7 exoplanets around TRAPPIST-1

[mfb]

NASA announcement
Wednesday, 1 pm EST. You can use the forum for time zone conversion: This post was posted 3:55 pm EST.

While the announcement doesn't have any details, digging a bit deeper: The livestream website calls the event "Spitzer Exoplanet Science Briefing", and of course we can see what the panel is doing:

- Thomas Zurbuchen has a management position at NASA, too unspecific.
- Michael Gillon is working on TRAPPIST, searching for exoplanets, especially Earth-like ones, with the transit method.
- Sean Carey works on the Spitzer telescope, an infrared telescope. It can find transit planets and map planetary disks around other stars. Microlensing events can also be observed.
- Nikole Lewis is an expert in exoplanet atmospheres, especially with measurements in transits.
- Sara Seager is another expert in exoplanet atmospheres, measured with transits.

Based on that panel, I'm quite sure the announcement will be related to the atmospheric composition of some exoplanet, measured in a transit.

Speculation: We had water (multiple times), carbon monoxide, carbon dioxide and methane already. We had hydrogen and helium. We also had sodium and titanium dioxide on very hot planets. A new observation of those gases around more exoplanets wouldn't need a press conference. Clouds were also discovered before. What is missing?
- Nitrogen is not in the list, but nitrogen is hard to observe.
- Oxygen would be a big sensation, as processes without life that produce oxygen are rare. While it is hard to observe, it will come with some ozone, which can be detected. Ozone has absorption bands in the infrared.
- Oxygen plus methane together would be even more spectacular, as the combination would be outside of chemical equilibrium.

This blog article predits 7 Earth-sized planets around TRAPPIST-1 - three are known already.

 

[.Scott]

- Oxygen plus methane together would be even more spectacular, as the combination would be outside of chemical equilibrium.

Would looking for oxygen plus smog be too optimistic?

 

[mfb]

Detecting industrial pollution in the atmospheres of earth-like exoplanets
The exoplanets have to be really bad, even if we have the JWST available, to have detectable industrial pollution.

A bit more sourced speculation about the press conference: 7 Earth-sized planets around TRAPPIST-1? 3 planets are known already, and the panel members were interested in follow-up observations if I interpret the blog sources correctly.

This catalog of potentially habitable exoplanets expects an update on Thursday. Do they know something we do not?

 

[Ygggdrasil]

Based on that panel, I'm quite sure the announcement will be related to the atmospheric composition of some exoplanet, measured in a transit.

Speculation: We had water (multiple times), carbon monoxide, carbon dioxide and methane already. We had hydrogen and helium. We also had sodium and titanium dioxide on very hot planets. A new observation of those gases around more exoplanets wouldn't need a press conference. Clouds were also discovered before. What is missing?
- Nitrogen is not in the list, but nitrogen is hard to observe.
- Oxygen would be a big sensation, as processes without life that produce oxygen are rare. While it is hard to observe, it will come with some ozone, which can be detected. Ozone has absorption bands in the infrared.
- Oxygen plus methane together would be even more spectacular, as the combination would be outside of chemical equilibrium.

Would oxygen be the main signature to indicate the possibility of life? Life existed on Earth for ~ 0.5 billion years before photosynthesis evolved (which began producing oxygen), and oxygen was not present in significant amounts in the atmosphere until about 2-2.5 billion years ago (for comparison, life is thought to have evolved ~ 4 billion years ago).

 

[mfb]

Life has to alter the atmosphere notably to be detectable with current technology, there should be no natural process leading to the same result, and we need a way to find this gas. The introduction of oxygen is one of the best possibilities. Sure, not all life will emit oxygen, but life emitting CO2 won't be detectable as there are large natural sources of CO2.

 

[mfb]

Yes, 7 planets around TRAPPIST-1, all about Earth-sized with quite precise radius estimates from transits, and approximate mass measurements from transit timing variation.

3 are too hot for liquid water (b,c,d), 3 of them in the habitable zone (e,f,g), 1 (h) is too cold. The three planets seen before were the innermost two and the outermost one, so all potentially habitable planets are new. Probably tidally locked (all?).

TRAPPIST-1e: ~0.92 times Earth radius, about half the mass
f: missed the radius, but also similar to Earth
g:1.05 times Earth radius, similar irradiation as Mars
h: Largest planet. Period is poorly known which is odd.

One has a density that suggests water present, but no confirmation of water yet. The orbits are in resonances, which suggests that they formed further out and migrated inwards, making water on them quite likely.

Hubble is currently studying the atmospheres, and various other telescopes are looking at the system. JWST will do so later as well. JWST will measure the greenhouse gases to improve the temperature estimate, and it will look for oxygen/ozone and methane.
We'll probably get good atmosphere estimates within the next 5 years.

