Evidence has been found for water in the debris of a disrupted extrasolar minor planet orbiting a white dwarf star. Spectroscopic analysis of the white dwarf's atmosphere revealed an excess of oxygen that cannot be explained by oxide minerals alone, indicating the parent body was originally composed of about 26% water by mass. This demonstrates that water-bearing planetesimals can form around higher mass stars that eventually become white dwarfs. The disrupted planetesimal is the source of a circumstellar debris disk closely orbiting the white dwarf remnant.
Ontology spectrum for geological data interoperability (PhD defense nov 2011)Xiaogang (Marshall) Ma
Ontology spectrum for geological data interoperability.
A 10-minutre layman presentation for my PhD defense at University of Twente, 2011/11/30. Full text of dissertation is accessible at: http://www.itc.nl/library/papers_2011/phd/ma.pdf
Significance of Trace Element Quantities in Osteomyelitis and Osteosarcoma_Cr...CrimsonpublishersCancer
To clarify the role of trace elements (TE) in the etiology and the pathogenesis of osteomyelitis (OM) and osteosarcoma (OS), a nondestructive neutron activation analysis were performed. The Ag, Co, Cr, Fe, Hg, Rb, Sb, Se, and Zn contents were measured in three groups of samples: normal bone samples from 27 persons with intact bone, and also in samples, obtained from open biopsies or after operation of 10 patients with OM and 27 patients with OS. The difference in the results between TE contents in the three groups was evaluated by the parametric Student’s t-test and non-parametric Wilcoxon-Mann-Whitney U-test. In the OM tissue the mean contents of Co, Cr, Fe, Se, and Zn are respectively 1.8, 1.7, 1.8, 1.7, and 1.5 times higher than those in normal bone tissues In the OS tissue the mean mass fractions of Co, Cr, Fe, Sb, Se, and Zn are respectively 4.6, 2.0, 4.8 2.4, 11.0, and 2.4 times higher while the mean mass fraction of Rb is more than 40% lower than in normal bone tissues. In the OS tissue the mean mass fractions of Co, Fe, Se, and Zn are significantly higher (2.6, 2.6, 6.2, and 1.6 times, respectively) and the mean mass fraction of Rb is more than 2 times lower than in inflamed bone. In addition, many inter-correlations between TE contents found in the control group were no longer evident in the inflamed and tumor transformed bone. Thus, considerable changes in TE content and their relationships were found in OM and OS and possible causes and effects of these alterations are discussed.
Ontology spectrum for geological data interoperability (PhD defense nov 2011)Xiaogang (Marshall) Ma
Ontology spectrum for geological data interoperability.
A 10-minutre layman presentation for my PhD defense at University of Twente, 2011/11/30. Full text of dissertation is accessible at: http://www.itc.nl/library/papers_2011/phd/ma.pdf
Significance of Trace Element Quantities in Osteomyelitis and Osteosarcoma_Cr...CrimsonpublishersCancer
To clarify the role of trace elements (TE) in the etiology and the pathogenesis of osteomyelitis (OM) and osteosarcoma (OS), a nondestructive neutron activation analysis were performed. The Ag, Co, Cr, Fe, Hg, Rb, Sb, Se, and Zn contents were measured in three groups of samples: normal bone samples from 27 persons with intact bone, and also in samples, obtained from open biopsies or after operation of 10 patients with OM and 27 patients with OS. The difference in the results between TE contents in the three groups was evaluated by the parametric Student’s t-test and non-parametric Wilcoxon-Mann-Whitney U-test. In the OM tissue the mean contents of Co, Cr, Fe, Se, and Zn are respectively 1.8, 1.7, 1.8, 1.7, and 1.5 times higher than those in normal bone tissues In the OS tissue the mean mass fractions of Co, Cr, Fe, Sb, Se, and Zn are respectively 4.6, 2.0, 4.8 2.4, 11.0, and 2.4 times higher while the mean mass fraction of Rb is more than 40% lower than in normal bone tissues. In the OS tissue the mean mass fractions of Co, Fe, Se, and Zn are significantly higher (2.6, 2.6, 6.2, and 1.6 times, respectively) and the mean mass fraction of Rb is more than 2 times lower than in inflamed bone. In addition, many inter-correlations between TE contents found in the control group were no longer evident in the inflamed and tumor transformed bone. Thus, considerable changes in TE content and their relationships were found in OM and OS and possible causes and effects of these alterations are discussed.
