Undergrad Will NASA Reveal Oxygen in TRAPPIST-1 Exoplanet Atmospheres?

[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 .

 

[Rubidium_71]

Neil deGrasse Tyson offered an opinion...

http://www.inquisitr.com/4021299/th...-trappist-1-neil-degrasse-tyson-has-bad-news/

 

[mfb]

The violent past of the star was discussed already, but if the density estimate for (f) is reliable, it has to have some volatiles left. It might have lost some water, but if it started with mainly water there could be enough water left.

The planets also started further outwards and migrated inwards later.

 

[1oldman2]

https://www.nasa.gov/feature/goddard/2017/probing-seven-worlds-with-nasas-james-webb-space-telescope
"If these planets have atmospheres, the James Webb Space Telescope will be the key to unlocking their secrets," said Doug Hudgins, Exoplanet Program Scientist at NASA Headquarters in Washington. "In the meantime, NASA’s missions like Spitzer, Hubble, and Kepler are following up on these planets."

 

[rootone]

Those planets could have liquid water, but in every other respect that solar system is utterly different to our one.
That does not mean life could not exist there, but if it does then it cannot be anything similar to Earth life.
Completely different scenario, (and all that pervasive UV)

 

[lightarrow]

What about possible grav. interactions between the planets, since they are so close to each-other?

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[mfb]

See post 13. Strong, but similar to the Moon's effect on Earth for the interesting planets.

 

[jordankonisky]

As we all know, seven earth-like planets have been discovered orbiting the low-mass-star TRAPPIST-1. TRAPPIST-1 is reported to be located only 12 parsecs (39 light yrs) from us. Can anyone described how this distance was determined? Thanks.

<Mentor note: Merged from a single thread to contain the discussion.>

 

[Bandersnatch]

Can anyone described how this distance was determined?

Trigonometric parallax by CTIOPI:
http://www.recons.org/published16.pdf
http://astronomy.swin.edu.au/cosmos/T/Trigonometric+Parallax

 

[mfb]

At that distance, the parallax method is very precise - the current uncertainty is 1.3 light years, and Gaia will reduce this uncertainty to less than 0.1 light years in 2-3 years.

 

[OmCheeto]

At that distance, the parallax method is very precise - the current uncertainty is 1.3 light years

I come up with 0.9 light years. Close enough for wiki inspired government work.

, and Gaia will reduce this uncertainty to less than 0.1 light years in 2-3 years.

According to my always questionable maths, GAIA will yield an accuracy of ±0.0005 ly for Trappist 1. [based on the numbers provided by Bandersnatch's second reference]
About the same distance as Neptune to Sol.

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[B's 2nd ref, edited for brevity]the Hipparcos Mission measured the parallax with an accuracy of 0.002 arcsec.
The GAIA mission will be able to measure parallaxes to an accuracy of 10^-6 arcsec

 

[mfb]

I used the uncertainty given in the Wikipedia article, but with the numbers from Bandersnatch's first reference I get nearly the same result. 2.58/82.58*39.5 = 1.23.

The second reference is massively outdated, and quotes an unrealistic precision for Gaia. For a mag 18 star like TRAPPIST-1, the precision is estimated to be somewhere between 20 (mag 15) and 200 (mag 20) microarcseconds. With 200 microseconds (worst case), the uncertainty would be 0.2/82.58*39.5 = 0.096 light years => "less than 0.1 light years".

 

[lightarrow]

See post 13. Strong, but similar to the Moon's effect on Earth for the interesting planets.

Thanks. What about possible deviations of their orbits? It doesn't seem they come closest always in the same point, if I'm correct.

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[mfb]

According to an orbital stability calculator posted earlier, the orbits are long-term stable for reasonable values of their eccentricity.

 

[lightarrow]

According to an orbital stability calculator posted earlier, the orbits are long-term stable for reasonable values of their eccentricity.

Thanks, mfb.