Ultracool dwarfs like TRAPPIST-1 start very active, could have blown away atmospheres from the planets in the past. Now (at least half a billion years old, hard to estimate better as the star doesn't change much any more) the star is very quiet.

Moons around planets so close to the stars are unlikely. Tidal forces from other planets would be relevant. Planets as seen by other planets would look as large as the Moon from Earth.

TRAPPIST program got extended to have more telescopes to observe more stars.
SETI looked at the system in the past but didn't find anything.

 

[Ygggdrasil]

From EurekaAlert press release:

The planetary orbits are not much larger than that of Jupiter's Galilean moon system, and much smaller than the orbit of Mercury in the Solar System. However, TRAPPIST-1's small size and low temperature mean that the energy input to its planets is similar to that received by the inner planets in our Solar System; TRAPPIST-1c, d and f receive similar amounts of energy to Venus, Earth and Mars, respectively.

All seven planets discovered in the system could potentially have liquid water on their surfaces, though their orbital distances make some of them more likely candidates than others. Climate models suggest the innermost planets, TRAPPIST-1b, c and d, are probably too hot to support liquid water, except maybe on a small fraction of their surfaces. The orbital distance of the system's outermost planet, TRAPPIST-1h, is unconfirmed, though it is likely to be too distant and cold to harbour liquid water -- assuming no alternative heating processes are occurring [5]. TRAPPIST-1e, f, and g, however, represent the holy grail for planet-hunting astronomers, as they orbit in the star's habitable zone[6].

https://www.eurekalert.org/pub_releases/2017-02/e-uda022117.php\

Here's the actual publication in Nature: Gillon et al. Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1. Nature 542: 456 (2017). http://dx.doi.org/10.1038/nature21360[/URL]

Abstract:
[quote]One aim of modern astronomy is to detect temperate, Earth-like exoplanets that are well suited for atmospheric characterization. Recently, three Earth-sized planets were detected that transit (that is, pass in front of) a star with a mass just eight per cent that of the Sun, located 12 parsecs away[URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref1[/URL]. The transiting configuration of these planets, combined with the Jupiter-like size of their host star—named TRAPPIST-1—makes possible in-depth studies of their atmospheric properties with present-day and future astronomical facilities[URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref1[/URL], [URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref2[/URL], [URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref3[/URL]. Here we report the results of a photometric monitoring campaign of that star from the ground and space. Our observations reveal that at least seven planets with sizes and masses similar to those of Earth revolve around TRAPPIST-1. The six inner planets form a near-resonant chain, such that their orbital periods (1.51, 2.42, 4.04, 6.06, 9.1 and 12.35 days) are near-ratios of small integers. This architecture suggests that the planets formed farther from the star and migrated inwards[URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref4[/URL], [URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref5[/URL]. Moreover, the seven planets have equilibrium temperatures low enough to make possible the presence of liquid water on their surfaces[URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref6[/URL], [URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref7[/URL], [URL]http://www.nature.com/nature/journal/v542/n7642/full/nature21360.html#ref8[/URL].[/quote]

Given that the planets are so close to the red dwarf, wouldn't the planets likely be tidally locked to the star? Seems similar to the case of [URL='https://www.physicsforums.com/threads/a-terrestrial-temperate-planet-around-proxima-centauri.882957/#post-5550240']Proxima b[/URL]

 

[hilbert2]

If I understood it correctly, they don't have IR spectral data yet, so we have to wait a while before they can tell something about the chemical composition of the atmospheres.

 

[Haelfix]

I wonder what the tidal forces would do for such a complicated system that are in such close proximity. The geological aspects would be fascinating. It's also not clear to me why people think they are all necessarily tidally locked.

 

[OmCheeto]

Changing my will.

NASA, ESA, et al, get everything.

 

[amarante]

The announcement was really amazing! Seven earth-like planets around a single star!
However, although they are located in the classical habitable zone, we need to be very cautious before calling them "habitable planets". The host star is not like our Sun and thus have some peculiarities. It is interesting to check these two papers about the Trappist system: Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1 and Water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of TRAPPIST-1 .

In short: the X-ray emission of Trappist-1 is strong enough that it could remove the atmosphere, or most of it, of the planets and also could evaporate their oceans.

 

[DennisN]

Two videos for us:

1) NASA & TRAPPIST-1: A Treasure Trove of Planets Found (Feb 22, 2017)


2) NASA full press conference on discovery of 7 Earth-like exoplanets (Feb 22, 2017)

 

[mfb]

Concerning tidal effects: They scale with mass/(distance^3). That allows a comparison with the tidal effects of Moon. The largest tidal impact will be from (c) on (b), as they come closest: 30 times the tides Moon generates when they have their minimal distance. (b) will be too hot for global oceans, however. If we go further outwards: (e) and (f) have similar mass, and their maximal tidal effect is just 120% of the effect Moon has.