Artigo relata como a Terra sofreu com os impactos de ateroides a 4 bilhões de anos atrás, e como a superfície do planeta foi remodelada e os oceanos formados.
"Keeping up with the plant destroyers." My talk at The Royal Society, 7 March...Sophien Kamoun
Tackling emerging threats to animal health, food security and ecosystem resilience, The Royal Society, Monday 7 – Tuesday 8 March 2016. https://royalsociety.org/events/2016/03/emerging-fungal-threats/
My talk at BASF Science Symposium: sustainable food chain - from field to table, Jun 23-24, 2015, Chicago.
Notes and acknowledgements at http://kamounlab.tumblr.com/post/122151022390/plant-pathology-in-the-post-genomics-era
Deep Learning-based Histological SegmentationDifferentiates Cavitation Patte...Wookjin Choi
Unsupervised segmentation (unlabeled regions of interest, ROIs) and autoencoder (AE)-based classification were used to classify differences in cavitation patterns in knees and digits using the stained images (n=20-30 images/group).
Each image was divided into 256 x 256 pixel patches, and a convolutional neural network (CNN)-based unsupervised segmentation was used to identify ROIs. These patches were subsequently fed into a CNN-based AE whose latent space layer was connected to a classifier for input patch classification.
The AE was trained using the ROIs identified by the unsupervised segmentation, and the image classes were used to train the classifier. Whole image classifications were determined by maximum voting of the patch results and evaluated by accuracy.
Microgravity is the condition in which people or objects appear to be weightless (In space). Astronauts and cosmonauts returning from long-term space missions exhibited various health problems, among them changes of the immune system, bone loss, muscle atrophy, ocular problems, and cardiovascular changes. Space biologists investigated various cell types in space to find the molecular mechanisms responsible for the observed immune disorders. Experimental cell research studying three-dimensional (3D) tissues in space and on Earth using new techniques to simulate microgravity is currently a hot topic in Gravitational Biology and Biomedicine.
GraphRAG is All You need? LLM & Knowledge GraphGuy Korland
Guy Korland, CEO and Co-founder of FalkorDB, will review two articles on the integration of language models with knowledge graphs.
1. Unifying Large Language Models and Knowledge Graphs: A Roadmap.
https://arxiv.org/abs/2306.08302
2. Microsoft Research's GraphRAG paper and a review paper on various uses of knowledge graphs:
https://www.microsoft.com/en-us/research/blog/graphrag-unlocking-llm-discovery-on-narrative-private-data/
LF Energy Webinar: Electrical Grid Modelling and Simulation Through PowSyBl -...DanBrown980551
Do you want to learn how to model and simulate an electrical network from scratch in under an hour?
Then welcome to this PowSyBl workshop, hosted by Rte, the French Transmission System Operator (TSO)!
During the webinar, you will discover the PowSyBl ecosystem as well as handle and study an electrical network through an interactive Python notebook.
PowSyBl is an open source project hosted by LF Energy, which offers a comprehensive set of features for electrical grid modelling and simulation. Among other advanced features, PowSyBl provides:
- A fully editable and extendable library for grid component modelling;
- Visualization tools to display your network;
- Grid simulation tools, such as power flows, security analyses (with or without remedial actions) and sensitivity analyses;
The framework is mostly written in Java, with a Python binding so that Python developers can access PowSyBl functionalities as well.
What you will learn during the webinar:
- For beginners: discover PowSyBl's functionalities through a quick general presentation and the notebook, without needing any expert coding skills;
- For advanced developers: master the skills to efficiently apply PowSyBl functionalities to your real-world scenarios.
Dev Dives: Train smarter, not harder – active learning and UiPath LLMs for do...UiPathCommunity
💥 Speed, accuracy, and scaling – discover the superpowers of GenAI in action with UiPath Document Understanding and Communications Mining™:
See how to accelerate model training and optimize model performance with active learning
Learn about the latest enhancements to out-of-the-box document processing – with little to no training required
Get an exclusive demo of the new family of UiPath LLMs – GenAI models specialized for processing different types of documents and messages
This is a hands-on session specifically designed for automation developers and AI enthusiasts seeking to enhance their knowledge in leveraging the latest intelligent document processing capabilities offered by UiPath.
