How in the world would we detect an exoplanet with a million year orbit? Just about every detection technique is based on observing something periodic about the system. And if you did manage to directly image an exoplanet you have no proof it is really is one and not something that simply lined up.
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- Thread starter lpetrich
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Shadowy Man
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I doubt lpetrich would have made that statement without evidence so I’m sure he’ll be around soon to provide a link to a description of an exoplanet with a million year orbital period.
bilby
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By definition, we cannot detect any exoplanets "in the world"
lpetrich
Contributor
Cool Companions on Ultrawide Orbits - COCONUTS - "is a large-scale survey for wide-orbit planetary and substellar companions considered the first survey of this type of celestial bodies." COCONUTS-2b and Massive COCONUTS exoplanet discovery led by UH grad student | University of Hawaiʻi System News and The Second Discovery from the COCONUTS Program: A Cold Wide-orbit Exoplanet around a Young Field M Dwarf at 10.9 pc - NASA/ADSFrom the abstract,
The star is the M3 dwarf L 34-26
The planet is the T9 dwarf WISEPA J075108.79-763449.6
"Given their common proper motions and parallaxes, these two field objects constitute a physically bound pair with a projected separation of 594″ (6471au)."
No mention of radial velocity, however. Parallax: distance, proper motion: transverse angular velocity.
"The primary star COCONUTS-2A has strong stellar activity (Hα, X-ray, and ultraviolet emission) and is rapidly rotating (Prot = 2.83 days), from which we estimate an age of 150-800 Myr."
Then speculating on how the planet was formed, and ending with "Finally, at a distance of 10.9 pc, COCONUTS-2b is the nearest imaged exoplanet to Earth known to date."
bilby
Fair dinkum thinkum
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The astronomical and space exploration communities sometimes seem to spend more time coming up with "cool" acronyms and initialisms than they do on their real jobs.
Feels like a lot more precision than the observations support. I see no uncertainties given for it's motion numbers and if I didn't mess the envelope up I'm getting an escape velocity from it's host around 300 m/s. I get very suspicious about numbers with no uncertainty and far more precision than could possibly be measured.
From the abstract,
The star is the M3 dwarf L 34-26
The planet is the T9 dwarf WISEPA J075108.79-763449.6
"Given their common proper motions and parallaxes, these two field objects constitute a physically bound pair with a projected separation of 594″ (6471au)."
No mention of radial velocity, however. Parallax: distance, proper motion: transverse angular velocity.
"The primary star COCONUTS-2A has strong stellar activity (Hα, X-ray, and ultraviolet emission) and is rapidly rotating (Prot = 2.83 days), from which we estimate an age of 150-800 Myr."
Then speculating on how the planet was formed, and ending with "Finally, at a distance of 10.9 pc, COCONUTS-2b is the nearest imaged exoplanet to Earth known to date."
Wikipedia gives a radial velocity.
Shadowy Man
Contributor
Hehe... I've sat around some acronym brainstorming sessions, indeed. However, I have always felt it was poor form to use letters from the middle or ends of words.
lpetrich
Contributor
The density difference of sub-Neptunes finally deciphered
noting
Resonant sub-Neptunes are puffier | Astronomy & Astrophysics (A&A)
Solar-System reference:
Planetary Fact Sheet - Ratio to Earth
To measure a planet's mean density, one needs both its mass and its radius. Its radius comes from transit depth (how much of its star's light that it blocked) and its mass from radial velocity, from the planet pulling on its star, or from transit timing variations, from the planet pulling on other planets. The latter effect can be amplified into observability by orbital resonances, which make a planet speed up over several orbits, then slow down over several orbits.
A curious result is that TTV-measured planet masses tend to be less than RV-measured planet masses for the same radius. Furthermore, the RV-measured planet masses have more scatter than the TTV-measured ones.
The authors address the question of whether this difference is a result of observational selection, of which ones are easier to observe than which other ones, and they conclude that it is real.
They then conclude that the difference is a result of different early histories. They propose that most planetary systems go through a phase of planets in orbital resonances, but that most of these resonances are not very stable over long times. When they go unstable, planets end up in orbits where they collide with each other, forming larger planets with higher densities than similar-mass originally-formed ones. This is because an originally-formed planet may have a thick layer of volatiles, while one formed by collisions would form from planets with much less.
noting
Resonant sub-Neptunes are puffier | Astronomy & Astrophysics (A&A)
Solar-System reference:
Planetary Fact Sheet - Ratio to Earth
To measure a planet's mean density, one needs both its mass and its radius. Its radius comes from transit depth (how much of its star's light that it blocked) and its mass from radial velocity, from the planet pulling on its star, or from transit timing variations, from the planet pulling on other planets. The latter effect can be amplified into observability by orbital resonances, which make a planet speed up over several orbits, then slow down over several orbits.
A curious result is that TTV-measured planet masses tend to be less than RV-measured planet masses for the same radius. Furthermore, the RV-measured planet masses have more scatter than the TTV-measured ones.
The authors address the question of whether this difference is a result of observational selection, of which ones are easier to observe than which other ones, and they conclude that it is real.
They then conclude that the difference is a result of different early histories. They propose that most planetary systems go through a phase of planets in orbital resonances, but that most of these resonances are not very stable over long times. When they go unstable, planets end up in orbits where they collide with each other, forming larger planets with higher densities than similar-mass originally-formed ones. This is because an originally-formed planet may have a thick layer of volatiles, while one formed by collisions would form from planets with much less.
lpetrich
Contributor
Super-Earths and sub-Neptunes explained by planetary migration - Earth.com
noting
A radius valley between migrated steam worlds and evaporated rocky cores | Nature Astronomy
That radius valley is 2 Earth radii, where planets are relatively rare. Below that size: super-Earths. Above that size: sub-Neptunes.
