Bayesian constraints on the origin and geology of exo-planetary material using a population of externally polluted white dwarfs

Abstract White dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. In this paper, we present a Bayesian model to explain the abundances observed in the atmospheres of 202 DZ white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. The majority (>60%) of systems are consistent with the accretion of primitive material. We attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. A range in Na abundances in the pollutant material is attributed to a range in formation temperatures from below 1,000 K to higher than 1,400 K, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. We also find that Solar System-like differentiation is common place in exo-planetary systems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. In systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. The 13 systems are estimated to have accreted masses ranging from the mass of the Moon to half that of Vesta. Our analysis suggests that accretion continues for 11Myrs on average.

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Volatile loss, Differentiation and Collisions: Key to the Composition of Rocky Exoplanets

10.5194/epsc2020-387 ◽

2020 ◽

Author(s):

Amy Bonsor ◽

John Harrison ◽

Oliver Shorttle ◽

Philip Carter ◽

Mihkel Kama ◽

...

Keyword(s):

Solar System ◽

Chemical Evolution ◽

White Dwarf ◽

Thermal Processing ◽

White Dwarfs ◽

Bulk Composition ◽

Galactic Chemical Evolution ◽

Common Process ◽

Planetary Bodies ◽

Volatile Loss

Volatile loss, Differentiation and Collisions: Key to the Composition of Rocky Exoplanets Many of the key characteristics and geology of our planet Earth today were determined during the planet&#8217;s formation. What about rocky exoplanets? How does rocky planet formation determine the properties, composition, geology and ultimately, presence of life on rocky exoplanets?&#160; In this talk I will discuss projects that investigate the link between rocky planet formation and the composition of rocky exoplanets. This work utilises unique observations that provide us with the bulk composition of rocky exoplanetary material. These observations come from the old, faint remnants of stars like our Sun, known as white dwarfs.&#160; White dwarfs should have clean hydrogen or helium atmospheres. This means that planetary bodies as small as asteroids can show up in the white dwarf&#8217;s atmosphere. Metallic species such as Fe, Mg or Ca provide the bulk composition of the accreted body. Several thousand polluted white dwarfs are now known. Models indicate that outer planetary systems, like our Solar System beyond Mars, should survive the star&#8217;s evolution to the white dwarf phase. Scattering is a common process, and any bodies that are scattered inwards, a bit like sun-grazing comets in our Solar System, would show up in the white dwarf atmosphere. What determines the composition of the rocky exoplanetary bodies accreted by white dwarfs?&#160; Models presented in Harrison et al, 2018, 2020 (submitted) find that the abundances observed in the atmospheres of white dwarfs can be explained by three key processes, notably galactic chemical evolution, loss of volatiles (thermal processing) and large scale melting&#160; which leads to the segregation of material between the core, mantle and crust. Galactic chemical evolution determines the initial composition of the planet forming material. Thermal processing determines the loss of volatiles, be that CO and other gases, water, or moderate volatile species such as Na. Collisions between planetary bodies that have differentiated to form a core can lead to fragments dominated by core-rich or mantle-rich material.&#160; Core-Mantle differentiation is a common process in exoplanetary systems High abundances of siderophile (iron-loving) compared to lithophile (silicate loving) speeches in some polluted white dwarfs indicate that accretion of a planetary body composed primarily of material from a planetary core (or alternatively mantle). Harrison et al, 2020, based on data from Hollands et al, 2017, 2018, present several examples of systems with extreme abundances, core-rich, mantle-rich or crust-rich.&#160; Bonsor et al, 2020 concludes that most polluted white dwarfs (>60%) have accreted the fragment of a differentiated exoplanetesimal.&#160; Post-Nebula volatilisation in exoplanetary bodies Mn and Na trace the loss of volatiles in planetary bodies. The difference in behaviour of Mn and Na under oxidising/reducing conditions makes them a strong indicator of the conditions prevalent when volatile loss occurred. Mn/Na for the Moon/Mars indicate post-Nebula volatile loss&#160; (Siebert et al, 2018). Harrison et al, 2020, in prep, provides the first evidence of post-nebula volatilisation in exoplanetary bodies utilising the Mn/Na abundances of polluted white dwarfs.&#160;

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Exogeology from Polluted White Dwarfs

Elements ◽

10.2138/gselements.17.4.241 ◽

2021 ◽

Vol 17 (4) ◽

pp. 241-244

Author(s):

Siyi Xu ◽

Amy Bonsor

Keyword(s):

Solar System ◽

White Dwarf ◽

White Dwarfs ◽

Planetary Systems ◽

Terrestrial Planets ◽

Strong Gravity ◽

Exoplanetary Systems ◽

Planetary Bodies

It is difficult to study the interiors of terrestrial planets in the Solar System and the problem is magnified for distant exoplanets. However, sometimes nature is helpful. Some planetary bodies are torn to fragments and consumed by the strong gravity close to the descendants of Sun-like stars, white dwarfs. We can deduce the general composition of the planet when we observe the spectroscopic signature of the white dwarf. Most planetary fragments that fall into white dwarfs appear to be rocky with a variable fraction of associated ice and carbon. These white dwarf planetary systems provide a unique opportunity to study the geology of exoplanetary systems.

