Strange new worlds

[Primula Baggins]

The universe is not only cooler than we imagine; it is cooler than we can imagine. (H/T J. B. S. Haldane)

I've been thinking that, given the rate of new discoveries in space and planetary science, maybe a thread is in order. Today's news made me go do it.

NASA announced this morning that they've found a star 40 light years away that has not one, not three, but seven planets, all probably rocky and all probably near the size of Earth, orbiting a single star—and all seven are in or at least at the edge of the "Goldilocks zone," the temperature zone around a star where liquid water could exist on the surface of a planet there. Three are right in the middle of the zone.

It gets weirder. The star in question is a cool M8 dwarf, about as small as a star can be and sustain a fusion reaction. The star itself is not much bigger than Jupiter. So these planets are very close in—all of their orbits would fit inside the orbit of Mercury in our solar system. They're very close together—if you were standing on the surface of one while the next planet in or the next one out was lined up with yours, the other planet would be maybe twice the size of the full moon in the sky. You could wave at the neighbors.

Because of how close they are to their sun, all are probably tide-locked, meaning they keep one face toward the star at all times. This is not necessarily a deal-breaker for being habitable; models indicate that an atmosphere as thick as ours or more would moderate the temperatures enough that there would be a wide area at comfortable temperatures. Crazy weather, absolutely, but not uninhabitable.

The sun is so dim that even in places where it was above the horizon, the light would be comparable to just after a red sunset on Earth. But it would be warm, because much of the star's light is in the infrared. Like orbiting a space heater.

This system will be one of the first targets of the new James Webb telescope, the replacement for Hubble, that will be placed in orbit in 2019.

As an SF writer, this has me going wugga wugga wugga. It will literally change some of the background story in my next novel—just by the fact that it exists. And how such a system ever evolved [SF mind says, did it evolve or was it made? Coooooool], and how it manages to be stable [if it is]. . . .

Here's a good link, with diagrams and artists' conceptions:
http://www.space.com/35790-seven-earth- ... overy.html

And another (yes, it's at Syfywire, but it's by Phil Plait of Bad Astronomy, which is now located there, and it's full of sciency goodness as well as a chart or two):
http://www.blastr.com/2017-2-22/exoplan ... earby-star

[Inanna]

WOW WoW WoW.

[yovargas]

I WANT TO GO TO THERE

[Jude]

So these planets are very close in—all of their orbits would fit inside the orbit of Mercury in our solar system.

So if they would fit inside the orbit of Mercury, why are they considered to be in the Goldilocks zone? Is it because the smallness of the star compensates for the closeness to it?

[Primula Baggins]

That's it, Jude. The star is so much smaller and dimmer than ours that they have to be that close to be in the zone, which is quite narrow. The closest one (which is probably too hot for liquid water) takes 1.5 days to orbit the star; the most distant is probably on the order of 3 weeks.

Though there's habitable and habitable. Here's a short, readable article by Katie Mack, an astrophysicist from Melbourne whom I follow on Twitter:

https://cosmosmagazine.com/space/goldil ... be-so-nice

There are a lot of reasons why the seven planets around Trappist-1 "might not be so nice," including strong tides, the light side/dark side problem, possibly flares from the star (which can strip away a planet's atmosphere if it doesn't have a strong magnetic field like Earth's), and probably a lot of volcanic activity because the planets' interiors are being constantly pulled at and squeezed by shifting gravitational effects of the close neighboring planets and the very close star. And of course, they may not have any water or atmosphere.

(Keep in mind that our sun has three planets in its habitable zone—Venus, Earth, and Mars. Location doesn't guarantee habitability.)

Still, the potential is there. We also don't know how old the star is, but M stars are incredibly stable; one this size could last for many trillions of years, where as our sun is good for 10 billion and will probably swell up and engulf Earth well before then.

Of course Trappist-1 can't be older than the universe, but it might last to the very end of it, if there is one.

[Primula Baggins]

And just check out the Google Doodle tonight! Astro-dorable.

[yovargas]

And just check out the Google Doodle tonight! Astro-dorable.

So cool!

[Frelga]

I understand habitable in this context as "capable of supporting liquid water and retaining an atmosphere"

My one-stop for the best of internet (other than here), Yonatan Zunger, wrote about what it may look like on the surface:
https://plus.google.com/u/1/+YonatanZun ... uwoeEiXntX

The system is unusual in that three of the planets may support life: Trappist-1d, e, and f. Even more interestingly, the three are similar enough that someone from one planet could potentially survive on the others. All three have roughly terrestrial gravity -- maybe 0.7g's on d and e, and 0.6g's on f. They are of similar sizes, having surface areas 60, 80, and 110% of Earth's, respectively.

