APOD: Three Worlds for TRAPPIST-1 (2016 May 07)

[APOD Robot]

Three Worlds for TRAPPIST-1

Explanation: Three new found worlds orbit the ultracool dwarf star TRAPPIST-1, a mere 40 light-years away. Their transits were first detected by the Belgian robotic TRAnsiting Planets and Planetesimals Small Telescope, TRAPPIST, at ESO's La Silla Observatory in Chile. The newly discovered exoplanets are all similar in size to Earth. Because they orbit very close to their faint, tiny star they could also have regions where surface temperatures allow for the presence of liquid water, a key ingredient for life. Their tantalizing proximity to Earth makes them prime candidates for future telescopic explorations of the atmospheres of these potentially habitable planets. All three worlds appear in this artist's vision, an imagined scene near the horizon of the system's outermost planet. Of course, the inner planet is transiting the dim, red, nearly Jupiter-sized parent star.

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[Donald Brandshaft]

It is frequently stated that worlds so close to their sun must be tidally locked so that only one side faces the sun. However, Mercury has a day every (Mercury) years. These worlds have years measured in days. I have no idea what kinds of tidal locks are possible for these worlds, or similar worlds orbiting small red stars, but it seems like this greatly increases the number of worlds that could support life.

[oldrcd]

PLEASE lose the "artists conception" illustrations. They are rampant nonsense; they ignore physics.
There are "millions" of amazing astro-photos. You don't need invented artwork.
I recommend apod.com to people who can learn the reality. If you keep adding non-scientific artwork, I'll stop recommending this site.

[Ann]

In my amateur opinion, red dwarf stars have one advantage over stars like the Sun, and that is time. Our own Sun may not be able to support life on Earth for much more than another billion years, and Mars too will become too hot in four billion years or so. And in yet another one or two billion years, the Sun will become a white dwarf, and be useless as a life-nurturing source of energy for the solar system.

But red dwarfs have all the time in the world. If they don't get their life-nurturing properties right the first time, or the second time, or the thousandth time, they can try again and again. Their own lives have just barely started. To put it differently, red dwarf stars can play the "life lottery" again and again and again for probably trillions of years.

Yes, but does that mean that red dwarfs are better, or just as good as, the Sun as a star that can uphold life on at least one of their planets now? Not in my opinion. Their habitable zones are incredibly close in - much closer than Mercury's orbit around the Sun! - so that the planets are not only going to have bound rotations (or possibly almost bound, like Mercury's) - but the planets will also be extremely vulnerable to any unforeseen outbursts on their suns. It's beyond me how people can be so hopeful of the chances of finding life now on any of the three worlds of TRAPPIST-1.

So the only reason for the enthusiasm that I can understand is that the TRAPPIST-1 planets are close enough to the Earth, and their star is sufficiently faint, that Earthly instruments can take a good look at the planets and really look for signs of life. If any of the planets have life that interacts with and alters the planet's atmosphere, Earthly instruments should be able to detect that.

But I'm reminded of the old story of the man who had lost his keys, and who looked for his keys under the streetlight. Another person asked him if he had lost his keys under the streetlight. No, the man replied, I lost them over there, but it's too dark to see them over there.

Ann

[aljo]

Is anyone else irritated by the lack of realism of the image? The right hand moon is blotting out the light from the sky, even though the moon is much further away, which is obviously impossible.

[geckzilla]

The artist's illustration is just that—an illustration. It is not a simulation and we do not know what that place looks like. That said, there are a few adjustments that could be made to make it at least a little more realistic.

The star's illumination is only a fraction of our own Sun's (at 0.000525±0.000036 solar luminance, per the paper), but even being so dim it is still considerably brighter than our Moon is when full, as far as I can tell. We can probably forget about the background star field. The star is dim enough that it might not be blindingly white to look at, though I imagine it would still be painful, at least for a moment until the pupils constrict. Anyway, I don't want to get caught up on that sort of thing and just want to stick to my goal—a little more realistic.

The two inner planets (b and c) are also much closer in size than depicted and would, of course, only appear as holes in the stellar disc and be completely in eclipse.

[Ann]

The artist's illustration is just that—an illustration. It is not a simulation and we do not know what that place looks like. That said, there are a few adjustments that could be made to make it at least a little more realistic.

The star's illumination is only a fraction of our own Sun's (at 0.000525±0.000036 solar luminance, per the paper), but even being so dim it is still considerably brighter than our Moon is when full, as far as I can tell. We can probably forget about the background star field. The star is dim enough that it might not be blindingly white to look at, though I imagine it would still be painful, at least for a moment until the pupils constrict. Anyway, I don't want to get caught up on that sort of thing and just want to stick to my goal—a little more realistic.

