Thread: Disintegrating Planets - some recent news

1. Disintegrating asteroid 6478 Gault: all the details

https://arxiv.org/abs/1907.06643

Physical Characterization of Active Asteroid (6478) Gault

Juan A. Sanchez, et al. (Submitted on 15 Jul 2019)

Main belt asteroid (6478) Gault has been dynamically linked with two overlapping asteroid families: Phocaea, dominated by S-type asteroids, and Tamara, dominated by low-albedo C-types. This object has recently become an interesting case for study, after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. Previous authors have proposed that the most likely scenarios to explain the observed activity on Gault were rotational excitation or merger of near-contact binaries. Here we use new photometric and spectroscopic data of Gault to determine its physical and compositional properties. Lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. Using WISE observations of Gault and the near-Earth Asteroid Thermal Model (NEATM) we determined that this asteroid has a diameter <6 km. NIR spectroscopic data obtained with the Infrared Telescope Facility (IRTF) showed a spectrum similar to that of S-complex asteroids, and a surface composition consistent with H chondrite meteorites. These results favor a compositional affinity between Gault and asteroid (25) Phocaea, and rules out a compositional link with the Tamara family. From the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes.

2. Disintegrating asteroid 6478 Gault turns out to be a blue Q, a silicate type, once the dust comes off.

https://arxiv.org/abs/1907.10077
Last edited by Roger E. Moore; 2019-Jul-26 at 04:52 PM. Reason: Fix url

3. Our old buddy WASP-12b is coming apart just everywhere, starting with the atmosphere.

https://arxiv.org/abs/1908.02527

Modelling atmospheric escape and MgII near-ultraviolet absorption of the highly irradiated hot Jupiter WASP-12b
N. K. Dwivedi, et al. (Submitted on 7 Aug 2019)

We present two-dimensional multi-fluid numerical modelling of the upper atmosphere of the hot Jupiter WASP-12b. The model includes hydrogen chemistry, and self-consistently describes the expansion of the planetary upper atmosphere and mass loss due to intensive stellar irradiation, assuming a weakly magnetized planet. We simulate the planetary upper atmosphere and its interaction with the stellar wind (SW) with and without the inclusion of tidal force and consider different XUV irradiation conditions and SW parameters. With the inclusion of tidal force, even for a fast SW, the escaping planetary material forms two streams, propagating towards and away from the star. The atmospheric escape and related mass loss rate reaching the value of 10^12 gs^-1 appear to be mostly controlled by the stellar gravitational pull. We computed the column density and dynamics of MgII ions considering three different sets of SW parameters and XUV fluxes. The simulations enable to compute the absorption at the position of the Mg h line and to reproduce the times of ingress and egress. In case of a slow SW and without accounting for tidal force, the high orbital velocity leads to the formation of a shock approximately in the direction of the planetary orbital motion. In this case, mass loss is proportional to the stellar XUV flux. At the same time, ignoring of tidal effects for WASP-12b is a strong simplification, so the scenario with a shock, altogether is an unrealistic one.

4. Short paper on how we can find our fate: detecting dying planets around white dwarfs

https://arxiv.org/pdf/1911.07889.pdf

The Search for Planet and Planetesimal Transits of White Dwarfs with the Zwicky Transient Facility
Keaton J. Bell

Planetary materials orbiting white dwarf stars reveal the ultimate fate of the planets of the Solar System and all known transiting exoplanets. Observed metal pollution and infrared excesses from debris disks support that planetary systems or their remnants are common around white dwarf stars; however, these planets are diﬃcult to detect since a very high orbital inclination angle is required for a small white dwarf to be transited, and these transits have very short (minute) durations. The low odds of catching individual transits could be overcome by a suﬃciently wide and fast photometric survey. I demonstrate that, by obtaining over 100 million images of white dwarf stars with 30-second exposures in its ﬁrst three years, the Zwicky Transient Facility (ZTF) is likely to record the ﬁrst exoplanetary transits of white dwarfs, as well as new systems of transiting, disintegrating planetesimals. In these proceedings, I describe my project strategy to discover these systems using the ZTF data.