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[fresh_42]

Nasa has released its raw data:
https://keplerscience.arc.nasa.gov/raw-data-for-k2-campaign-12-and-trappist-1-now-available.html

 

[lpetrich]

Here are some preprints from arxiv about TRAPPIST-1 and its planets:

[1703.01424] Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1 -- the announcement paper for the seven planets. Some of them had been written about in earlier publications, however.

[1703.04166] A terrestrial-sized exoplanet at the snow line of TRAPPIST-1 (12 Mar 2017) -- from the K2 observations, it's been possible to get the mass of planet h.

[1704.02957] Limits on the Stability of TRAPPIST-1 (10 Apr 2017) -- "Due to uncertain system parameters, most orbital configurations drawn from the inferred posterior distribution are unstable on short timescales, even when including the eccentricity damping effect of tides."

[1704.04290] Updated Masses for the TRAPPIST-1 Planets (13 Apr 2017) -- some of the mass values revised downward, and a mass estimate for h. The new masses are more dynamically stable, and e, f, g, and h are most consistent with being water worlds, planets with superdeep water oceans. Planet b is likely a water world also, planet d straddles the all-rock line, and planet c is between all-rock and all-iron, much like the Earth and Venus.

 

[mfb]

OU astrophysicist identifies composition of Earth-size planets in TRAPPIST-1 system

Using thousands of numerical simulations to identify the planets stable for millions of years, Quarles concluded that six of the seven planets are consistent with an Earth-like composition. The exception is TRAPPIST-1f, which has a mass of 25 percent water, suggesting that TRAPPIST-1e may be the best candidate for future habitability studies.

Now we need JWST and E-ELT to study their atmospheres.

 

[lpetrich]

OU astrophysicist identifies composition of Earth-size planets in TRAPPIST-1 system

It's in arxiv as [1704.02261] Plausible Compositions of the Seven TRAPPIST-1 Planets Using Long-term Dynamical Simulations

I'll also put in the masses found from [1704.04290] Updated Masses for the TRAPPIST-1 Planets, as determined from Transit Timing Variations (TTV"s).

I calculated the test parameter for Student's t test for the differences between the two results:
t = \frac{x_2 - x_1}{\sqrt{\sigma_1{}^2 + \sigma_2{}^2}}
where the x's are the values to be compared and the σ's are their standard deviations.

• b: 0.88+0.62-0.53 ... 0.79+-0.27 ... -0.15
• c: 1.35+0.61-0.59 ... 1.63+-0.63 ... +0.32
• d: 0.42+0.25-0.21 ... 0.33+-0.15 ... -0.35
• e: 0.55+0.51-0.35 ... 0.24+0.56-0.24 ... -0.47
• f: 0.68+0.17-0.18 ... 0.36+-0.12 ... -1.48
• g: 1.39+0.76-0.69 ... 0.566+-0.038 ... -1.19
• h: 0.47+0.26-0.26 ... 0.086+-0.084 ... -1.41

So most of the updated-mass results are less than most of the dynamical-stability results, with only one exception, a small one. This is enough to force planets e, f, g, h down from being mostly rocky to being mostly watery.

Li Zeng's page Planet Models contains some tables of radius as a function of mass for various compositions: iron to rock to water, then hydrogen-helium. The most detailed table: has "100%fe 95%fe 90%fe 85%fe 80%fe 75%fe 70%fe 65%fe 60%fe 55%fe 50%fe 45%fe 40%fe 35%fe 30%fe 25%fe 20%fe 15%fe 10%fe 5%fe rocky 5%h2o 10%h2o 15%h2o 20%h2o 25%h2o 30%h2o 35%h2o 40%h2o 45%h2o 50%h2o 55%h2o 60%h2o 65%h2o 70%h2o 75%h2o 80%h2o 85%h2o 90%h2o 95%h2o 100%h2o cold_h2/he max_coll_strip"
The rock used was MgSiO3 in a perovskite structure.

 

[lpetrich]

The TRAPPIST-1 planets have the remarkable property of being in a chain of mean-motion resonances. Mean motion = mean angular velocity = (2*pi)/period.