Speakers:
👨🏫 Andras Palfi, Senior Product Manager, UiPath
👩🏫 Lenka Dulovicova, Product Program Manager, UiPath
Generating a custom Ruby SDK for your web service or Rails API using Smithyg2nightmarescribd
Have you ever wanted a Ruby client API to communicate with your web service? Smithy is a protocol-agnostic language for defining services and SDKs. Smithy Ruby is an implementation of Smithy that generates a Ruby SDK using a Smithy model. In this talk, we will explore Smithy and Smithy Ruby to learn how to generate custom feature-rich SDKs that can communicate with any web service, such as a Rails JSON API.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
Accelerate your Kubernetes clusters with Varnish CachingThijs Feryn
A presentation about the usage and availability of Varnish on Kubernetes. This talk explores the capabilities of Varnish caching and shows how to use the Varnish Helm chart to deploy it to Kubernetes.
This presentation was delivered at K8SUG Singapore. See https://feryn.eu/presentations/accelerate-your-kubernetes-clusters-with-varnish-caching-k8sug-singapore-28-2024 for more details.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Epistemic Interaction - tuning interfaces to provide information for AI supportAlan Dix
Paper presented at SYNERGY workshop at AVI 2024, Genoa, Italy. 3rd June 2024
https://alandix.com/academic/papers/synergy2024-epistemic/
As machine learning integrates deeper into human-computer interactions, the concept of epistemic interaction emerges, aiming to refine these interactions to enhance system adaptability. This approach encourages minor, intentional adjustments in user behaviour to enrich the data available for system learning. This paper introduces epistemic interaction within the context of human-system communication, illustrating how deliberate interaction design can improve system understanding and adaptation. Through concrete examples, we demonstrate the potential of epistemic interaction to significantly advance human-computer interaction by leveraging intuitive human communication strategies to inform system design and functionality, offering a novel pathway for enriching user-system engagements.
Elevating Tactical DDD Patterns Through Object CalisthenicsDorra BARTAGUIZ
After immersing yourself in the blue book and its red counterpart, attending DDD-focused conferences, and applying tactical patterns, you're left with a crucial question: How do I ensure my design is effective? Tactical patterns within Domain-Driven Design (DDD) serve as guiding principles for creating clear and manageable domain models. However, achieving success with these patterns requires additional guidance. Interestingly, we've observed that a set of constraints initially designed for training purposes remarkably aligns with effective pattern implementation, offering a more ‘mechanical’ approach. Let's explore together how Object Calisthenics can elevate the design of your tactical DDD patterns, offering concrete help for those venturing into DDD for the first time!
Leading Change strategies and insights for effective change management pdf 1.pdf
Minor Planet Evidence for Water in the Rocky Debris of a Disrupted Extrasolar MInor Planet
1. DOI: 10.1126/science.1239447
, 218 (2013);342Science
et al.J. Farihi
Minor Planet
Evidence for Water in the Rocky Debris of a Disrupted Extrasolar
This copy is for your personal, non-commercial use only.
clicking here.colleagues, clients, or customers by
, you can order high-quality copies for yourIf you wish to distribute this article to others
here.following the guidelines
can be obtained byPermission to republish or repurpose articles or portions of articles
):October 11, 2013www.sciencemag.org (this information is current as of
The following resources related to this article are available online at
http://www.sciencemag.org/content/342/6155/218.full.html
version of this article at:
including high-resolution figures, can be found in the onlineUpdated information and services,
http://www.sciencemag.org/content/suppl/2013/10/09/342.6155.218.DC1.html
can be found at:Supporting Online Material
http://www.sciencemag.org/content/342/6155/218.full.html#ref-list-1
, 5 of which can be accessed free:cites 35 articlesThis article
http://www.sciencemag.org/cgi/collection/astronomy
Astronomy
subject collections:This article appears in the following
registered trademark of AAAS.
is aScience2013 by the American Association for the Advancement of Science; all rights reserved. The title
CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005.
(print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience
onOctober11,2013www.sciencemag.orgDownloadedfromonOctober11,2013www.sciencemag.orgDownloadedfromonOctober11,2013www.sciencemag.orgDownloadedfromonOctober11,2013www.sciencemag.orgDownloadedfrom
2. and morphometric measurements of the tissues
in the developing mouse gut (Fig. 6C). Using
these measurements as inputs in our model suf-
fices to quantitatively predict the formation of
villi (supplementary materials, Fig. 6D, and movie
S3). Compared with the chick, where the endo-
derm is more than 10 times stiffer than the ad-
jacent mesenchyme, the mouse endoderm is only
about 1.5 times as stiff as the mesenchyme (fig.