5. For the first time, astronomers are positive they've found a planet whose orbit is decaying... and it's our old friend, WASP-12b, falling into a blazing type F sun.

https://arxiv.org/abs/1911.09131

The Orbit of WASP-12b is Decaying
Samuel W. Yee, Joshua N. Winn, Heather A. Knutson, Kishore C. Patra, Shreyas Vissapragada, Michael M. Zhang, Matthew J. Holman, Avi Shporer, Jason T. Wright
(Submitted on 20 Nov 2019)

WASP-12b is a transiting hot Jupiter on a 1.09-day orbit around a late-F star. Since the planet's discovery in 2008, the time interval between transits has been decreasing by 29 ± 2 msec year−1. This is a possible sign of orbital decay, although the previously available data left open the possibility that the planet's orbit is slightly eccentric and is undergoing apsidal precession. Here, we present new transit and occultation observations that provide more decisive evidence for orbital decay, which is favored over apsidal precession by a ΔBIC of 22.3 or Bayes factor of 70,000. We also present new radial-velocity data that rule out the Rømer effect as the cause of the period change. This makes WASP-12 the first planetary system for which we can be confident that the orbit is decaying. The decay timescale for the orbit is P/P˙=3.25 ± 0.23 Myr. Interpreting the decay as the result of tidal dissipation, the modified stellar tidal quality factor is Q′⋆=1.8 × 10^5.

6. Three just-discovered papers on disintegrating planets, familiar and new.

The dynamical history of the evaporating or disrupted ice giant planet around white dwarf WD J0914+1914
Veras, Dimitri; Fuller, Jim

Robust evidence of an ice giant planet shedding its atmosphere around the white dwarf WD J0914+1914 represents a milestone in exoplanetary science, allowing us to finally supplement our knowledge of white dwarf metal pollution, debris discs and minor planets with the presence of a major planet. Here, we discuss the possible dynamical origins of this planet, WD J0914+1914b. The very young cooling age of the host white dwarf (13 Myr) combined with the currently estimated planet-star separation of about 0.07 au imposes particularly intriguing and restrictive coupled constraints on its current orbit and its tidal dissipation characteristics. The planet must have been scattered from a distance of at least a few au to its current location, requiring the current or former presence of at least one more major planet in the system. We show that WD J0914+1914b could not have subsequently shrunk its orbit through chaotic f-mode tidal excitation (characteristic of such highly eccentric orbits) unless the planet was or is highly inflated and had at least partially thermally self-disrupted from mode-based energy release. We also demonstrate that if the planet is currently assumed to reside on a near-circular orbit at 0.07 au, then non-chaotic equilibrium tides impose unrealistic values for the planet's tidal quality factor. We conclude that WD J0914+1914b either resembles a disrupted "Super-Puff" whose remains reside on a circular orbit, or a larger or denser ice giant on a currently eccentric orbit. Distinguishing these two possibilities strongly motivates follow-up observations.

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An apparently eccentric orbit of the exoplanet WASP-12 b as a radial velocity signature of planetary-induced tides in the host star
Maciejewski, Gracjan; Niedzielski, Andrzej; Villaver, Eva; Konacki, Maciej; Pawlaszek, Rafal K.

Massive exoplanets on extremely tight orbits, such as WASP-12 b, induce equilibrium tides in their host stars. Following the orbital motion of the planet, the tidal fluid flow in the star can be detected with the radial velocity method. Its signature manifests as the second harmonics of the orbital frequency that mimics a non-zero orbital eccentricity. Using the new radial velocity measurements acquired with the HARPS-N spectrograph at the Telescopio Nazionale Galileo and combining them with the literature data, we show that the apparent eccentricity of WASP-12 b's orbit is non-zero at a 5.8 sigma level, and the longitude of periastron of this apparently eccentric orbit is close to 270 degrees. This orbital configuration is compatible with a model composed of a circular orbit and a signature of tides raised in the host star. The radial velocity amplitude of those tides was found to be consistent with the equilibrium tide approximation. The tidal deformation is predicted to produce a flux modulation with an amplitude of 80 ppm which could be detected using space-born facilities.

