-2000 km/s, and definitely can strip the atmospheres of planets in their habitable zones.)


Thu Aug 25, 2016 6:08 pm
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Post Re: The Astronomy Thread
So we know nothing, and will have to wait until our robot probes can send back data, or until we built a VLA array of telescope-satellites in our own solar system.

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Fri Aug 26, 2016 2:59 am
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Post Re: The Astronomy Thread
It looks to me like most of the smaller red stars are "flare stars." I think the proposed reason for this is that small stars below a certain mass are fully convective, that is, the helium doesn't collect at the core, and the whole interior of the star is a convection zone (unlike a narrow band as in larger stars). Since the churning of the plasma in the convection zone is the primary generator of the star's magnetic field, and since the magnetic field is what causes sunspots and flares, these small stars have disproportionately large flare activity. (Also, because the nuclear ash doesn't collect at the core, these stars can burn their entire supply of hydrogen fuel instead of blowing it into space, which combined with their slow burn rate means these stars can have unbelievably long lifespans.)

However, it looks from the information I glanced over that the flare intensity, while large for such a small star, is not much greater than that of our own Sun. So the X-factor is the closeness of the orbit that a planet would have to be in to be in a red star's habitable zone, which would be like Mercury orbit or closer. A planet with an atmosphere and magnetic field should be able to protect against normal solar flares, but would such an atmosphere and magnetic field be able to develop so close to an active star? These are the things we don't know. Venus is Earth-sized and even hotter than Earth, yet has almost no magnetic field of its own.

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Fri Aug 26, 2016 10:24 am
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Post Re: The Astronomy Thread
Arioch wrote:
It looks to me like most of the smaller red stars are "flare stars." I think the proposed reason for this is that small stars below a certain mass are fully convective, that is, the helium doesn't collect at the core, and the whole interior of the star is a convection zone (unlike a narrow band as in larger stars). Since the churning of the plasma in the convection zone is the primary generator of the star's magnetic field, and since the magnetic field is what causes sunspots and flares, these small stars have disproportionately large flare activity. (Also, because the nuclear ash doesn't collect at the core, these stars can burn their entire supply of hydrogen fuel instead of blowing it into space, which combined with their slow burn rate means these stars can have unbelievably long lifespans.)

However, it looks from the information I glanced over that the flare intensity, while large for such a small star, is not much greater than that of our own Sun. So the X-factor is the closeness of the orbit that a planet would have to be in to be in a red star's habitable zone, which would be like Mercury orbit or closer. A planet with an atmosphere and magnetic field should be able to protect against normal solar flares, but would such an atmosphere and magnetic field be able to develop so close to an active star? These are the things we don't know. Venus is Earth-sized and even hotter than Earth, yet has almost no magnetic field of its own.
Yeah, depending on details, I guess this one could be anything from a super-Mercury, to a nano-Jupiter (in case of a high solar wind velocity, but little enough density to balance out losses along the edge).


Fri Aug 26, 2016 3:37 pm
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Post Re: The Astronomy Thread
hi hi

For all you dark-matter skeptics out there, you might be interested to see this recent article: Emergent Gravity and the Dark Universe

I've got my usual healthy dose of skepticism, but it would be pretty interesting to see this pan out as an actual way to explain quantum gravity.


Fri Nov 11, 2016 12:34 pm
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Post Re: The Astronomy Thread
Direct imaging of four exoplanets orbiting HR 8799, an A-type star roughly 130 light years away.


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Wed Feb 01, 2017 11:14 am
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Post Re: The Astronomy Thread
hi hi

https://exoplanets.nasa.gov/news/1419/n ... ngle-star/

7 earth sized planets found orbiting a single dwarf star. Even if there isn't life on them, it would be truly amazing to go there and watch the other planets go by in the sky.


Wed Feb 22, 2017 1:10 pm
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Post Re: The Astronomy Thread
It's hard to imagine that so many Earth-sized planets could exist in such tight orbits for very long without eventually kicking each other out of orbit (the inner planet's orbit at 0.01111 AU is only 5.5 light seconds -- about 4 times larger than that of Earth's moon!). It's certainly interesting from a planet-formation and orbital dynamics point of view, as according to our current models, such systems shouldn't exist.

But the assertion in the article that several of the planets are in the "habitable zone" ignores that fact that red dwarfs have disproportionately large flare activity, which so close to these planets would very likely strip away any atmospheres that they might have had.

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Wed Feb 22, 2017 1:29 pm
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Post Re: The Astronomy Thread
hi hi

Our current models of planet placement are pretty weak, and still can't really account for Hot Jupiters with much certainty. But really, it is more like the system of moons orbiting Jupiter than it is the planets orbiting the sun, in terms of distance vs relative size.


Wed Feb 22, 2017 1:53 pm
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Post Re: The Astronomy Thread
icekatze wrote:
Our current models of planet placement are pretty weak, and still can't really account for Hot Jupiters with much certainty. But really, it is more like the system of moons orbiting Jupiter than it is the planets orbiting the sun, in terms of distance vs relative size.

Yeah, the exciting thing is that we don't know how to explain half the stuff we're seeing in exoplanet arrangement. It's very unexpected.

The orbital distances of the TRAPPIST-1 planets are very much in line with a Jupiter-style moon system, but the masses are orders of magnitude larger. You've got cases of two Earth-mass planets passing within Earth-Moon distances of each other. That's kinda nuts.

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Wed Feb 22, 2017 2:01 pm
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Post Re: The Astronomy Thread
Supposing it's stable, I'd be on the look-out for orbit-swapping.