The two inner planets (b and c) are also much closer in size than depicted and would, of course, only appear as holes in the stellar disc and be completely in eclipse.

eso1615a.jpg

A question, Geck. In the APOD, the background sky is seen to be very dark. It is so dark, in fact, that stars can be seen in the daytime sky. I have no problems regarding that as unrealistic.

Nevertheless, the light from this small cool sun would be almost exclusively red, orange and yellow. Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

Ann

[geckzilla]

It would depend on the camera exposure. You've no doubt seen a night photo of the moon looking like a bright sun in a daytime sky. I am sure there are still things wrong with the picture. Martin responded to my version on Twitter a bit annoyed. Called it piss yellow. Haha.

[rstevenson]

... Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.

Rob

[Asterhole]

Aw, it's not such a bad depiction, y'all. There's a bit artistic embellishment, of course and the real thing may not even remotely resemble this fanciful image. I used to dabble in digital landscape rendering myself, so I have some appreciation for this posting.

[JohnD]

I was going to ask that APOD didn't use these 'artist's impressions', except when they were to illustrate a point, but oldrcd has done so, more forcefully!

The scene in the sky may or may not be accurate, but the foreground is mere speculation. Fine for a cover of an SF book, preferably with the addition of an alien spaceship, but this is a science truth website.

John, In Puritan mode

[bystander]

viewtopic.php?t=35891

[neufer]

the light from this small cool sun would be almost exclusively red, orange and yellow. Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

When blue & green light is scarce
red, orange & yellow light scatter quite well in an Earth-like atmosphere:

http://apod.nasa.gov/apod/ap150908.html

Nevertheless... the red skies here are most likely due to wind blown ice crystals.

<<It is important to note that tidally locked planets likely have very large differences in temperature between their permanently lit daysides and their permanently dark nightsides, which could produce very strong winds circling the planets while making the best places for life close to the mild twilight regions between the 2 sides.>>

[neufer]

It is frequently stated that worlds so close to their sun must be tidally locked so that only one side faces the sun. However, Mercury has a day every (Mercury) years. These worlds have years measured in days.

You left out the "2" : Mercury has a day every 2 (Mercury) years.

These tidally locked worlds have no "days" in the normal sense.

[Chris Peterson]

... Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.

Not just as bright, but also as white.

[Ann]

... Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.

Not just as bright, but also as white.

I wasn't talking about denizens of those worlds. I was talking about us. Would the daytime sky on a planet orbiting TRAPPIST-1 be as bright and as white (make that blue) to us as the Earth sky is?

I know that our eyes are extremely good at adapting to different kinds of ambient light, but for myself, there is just no way I can believe that I would mistake the sky of a TRAPPIST-1 planet for our own clear sky. There is no way I can believe I would find their skies as bright as our own clear daytime sky, or that I would in any way mistake the color of their skies for our own.

I realize that the brightness of their skies has at least something to do with how closely the planet is orbiting the faint orange sun. But even so... no, their skies would not be as bright as the Earth's daytime blue sky and not the same color. At all.

Yes, I realize that I would have to have some "absolute comparison" in order to be sure that their skies and daylight was really truly different from our own. So imagine I could bring this boy with me to the TRAPPIST-1 world. If his relatively dark orange shorts and dark orange breast pocket looked brighter than his light blue shirt, I would know that I was on a planet whose daylight was different from our own.

Ann

[Ann]

the light from this small cool sun would be almost exclusively red, orange and yellow. Would the daytime sky really be as bright as you have shown it? Red, orange and yellow light would not scatter very well in an Earth-like atmosphere.

When blue & green light is scarce
red, orange & yellow light scatter quite well in an Earth-like atmosphere:

http://apod.nasa.gov/apod/ap150908.html

Yes, we all know that the sunset and sunrise skies of the Earth can be quite red. But that color soon disappears as the revolving of the Earth makes the Sun appear to rise higher, or sink deeper below the horizon.

Earth skies can also be quite red if the air is strongly polluted. But I am talking about the color of the clear daytime and relatively unpolluted Earth sky.

Ann

[Chris Peterson]

I suppose, if we're imagining a world like this, we might as well imagine denizens of the world. And this could be the view they'd see, with their own locally adapted eyes. I can imagine a rule for exo-evolution: whatever eyes develop within daytime dwelling animals on the surface of any exoplanet will see that planet's daytime sky as bright.

Not just as bright, but also as white.

I wasn't talking about denizens of those worlds. I was talking about us. Would the daytime sky on a planet orbiting TRAPPIST-1 be as bright and as white (make that blue) to us as the Earth sky is?