S3). Our simulations show that the soft endoderm
in mouse is essential for the initial folding that oc-
curs in endoderm alone and for the direct formation
of an array of previllous bumps, rather than zig-
zags, which are qualitatively similar to sulcus for-
mation on biaxially compressed gel surfaces that
lack a stiff top layer (24). The spacing of bumps
and, consequently, the spacing of villi are compa-
rable to the thickness of the whole endoderm-
mesenchyme composite (Fig. 6C), similar to chick.
The process of villification occurs before the
differentiation of the gut endoderm into various
epithelial cell types (25–27) and well before the
postnatal process of crypt formation. In vitro cul-
ture of intestinal stem cells results in the forma-
tion of intestinal organoids that reproduce crypt
structure (28). These organoids consist of an
inner epithelium with villuslike cell types and
outwardly projecting cryptlike structures. How-
ever, no morphological structures are present in
these in vitro cultures resembling the physical
villi. These results suggest that crypt formation
likely does not require the same muscle-driven
compression that is necessary for villi to form.
Additionally, further study is needed to un-
derstand whether structural differences in the
lumen of different regions of the gut are attrib-
utable to distinctions in the parameters we have
measured. For example, the short, wide villi that
coat large longitudinal folds of the chick colon
may be attributable to the thicker muscle layers
of the colon. Consistent with the muscle playing
such a role, studies have shown that transposi-
tion of a ring containing all radial layers of the
colon into regions of the small intestine preserve
villi morphology (29).
Our previous work provided a mechanical
basis for the diversity of macroscopic looping
patterns of the gut based on geometry, differen-
tial growth, and tissue mechanics (30), and our
present results demonstrate that the same phys-
ical principles drive morphological variation on
the luminal surface of the gut. Further, we see
that relatively minor changes in the geometry,
growth, and physical properties of the develop-
ing tissue in the guts of various species can
substantially alter both the process and the form
of villus patterning. A deep understanding of how
patterns vary requires us to combine our knowl-
edge of biophysical mechanisms with the genetic
control of cell proliferation and growth; indeed
this variation can occur in an organism as a func-
tion of its diet, across species, and over evolu-
tionary time scales via natural selection.
References and Notes
1. V. A. McLin, S. J. Henning, M. Jamrich, Gastroenterology
136, 2074–2091 (2009).
2. T. K. Noah, B. Donahue, N. F. Shroyer, Exp. Cell Res. 317,
2702–2710 (2011).
3. W. J. Krause, Anat. Histol. Embryol. 40, 352–359
(2011).
4. J. W. McAvoy, K. E. Dixon, J. Anat. 125, 155–169 (1978).
5. S. Ferri, L. C. U. Junqueira, L. F. Medeiros, L. O. Mederios,
J. Anat. 121, 291–301 (1976).
6. D. R. Burgess, Embryol Exp. Morph. 34, 723–740 (1975).
7. W. His, Anatomie Menschlicher Embryonen (Vogel,
Leipzig, Germany, 1880).
8. D. E. Moulton, A. Goriely, J. Mech. Phys. Solids 59,
525–537 (2011).
9. L. Bell, L. Williams, Anat. Embryol. 165, 437–455 (1982).
10. M. Kurahashi et al., Neurogastroenterol. Motil. 20,
521–531 (2008).
11. K. Fukuda, Y. Tanigawa, G. Fujii, S. Yasugi, S. Hirohashi,
Development 125, 3535–3542 (1998).
12. H. Benabdallah, D. Messaoudi, K. Gharzouli, Pharmacol.
Res. 57, 132–141 (2008).
13. N. Harada, Y. Chijiiwa, T. Misawa, M. Yoshinaga,
H. Nawata, Life Sci. 51, 1381–1387 (1992).
14. M. L. Lovett, C. M. Cannizzaro, G. Vunjak-Novakovic,
D. L. Kaplan, Biomaterials 29, 4650–4657 (2008).
15. N. Bowden, S. Brittain, A. G. Evans, J. W. Hutchinson,
G. W. Whitesides, Nature 393, 146–149 (1998).
16. L. Mahadevan, S. Rica, Science 307, 1740 (2005).
17. B. Audoly, A. Boudaoud, J. Mech. Phys. Solids 56,
2444–2458 (2008).