This chain has ratios
8:5:3:2, 3:2, 4:3:2
It includes all 7 known planets of the TRAPPIST-1 star.

One can find a "resonance gap" angular velocity from
\omega_{res} = \frac{n_2 \omega_1 - n_1 \omega_2}{n_2 - n_1}
where the n's are the resonance numbers and the ω's are angular velocities.

The resonances all share a fundamental frequency, a frequency that corresponds to a period of around 1.35 years. I checked on the observations of TRAPPIST-1, and I found:

• La Silla, Chile, 60cm, TRAPPIST-South -- 2015 Sep 17 - Dec 31, ... 2016 Apr 30 - Oct 11
• Oukaïmeden, Morocco, 60cm, TRAPPIST-North -- 2016 Jun 1 - Oct 12
• India, 2m, Himalayan Chandra Telescope (HCT) -- 2015 Nov 18
• Paranal, Chile, 8m, Very Large Telescope (VLT) -- 2015 Nov 8
• Hawaii, US, 3.8m, UK Infrared Telescope (UKIRT) -- 2015 Dec 5, 6, 8, 10, 11, ... 2016 Jun 24, Jul 16, 18, 29, 30, Aug 1
• La Palma, Canary Islands, 4.3m William Herschel Telescope -- 2016 Aug 23 - 35
• Sutherland, South Africa, 1m, South African Astronomical Observatory -- 2016 June 18, 19, 21, 22, Jul 2, 3
• Spitzer Space Telescope -- 2016 Feb 21, Mar 3, 4, 7, 13, 15, Sep 19 - Oct 10
• Kepler Space Telescope -- 2016 Dec 15 - 2017 Feb 1, 2017 Feb 6 - Mar 4

TRAPPIST = TRansiting Planets and PlanetesImals Small Telescope

So TRAPPIST-1 has been observed off-and-on over from 2015 Sep 17 to 2017 Mar 4, nearly 1 1/2 years, a little more than my calculated resonance period.

But TRAPPIST-1's observers have likely scheduled some additional observing time, and they may already have started some more observations of the star.

[1605.07211] Temperate Earth-sized planets transiting a nearby ultracool dwarf star
[1703.01424] Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
[1703.04166] A seven-planet resonant chain in TRAPPIST-1
[1704.04290] Updated Masses for the TRAPPIST-1 Planets

 

[halbhh]

Regarding the surprising idea earlier that Trappist 1 is a "quiet" star, that's now to be replaced with this -- "The energy distribution of the 42 observed flares shows that TRAPPIST-1 belongs to the more active group of M-dwarfs."
https://phys.org/news/2017-04-frequent-flaring-trappist-1unsuited-habitability.html

So, then the expected effect of frequent flaring would be...atmospheric loss, unless a very unusually strong magnetic field is present, and also intense radiation. But this was only the typically expected situation, isn't that right, because red dwarfs typically are active (but now I see the thread the needle idea that until this large amount of small flares is considered, that previously it was thought if the planets formed far away during a more intense flaring stage and then with the hypothesis the star is quieter (but even for larger flares, just precisely how much frequency, since it could only take a 1 or a few direct hits of bigger flares to end any life as we know it?) then the planets migrate into near a hypothesized 'quiet' star, so the April results are closing that scenario down more firmly. When first announced about the 7 planets and the phrase "Earth like", this was the first thought that came to mind -- flares. If even before the frequent flares shown back in April, the scenario was depending on so many just-right outcomes, then we should never have thought "good candidates", but instead "long shot candidates".

 

[lpetrich]

So those planets would be much like Venus and Mars -- most of their surface and atmospheric water stripped off. That raises the question of what would happen to an ocean planet. How much of such a planet's super ocean would survive to the present? Would it all get stripped off, leaving a rocky core?

 

[mfb]

The density measurements are for the current situation. We don't know how large the initial oceans were, but if the density now indicates large oceans then apparently a large ocean survived. Or the planet is made out of something we don't expect.

