Exoplanet Stuff

[lpetrich]

 Carbon planet notes that the C/O ratio is the ratio of the number of atoms of each element (2013 paper: The carbon-to-oxygen ratio in stars with planets | Astronomy & Astrophysics (A&A))

A carbon planet is what would result from more carbon than oxygen. [astro-ph/0504214] Extrasolar Carbon Planets

If solar composition gas at 10−4 bars is cooled slowly from high temperatures, several major building blocks of the solar system condense out one by one. First metal oxides and iron-peak elements condense at ∼1500 K, then silicates condense at 1200–1400 K, water at ∼180 K, and eventually, ammonia and methane at lower temperatures (e.g., Lodders 2003). This equilibrium condensation sequence apparently describes the gross compositions of the inner solar system planets: Fe and Ni cores surrounded by silicate mantles, topped by more complicated veneers containing water and more volatile compounds.

...
In gas with C/O ratio > 0.98, the condensation sequence changes dramatically (Larimer 1975). In carbon-rich gas, the highest temperature condensates (T ≈ 1200–1600 K) are carbon-rich compounds: graphite, carbides, nitrides, and sulfides.

...
Low-mass planets formed via these carbon-rich condensation sequences would be carbon planets, initially composed largely of the high-temperature condensates formed in carbon-rich gas, like graphite and silicon carbide.

...
Carbon condensation is strikingly different from the oxygen-rich condensation sequence because of the availability of graphite as a high-temperature condensate; there is no analogous high temperature condensate of pure oxygen. In a typical condensation sequence for carbon enriched gas (Lodders & Fegley 1997), CO forms, using up all of the oxygen, and then carbon left over from CO formation (called “condensable carbon”) condenses as SiC or TiC using about half of the Si (e.g., Lodders & Fegley 1997). Most of the carbon left over after SiC and TiC formation condenses as graphite; the higher the C/O ratio, the more graphite forms. Pure carbon can dissolve in metals and in the planet’s carbide mantle, but since graphite is less dense than SiC (2 g cm^−3 compared to 3.2 g cm^−3), we might expect a pure carbon layer to form on top of the SiC in a completely differentiated planet.

So the planet may form layers: graphite on top of silicon and metal carbides. If the graphite is thick enough, a few hundred kilometers at the Earth's surface gravity, then the bottom part will likely become diamond.

The atmosphere of an Earth-mass carbon planet would likely have a lot of carbon monoxide and/or methane. Photochemical reactions would likely make long-chain hydrocarbons: tar.

 

[lpetrich]

NASA’s Webb Spots Swirling, Gritty Clouds on Remote Planet

Weather report: Expect scattered, patchy clouds made up of silicates on planet VHS 1256 b.

Ever had hot sand whip across your face? That’s a soothing experience compared to the volatile conditions discovered high in the atmosphere of planet VHS 1256 b. Researchers using NASA’s James Webb Space Telescope proved that its clouds are made up of silicate particles, ranging from fine specks to small grains. Plus, its near-constant cloud cover is on the move! The team projects that the silicates swirling in these clouds periodically get too heavy and rain into the depths of the planet’s atmosphere. Webb’s observations also show clear signatures of water, methane and carbon monoxide, and provide evidence for carbon dioxide. ...

Researchers observing with NASA’s James Webb Space Telescope have pinpointed silicate cloud features in a distant planet’s atmosphere. The atmosphere is constantly rising, mixing, and moving during its 22-hour day, bringing hotter material up and pushing colder material down. The resulting brightness changes are so dramatic that it is the most variable planetary-mass object known to date. The team, led by Brittany Miles of the University of Arizona, also made extraordinarily clear detections of water, methane and carbon monoxide with Webb’s data, and found evidence of carbon dioxide. This is the largest number of molecules ever identified all at once on a planet outside our solar system.

Cataloged as VHS 1256 b, the planet is about 40 light-years away and orbits not one, but two stars over a 10,000-year period. “VHS 1256 b is about four times farther from its stars than Pluto is from our Sun, which makes it a great target for Webb,” Miles said. “That means the planet’s light is not mixed with light from its stars.” Higher up in its atmosphere, where the silicate clouds are churning, temperatures reach a scorching 1,500 degrees Fahrenheit (830 degrees Celsius).