18. E. Hannezo, J. Prost, J.-F. Joanny, Phys. Rev. Lett. 107,
078104 (2011).
19. M. Ben Amar, F. Jia, Proc. Natl. Acad. Sci. U.S.A. 110,
10525–10530 (2013).
20. R. Sbarbati, J. Anat. 135, 477–499 (1982).
21. K. D. Walton et al., Proc. Natl. Acad. Sci. U.S.A. 109,
15817–15822 (2012).
22. A. Sukegawa et al., Development 127, 1971–1980 (2000).
23. M. Ramalho-Santos, D. A. Melton, A. P. McMahon,
Development 127, 2763–2772 (2000).
24. T. Tallinen, J. S. Biggins, L. Mahadevan, Phys. Rev. Lett.
110, 024302 (2013).
25. M. Dauça et al., Int. J. Dev. Biol. 34, 205–218 (1990).
26. Z. Uni, A. Smirnov, D. Sklan, Poult. Sci. 82, 320–327
(2003).
27. F. T. Bellware, T. W. Betz, J. Embryol. Exp. Morphol. 24,
335–355 (1970).
28. T. Sato et al., Nature 459, 262–265 (2009).
29. W. H. St. Clair, C. A. Stahlberg, J. W. Osborne, Virchows
Arch. B Cell Pathol. Incl. Mol. Pathol. 47, 27–33 (1984).
30. T. Savin et al., Nature 476, 57–62 (2011).
Acknowledgments: We thank M. Kirschner for providing
Xenopus tadpoles and O. Pourquie for providing snake embryos.
D.L.K. and Tufts University hold a series of patents that cover the
processing of silk into material structures, including those used
in the research reported here. T.T. acknowledges the Academy of
Finland for support. Computations were run at CSC–IT Center
for Science, Finland. C.J.T. acknowledges the support of a grant
from NIH RO1 HD047360. L.M. acknowledges the support of
the MacArthur Foundation.
Supplementary Materials
www.sciencemag.org/content/342/6155/212/suppl/DC1
Materials and Methods
Supplementary Text
Figs. S1 to S11
Movies S1 to S3
8 April 2013; accepted 13 August 2013
Published online 29 August 2013;
10.1126/science.1238842
REPORTS
Evidence for Water in the Rocky Debris
of a Disrupted Extrasolar Minor Planet
J. Farihi,1
* B. T. Gänsicke,2
D. Koester3
The existence of water in extrasolar planetary systems is of great interest because it constrains the
potential for habitable planets and life. We have identified a circumstellar disk that resulted
from the destruction of a water-rich and rocky extrasolar minor planet. The parent body formed
and evolved around a star somewhat more massive than the Sun, and the debris now closely orbits
the white dwarf remnant of the star. The stellar atmosphere is polluted with metals accreted
from the disk, including oxygen in excess of that expected for oxide minerals, indicating that the
parent body was originally composed of 26% water by mass. This finding demonstrates that
water-bearing planetesimals exist around A- and F-type stars that end their lives as white dwarfs.
T
he enormous recent progress in the dis-
covery of exoplanetary systems provides a
growing understanding of their frequency
and nature, but our knowledge is still limited in
many respects. There is now observational evi-
dence of rocky exoplanets (1, 2), and the mass
and radius (and hence density) of these planets
can be calculated from transit depth and radial
velocity amplitude; however, estimates of their
bulk composition remain degenerate and model-
dependent. Transit spectroscopy offers some in-
formation on giant exoplanet atmospheres (3), and
planetesimal debris disks often reveal the signa-
ture of emitting dust and gas species (4), yet both
techniques only scratch the surface of planets, as-
teroids, and comets. Interestingly, white dwarfs—
the Earth-sized embers of stars like the Sun—offer
a unique window onto terrestrial exoplanetary sys-
tems: These stellar remnants can distill entire
1
Institute of Astronomy, University of Cambridge, Cambridge
CB3 0HA, UK. 2
Department of Physics, University of Warwick,
Coventry CV5 7AL, UK. 3
Institut für Theoretische Physik und
Astrophysik, University of Kiel, 24098 Kiel, Germany.
