scholarly journals Exogeology from Polluted White Dwarfs

Elements ◽  
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.

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

2021 ◽  
Author(s):  
John H D Harrison ◽  
Amy Bonsor ◽  
Mihkel Kama ◽  
Andrew M Buchan ◽  
Simon Blouin ◽  
...  
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Bayesian Model ◽  
Total Mass ◽  
White Dwarfs ◽  
Bulk Composition ◽  
Planetary Systems ◽  
The Moon ◽  
Planetary Bodies ◽  
Nearby Stars

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.

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

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

<p><strong>Volatile loss, Differentiation and Collisions: Key to the Composition of Rocky Exoplanets</strong></p> <p>Many of the key characteristics and geology of our planet Earth today were determined during the planet’s formation. What about rocky exoplanets? How does rocky planet formation determine the properties, composition, geology and ultimately, presence of life on rocky exoplanets?<span class="Apple-converted-space"> </span></p> <p>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.<span class="Apple-converted-space"> </span></p> <p>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’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.</p> <p>Models indicate that outer planetary systems, like our Solar System beyond Mars, should survive the star’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.</p> <p><strong>What determines the composition of the rocky exoplanetary bodies accreted by white dwarfs?<span class="Apple-converted-space"> </span></strong></p> <p>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<span class="Apple-converted-space">  </span>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.<span class="Apple-converted-space"> </span></p> <p><strong>Core-Mantle differentiation is a common process in exoplanetary systems</strong></p> <p>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.<span class="Apple-converted-space"> </span></p> <p>Bonsor et al, 2020 concludes that most polluted white dwarfs (>60%) have accreted the fragment of a differentiated exoplanetesimal.<span class="Apple-converted-space"> </span></p> <p><strong>Post-Nebula volatilisation in exoplanetary bodies</strong></p> <p>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<span class="Apple-converted-space">  </span>(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.<span class="Apple-converted-space"> </span></p>

Exploring the Solar System

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?

scholarly journals Planetary populations according to the orbital angular momentum

2009 ◽  
Vol 5 (S265) ◽  
pp. 420-421
Author(s):  
João A. S. Amarante ◽  
Helio J. Rocha-Pinto
Keyword(s):  
Angular Momentum ◽  
Solar System ◽  
Orbital Angular Momentum ◽  
Momentum Distribution ◽  
Semimajor Axis ◽  
Terrestrial Planets ◽  
Planetary Mass ◽  
Exoplanetary Systems ◽  
Planetary Migration ◽  
Two Populations

AbstractWe investigate the angular momentum distribution of known exoplanetary systems, as a function of the planetary mass, orbital semimajor axis and metallicity of the host star. We find exoplanets seems to be classified according to at least two ‘populations’, with respect to their angular momentum properties. This classification is independent on the composition of the planet and seems to be valid for both jovian and neptunian planets, and probably can be extrapolated to the terrestrial planets of the Solar System. We analyse these ‘populations’ considering the phenomenon of planetary migration.

scholarly journals Host-star and exoplanet compositions: a pilot study using a wide binary with a polluted white dwarf

2021 ◽  
Vol 503 (2) ◽  
pp. 1877-1883
Author(s):  
Amy Bonsor ◽  
Paula Jofré ◽  
Oliver Shorttle ◽  
Laura K Rogers ◽  
Siyi Xu(许偲艺) ◽  
...  
Keyword(s):  
White Dwarf ◽  
Planetary System ◽  
Kuiper Belt ◽  
Wide Binary ◽  
Elemental Abundances ◽  
Exoplanetary Systems ◽  
Planetary Bodies ◽  
Refractory Composition ◽  
Observational Errors ◽  
Host Stars

ABSTRACT Planets and stars ultimately form out of the collapse of the same cloud of gas. Whilst planets, and planetary bodies, readily loose volatiles, a common hypothesis is that they retain the same refractory composition as their host star. This is true within the Solar system. The refractory composition of chondritic meteorites, Earth, and other rocky planetary bodies are consistent with solar, within the observational errors. This work aims to investigate whether this hypothesis holds for exoplanetary systems. If true, the internal structure of observed rocky exoplanets can be better constrained using their host star abundances. In this paper, we analyse the abundances of the K-dwarf, G200-40, and compare them to its polluted white dwarf companion, WD 1425+540. The white dwarf has accreted planetary material, most probably a Kuiper belt-like object, from an outer planetary system surviving the star’s evolution to the white dwarf phase. Given that binary pairs are chemically homogeneous, we use the binary companion, G200-40, as a proxy for the composition of the progenitor to WD 1425+540. We show that the elemental abundances of the companion star and the planetary material accreted by WD 1425+540 are consistent with the hypothesis that planet and host-stars have the same true abundances, taking into account the observational errors.

scholarly journals Lithium pollution of a white dwarf records the accretion of an extrasolar planetesimal

Science ◽  
2020 ◽  
Vol 371 (6525) ◽  
pp. 168-172
Author(s):  
B. C. Kaiser ◽  
J. C. Clemens ◽  
S. Blouin ◽  
P. Dufour ◽  
R. J. Hegedus ◽  
...  
Keyword(s):  
Solar System ◽  
White Dwarf ◽  
Big Bang ◽  
Early Solar System ◽  
Big Bang Nucleosynthesis ◽  
Lithium Abundance ◽  
Sodium Potassium ◽  
Elemental Abundances ◽  
Exoplanetary Systems ◽  
Gaia Dr2