Wed Feb 22, 2017 9:54 pm
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Post Re: The Astronomy Thread
hi hi

I was just reading up on Epimetheus and Janus. I hadn't really looked into that kind of exchange orbit before, and it is really kind of crazy.


Wed Feb 22, 2017 11:02 pm
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Post Re: The Astronomy Thread
I've first read of Janus and Epimetheus in a SciFi book "Pushing Ice".
The orbital dance of Epimetheus and Janus on planetary.org.


Yeah, I've read a bit about the 7 planet-system TRAPPIST-1 (anyone in for a beer? Westmalle, or Chimay?).
Imagine standing on one of those planets, and watch another planet pass by and being able to see the clouds, and possibly even landmark features on the other planet by naked eye.

How's that for an incentive to go and start a space race?

I imagine smart beings having evolved on those planets being very enticed to go and visit other planets.
And possibly have an interplanetary war before we even got to the moon....

Anyway, with possible flare activities, I do not want to be on a planet that close to the sun.

But this also reminds me of an episode of "Outer Limits", where Humans have colonised a planet, which apparently had been colonised before by other intelligent beings. Then they find out that the sun has very strong solar flares, killing all life, but that the life on the planet has found ways to cope with sun flare, and that even intelligent life exists on that planet, and that it just became dormant because of an impending solar flare. The episode ends with the Human colony being wiped by a solar flare, after a scientist was able to make a part of the alien life awaken, among which one intelligent being, which towards the end of the solar cycle tells him that they evolved and actually make use of these flares by luring intelligent aliens to found a colony, bring their technology, and then, after the flare, they grab all that's left behind, technology and all. Like beach pirates.
That they prefer if the aliens (from their viewpoint) die in the solar flare, but that they won't hesitate to kill them themselves if they somehow survived the flare. Or enslave them to find out more about the technology, if feasible.

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Thu Feb 23, 2017 1:42 am
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Post Re: The Astronomy Thread
Krulle wrote:
Yeah, I've read a bit about the 7 planet-system TRAPPIST-1 (anyone in for a beer? Westmalle, or Chimay?).
Imagine standing on one of those planets, and watch another planet pass by and being able to see the clouds, and possibly even landmark features on the other planet by naked eye.
Krulle wrote:
Anyway, with possible flare activities, I do not want to be on a planet that close to the sun.
With severe flare activity, I'd be suspecting/expecting sonar as a replacement for sight. They wouldn't even know they were there until they developed radar.

So, Hitchhiker's Cricket, anyone?


Wed Mar 01, 2017 1:18 am
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Post Re: The Astronomy Thread
You mean the Krikkit?

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Wed Mar 01, 2017 2:41 am
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Post Re: The Astronomy Thread
Arioch wrote:
icekatze wrote:
Our current models of planet placement are pretty weak, and still can't really account for Hot Jupiters with much certainty. But really, it is more like the system of moons orbiting Jupiter than it is the planets orbiting the sun, in terms of distance vs relative size.

Yeah, the exciting thing is that we don't know how to explain half the stuff we're seeing in exoplanet arrangement. It's very unexpected.

The orbital distances of the TRAPPIST-1 planets are very much in line with a Jupiter-style moon system, but the masses are orders of magnitude larger. You've got cases of two Earth-mass planets passing within Earth-Moon distances of each other. That's kinda nuts.


I think the genuinely frustrating thing is that we can't hop some scientists on a ship and Warp 9 out there to see WTF is happening up-close and personal.


Wed Mar 01, 2017 7:22 am
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Post Re: The Astronomy Thread
Krulle wrote:
You mean the Krikkit?
The sports reference was also intentional.


Thu Mar 02, 2017 12:38 am
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Post Re: The Astronomy Thread
hi hi

Since I know there are some other Planet Nine skeptics around here, I figured I would share this with ya.

Models of newly discovered body SY99 show that diffusion may be the cause of aligned orbits

While I try to remain unbiased, I really can't deny the fact that Michael Brown's smug attitude makes it easier for me to be on team skeptic. :roll:


Wed Apr 19, 2017 8:58 am
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Post Re: The Astronomy Thread
icekatze wrote:
While I try to remain unbiased, I really can't deny the fact that Michael Brown's smug attitude makes it easier for me to be on team skeptic. :roll:

Heheh, I have to agree. Unfortunately, it's almost impossible to prove it's not there, so this issue may linger for a long time.

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Wed Apr 19, 2017 9:27 am
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Post Re: The Astronomy Thread
Earth's radio signals may be protecting it from space radiation: Link

Interessting, but short article about the Van Allen Belt and its (possible) interaction with radio signals from earth.

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Fri May 19, 2017 3:43 pm
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Post Re: The Astronomy Thread
Would have been nice if they had said whether they were just talking about loose electrons, or actual photons being pushed back.


Fri May 19, 2017 7:30 pm
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Post Re: The Astronomy Thread
Wow.



I've watch a lot of animated cloud movement stuff for Jupiter, but never before noticed how fast the central band's movement is compared to the rest of the latitudes.

https://apod.nasa.gov/apod/astropix.html

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Mon May 22, 2017 10:55 pm
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Post Re: The Astronomy Thread
hi hi

Here's an interesting one: Smallest star identified by astronomers, only slightly larger in diameter than Saturn.


Wed Jul 12, 2017 9:26 pm
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Post Re: The Astronomy Thread


Wow. 300 g at its 'surface'? Why, the Sun barely pulls 28 times our body weight.

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Thu Jul 13, 2017 7:19 am
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