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Hot Jupiters Are Destroyed by Tides While Their Host Stars Are on the Main Sequence
Hamer, Jacob H.; Schlaufman, Kevin C.

While cooler giant planets are often observed with nonzero eccentricities, the short-period circular orbits of hot Jupiters suggest that they lose orbital energy and angular momentum due to tidal interactions with their host stars. However, orbital decay has never been unambiguously observed. We use data from Gaia Data Release 2 to show that hot Jupiter host stars have a smaller Galactic velocity dispersion than a similar population of stars without hot Jupiters. Since Galactic velocity dispersion is correlated with age, this observation implies that the population of hot Jupiter host stars is on average younger than the field population. The best explanation for this inference is that tidal interactions cause hot Jupiters to inspiral while their host stars are on the main sequence. This observation requires that the typical modified stellar tidal quality factor {Q}* {\prime } for solar-type stars is in the range {log}}10{Q}* {\prime }≲ 7.

7. Join Date
Dec 2019
Posts
46
Without experiments all these hypotheses about exoplanets are just noise.

Sent from my A502DL using Tapatalk

8. Originally Posted by showmeonthedollwhere
Without experiments all these hypotheses about exoplanets are just noise.
Could you please explain what sort of experiment we could carry out that would satisfy you?

9. Two papers on the destruction of giant, Jovian-type planets in white dwarf systems.

https://arxiv.org/abs/1912.02345
Cold giant planets evaporated by hot white dwarfs
Matthias R. Schreiber, Boris T. Gaensicke, Odette Toloza, Mercedes-S. Hernandez, Felipe Lagos
(Submitted on 5 Dec 2019)
Atmospheric escape from close-in Neptunes and hot Jupiters around sun-like stars driven by extreme ultraviolet (EUV) irradiation plays an important role in the evolution of exo-planets and in shaping their ensemble properties. Intermediate and low mass stars are brightest at EUV wavelengths at the very end of their lives, after they have expelled their envelopes and evolved into hot white dwarfs. Yet the effect of the intense EUV irradiation of giant planets orbiting young white dwarfs has not been assessed. We show that the giant planets in the solar system will experience significant hydrodynamic escape caused by the EUV irradiation from the white dwarf left behind by the Sun. A fraction of the evaporated volatiles will be accreted by the solar white dwarf, resulting in detectable photospheric absorption lines. As a large number of the currently known extra-solar giant planets will survive the metamorphosis of their host stars into white dwarfs, observational signatures of accretion from evaporating planetary atmospheres are expected to be common. In fact, one third of the known hot single white dwarfs show photospheric absorption lines of volatile elements, which we argue are indicative of ongoing accretion from evaporating planets. The fraction of volatile contaminated hot white dwarfs strongly decreases as they cool. We show that accretion from evaporating planetary atmospheres naturally explains this temperature dependence if more than 50 per cent of hot white dwarfs still host giant planets.

https://arxiv.org/abs/1912.01611
Accretion of a giant planet onto a white dwarf
Boris T. Gaensicke, Matthias R. Schreiber, Odette Toloza, Nicola P. Gentile Fusillo, Detlev Koester, Christopher J. Manser
(Submitted on 3 Dec 2019)
The detection of a dust disc around G29-38 and transits from debris orbiting WD1145+017 confirmed that the photospheric trace metals found in many white dwarfs arise from the accretion of tidally disrupted planetesimals. The composition of these planetesimals is similar to that of rocky bodies in the inner solar system. Gravitationally scattering planetesimals towards the white dwarf requires the presence of more massive bodies, yet no planet has so far been detected at a white dwarf. Here we report optical spectroscopy of a ≃27750 K hot white dwarf that is accreting from a circumstellar gaseous disc composed of hydrogen, oxygen, and sulphur at a rate of ≃3.3 × 10^9 gs−1. The composition of this disc is unlike all other known planetary debris around white dwarfs, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with H2O and H2S being major constituents. A giant planet orbiting a hot white dwarf with a semi-major axis of ≃15 solar radii will undergo significant evaporation with expected mass loss rates comparable to the accretion rate onto the white dwarf. The orbit of the planet is most likely the result of gravitational interactions, indicating the presence of additional planets in the system. We infer an occurrence rate of spectroscopically detectable giant planets in close orbits around white dwarfs of ≃10^−4.