 

[levadny]

It seems to me that this is not the first time found a planet similar to ours.

 

[Rubidium_71]

the star is very quiet.

I know a lot of white and red dwarf stars qualify as flare stars. Since Trappist -1 is an ultra cool dwarf, and as you've pointed out it quiets down with age, would this make flares less likely? In combination with the x-rays that have been mentioned, flare activity would not bode well for any "habitable zone" planet.
Could one of these worlds possibly have a magnetic field strong enough to protect it from these issues, or is the x-ray radiation too powerful?

 

[mfb]

In the press conference they said the star is now very quiet, and they got a lot of telescope time to study potential atmospheres, so they certainly hope to find something.

It seems to me that this is not the first time found a planet similar to ours.

For exoplanets searches, planets like Venus and Mars are "similar" to Earth. By that metric, three of the TRAPPIST-1 planets are similar, and we have many others that are similar as well. Here are lists.

 

[Borg]

As I understand it, most (or all) of these planets are probably tidally locked. If there was liquid water on the warm side, wouldn't the water evaporate into the air, get blown to the dark side, precipitate out as snow and never get back to the other side? I guess you could get some melting on the fringes but I would think that the sunlit side would be pretty dry within a few million years at most.

 

[mfb]

Hot gases from the sunlit side can heat the other side.
Ice can move towards the sunlit side.

Antarctica doesn't trap all the water on Earth either, and its temperature is constantly below zero.

 

[Borg]

Hot gases from the sunlit side can heat the other side.
Ice can move towards the sunlit side.

Antarctica doesn't trap all the water on Earth either, and its temperature is constantly below zero.

I understand. I guess that it's more of an equilibrium question and Antarctica is a good example of equilibrium on our planet. I didn't think about an ocean near the fringes but I still wonder what the final equilibrium would be like.

 

[mfb]

We have Venus as interesting example. Its rotation is very slow (and retrograde), solar days are 116 Earth days long. Its atmosphere is so thick and moves so fast (in the upper layers) that the surface temperature does not change much during the day.

 

[Borg]

OK, thanks for the example.

 

[OmCheeto]

2550 K doesn't really sound that "ultracool" to me.
Perhaps, it has a more 60's-ish; "This is ultra cool, man" meaning.

​

 

[mfb]

Just 3% the surface brightness of sun in infrared, just 0.03% in visible light. At the same total flux, the planets have just 1% the visible light we have on Earth. Even in bright daylight it is darker than a very cloudy day on Earth.

 

[OmCheeto]

Just 3% the surface brightness of sun in infrared, just 0.03% in visible light. At the same total flux, the planets have just 1% the visible light we have on Earth. Even in bright daylight it is darker than a very cloudy day on Earth.

1%? hmmmm... <google google google>

per wiki; "The full Moon is about 1,000,000 times fainter than the Sun."[ref]

So... It's about 10,000 time brighter than a full moon?

hmmmm...

Anyways, I'm curious about their eyes. I know that some Earth based creatures can sense IR.
We "whomans" seem to have evolved to collect the most popular local solar spectra.
I would imagine that exobiologists will be arguing about this, for years.

 

[jim mcnamara]

Are we speculating here? Heck, no :)

Plus. Don't skim over over 4+ billion years, using Earth as a model, it took for our current fun flora and fauna to come along.

After things cooled down, about the first 2 billion years were dominated by what @Chronos calls 'refrigerator parasites' - prokaryotic life. Then after that we have prokaryotic life spewing out oxygen over eons, and changing Earth forever. After enough toxic-to-anerobic-life oxygen from cyanobacteria built up, aerobic respiration took over as the winning combination. After all this long period, interesting complex multicellular organisms and complex ecosystems still took even more time to get going. So from 0 to ~4 billion years of Earth's existence and still nothing living that is cute and fuzzy, or even nightmarish and scaly for us to contemplate.

So, assuming that we all favor the cute and fuzzy mode here, at about year 4 billion or later using our Earth model, these lines of thought might get us further down the road.

1. What is the estimated age of the star?
2. Any oxygen atmospheres? - This might save us waiting additional billions of years. I think additional data is forthcoming.
3. Any notion of tidal interactions between planets or from the Jupiter 'plus size' tiny sun? - would our newly found planetary surfaces be undergoing gravitational fracturing like Europa?
4. Is there any sense to intensifying our current search methodologies some way to favor M-class stars and smaller over larger ones?