Tidal disruption and subsequent accretion of planetesimals by white dwarfs can reveal the elemental abundances of rocky bodies in exoplanetary systems. Those abundances provide information on the composition of the nebula from which the systems formed, which is analogous to how meteorite abundances inform our understanding of the early Solar System. We report the detection of lithium, sodium, potassium, and calcium in the atmosphere of the white dwarf Gaia DR2 4353607450860305024, which we ascribe to the accretion of a planetesimal. Using model atmospheres, we determine abundance ratios of these elements, and, with the exception of lithium, they are consistent with meteoritic values in the Solar System. We compare the measured lithium abundance with measurements in old stars and with expectations from Big Bang nucleosynthesis.

scholarly journals Formation and Orbital Evolution of Planets

2011 ◽  
Vol 7 (S282) ◽  
pp. 429-436
Author(s):  
Wilhelm Kley
Keyword(s):  
Solar System ◽  
Gravitational Instability ◽  
Planetary Systems ◽  
Large Mass ◽  
Orbital Evolution ◽  
Protoplanetary Disk ◽  
Dynamical Structure ◽  
High Eccentricity ◽  
Exoplanetary Systems ◽  
Alternative Processes

AbstractThe formation of planetary systems is a natural byproduct of the star formation process. Planets can form inside the protoplanetary disk by two alternative processes. Either through a sequence of sticking collisions, the so-called sequential accretion scenario, or via gravitational instability from an over-dense clump inside the protoplanetary disk. The first process is believed to have occurred in the solar system. The most important steps in this process will be outlined. The observed orbital properties of exoplanetary systems are distinctly different from our own Solar System. In particular, their small distance from the star, their high eccentricity and large mass point to the existence of a phase with strong mutual excitations. These are believed to be a result of early evolution of planets due to planet-disk interaction. The importance of this process in shaping the dynamical structure of planetary systems will be presented.

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

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.

scholarly journals Orbital eccentricity–multiplicity correlation for planetary systems and comparison to the Solar system

2020 ◽  
Vol 500 (1) ◽  
pp. 1313-1322
Author(s):  
Nanna Bach-Møller ◽  
Uffe G Jørgensen
Keyword(s):  
Solar System ◽  
Power Law ◽  
Planetary System ◽  
Planetary Systems ◽  
Detection Methods ◽  
Orbital Eccentricity ◽  
Full Data ◽  
Exoplanetary Systems ◽  
The One ◽  
Good Agreement

ABSTRACT The orbit eccentricities of the Solar system planets are unusually low compared to the average of known exoplanetary systems. A power-law correlation has previously been found between the multiplicity of a planetary system and the orbital eccentricities of its components, for systems with multiplicities above two. In this study we investigate the correlation for an expanded data sample by focusing on planetary systems as units (unlike previous studies that have focused on individual planets). Our full data sample contains 1171 exoplanets, in 895 systems, and the correlation between eccentricity and multiplicity is found to follow a clear power law for all multiplicities above one. We discuss the correlation for several individual subsamples and find that all samples consistently follow the same basic trend regardless of e.g. planet types and detection methods. We find that the eccentricities of the Solar system fit the general trend and suggest that the Solar system might not show uncommonly low eccentricities (as often speculated) but rather uncommonly many planets compared to a ‘standard’ planetary system. The only outlier from the power-law correlation is, consistently in all the samples, the one-planet systems. It has previously been suggested that this may be due to additional unseen exoplanets in the observed one-planet systems. Based on this assumption and the power-law correlation, we estimate that the probability of a system having eight planets or more is of the order of 1 per cent, in good agreement with recent predictions from analyses based on independent arguments.

scholarly journals Are exoplanetesimals differentiated?

2020 ◽  
Vol 492 (2) ◽  
pp. 2683-2697 ◽  
Author(s):  
Amy Bonsor ◽  
Philip J Carter ◽  
Mark Hollands ◽  
Boris T Gänsicke ◽  
Zoë Leinhardt ◽  
...  
Keyword(s):  
White Dwarfs ◽  
Planetary Systems ◽  
Mantle Material ◽  
Planetary Body ◽  
Single Body ◽  
Exoplanetary Systems ◽  
Large Numbers ◽  
Metal Abundances ◽  
Larger Sample ◽  
Collisional Evolution

ABSTRACT Metals observed in the atmospheres of white dwarfs suggest that many have recently accreted planetary bodies. In some cases, the compositions observed suggest the accretion of material dominantly from the core (or the mantle) of a differentiated planetary body. Collisions between differentiated exoplanetesimalrrs produce such fragments. In this work, we take advantage of the large numbers of white dwarfs where at least one siderophile (core-loving) and one lithophile (rock-loving) species have been detected to assess how commonly exoplanetesimals differentiate. We utilize N-body simulations that track the fate of core and mantle material during the collisional evolution of planetary systems to show that most remnants of differentiated planetesimals retain core fractions similar to their parents, while some are extremely core rich or mantle rich. Comparison with the white dwarf data for calcium and iron indicates that the data are consistent with a model in which $66^{+4}_{-6}{{\ \rm per\ cent}}$ have accreted the remnants of differentiated planetesimals, while $31^{+5}_{-5}{{\ \rm per\ cent}}$ have Ca/Fe abundances altered by the effects of heating (although the former can be as high as $100{{\ \rm per\ cent}}$, if heating is ignored). These conclusions assume pollution by a single body and that collisional evolution retains similar features across diverse planetary systems. These results imply that both collisions and differentiation are key processes in exoplanetary systems. We highlight the need for a larger sample of polluted white dwarfs with precisely determined metal abundances to better understand the process of differentiation in exoplanetary systems.

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