10. Good overview of disintegrating KELT-9b, with GIF-like art of KELT-9b going around its parent star.

https://www.jpl.nasa.gov/news/news.php?feature=7583

11. An asteroid around a white dwarf that may have torn itself to pieces.

https://arxiv.org/abs/2001.08223

Constraining the origin of the planetary debris surrounding ZTF J0139+5245 through rotational fission of a triaxial asteroid
Dimitri Veras, Catriona H. McDonald, Valeri V. Makarov
(Submitted on 22 Jan 2020)

White dwarfs containing orbiting planetesimals or their debris represent crucial benchmarks by which theoretical investigations of post-main-sequence planetary systems may be calibrated. The photometric transit signatures of likely planetary debris in the ZTF J0139+5245 white dwarf system has an orbital period of about 110 days. An asteroid which breaks up to produce this debris may spin itself to destruction through repeated close encounters with the star without entering its Roche radius and without influence from the white dwarf's luminosity. Here, we place coupled constraints on the orbital pericentre (q) and the ratio (β) of the middle to longest semiaxes of a triaxial asteroid which disrupts outside of this white dwarf's Roche radius (r Roche) soon after attaining its 110-day orbit. We find that disruption within tens of years is likely when β ≲ 0.6 and q ≈ 1.0−2.0 r Roche, and when β ≲ 0.2 out to q≈2.5 r Roche. Analysing the longer-timescale disruption of triaxial asteroids around ZTF J0139+5245 is desirable but may require either an analytical approach relying on ergodic theory or novel numerical techniques.
Last edited by Roger E. Moore; 2020-Jan-25 at 01:57 PM.

12. Asteroids (and planets?) can be reduced to millimeter-sized debris by repeated close approaches to their stars.

https://arxiv.org/abs/2001.09839

Supercatastrophic disruption of asteroids in the context of SOHO comet, fireball and meteor observations
Paul Wiegert, Peter Brown, Petr Pokorný, Quanzhi Ye, Cole Gregg, Karina Lenartowicz, Zbigniew Krzeminski, David Clark
(Submitted on 27 Jan 2020)

Granvik et al. (2016) report an absence of asteroids on orbits with perihelia near the Sun that they attribute to the 'supercatastrophic disruption' of these bodies. Here we investigate whether there is evidence for this process among other bodies with similarly low perihelia: near-Earth asteroids, SOHO comets, as well as meter-sized and millimeter-sized meteoroids. We determine no known near-Earth asteroids have past (last 10^4 years) histories residing significantly inside the Granvik et al. (2016) limit, indirectly supporting the disruption hypothesis. The exception is asteroid (467372) 2004 LG which spent 2500 years within this limit, and thus presents a challenge to that theory. Phaethon has a perihelion distance hovering just above the limit and may be undergoing slow disruption, which may be the source of its dust complex. We find that the rate at which ungrouped SOHO comets are observed is consistent with expected rates for the injection of small (25 m) class asteroids into the near-Sun region and suggest that this fraction of the SOHO-observed comet population may in fact be asteroidal in origin. We also find that there is an absence of meter-sized bodies with near-Sun perihelia but an excess of millimeter-sized meteoroids. This implies that if near-Sun asteroids disrupt, they do not simply fragment into meter-sized chunks but disintegrate ultimately into millimeter-sized particles. We propose that the disruption of near-Sun asteroids as well as the anomalous brightening and destruction processes that affect SOHO comets occur through meteoroid erosion, that is, the removal of material through impacts by high-speed near-Sun meteoroids.