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Exploring the Solar System

10.1093/oso/9780198799894.003.0003 ◽

2018 ◽

Author(s):

Karel Schrijver

Keyword(s):

Solar System ◽

Planetary Systems ◽

Interplanetary Dust ◽

Terrestrial Planets ◽

The Moon ◽

System P ◽

Asteroids And Comets

In this chapter, the author summarizes the properties of the Solar System, and how these were uncovered. Over centuries, the arrangement and properties of the Solar System were determined. The distinctions between the terrestrial planets, the gas and ice giants, and their various moons are discussed. Whereas humans have walked only on the Moon, probes have visited all the planets and several moons, asteroids, and comets; samples have been returned to Earth only from our moon, a comet, and from interplanetary dust. For Earth and Moon, seismographs probed their interior, whereas for other planets insights come from spacecraft and meteorites. We learned that elements separated between planet cores and mantels because larger bodies in the Solar System were once liquid, and many still are. How water ended up where it is presents a complex puzzle. Will the characteristics of our Solar System hold true for planetary systems in general?

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9. Volcanoes beyond Earth

Volcanoes: A Very Short Introduction ◽

10.1093/actrade/9780199582204.003.0009 ◽

2020 ◽

pp. 128-142

Author(s):

Michael J. Branney ◽

Jan Zalasiewicz

Keyword(s):

Solar System ◽

Plate Tectonics ◽

Planetary Systems ◽

The Moon ◽

Mountain Belts ◽

Tectonic Forces

‘Volcanoes beyond Earth’ highlights volcanoes on other planets. There are many more volcanoes on Venus than there are on Earth, and many remain active. In the absence of plate tectonics and the kind of tectonic forces that raise Earth-style mountain belts, and of streams, rivers, and shorelines, it is volcanism and volcanic products that dominate the surface of this planet. Fossil volcanism occurs in the Moon, Mercury, and Mars; Io, the hypervolcanic moon of Jupiter; and the ice volcanoes of the Solar System. There is potential for volcanism on exoplanets within distant planetary systems.

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Advances in Cosmochemistry Enabled by Antarctic Meteorites

Annual Review of Earth and Planetary Sciences ◽

10.1146/annurev-earth-082719-055815 ◽

2020 ◽

Vol 48 (1) ◽

pp. 233-258

Author(s):

Meenakshi Wadhwa ◽

Timothy J. McCoy ◽

Devin L. Schrader

Keyword(s):

Solar System ◽

Planetary Science ◽

The Moon ◽

Origin And Evolution ◽

Lunar Meteorite ◽

Planetary Bodies ◽

The Antarctic ◽

Melt Pockets ◽

Scientific Advances

At present, meteorites collected in Antarctica dominate the total number of the world's known meteorites. We focus here on the scientific advances in cosmochemistry and planetary science that have been enabled by access to, and investigations of, these Antarctic meteorites. A meteorite recovered during one of the earliest field seasons of systematic searches, Elephant Moraine (EET) A79001, was identified as having originated on Mars based on the composition of gases released from shock melt pockets in this rock. Subsequently, the first lunar meteorite, Allan Hills (ALH) 81005, was also recovered from the Antarctic. Since then, many more meteorites belonging to these two classes of planetary meteorites, as well as other previously rare or unknown classes of meteorites (particularly primitive chondrites and achondrites), have been recovered from Antarctica. Studies of these samples are providing unique insights into the origin and evolution of the Solar System and planetary bodies. ▪ Antarctic meteorites dominate the inventory of the world's known meteorites and provide access to new types of planetary and asteroidal materials. ▪ The first meteorites recognized to be of lunar and martian origin were collected from Antarctica and provided unique constraints on the evolution of the Moon and Mars. ▪ Previously rare or unknown classes of meteorites have been recovered from Antarctica and provide new insights into the origin and evolution of the Solar System.