 

[jim mcnamara]

@OmCheeto - you may want to widen the area under the curve for animal vision:

https://en.wikipedia.org/wiki/Infrared_sensing_in_snakes

 

[OmCheeto]

@OmCheeto - you may want to widen the area under the curve for animal vision:

https://en.wikipedia.org/wiki/Infrared_sensing_in_snakes

I mentioned our cousins...

I know that some Earth based creatures can sense IR.

 

[mfb]

1. What is the estimated age of the star?

See post #6. At least 0.5 billion years, but it is hard to say more.

2. Any oxygen atmospheres?

See post #6. Atmospheres are under study by Hubble and some other telescopes. JWST and maybe E-ELT/GMT will give more details.

3. Any notion of tidal interactions between planets or from the Jupiter 'plus size' tiny sun?

See post #13. Strong, but comparable to the Moon between the interesting planets. Very strong from the central star, which means the planets are probably tidally locked.

 

[newjerseyrunner]

A question about oxygen, wouldn't a thawing planet have oxygen in the atmosphere? I was under the impression that at least some of the oxygenation event due to the thawing of snowball earth. Water ice, bombarded with UV creates peroxide, which when dissolved back in water will release its extra oxygen atom.

 

[jim mcnamara]

@mfb - thanks for the information and clarifications. The less than 1 billion year age, to me, means really early protolife, which si till interesting to say the least.
Tidally locked. There was a thread on PF about tidally locked planets. I think there was a post about a theoretical paper that indicated it might not be a deal break for life get a start. Do you recall?

edit: this locked thread I think was the discussion. Just an ad hoc model I guess.
https://www.physicsforums.com/threads/habitability-of-tidally-locked-exoplanets.663409/

@OmCheeto - I'm not trying to give you a bad time, your posts are fun, but the graph misrepresents things about metazoan vision capabilities here on earth. Active vision in vertebrates ranges from about 350nm to 1200 nm. On the more extreme side, pit vipers and some other reptiles go way into IR. Other organisms are ridiculous, almost. Melanophila beetles see way beyond 1.6μm. Out to 4μm. Your chart is off, if I am not misinterpreting the axes labels. If I am I apologize.
See:
Journal of Comparative Physiology A
April 1998, Volume 182, Issue 5, pp 647–657
The photomechanic infrared receptor for the detection of forest fires in the beetle
Melanophila acuminata (Coleoptera: Buprestidae) (Black fire beetle)

These little guys look for areas in forests that are very recently burned. Or are still smoldering.
http://bugguide.net/node/view/457912 Really cool bugs!

 

[mfb]

The less than 1 billion year age

We don't know that. We just know it has to be older than 0.5 billion years. It could be 5 billion years old. Maybe even 10 (would need a careful check of the metallicity).

 

[snorkack]

Just 3% the surface brightness of sun in infrared, just 0.03% in visible light. At the same total flux, the planets have just 1% the visible light we have on Earth. Even in bright daylight it is darker than a very cloudy day on Earth.

Over 1000 lux? That´s more than most homes provide by incandescent bulbs.
How does the spectrum of Trappist 1 compare against an incandescent bulb? Against fire?

 

[mfb]

2550 K surface temperature, Wikipedia calls that color temperature "Soft white incandescent lamps", but it looks red. As comparison: Arcturus has a surface temperature of 4300 K - much closer to the sun - and it still looks red (one of the few objects in the sky bright enough to see the color with the naked eye).

 

[mfb]

I found this interesting article. Many points mentioned there are in this article already, but there are also some new aspects:

- Kepler is observing the system right now! It started "Field 12", which includes TRAPPIST-1, mid December and will continue observing it until March. Nearly three months of continuous observations will help identifying the period of the 7th planet, and the large number of observed transits will improve the mass estimates (via transit timing variation). There is even the option of more planets further out.
- Hubble can see if the atmosphere is hydrogen-dominated ("Mini Neptune"), but it is not sensitive enough to search for water vapor, carbon dioxide and methane. JWST will be needed for those studies.
- while e,f,g are quite comfortable in the habitable zone, d could be inside as well - if it rotates slowly and has enough clouds at the day side. The climate of those planets is not well understood.
- Planet f has a density estimate that would suggest a lot of water, or even a mini Neptune. Better mass estimates in the future will help, and Hubble observations will check the mini Neptune option.

 

[Paulibus]

The Trappist discovery has caught the attention of the world outside Physics Forums to an extent which could justify calling this discovery bizarre. How justified is such a label? Enough to mention a bizarre possibility? One which in another context would surprise few -- namely that maybe Somebody made it like that -- a possibility that might be readily accepted by many outside these forums, but rejected by folk who post here, and by myself.

But the possibility that a tidy set of planets is the first large-scale manifestation of manipulative life beyond our physical reach at work that we've observed can't be ruled out unless we listen hard for signs of it at work. I'd like to suggest that we should do so in the near future, focussing on Trappist .