13. An ice giant comes apart as it closely orbits a white dwarf star--the first giant planet seen to do this with a WD sun.

https://arxiv.org/abs/1912.02199

The dynamical history of the evaporating or disrupted ice giant planet around white dwarf WD J0914+1914
Dimitri Veras, Jim Fuller
(Submitted on 4 Dec 2019 (v1), last revised 30 Jan 2020 (this version, v2))

Robust evidence of an ice giant planet shedding its atmosphere around the white dwarf WD J0914+1914 represents a milestone in exoplanetary science, allowing us to finally supplement our knowledge of white dwarf metal pollution, debris discs and minor planets with the presence of a major planet. Here, we discuss the possible dynamical origins of this planet, WD J0914+1914 b. The very young cooling age of the host white dwarf (13 Myr) combined with the currently estimated planet-star separation of about 0.07 au imposes particularly intriguing and restrictive coupled constraints on its current orbit and its tidal dissipation characteristics. The planet must have been scattered from a distance of at least a few au to its current location, requiring the current or former presence of at least one more major planet in the system in the absence of a hidden binary companion. We show that WD J0914+1914 b could not have subsequently shrunk its orbit through chaotic f-mode tidal excitation (characteristic of such highly eccentric orbits) unless the planet was or is highly inflated and possibly had partially thermally self-disrupted from mode-based energy release. We also demonstrate that if the planet is currently assumed to reside on a near-circular orbit at 0.07 au, then non-chaotic equilibrium tides impose unrealistic values for the planet's tidal quality factor. We conclude that WD~J0914+1914~b either (i) actually resides interior to 0.07 au, (ii) resembles a disrupted "Super-Puff" whose remains reside on a circular orbit, or (iii) resembles a larger or denser ice giant on a currently eccentric orbit. Distinguishing these three possibilities strongly motivates follow-up observations.

14. Stars might eventually destroy the majority of all asteroids in the cosmos from radiation alone.

https://www.sciencedaily.com/release...0210112236.htm

15. DMPP-1, a star with an ultrahot planet bleeding its atmosphere into space.

https://exoplanets.nasa.gov/news/162...m-is-bleeding/

16. A review paper on disintegrating exoplanets and what they can tell us.

https://arxiv.org/abs/2002.10370

Extrasolar enigmas: from disintegrating exoplanets to exoasteroids
Jan Budaj, Petr Kabath, Enric Palle
(Submitted on 24 Feb 2020)

Thousands of transiting exoplanets have been discovered to date, thanks in great part to the {\em Kepler} space mission. As in all populations, and certainly in the case of exoplanets, one finds unique objects with distinct characteristics. Here we will describe the properties and behaviour of a small group of disintegrating' exoplanets discovered over the last few years (KIC 12557548b, K2-22b, and others). They evaporate, lose mass unraveling their naked cores, produce spectacular dusty comet-like tails, and feature highly variable asymmetric transits. Apart from these exoplanets, there is observational evidence for even smaller exo-'objects orbiting other stars: exoasteroids and exocomets. Most probably, such objects are also behind the mystery of Boyajian's star. Ongoing and upcoming space missions such as {\em TESS} and PLATO will hopefully discover more objects of this kind, and a new era of the exploration of small extrasolar systems bodies will be upon us.

17. Asteroid Phaethon, falling apart due to the speed of its spin.

https://arxiv.org/abs/2003.03495

Mass shedding activities of Asteroid (3200) Phaethon enhanced by its rotation
Ryota Nakano, Masatoshi Hirabayashi
(Submitted on 7 Mar 2020)