 VHS J1256–1257 -- at its distance, its heat must be internal.

Within those clouds, Webb detected both larger and smaller silicate dust grains, which are shown on a spectrum. “The finer silicate grains in its atmosphere may be more like tiny particles in smoke,” noted co-author Beth Biller of the University of Edinburgh in Scotland. “The larger grains might be more like very hot, very small sand particles.”

VHS 1256 b has low gravity compared to more massive brown dwarfs, which means that its silicate clouds can appear and remain higher in its atmosphere where Webb can detect them. Another reason its skies are so turbulent is the planet’s age. In astronomical terms, it’s quite young. Only 150 million years have passed since it formed – and it will continue to change and cool over billions of years.

An age inferred from its inferred surface temperature, I'm sure.

 

[lpetrich]

NASA’s Webb Measures the Temperature of a Rocky Exoplanet - NASA

An international team of researchers has used NASA’s James Webb Space Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1 b. The measurement is based on the planet’s thermal emission: heat energy given off in the form of infrared light detected by Webb’s Mid-Infrared Instrument (MIRI). The result indicates that the planet’s dayside has a temperature of about 500 kelvins (roughly 450 degrees Fahrenheit) and suggests that it has no significant atmosphere.

How did they do it?

The team used a technique called secondary eclipse photometry, in which MIRI measured the change in brightness from the system as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to give off its own visible light, it does have an infrared glow. By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.

That works only for the daytime side of a planet, "full planet", it must be noted. But if one's measurements are good enough, one can observe changes of brightness over the planet's orbit.

Webb’s detection of a secondary eclipse is itself a major milestone. With the star more than 1,000 times brighter than the planet, the change in brightness is less than 0.1%.

“There was also some fear that we’d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,” said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analyzed the data. “But it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.”

What they found was consistent with bare rock or a thin atmosphere, as opposed to some thick, Venus-like atmosphere.

The team hopes to observe TRAPPIST 1 for some full orbits of planet b, to try to catch it in "crescent planet" and "half planet" and "gibbous planet".

 Phase curve (astronomy)

ANALYTIC MODELS FOR ALBEDOS, PHASE CURVES, AND POLARIZATION OF REFLECTED LIGHT FROM EXOPLANETS - IOPscience

So if one has a phase curve, one has a constraint on how anisotropic the surface's light reflection is. Is it consistent with bulk rock? Rock dust? Ice? Snow? Oceans? Clouds?

 

[lpetrich]

• Cornell postdoc detects possible exoplanet radio emission | Cornell Chronicle
• Scientists think they've detected radio emissions from an alien world | Space
• The search for radio emission from the exoplanetary systems 55 Cancri, υ Andromedae, and τ Boötis using LOFAR beam-formed observations | Astronomy & Astrophysics (A&A)

Possible radio emissions from the magnetosphere of a planet of the star Tau Boötis. But it's a borderline result, and one unconfirmed by others.

 

[lpetrich]

• Repeating radio signal leads astronomers to an Earth-size exoplanet | CNN
• Coherent radio bursts from known M-dwarf planet-host YZ Ceti | Nature Astronomy

From Nature paper's abstract:

Here we present 2–4 GHz detections of coherent radio bursts on the slowly rotating M dwarf YZ Ceti, which hosts a compact system of terrestrial planets, the innermost of which orbits with a two-day period. Two coherent bursts occur at similar orbital phases of YZ Ceti b, suggestive of an enhanced probability of bursts near that orbital phase.

But they will need to compare the radio emissions of similar stars. "However, we cannot rule out stellar magnetic activity without a well-characterized rate of non-planet-induced coherent radio bursts on slow rotators."

One must then compare stars with known planets to stars without known planets, though a star can have no known planets if its planets' orbits are too tilted to make transits, the main way of detecting planets around red dwarfs.

 

[lpetrich]

Why Only Earth Has Fire - YouTube
The Earth as the fire planet?

First, let us clarify what we mean by fire: a chemical reaction that produces enough heat to glow in visible light, and not simply something hot enough to glow or even something glowing in general.