Trappist-1d is the most Earthlike: the average temperature is 288K (15C, 59F), the same as on Earth. If you looked up in the sky there with human eyes, you would see a salmon-colored star, about five and a half times the apparent diameter of our own Sun, but somewhat dimmer; at noon, it would be about 15% brighter than it is on Earth. Of course, eyes which evolved on Trappist-1d wouldn't be tuned to the yellow light of our own Sun; they would be much more likely to see light much further into the infrared and less into the blues, and the light would look a "neutral white" to local eyes, just like our own Sun does to us.

If anything has evolved to photosynthesize in the Trappist-1 system, its analogue of chlorophyll would be principally absorbing in the far infra-red, and the local plants would look dark and reddish to our eyes; the oranges and yellows that make up so much of our own vision would be as exotic to Trappists as the ultraviolet which bees see is to us.

[Primula Baggins]

My husband the biologist says that the low-frequency light coming from the sun is a big problem for life. There isn't a molecule that can do what chlorophyll does that can be excited enough by such low-frequency light. Those molecules need strong light in the ranges we see as orange to blue. I didn't realize this, but as a chemistry person, I get it. What makes plants into food is that they store energy from the sun, because sunlight excites molecules into higher energy states that then gets stored as sugars and starches.

Not going to happen in dark red light. So there are limits to what life can accomplish on a world like that.

Also there is no noon unless you stood at the center of the light side. The sun never moves in the sky.

Alien worlds are alien!

[Sunsilver]

Several of my FB friends have posted about these planets, and it's even made the news-of-the=day on Google!

(What can I say....I have geeky friends! LOL!

https://www.google.ca/webhp?hl=en&ictx= ... LOBEAQPQgD

[Frelga]

I can't figure out tidal locking. I know what it IS, I just can't model it in my head.

[Primula Baggins]

Try this: https://en.wikipedia.org/wiki/Tidal_locking

The "Mechanism" section puts it succinctly, with diagrams.

But basically, the tidal force between two bodies distorts them both (they each bulge toward and away from the other in a kind of egg shape, and the effect is much stronger on the smaller body). This is what causes the tides on Earth, as the oceans bulge toward the moon (and also the sun, which is why the highest and lowest tides occur when the moon is either full or new—in either case, lined up with the Earth and sun so they're both pulling on the water in the same direction).

But the planetary structure is also affected, and over time the bulging (which lags the rotation) slows the rotation [see diagram in link] until eventually a permanent bulge is created in the planet, which ends up permanently pointed toward and away from the star. This is what happened between the moon and Earth. This only works if the gravitational force between the bodies is strong—so it usually happens when one body is large and they're quite close to each other.

[yovargas]

My husband the biologist says that the low-frequency light coming from the sun is a big problem for life. There isn't a molecule that can do what chlorophyll does....

....that we know of. I very much doubt that we would have guessed that a molecule that does what chlorophyll was possible without actually having chlorophyll in front of us. Aliens looking at us might very well be saying "the high-frequency light coming from their sun is a big problem for life since there isn't a molecule that can do what <insert molecule here> does."

[Voronwë the Faithful]

Exactly what I was thinking, yov!

[Primula Baggins]

Chlorophyll's a unique type of molecule, and it's true that photosynthesis has an activation energy that requires a set amount of energy input. Light of longer wavelengths doesn't provide energy that will bump the reaction over the threshold (I seem to recall it involves moving hydrogen ions around, which requires a set amount of energy to accomplish). No doubt River will set me straight on some things.

There are certainly other ways for life to function—chemosynthesis rather than photosynthesis—but an ecosystem without photosynthesis would have less available food in it. We don't photosynthesize, but a lot of what made larger and more complex forms of life possible was the development of an ecosystem with photosynthesis at the bottom of it, directly tapping the energy of the sun to provide rich food sources for those more complex forms.

[Maria]

I thought tide locked planets would have their atmosphere freeze onto the dark side? Or was that just a novel I read long ago? I can't remember.

[Primula Baggins]

That was thought to be the case for a long time, Maria, but with better computer models for winds, etc., on such worlds, it now appears that an atmosphere would probably survive in many cases, and that the light and dark side would be habitable for a wide stretch on both sides of the terminator.

[Maria]

Nifty. The next time I watch the SG1 episode with the tidelocked planet, I won't grumble about the presence of an atmosphere.

[Primula Baggins]

Well, next year's theory may be different.

But once the Webb telescope starts studying these planets, we'll probably get a definite answer based on observation.

[Voronwë the Faithful]

Just as an aside, it is very refreshing to get to come into this forum and talk about something other than politics. Not that the political discussion isn't important, but it is still nice to discuss something else that is also important.