Asteroid (3200) Phaethon, a B-type asteroid, has been active during its perihelion passages. This asteroid is considered to be a source of the Geminid meteor stream. It is reported that this asteroid is spinning at a rotation period of 3.60 hr and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of 6.25 km. Here, we report that Phaethon's rotation state may be close to or above its critical rotation period when the bulk density is 0.5 − 1.5 g/cm^3 (a typical bulk density of a B-type asteroid). We found that in this condition, the structure of Phaethon is sensitive to failure unless the cohesive strength is ∼50 Pa − ∼260 Pa. This result implies that if there are some surface processes driven by, for example, thermal waves, large-scaled deformation may happen and cause mass shedding. From this interpretation, we propose the processes that produced the Geminid meteor stream in the past and dust tails recently. Phaethon initially rotated at a spin period shorter than the current period. The magnitude of structural deformation at this stage was higher than the present spin condition, and a large mass shedding event, i.e., the Geminid meteor stream, occurred. After this deformation process, the body became more oblate, and its spin slowed down. At this point, while the spin was high enough for the body to have mass shedding events, the magnitude of these events became small.

18. What do you call the study of "dead" planets?

https://arxiv.org/abs/2003.08410

Necroplanetology: Simulating the Tidal Disruption of Differentiated Planetary Material Orbiting WD 1145+017
Girish M. Duvvuri, Seth Redfield, Dimitri Veras
(Submitted on 18 Mar 2020)

The WD 1145+017 system shows irregular transit features that are consistent with the tidal disruption of differentiated asteroids with bulk densities < 4 g cm^−3 and bulk masses ≲ 10^21 kg (Veras et al., 2017; arXiv:1610.06926). We use the open-source N-body code REBOUND (Rein and Liu, 2011; arXiv:1110.4876) to simulate this disruption with different internal structures: varying the core volume fraction, mantle/core density ratio, and the presence/absence of a thin low-density crust. We allow the rubble pile to partially disrupt and capture lightcurves at a specific point during the disruption at cadences comparable to those from ground-based photometry. As a proof-of-concept we show that varying these structural parameters have observationally distinguishable effects on the transit light curve as the asteroid is disrupted and compare the simulation-generated lightcurves to data from Gary et al., 2017 (arXiv:1608.00026). With the caveat that our simulations do not model the sublimation in detail or account for its effects on orbital evolution, we find that a low core fraction and low mantle/core density ratio asteroid is most consistent with the stable transit feature present for multiple weeks circa April 2016 (referred to as G6121 in Gary et al., 2017 (arXiv:1608.00026) and A1 in Hallakoun et al., 2017 (arXiv:1702.05483). Connecting tidal disruption simulations to photometry suggests characteristics for the interior structure and composition of an exoplanetary body, information that is only possible because we are observing the death of the planetary system in action. All-sky survey missions such as TESS and LSST will be able to detect other systems like WD 1145+017, creating a sample of subjects for a new subfield of planetary science: necroplanetology.

19. Giant planets eaten by red giants

https://arxiv.org/abs/2003.11499
Giants eating giants: Mass loss and giant planets modifying the luminosity of the Tip of the Giant Branch
Raul Jimenez, Uffe Grae Jorgensen, Licia Verde
(Submitted on 25 Mar 2020)
During the red giant phase, stars loose mass at the highest rate since birth. The mass-loss rate is not fixed, but varies from star-to-star by up to 5%, resulting in variations of the star's luminosity at the tip of the red giant branch (TRGB). Also, most stars, during this phase, engulf part of their planetary system, including their gas giant planets. Gas giant planet masses range between 0.1 to 2% of the host star mass. The engulfing of their gas giants planets can modify their luminosity at the TRGB, i.e. the point at which the He-core degeneracy is removed. We show that the increase in mass of the star by the engulfing of the gas giant planets only modifies the luminosity of a star at the TRGB by less than 0.1%, while metallicity can modify the luminosity of a star at the TRGB by up to 0.5%. However, the increase in turbulence of the convective envelope of the star, i.e., modification of the mixing length, has a more dramatic effect, on the star's luminosity, which we estimate could be as large as 5%. The effect is always in the direction to increase the turbulence and thus the mixing length which turns into a systematic decrease of the luminosity of the star at the TRGB. We find that the star-to-star variation of the mass-loss rate will dominate the variations in the luminosity of the TRGB with a contribution at the 5% level. If the star-to-star variation is driven by environmental effects --as it is reasonable to assume--, the same effects can potentially create an environmentally-driven mean effect on the luminosity of the tip of the red giant branch of a galaxy. Finally, we touch upon how to infer the frequency, and identify the engulfment, of exoplanets in low-metallicity RGB stars through high resolution spectroscopy as well as how to quantify mass loss rate distributions from the morphology of the horizontal branch.