Oxygen and fluorine can make fires by combining with anything chemically reduced, like metals and organic/biological materials, but fluorine is too rare to be a significant part of atmospheres. So that leaves oxygen.

 Limiting oxygen concentration - minimum to sustain a fire

• Hydrogen: 5%
• Light hydrocarbons (C1 - C4): 12%
• Hydrocarbon plastics (PEth, PPrp): 16%
• Acrylic plastic (PMMA): 16%
• Vinyl plastic (PVC): 17%
• Paper: 14%
• Cardboard,: 15%
• Wood: 17%

Baseline intrinsic flammability of Earth’s ecosystems estimated from paleoatmospheric oxygen over the past 350 million years - PMC

We reveal that fire activity would be greatly suppressed below 18.5% O2, entirely switched off below 16% O2, and rapidly enhanced between 19–22% O2. We show that fire activity and, therefore, its influence on the Earth system would have been high during the Carboniferous (350–300 Ma) and Cretaceous (145–65 Ma) periods; intermediate in the Permian (299–251 Ma), Late Triassic (285–201 Ma), and Jurassic (201–145 Ma) periods; and surprisingly low to lacking in the Early–Middle Triassic period between 250–240 Ma.

The present concentration of O2 is 20.9%. The authors restricted themselves to one material: "Pure sphagnum moss peat was used as the fuel because it is highly flammable, easily ignitable, and burns in modern natural fires." They may also have done so because it may be easy to get homogeneous samples.

Land-plant evolution:

• Cooksonia - 430 Mya - height 1 - 3 cm
• Rhynia - 405 Mya - height 15 cm
• Wattieza - 375 Mya - 8 m
• Archaeopteris - 353 Mya - height 24 m

A persistently low level of atmospheric oxygen in Earth’s middle age | Nature Communications - about 1.6% PAL (Present Atmospheric Level) over most of the Proterozoic. It started rising at the base of the Cambrian or a little before, reaching roughly present levels by the mid-Paleozoic.

There is abundant evidence of forest fires only after the Devonian-Carboniferous boundary, some 359 Mya, though there is some evidence of forest and vegetation fires before then - (PDF) Forest Fire in the Fossil Record and  Fossil record of fire

Some of the oldest evidence: A forest fire and soil erosion event during the Late Devonian mass extinction - ScienceDirect - evidence from 372 Mya

 

[lpetrich]

NASA Exoplanet Archive

• All Exoplanets: 5569
• Confirmed Planets Discovered by Kepler: 2778
• Kepler Project Candidates Yet To Be Confirmed: 1984
• Confirmed Planets Discovered by K2: 548
• K2 Candidates Yet To Be Confirmed: 977
• Confirmed Planets Discovered by TESS: 415
• TESS Project Candidates Integrated into Archive: 7027
• Current date TESS Project Candidates at ExoFOP: 7027
• TESS Project Candidates Yet To Be Confirmed: 4583

ExoFOP? The Exoplanet Follow-up Observing Program: ExoFOP | IPAC

Discovery method:

• Transit: 4151
• Radial Velocity: 1075
• Microlensing: 207
• Imaging: 69
• Transit timing variations: 28
• Eclipse timing variations: 17
• Orbital brightness modulations: 9
• Pulsar timing variations: 7
• Astrometry: 3
• Pulsation timing variations: 2
• Disk Kinematics: 1

 

[lpetrich]

Planets with known features:

• Confirmed Planets with mass: 1617
• Confirmed Planets with m*sin(i): 968
• Confirmed Planets with radius: 4127

(no list of planets with both mass and radius known)

By radius:

• R ≤ 1.25 R_Earth: 521
• 1.25 < R ≤ 2 R_Earth: 1063
• 2 < R ≤ 6 R_Earth: 1803
• 6 < R ≤ 15 R_Earth: 610
• 15 R_Earth < R: 200

Mercury 0.383, Mars 0532, Venus 0.949, Earth 1, Neptune 3.88, Uranus 4.01, Saturn 9.45, Jupiter 11.21

By mass:

• M ≤ 3 M_Earth: 83
• 3 < M ≤ 10 M_Earth: 251
• 10 < M ≤ 30 M_Earth: 178
• 30 < M ≤ 100 M_Earth: 157
• 100 < M ≤ 300 M_Earth: 302
• 300 M_Earth < M: 646

Mercury 0.0553, Mars 0.107, Venus 0.815, Earth 1, Uranus 14.5, Neptune 17.1, Saturn 95.2, Jupiter 317.8

 

[lpetrich]

Pre-generated Exoplanet Plots -- the transit-discovered planets have gap in them between terrestrial and Jovian planets. Also, the densities have a V-shaped curve, from high for super-Earths for low near Saturn's mass then high again for more than 10 Jupiter masses.

2024 Exoplanet Archive News mentions discovery of some exoplanets with another resonance chain, even if that chain is not quite as long as that of TRAPPIST-1

 HD 110067 and HD 110067 | NASA Exoplanet Archive and A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067 - NASA/ADS and A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067 | Nature and [2311.17775] A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067

HD 110067 is about 32 parsecs / 105 light-years away from the Solar System, and its mass, radius, and surface temperature are somewhat less than the Sun's, and close to 70 Ophiuchi's.

Mass: 0.798 Msun, radius: 0.788 Rsun, luminosity 0.43 Lsun, surface temperature 5266 K, spectral type K0V, age 8.1 Gyr.

Period of a planet that receives the same amount of light from it than the Earth receives: 220 days (Earth solar days)

The planets have periods from 9 to 55 days, with equilibrium temperatures ranging from 440 K to 800 K. The equivalent number for the Earth is 278 K or 5 C. The outermost planet is thus has Mercury's incoming light.

Their radii are 2.2 to 2.9 Earth radii, and three of their masses are known: 5.0 to 8.5 Earth masses, close to their detection limits. Their densities are 1.6 to 2.9 g/cm^3, meaning that they likely have super oceans or super thick atmospheres.

 

[bilby]

The reason that fluorine is rare as an atmospheric gas is the same reason that oxygen is rare - it's too reactive, so in the absence of a mechanism to release it from its compounds, it simply won't be found in any more than trace quantities.

Earth is the fire planet because it is the oxygen planet.

Earth is the oxygen planet because it is the photosynthesis planet.

Earth is the photosynthesis planet because it is the life bearing planet.

The question "why is Earth the only planet with fire" must have exactly the same answers as "why is the Earth the only planet with life"; And the answer is probably that it isn't the only one, just the only one we have so far detected.

I would argue very strongly that any planet with sufficient atmospheric O₂ to support fire must also have photosynthetic organisms. This makes exoplanet atmospheric spectroscopy a very powerful tool for detecting life; A strong and sustained O₂ signature really cannot have any other cause.

Any free O₂ produced by non-biological means will inevitably react with other elements (carbon, silicon, iron, or whatever else is around) before atmospheric concentrations rise above trace levels. Even as little as 1% O₂ would be a remarkable and inexplicable level to find on a planet without photosynthetic life.

 

[Loren Pechtel]

Any free O₂ produced by non-biological means will inevitably react with other elements (carbon, silicon, iron, or whatever else is around) before atmospheric concentrations rise above trace levels. Even as little as 1% O₂ would be a remarkable and inexplicable level to find on a planet without photosynthetic life.

Scenarios that produce oxygen atmospheres on non-living worlds have been proposed.

Consider a world that was pelted far harder than Earth at the end of the bombardment era. This is an old world from when heavy elements were less common. The core didn't start with at much U and by now it's cooled enough the tectonic activity has stopped. The comets were selectively from an orbit that favored water ice--not far enough out for the hydrocarbons to condense out.

It has far more water than Earth. Now it's warmer than Earth--the upper atmosphere isn't so bitterly cold as on Earth. That bitter cold is an important protection for Earth because water vapor that rises high enough gets photodisassociated and Earth-like worlds can't hold onto hydrogen well at all. (Earth is expected to lose it's oceans to this in a billion years as warming increases the vapor pressure of water in the upper atmosphere.) Note that leaves a lot of free oxygen. The surface materials become fully oxidized, without geologic processes bringing up more material there will eventually be no oxygen sink.