 

[halbhh]

An ocean world is an interesting possibility. It would be good to see a simulation, because of the fact that the flares are not that weak, and the planets so very much closer than Earth. Even with a nicely high magnetic field say twice as strong as Earth's (an optimistic scenario?), I'd guess before seeing the simulation that it is not enough protection that close to the star. The ocean could protect against the radiation intensity, but not against the atmosphere loss unless the magnetic field is enough, and if a larger flare hits, that level of 'enough' is very high I'm guessing, since I read these little red dwarfs can flare just as strongly as our much larger sun. Do coronal mass ejection intensities fall off with the square of distance, or are they held together magnetically? The planets are 25 - 35 times closer than Earth is to the Sun... 900 times intensity would matter, and then how could the magnetic field be enough? And even if it was merely linear, even just a factor of 25 is pretty drastic. I'd want to see the simulation. (Of course, in time, our observations will trump the simulations.)

Here's one paper I see from a wiki:

^ Khodachenko, Maxim L.; et al. (2007). "Coronal Mass Ejection (CME) Activity of Low Mass M Stars as An Important Factor for The Habitability of Terrestrial Exoplanets. I. CME Impact on Expected Magnetospheres of Earth-Like Exoplanets in Close-In Habitable Zones". Astrobiology. 7 (1): 167–184. Bibcode:2007AsBio...7..167K. doi:10.1089/ast.2006.0127. PMID 17407406.

"Abstract
Low mass M- and K-type stars are much more numerous in the solar neighborhood than solar-like G-type stars. Therefore, some of them may appear as interesting candidates for the target star lists of terrestrial exoplanet (i.e., planets with mass, radius, and internal parameters identical to Earth) search programs like Darwin (ESA) or the Terrestrial Planet Finder Coronagraph/Inferometer (NASA). The higher level of stellar activity of low mass M stars, as compared to solar-like G stars, as well as the closer orbital distances of their habitable zones (HZs), means that terrestrial-type exoplanets within HZs of these stars are more influenced by stellar activity than one would expect for a planet in an HZ of a solar-like star. Here we examine the influences of stellar coronal mass ejection (CME) activity on planetary environments and the role CMEs may play in the definition of habitability criterion for the terrestrial type exoplanets near M stars. We pay attention to the fact that exoplanets within HZs that are in close proximity to low mass M stars may become tidally locked, which, in turn, can result in relatively weak intrinsic planetary magnetic moments. Taking into account existing observational data and models that involve the Sun and related hypothetical parameters of extrasolar CMEs (density, velocity, size, and occurrence rate), we show that Earth-like exoplanets within close-in HZs should experience a continuous CME exposure over long periods of time. This fact, together with small magnetic moments of tidally locked exoplanets, may result in little or no magnetospheric protection of planetary atmospheres from a dense flow of CME plasma. Magnetospheric standoff distances of weakly magnetized Earth-like exoplanets at orbital distances <or=0.1 AU can be shrunk, under the action of CMEs, to altitudes of about 1,000 km above the planetary surface. Such compressed magnetospheres may have crucial consequences for atmospheric erosion processes."

 

[halbhh]

Was just seeing this --

"But actual mathematical models conclude that,[33][34] even under the highest attainable dynamo-generated magnetic field strengths, exoplanets with masses like that of Earth lose a significant fraction of their atmospheres by the erosion of the exobase's atmosphere by CME bursts and XUV emissions (even those Earth-like planets closer than 0.8 AU—affecting also GK stars— probably lose their atmospheres)."

Ouch.

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

Totally worth observing, but I'm expecting no atmosphere. My guess is we need a solar system much more similar to our own to find something we ourselves would be able to inhabit other than underground (though I'd be pleased to find out otherwise, it just doesn't seem realistic given current information).

 

[mfb]

A deep ocean could replenish the atmosphere for quite some time (even Earth has about 300 times the atmospheric mass as oceans, and we are not living on an ocean planet), simply by evaporating. Oceans only go away once all the water has escaped - and you need both hydrogen and oxygen to escape. If only hydrogen escapes, you might get a very dense oxygen/water atmosphere.