20. Evaluative comment: I had not expected that there were so many ways of destroying whole planets, from asteroids to gas giants. To actually have proof of them being destroying, even more amazing.

21. Planets eaten by red giants might cause the giant to shine less, become dimmer.

https://www.sciencenews.org/article/...-less-brightly

22. If the planet itself is not disintegrating, per se, its atmosphere certainly can.

https://arxiv.org/abs/2002.06466
Coupled Thermal and Compositional Evolution of Photo Evaporating Planet Envelopes
Isaac Malsky, Leslie A. Rogers
Photo-evaporative mass loss sculpts the atmospheric evolution of tightly-orbiting sub-Neptune-mass exoplanets. To date, models of the mass loss from warm Neptunes have assumed that the atmospheric abundances remain constant throughout the planet's evolution. However, the cumulative effects of billions of years of escape modulated by diffusive separation and preferential loss of hydrogen can lead to planetary envelopes that are enhanced in helium and metals relative to hydrogen (Hu et al. 2015). We have performed the first self-consistent calculations of the coupled thermal, mass-loss, and compositional evolution of hydrogen-helium envelopes surrounding sub-Neptune mass planets. We extended the MESA (Modules for Experiments in Stellar Astrophysics) stellar evolution code to model the evolving envelope abundances of photo-evaporating planets. We find that GJ 436b, the planet that originally inspired Hu et al. (2015) to propose the formation of helium enhanced planetary atmospheres, requires a primordial envelope that is too massive to become helium enhanced. Nonetheless, we show that helium enhancement is possible for planets with masses similar to GJ 436b after only several Gyr of mass loss. These planets have Rp≲3.00 R⊕, initial fenv<0.5%, irradiation flux ∼10^1-10^3 times that of Earth, and obtain final helium fractions in excess of Y=0.40 in our models. The results of preferential envelope loss may have observable consequences on mass-radius relations and atmospheric spectra for sub-Neptune populations.

23. Just noticed that Wikipedia has a page on Disrupted Planets, pretty much what we're talking about here but with a few new additions. Worth a look if you are into the topic. Star names I had not heard before.

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

24. Et tu, Fomalhaut b?

New HST data and modeling reveal a massive planetesimal collision around Fomalhaut
Authors: Andras Gaspar and George H. Rieke

The apparent detection of an exoplanet orbiting Fomalhaut was announced in 2008. However, subsequent observations of Fomalhaut b raised questions about its status: Unlike other exoplanets, it is bright in the optical and nondetected in the infrared, and its orbit appears to cross the debris ring around the star without the expected gravitational perturbations. We revisit previously published data and analyze additional Hubble Space Telescope (HST) data, finding that the source is likely on a radial trajectory and has faded and become extended. Dynamical and collisional modeling of a recently produced dust cloud yields results consistent with the observations. Fomalhaut b appears to be a directly imaged catastrophic collision between two large planetesimals in an extrasolar planetary system. Similar events should be very rare in quiescent planetary systems of the age of Fomalhaut, suggesting that we are possibly witnessing the effects of gravitational stirring due to the orbital evolution of hypothetical planet(s) around the star.

25. Originally Posted by ngc3314
Et tu, Fomalhaut b?
New HST data and modeling reveal a massive planetesimal collision around Fomalhaut
Authors: Andras Gaspar and George H. Rieke
Never, ever, name a planet after a Cthulhu deity, or the planet will explode. (It was called Dagon.)