Abstract of the Nature paper:
noting
A radius valley between migrated steam worlds and evaporated rocky cores | Nature Astronomy
That radius valley is 2 Earth radii, where planets are relatively rare. Below that size: super-Earths. Above that size: sub-Neptunes.
Abstract of the Nature paper:
Sub-Neptunes have a lot of H2O, H2, and He. They form at much larger distances, and they may then spiral inward, much like "hot Jupiters".
lpetrich
Contributor
[2406.04311] From super-Earths to sub-Neptunes: Observational constraints and connections to theoretical models
Earthlike planets go to roughly 2 Re and 10 Me.
Neptune-like planets go from roughly 2 Re and 5 Me to roughly 11 Re and 100 Me.
Jupiter-like planets continue at radius 11 Re. So Jupiter is almost as large as a planet can be, even if not the most massive.
Solar System: Moon 0.2724 0.0123, Mercury 0.383 0.0553, Mars 0.2724 0.0123, Venus 0.949 0.815, Earth 1 1 (reference), Uranus 4.01 14.5, Neptune 3.88 17.1, Saturn 9.45 95.2, Jupiter 11.21 317.8
Their fit of planets' masses and radii to some power laws:
(radius) ~ (mass)^p for p ~ 0.28 for Earthlike planets, 0.61 for Neptune-like planets, and 0.01 for Jovian planets
(mass) ~ (radius)^p where p ~ 3.57 for Earthlike planets and 1.49 for Neptune-like planets.
This is consistent with Earthlike planets being mostly rocky with some compression, and with Neptune-like planets being more and more volatiles with increasing mass.
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They also consider the distribution of planets from Earth size to Neptune size, and they find that F, G, and K main-sequence stars have similar distributions, with a lot of super-Earths and sub-Neptunes, and that M stars have mostly Earth-size planets and super-Earths.
This says something about differences in how planets form.
A complication in such an assessment is where the planets are relative to the star's habitable zone. Those that are easily observable for M stars are in or near their star's habitable zone, while those that are easily observable for Sunlike stars (spectral class G2V) are well inside the star's habitable zone.
Earthlike planets go to roughly 2 Re and 10 Me.
Neptune-like planets go from roughly 2 Re and 5 Me to roughly 11 Re and 100 Me.
Jupiter-like planets continue at radius 11 Re. So Jupiter is almost as large as a planet can be, even if not the most massive.
Solar System: Moon 0.2724 0.0123, Mercury 0.383 0.0553, Mars 0.2724 0.0123, Venus 0.949 0.815, Earth 1 1 (reference), Uranus 4.01 14.5, Neptune 3.88 17.1, Saturn 9.45 95.2, Jupiter 11.21 317.8
Their fit of planets' masses and radii to some power laws:
(radius) ~ (mass)^p for p ~ 0.28 for Earthlike planets, 0.61 for Neptune-like planets, and 0.01 for Jovian planets
(mass) ~ (radius)^p where p ~ 3.57 for Earthlike planets and 1.49 for Neptune-like planets.
This is consistent with Earthlike planets being mostly rocky with some compression, and with Neptune-like planets being more and more volatiles with increasing mass.
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They also consider the distribution of planets from Earth size to Neptune size, and they find that F, G, and K main-sequence stars have similar distributions, with a lot of super-Earths and sub-Neptunes, and that M stars have mostly Earth-size planets and super-Earths.
This says something about differences in how planets form.
A complication in such an assessment is where the planets are relative to the star's habitable zone. Those that are easily observable for M stars are in or near their star's habitable zone, while those that are easily observable for Sunlike stars (spectral class G2V) are well inside the star's habitable zone.
lpetrich
Contributor
List of exoplanet search projects includes several of them that are in various stages of proposal, planning, design, and construction. TOLIMAN - "The TOLIMAN (Telescope for Orbit Locus Interferometric Monitoring of our Astronomical Neighbourhood) space telescope is a low-cost mission concept aimed at detecting of exoplanets via the astrometry method, and specifically targeting the Alpha Centauri system." - late this year? PLATO (spacecraft) Nancy Grace Roman Space Telescope - "The Nancy Grace Roman Space Telescope (shortened as Roman or the Roman Space Telescope, and formerly the Wide-Field Infrared Survey Telescope or WFIRST) is a NASA infrared space telescope in development and scheduled to launch to a Sun–Earth L2 orbit by May 2027.[5]" ARIEL - "The Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) is a space telescope and the fourth medium-class mission of the European Space Agency's Cosmic Vision programme. The mission is aimed at observing at least 1000 known exoplanets using the transit method, studying and characterising the planets' chemical composition and thermal structures." - 2029
lpetrich
Contributor
Why is JWST Having So Much Trouble with the TRAPPIST-1 System? - Universe Today
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Roadmap details how to improve exoplanet exploration using the JWST | MIT News | Massachusetts Institute of Technology
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A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST | Nature Astronomy
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Roadmap details how to improve exoplanet exploration using the JWST | MIT News | Massachusetts Institute of Technology
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A roadmap for the atmospheric characterization of terrestrial exoplanets with JWST | Nature Astronomy
Because of starspots and the like.