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The Origin and Evolution of the Comets and Other Small Bodies in the Solar System

Symposium - International Astronomical Union ◽

10.1017/s0074180900006847 ◽

1972 ◽

Vol 45 ◽

pp. 413-418 ◽

Cited By ~ 2

Author(s):

S. K. Vsekhsvyatskij

Keyword(s):

Solar System ◽

Internal Energy ◽

Total Mass ◽

Small Bodies ◽

Origin And Evolution ◽

Meteor Streams ◽

Short Period ◽

Planetary Bodies

It has become evident that comets and other small bodies are indications of eruptive evolution processes occurring in many of the planetary bodies of the solar system. The total number of near-parabolic comets moving in the solar system is 1011 to 1012, but as many as 10 to 15 percent of them are leaving the solar system with hyperbolic velocities. Taking into account also the number of short-period comets that degenerate into asteroids and meteor streams, we have estimated the total number of comets formed during the lifetime of the solar system as 1015 to 1016 (and total mass 1029 to 1031 g). The investigation of comets and other small bodies enables us to evaluate the scale of the processes of cosmic vulcanism and the tremendous internal energy of the planets, that energy being derived from the initial stellar nature of planetary material.

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The Coalescence of White Dwarfs And Type I Supernovae

International Astronomical Union Colloquium ◽

10.1017/s025292110010017x ◽

1989 ◽

Vol 114 ◽

pp. 515-518

Author(s):

Robert Mochkovitch ◽

Mario Livio

Keyword(s):

Angular Momentum ◽

White Dwarf ◽

Total Mass ◽

White Dwarfs ◽

Thick Disk ◽

Initial System ◽

Type I ◽

Low Density ◽

Coalescence Model ◽

Merging Process

AbstractIn the context of the white dwarf coalescence model for type la supernovae, we compute post-coalescence configurations involving a thick disk, rotating around a central white dwarf (the original primary), having the same total mass, angular momentum and energy as the initial system. We show that carbon ignition in rather low density material (105 – 10° g.cm−3) can be triggered during the merging process itself or later, by dissipation due to turbulence in the disk. The evolution of the object following carbon ignition is very uncertain.

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The search for planet and planetesimal transits of white dwarfs with the Zwicky Transient Facility

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000204 ◽

2019 ◽

Vol 15 (S357) ◽

pp. 37-40

Author(s):

Keaton J. Bell

Keyword(s):

Solar System ◽

White Dwarf ◽

Metal Pollution ◽

White Dwarfs ◽

Dwarf Stars ◽

Orbital Inclination ◽

White Dwarf Stars ◽

Ultimate Fate ◽

Project Strategy ◽

Very High

AbstractPlanetary 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.

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Ethical and Social Aspects of a Return to the Moon—A Geological Perspective

Geosciences ◽

10.3390/geosciences9010012 ◽

2018 ◽

Vol 9 (1) ◽

pp. 12 ◽

Cited By ~ 2

Author(s):

Vera Assis Fernandes

Keyword(s):

Solar System ◽

Lunar Surface ◽

Surface Current ◽

Social Impacts ◽

Social Aspects ◽

The Moon ◽

International Treaties ◽

Self Reflection ◽

Planetary Bodies ◽

Collaborative Space

The forward planning of the return of Humans to the lunar surface as envisioned by different national and collaborative space agencies requires consideration of the fragility and pristine nature of the lunar surface. Current international treaties are outdated and require immediate action for their update and amendment. This should be taken as an opportunity for self-reflection and potential censoring, enabling a mature, responsible, and iterated sequence of decisions prior to returning. The protocols developed for assessing the ethical and social impacts of Humans on the lunar surface will provide a blueprint for planning future exploration activities on other planetary bodies in the Solar System and beyond.

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Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets

Science ◽

10.1126/science.aax3901 ◽

2019 ◽

Vol 366 (6463) ◽

pp. 356-359 ◽

Cited By ~ 31

Author(s):

Alexandra E. Doyle ◽

Edward D. Young ◽

Beth Klein ◽

Ben Zuckerman ◽

Hilke E. Schlichting

Keyword(s):

Solar System ◽

Oxygen Fugacity ◽

White Dwarfs ◽

Planetary Systems ◽

Elemental Abundances ◽

Oxidized Iron ◽

Solar Composition

Oxygen fugacity is a measure of rock oxidation that influences planetary structure and evolution. Most rocky bodies in the Solar System formed at oxygen fugacities approximately five orders of magnitude higher than a hydrogen-rich gas of solar composition. It is unclear whether this oxidation of rocks in the Solar System is typical among other planetary systems. We exploit the elemental abundances observed in six white dwarfs polluted by the accretion of rocky bodies to determine the fraction of oxidized iron in those extrasolar rocky bodies and therefore their oxygen fugacities. The results are consistent with the oxygen fugacities of Earth, Mars, and typical asteroids in the Solar System, suggesting that at least some rocky exoplanets are geophysically and geochemically similar to Earth.

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