The Astronomy Thread

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Absalom
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Re: The Astronomy Thread

Post by Absalom »

GeoModder wrote:Unfortunately Proxima Centauri is quite an active flare star. :(
Given the proposed year, the planet should probably be tidally locked, greatly reducing the difficulty imposed by flares. Just move a bit closer to the equator (which in this case would be the plane perpendicular to the vector running between planet and star), and you have more atmosphere between you and the star, thereby producing something of a goldilocks zone on the planet (specifically, the temperate area with sunproximalight).

I imagine that the wind currents are impressive. Supposing that it is tidally locked, I'd expect a generalized high-level movement towards the cold side, and low-level flow towards the hot side, producing a decently gentle temperature gradiant in the "dawn-torials". Of course, if there's neither bulk atmosphere nor bulk sea/ocean, then this is bunk and it's likely to be the same half-char/half-raw meatloaf that you'd normally expect from tidal locking; and possibly the same if two semi-fixed weather fronts dominate the atmosphere, instead of a generalized mid-level mixing trend.

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icekatze
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Re: The Astronomy Thread

Post by icekatze »

hi hi

If it is more massive than Earth, I would think it is more likely to have an atmosphere than not. Granted the sample size of our own solar system has repeatedly proved to be a poor indicator of what other star systems are like, but if it's massive enough to retain an atmosphere, it just needs to find one somewhere. ;)

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Re: The Astronomy Thread

Post by Krulle »

And while Proxima Centauri is a Red Dwarf, at that distance solar wind may still have blown all volatile elements of the atmosphere away. So we run into another problem.
A planet? Yes.
(Liquid) Water? Possibly.
Life? Very unlikely.
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Re: The Astronomy Thread

Post by GeoModder »

Arioch wrote:
GeoModder wrote:And what happened with the Alpha Centauri Bb claim back in 2012? The article jumps from Epsilon Eridani b to Proxima without even mentioning it!
As I understand it, the methods used to detect αCenBb were called into question and then essentially demonstrated as inadequate; even the discoverer agreed that it probably doesn't exist.
Ah, I missed that news.
Image

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icekatze
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Re: The Astronomy Thread

Post by icekatze »

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.

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Re: The Astronomy Thread

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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.

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Re: The Astronomy Thread

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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.)

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Re: The Astronomy Thread

Post by Krulle »

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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Re: The Astronomy Thread

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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.

Absalom
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Re: The Astronomy Thread

Post by Absalom »

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).

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Re: The Astronomy Thread

Post by icekatze »

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.

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Re: The Astronomy Thread

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Direct imaging of four exoplanets orbiting HR 8799, an A-type star roughly 130 light years away.


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Re: The Astronomy Thread

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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.

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Re: The Astronomy Thread

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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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Re: The Astronomy Thread

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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.

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Re: The Astronomy Thread

Post by Arioch »

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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Re: The Astronomy Thread

Post by Absalom »

Supposing it's stable, I'd be on the look-out for orbit-swapping.

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Re: The Astronomy Thread

Post by icekatze »

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.

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Re: The Astronomy Thread

Post by Krulle »

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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Absalom
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Re: The Astronomy Thread

Post by Absalom »

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?

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