*Corresponding author. E-mail: jfarihi@ast.cam.ac.uk
11 OCTOBER 2013 VOL 342 SCIENCE www.sciencemag.org218
3. planetesimals into their constituent elements,
thus providing the bulk chemical composition for
the building blocks of solid exoplanets.
Owing to high surface gravities, any atmo-
spheric heavy elements sink rapidly as white
dwarfs cool below 25,000 K (5), leaving be-
hind only hydrogen and helium in their outer-
most layers—a prediction that is corroborated
by observation (6). Those white dwarfs with rocky
planetary system remnants can become con-
taminated by the accretion of small, but spec-
troscopically detectable, amounts of metals (7).
Heavy element absorption lines in cool white
dwarfs are a telltale of external pollution, often
implying either ongoing mass accretion rates
above 108
g s−1
(8) or large asteroid-sized masses
of metals within the convection zone of the
star (9).
In recent years, metal-rich dust (10, 11) and gas
(12) disks, likely produced by the tidal disruption
of a large asteroid (13), have been observed to
be closely orbiting 30 cool white dwarfs [e.g.,
(14–19)] and provide a ready explanation for
the metal absorption features seen in their atmo-
spheres (20). The circumstellar material being
gradually accreted by the white dwarf can be
directly observed in the stellar photosphere to
reveal its elemental abundances (21). These plan-
etary system remnants offer empirical insight
into the assembly and chemistry of terrestrial exo-
planets that is unavailable for any exoplanet or-
biting a main-sequence star.
Until now, no white dwarf has shown re-
liable evidence for the accretion of water-rich,
rocky planetary material. Unambiguous signa-
tures of icy asteroids at white dwarfs should
include (i) atmospheric metal pollution rich in
refractory elements; (ii) trace oxygen in excess
of that expected for metal oxides; (iii) circum-
stellar debris from which these elements are ac-
creted; and, where applicable, (iv) trace hydrogen
(in a helium-dominated atmosphere) sufficient
to account for the excess oxygen as H2O. The
presence of a circumstellar disk signals that ac-
cretion is ongoing, identifies the source material,
and enables a confident quantitative assessment
of the accreted elemental abundances, which in
turn allows a calculation of the water fraction of
the disrupted parent body.
The metal-enriched white dwarfs GD 362 and
GD 16 both have circumstellar disks and relatively
large trace hydrogen abundances in helium-
dominated atmospheres (22), but as yet no as-
sessment of photospheric oxygen is available
(21, 23). These two stars have effective temper-
atures below 12,000 K, and their trace hydrogen
could potentially be the result of helium dredge-
up in a previously hydrogen-rich atmosphere (24).
The warmer, metal-lined white dwarfs GD 61
and GD 378 have photospheric oxygen (25), but
the accretion history of GD 378 is unconstrained
(i.e., it does not have a detectable disk), and
without this information, the atmospheric oxygen
could be consistent with that contained in dry min-
erals common in the inner solar system (26). In
the case of GD 61, elemental abundance uncer-
tainties have previously prevented a formally sig-
nificant detection of oxygen excess (27).
We used the Cosmic Origins Spectrograph
(COS) onboard the Hubble Space Telescope to
obtain ultraviolet spectroscopy of the white dwarf
GD 61, and, together with supporting ground-
based observations, we derived detections or lim-
its for all the major rock-forming elements (O,
Mg, Al, Si, Ca, Fe). These data permit a con-
fident evaluation of the total oxygen fraction
present in common silicates within the parent
body of the infalling material, and we identified
excess oxygen attributable to H2O as follows.
(i) The observed carbon deficiency indicates that
this element has no impact on the total oxygen
budget, even if every atom is delivered as CO2.
(ii) The elements Mg, Al, Si, and Ca are as-
sumed to be carried as MgO, Al2O3, SiO2, and
CaO at the measured or upper-limit abundance.
(iii) The remaining oxygen exceeds that which
can be bound in FeO, and the debris is interpreted
to be water-rich. By this reasoning, we found oxy-
gen in excess of that expected for anhydrous min-
erals in the material at an H2O mass fraction of
0.26 (Table 1 and Fig. 1).