26. Our old disintegrating buddy KELT-9b is back and still losing mass.

https://arxiv.org/abs/2004.13733
Mass loss rate and local thermodynamic state of KELT-9 b thermosphere from the hydrogen Balmer series
A. Wyttenbach, P. Mollière, D. Ehrenreich, H. M. Cegla, V. Bourrier, C. Lovis, L. Pino, R. Allart, J. V. Seidel, H. J. Hoeijmakers, L. D. Nielsen, B. Lavie, F. Pepe, X. Bonfils, I. A. G. Snellen
[Submitted on 28 Apr 2020]
KELT-9 b, the hottest known exoplanet with Teq ∼4400K, is the archetype of the new planet class of ultra hot Jupiters. These exoplanets are thought to have an atmosphere dominated by neutral and ionized atomic species. Particularly, the Hα and Hβ Balmer lines have been detected in the KELT-9b upper atmosphere, suggesting that the hydrogen is filling the planetary Roche lobe and escapes from the planet. [Paper goes on to estimate mass loss from stellar irradiation.]
Last edited by Roger E. Moore; 2020-May-01 at 01:10 AM.

27. More on KELT-9b, the ultra-hot Jupiter in a polar orbit over a fast-spinning A-type star. This should have been on Star Trek.

https://arxiv.org/abs/2004.14812
KELT-9 b's Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin-Orbit Misalignment
John P. Ahlers, Marshall C. Johnson, Keivan G Stassun, Knicole D. Colon, Jason W. Barnes, Daniel J. Stevens, Thomas Beatty, B. Scott Gaudi, Karen A. Collins, Joseph Rodriguez, George Ricker, Roland Vanderspek, David Latham, Sara Seager, Joshua Winn, Jon M. Jenkins, Douglas A. Caldwell, Robert F. Goeke, Hugh P. Osborn, Martin Paegert, Pam Rowden, Peter Tenenbaum
[Submitted on 28 Apr 2020]
KELT-9 b is an ultra hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b's transit light curve using photometry from the Transiting Exoplanet Survey Satellite to constrain the planet's true spin-orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star's equatorial radius to be 1.089 ± 0.017 times as large as its polar radius and its local surface brightness to vary by ∼38% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light curve asymmetry to constrain KELT-9 b's true spin orbit angle (87∘ +10∘//−11∘), agreeing with Gaudi 2017 that KELT-9 b is in a nearly polar orbit. We also apply a gravity darkening correction to the spectral energy distribution model from Gaudi 2017 and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star's polar effective temperature.

28. Originally Posted by Roger E. Moore
Never, ever, name a planet after a Cthulhu deity, or the planet will explode. (It was called Dagon.)
The name Dagon was old long before Lovecraft was ever born. https://en.wikipedia.org/wiki/Dagon

29. Two recent papers in which stars are discovered that could have engulfed their own planets.

The Chemical Signatures of Planetary Engulfment Events in Binary Systems
Nagar, Tushar; Spina, Lorenzo; Karakas, Amanda I.
Abstract: Planetary engulfment events involve the chemical assimilation of a planet into a star’s external layer. This can cause a change in the chemical pattern of the stellar atmosphere in a way that mirrors the composition of the rocky object engulfed, with the refractory elements being more abundant than the volatiles. Due to these stellar chemical changes, planetary engulfment events can render the process of chemical tagging potentially inaccurate. A line-by-line differential analysis of twin stars in wide binary systems allows us to test the chemical homogeneity of these associations with typical individual stellar Fe I uncertainties of 0.01 dex and eventually unveil chemical anomalies that could be attributed to planetary engulfment events. Out of the 14 systems analyzed here, we report the discovery of the most chemically inhomogeneous system to date (HIP 34407/HIP 34426). The median difference in abundances of refractory elements within the pair is 0.19 dex and the trend between the differential abundances and condensation temperature suggests that the anomaly is likely due to a planetary engulfment event. Within our sample, five other chemically anomalous systems are found.
Publication: The Astrophysical Journal Letters, Volume 888, Issue 1, article id. L9, 7 pp. (2020).
Pub Date: January 2020