Yes, I know that's what you were talking about. But Rob was, and I was simply expanding on his comments.

Visually, I think we'd see the star as less red than it appears in the illustration- probably a warm white, the same way we see these kinds of stars when we view them in our sky. What color the sky would look is harder to judge. I think we'd see some reddish scatter near the star, but in other parts of the sky it's perfectly possible we'd see blue, but the sky would be much darker than on Earth because there would be much less scatter. Seeing stars in the daytime seems all but certain. The light on the landscape (especially snow) would look reddish at first, but our natural white balance system would probably desaturate that considerably after a few minutes.

I know that our eyes are extremely good at adapting to different kinds of ambient light, but for myself, there is just no way I can believe that I would mistake the sky of a TRAPPIST-1 planet for our own clear sky.

I agree.

There is no way I can believe I would find their skies as bright as our own clear daytime sky, or that I would in any way mistake the color of their skies for our own.

Color, certainly. Brightness is much more complex, because of the way we accommodate.

[Steven Dutch]

You would not see stars in the sky, especially close to the sun. Also, if the star is emitting enough light to keep the planets warm, it wouldn't appear red. It would saturate your retina and look white. Possibly the sky or shadows might have a reddish cast. Anyway, "red" stars are more pinkish orange than red. Finally, if the planets were close enough to have easily visible disks, especially orbiting a star with small mass, they'd destabilize each others' orbits.

[Chris Peterson]

You would not see stars in the sky, especially close to the sun.

I don't agree. You can see a handful of stars in our own daylit sky if you know exactly where to look. In the case of a star that is 2000 times dimmer (more than 8 magnitudes), and with a spectrum that produces less atmospheric scatter, I think we'd easily see a great many stars. Not as many as seen in this rendering, but hundreds at least.

[neufer]

You would not see stars in the sky, especially close to the sun.

I don't agree. You can see a handful of stars in our own daylit sky if you know exactly where to look. In the case of a star that is 2000 times dimmer (more than 8 magnitudes), and with a spectrum that produces less atmospheric scatter, I think we'd easily see a great many stars. Not as many as seen in this rendering, but hundreds at least.

The star overall radiation is indeed ~1900 times dimmer than the Sun but this is cancelled out by the planet being ~43 times closer (such that the planet receives about the same overall warming radiation as the Earth). However, most of this is infrared radiation and the visual luminosity is ~270,000 times dimmer than the Sun which from the close planet is only 0.7% as bright as the Sun. In any event, the main factor is that the atmosphere is assumed to be very thin except for wind blown particles.

[Chris Peterson]

You would not see stars in the sky, especially close to the sun.

I don't agree. You can see a handful of stars in our own daylit sky if you know exactly where to look. In the case of a star that is 2000 times dimmer (more than 8 magnitudes), and with a spectrum that produces less atmospheric scatter, I think we'd easily see a great many stars. Not as many as seen in this rendering, but hundreds at least.

The star overall radiation is indeed ~1900 times dimmer than the Sun but this is cancelled out by the planet being ~43 times closer (such that the planet receives about the same overall warming radiation as the Earth). However, most of this is infrared radiation and the visual luminosity is ~270,000 times dimmer than the Sun which from the close planet is only 0.7% as bright as the Sun. In any event, the main factor is that the atmosphere is assumed to be very thin except for wind blown particles.

That's a good point about the distance. Still, given a visual luminosity on the order of 1% that of the Sun, we'd expect the daytime limiting magnitude- given an Earth-like atmosphere- to be around mag 3, which means there would be about 200 stars visible in the sky, say 50-100 in a given hemisphere, depending on conditions. Of course, more would be visible if the atmosphere were thinner than Earth's, and not overly dusty.

[geckzilla]

Given the parameters of planet d (and presuming we are on planet d) the sky and the brightness of the star can be quite variable. The star would appear in the sky anywhere between 2.76° to .42° in angular diameter. We wouldn't see a large orb in the sky as depicted, at least not without a telephoto lens. With a narrow field of view there could be stars visible or there might not be, with or without a substantial atmosphere.

You could do a few different things with the illustration and still be within the realm of plausibility, but certainly planets b and c would not look as they do. The one on the right might look like a ring (think Titan) if it had a thick, extended atmosphere. It most definitely would not look like a crescent. If it was on the other side of the star it would be a very faint, barely visible, fully illuminated disc. There is no way for it to be a crescent.

[Boomer12k]

I hate losing my keys.... he should have used a FLASHLIGHT....duh...

Interesting to learn about these planets...

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[Boomer12k]

So, they have MONKS there???

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