Because we have assumed the maximum al-
lowed FeO, and because some fraction of metal-
lic iron is possible, the inferred water fraction of
the debris is actually bound between 0.26 and
0.28. Although this makes little difference in the
case of GD 61, where the parent body material
appears distinctly mantle-like (27), there are at least
two cases where metallic iron is a major (and
even dominant) mass carrier within the parent
bodies of circumstellar debris observed at white
dwarfs (28). Overall, these data strongly suggest
that the material observed in and around polluted
white dwarfs had an origin in relatively massive
and differentiated planetary bodies.
We have assumed a steady state between ac-
cretion and diffusion in GD 61. However, a typ-
ical metal sinking time scale for this star is 105
years, and thus the infalling disk material could
potentially be in an early phase of accretion where
material accumulates in the outer layers, prior
to appreciable sinking (27). In this early-phase
scenario, the oxygen excess and water fraction
would increase relative to those derived from
the steady-state assumption, and hence we confi-
dently conclude that the debris around GD 61
originated in a water-rich parent body. Although
the lifetimes of disks at white dwarfs are not
robustly constrained, the best estimates imply
Table 1. Oxide and water mass fractions in
the planetary debris at GD 61. We adopt the
steady-state values, which assume accretion-diffusion
equilibrium.
Oxygen carrier Steady state Early phase
CO2 <0.002 <0.002
MgO 0.17 0.18
Al2O3 <0.02 <0.02
SiO2 0.32 0.27
CaO 0.02 0.01
FeO* 0.05 0.02
Excess 0.42 0.50
H2O in debris 0.26 0.33
*All iron is assumed to be contained in FeO; some metallic Fe
will modestly increase the excess oxygen.
Fig. 1. Oxygen budget in GD 61 and terrestrial bodies. The first two columns are the early phase
(EP) and steady-state (SS) fractions of oxygen carried by all the major rock-forming elements in GD 61,
assuming that all iron is carried as FeO. Additional columns show the oxide compositions of the bulk
silicate (crust plus mantle) Earth, Moon, Mars, and Vesta (35). Their totals do not reach 1.0 because trace
oxides have been omitted. The overall chemistry of GD 61 is consistent with a body composed almost
entirely of silicates, and thus appears relatively mantle-like but with substantial water. In contrast, Earth is
relatively water-poor and contains approximately 0.023% H2O (1.4 × 1024
g).
www.sciencemag.org SCIENCE VOL 342 11 OCTOBER 2013 219
REPORTS
4. that the chance of catching GD 61 in an early
phase is less than 1% (17, 29–31).
The helium-rich nature of GD 61 permits an
assessment of its trace hydrogen content and
total asteroid mass for a single parent body. The
total metal mass within the stellar convection
zone is 1.3 × 1021
g, roughly equivalent to that
of an asteroid 90 km in diameter. However, be-
cause metals continuously sink, it is expected
that the destroyed parent body was substantially
more massive, unless the star is being observed
shortly after the disruption event. In contrast, hy-
drogen floats and accumulates, and thus places
an upper limit on the total mass of accreted water-
rich debris. If all the trace hydrogen were deliv-
ered as H2O from a single planetesimal, the total
accreted water mass would be 5.2 × 1022
g, and a
26% H2O mass fraction would imply a parent
body mass of 2 × 1023
g, which is similar to that
of the main-belt asteroid 4 Vesta (32).
These data imply that water in planetesi-
mals can survive post–main sequence evolution.
One possibility is that solid or liquid water is
retained beneath the surface of a sufficiently large
(diameter >100 km) parent body (26), and is
thus protected from heating and vaporization
by the outermost layers. Upon shattering during
a close approach with a white dwarf, any ex-
posed water ice (and volatiles) should rapidly
sublimate but will eventually fall onto the star;
the feeble luminosities of white dwarfs are in-
capable of removing even light gases by radia-
tion pressure (31). Another possibility is that a
substantial mass of water is contained in hydrated
minerals (e.g., phyllosilicates), as observed in main-
belt asteroids via spectroscopy and inferred from
the analysis of meteorites (33). In this case, the
H2O equivalent is not removed until much higher
temperatures are attained, and such water-bearing
asteroids may remain essentially unaffected by
the giant phases of the host star.
The white dwarf GD 61 contains the unmis-
takable signature of a rocky minor planet anal-
ogous to the asteroid 1 Ceres in water content
(34) and probably analogous to Vesta in mass.