 

[lpetrich]

 Orbital resonance - they are not very common,

Given as ratios of periods of neighbors; listed going outward.

Solar System:

• Sun: Neptune, Pluto: 3/2
• Jupiter: Io, Europa, Ganymede: 2, 2
• Saturn: Mimas, Tethys: 2, Enceladus, Dione: 2, Titan, Hyperion: 4/3

Exoplanets:

• Kepler-88: 2
• HD 41248: 7/5
• Kepler-36: 7/6
• Kepler-1649: 9/4
• Kepler-29: 9/7
• Gliese 876: 2, 2
• Kepler-37: 8/5, 15/8
• V1298 Tauri: 3/2, 2
• HD 158259: 3/2, 3/2, 3/2
• Kepler-223: 4/3, 3/2, 4/3
• K2-32: 2, 9/4, 3/2
• Kepler-80: 3/2, 3/2, 4/3, 3/2
• K2-138: 3/2, 3/2, 3/2, 3/2
• TOI-178: 5/3, 2, 3/2, 3/2, 4/3
• HD 110067: 3/2, 3/2, 3/2, 4/3
• TRAPPIST-1: 8/5, 5/3, 3/2, 3/2, 4/3, 3/2
• Kepler-90: 5/4, 5/3, 4, 3/2, 4/3, 5/3, 8/5

A common ratio is (n+1)/n and less common is (n+2)/n, where n is some positive integer. This is what one would expect from calculations of orbit perturbations.

 

[lpetrich]

NASA Exoplanet Archive

Planetary Systems - every solution a separate entry in the table

Planetary Systems Composite - each planet's entry has every solution for that planet

Stellar Hosts - features of every star with a known exoplanet. From the looks of it, most such stars are main sequence or headed to red-gianthood.

All these tables have the option of plotting their data, and one can enter filters in the text fields in the column numbers. Like >1 for "number of planets" to select every planetary system with more than one known planet.

 

[lpetrich]

The James Webb Space Telescope is proving its worth in studying exoplanets, finding a spectrum by finding a transiting planet's apparent size at different infrared wavelengths. The larger, the more extinction (absorption, scattering) in the planet's atmosphere.

•  WASP-39b
• NASA’s Webb Detects Carbon Dioxide in Exoplanet Atmosphere - NASA
• Identification of carbon dioxide in an exoplanet atmosphere | Nature
• Early Release Science of the exoplanet WASP-39b with JWST NIRISS | Nature
• Early Release Science of the exoplanet WASP-39b with JWST NIRSpec PRISM | Nature
• Early Release Science of the exoplanet WASP-39b with JWST NIRSpec G395H | Nature
• Detection of Carbon Monoxide's 4.6 Micron Fundamental Band Structure in WASP-39b's Atmosphere with JWST NIRSpec G395H - IOPscience
• WASP-39b: a highly inflated Saturn-mass planet orbiting a late G-type star | Astronomy & Astrophysics (A&A)
• Exoplanet WASP-39 b and Its Star (Illustration) | Webb
• Wasp-39b and its parent star (artist’s impression) | ESA/Hubble
• Exoplanet-catalog – Exoplanet Exploration: Planets Beyond our Solar System WASP-39 b
• Planet WASP-39 b

This planetary system is about 700 light years (200 parsecs) away, the star is about the same size and mass and temperature as the Sun, and the planet has roughly the same mass as Saturn. It is a bit larger - a "puffy planet".

It orbits with a period of 4 days, and its surface temperature is around 1200 K (900 C). This is above the  Draper point - 798 K - the temperature where solid materials will become self-luminous. So this planet glows a red-orange.

What did JWST detect evidence of?

Na, H2O, CO, CO2, SO2, though no evidence of CH4

 

[lpetrich]

•  LHS 475 b
• NASA’s Webb Confirms Its First Exoplanet - NASA
• [2301.04191] A JWST transmission spectrum of a nearby Earth-sized exoplanet
• Exoplanet-catalog – Exoplanet Exploration: Planets Beyond our Solar System LHS 475 b
• A JWST transmission spectrum of the nearby Earth-sized exoplanet LHS 475 b | Nature Astronomy

The system is 41 light years / 12 parsecs away, the star is a red dwarf, and the planet is Earth-sized. It orbits its star with a period of 2 days, and its surface temperaure is around 600 K (300 C).

From ArXiv and Nature Astronomy,

With two transit observations, we rule out primordial hydrogen-dominated and cloudless pure methane atmospheres. Thus far, the featureless transmission spectrum remains consistent with a planet that has a high-altitude cloud deck (similar to Venus), a tenuous atmosphere (similar to Mars) or no appreciable atmosphere at all (akin to Mercury).

• [2209.00620] The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b
• JWST’s first direct spectrum of planetary-mass object reveals dynamic atmosphere
• Planet VHS 1256-1257 b

The system is 41 ly (12 pc) away, the star is a red dwarf, and the planet is Jupiter-sized.

Its atmosphere contains H2O, CH4, CO, CO2, Na, K, and silicate clouds: rock dust.

 

[lpetrich]

 List of space telescopes - including telescopes for searching for exoplanets

Lists gamma-ray, X-ray, ultraviolet-light, visible-light, infrared-light, submillimeter, microwave, radio-frequency, and particle-detection ones.

Two exoplanet-observation spacecraft in the works:

 PLATO (spacecraft) - "PLAnetary Transits and Oscillations of stars" - ESA - Plato factsheet - | Planetary Transits and Oscillations of Stars: the ESA M3 mission in the Cosmic Vision 2015-2025 - expected launch date: 2026

 ARIEL - "Atmospheric Remote-sensing Infrared Exoplanet Large-survey" - ESA - Ariel factsheet - Ariel Space Mission – European Space Agency M4 Mission - expected launch date: 2029


ExoClock - a project to monitor transiting exoplanets and ExoClock Project. III. 450 New Exoplanet Ephemerides from Ground and Space Observations - NASA/ADS

They have this format: epoch (reference time), period.

 

[lpetrich]

NASA Exoplanet Archive - my favorite exoplanet archive site

Encyclopaedia of exoplanetary systems - another archive site

Both sites offer the ability to make graphs / plots / charts of their listed planets by various variables, like calculated surface temperaeture and mass.

 

[bilby]

It orbits with a period of 4 days

I assume that the incredibly short orbital periods that seem to be characteristic of exoplanets is an artefact of the detection methods so far used to identify them, but my mind nevertheless boggles at just how fast and close in to their stars these planets seem to be. Particularly for mostly gaseous planets (eg "Hot Jupiters")

Are these abnormal stellar systems, or is ours the outlier? Jupiter's orbital period is a thousand times greater than this, which seems like a jarringly large discreapancy to me.

 

[Shadowy Man]

It orbits with a period of 4 days

I assume that the incredibly short orbital periods that seem to be characteristic of exoplanets is an artefact of the detection methods so far used to identify them, but my mind nevertheless boggles at just how fast and close in to their stars these planets seem to be. Particularly for mostly gaseous planets (eg "Hot Jupiters")

Are these abnormal stellar systems, or is ours the outlier? Jupiter's orbital period is a thousand times greater than this, which seems like a jarringly large discreapancy to me.

Planetary system formation theories, which used to only have one example to compare to, now have to catch up with all the data.

Given the intrinsic biases as you point out it is too early to contextualize any system to know what is “abnormal”.

It would take decades of observation using planet occultations to definitively observe a system similar to the Solar System.

 

[lpetrich]

It orbits with a period of 4 days

I assume that the incredibly short orbital periods that seem to be characteristic of exoplanets is an artefact of the detection methods so far used to identify them, but my mind nevertheless boggles at just how fast and close in to their stars these planets seem to be. Particularly for mostly gaseous planets (eg "Hot Jupiters")

bilby, it's easy to do research on exoplanet orbit periods. They range from a few hours to as much as a million years.

Are these abnormal stellar systems, or is ours the outlier? Jupiter's orbital period is a thousand times greater than this, which seems like a jarringly large discreapancy to me.

There are plenty of known exoplanets with orbit periods around Jupiter's.