The absence of detectable carbon indicates that
the parent body of the circumstellar debris was
not an icy planetesimal analogous to comets, but
was instead similar in overall composition to
asteroids in the outer main belt. This exoplan-
etary system originated around an early A-type
star that formed large planetesimals similar to
those in the inner solar system that were the
building blocks for Earth and other terrestrial
planets.
References and Notes
1. N. M. Batalha et al., Astrophys. J. 729, 27 (2011).
2. F. Fressin et al., Nature 482, 195–198 (2012).
3. D. K. Sing et al., Mon. Not. R. Astron. Soc. 416, 1443–1455
(2011).
4. C. M. Lisse et al., Astrophys. J. 747, 93 (2012).
5. D. Koester, Astron. Astrophys. 498, 517–525 (2009).
6. B. Zuckerman, D. Koester, I. N. Reid, M. Hünsch,
Astrophys. J. 596, 477–495 (2003).
7. Astronomers use the term “metal” when referring to
elements heavier than helium.
8. D. Koester, D. Wilken, Astron. Astrophys. 453, 1051–1057
(2006).
9. J. Farihi, M. A. Barstow, S. Redfield, P. Dufour,
N. C. Hambly, Mon. Not. R. Astron. Soc. 404, 2123 (2010).
10. M. Jura, J. Farihi, B. Zuckerman, Astron. J. 137,
3191–3197 (2009).
11. W. T. Reach et al., Astrophys. J. 635, L161–L164
(2005).
12. B. T. Gänsicke, T. R. Marsh, J. Southworth, A. Rebassa-Mansergas,
Science 314, 1908–1910 (2006).
13. J. H. Debes, K. J. Walsh, C. Stark, Astrophys. J. 747, 148
(2012).
14. J. Farihi et al., Mon. Not. R. Astron. Soc. 421, 1635–1643
(2012).
15. J. Farihi, M. Jura, J. E. Lee, B. Zuckerman, Astrophys. J.
714, 1386–1397 (2010).
16. S. Xu, M. Jura, Astrophys. J. 745, 88 (2012).
17. J. Girven et al., Astrophys. J. 749, 154 (2012).
18. J. Farihi, M. Jura, B. Zuckerman, Astrophys. J. 694,
805–819 (2009).
19. M. Jura, J. Farihi, B. Zuckerman, Astrophys. J. 663,
1285–1290 (2007).
20. M. Jura, Astrophys. J. 584, L91–L94 (2003).
21. B. Zuckerman, D. Koester, C. Melis, B. M. S. Hansen,
M. Jura, Astrophys. J. 671, 872–877 (2007).
22. M. Jura, M. Muno, J. Farihi, B. Zuckerman, Astrophys. J.
699, 1473–1479 (2009).
23. D. Koester, R. Napiwotzki, B. Voss, D. Homeier,
D. Reimers, Astron. Astrophys. 439, 317–321 (2005).
24. P. E. Tremblay, P. Bergeron, Astrophys. J. 672, 1144–1152
(2008).
25. S. Desharnais, F. Wesemael, P. Chayer, J. W. Kruk,
R. A. Saffer, Astrophys. J. 672, 540–552 (2008).
26. M. Jura, S. Xu, Astron. J. 140, 1129–1136 (2010).
27. J. Farihi et al., Astrophys. J. 728, L8 (2011).
28. B. T. Gänsicke et al., Mon. Not. R. Astron. Soc. 424,
333–347 (2012).
29. B. Klein, M. Jura, D. Koester, B. Zuckerman, C. Melis,
Astrophys. J. 709, 950–962 (2010).
30. M. Jura, Astron. J. 135, 1785–1792 (2008).
31. J. Farihi, B. Zuckerman, E. E. Becklin, Astrophys. J. 674,
431–446 (2008).
32. C. T. Russell et al., Science 336, 684–686 (2012).
33. A.S.Rivkin, E.S.Howell, F.Vilas, L.A. Lebofsky, in Asteroids
III, W. F. Bottke Jr., A. Cellino, P. Paolicchi, R. P. Binzel, Eds.
(Univ. of Arizona Press, Tucson, AZ, 2002), pp. 235–253.
34. P. C. Thomas et al., Nature 437, 224–226 (2005).
35. C. Visscher, B. Fegley Jr., Astrophys. J. 767, L12 (2013).
Acknowledgments: This work is based on observations
made with the Hubble Space Telescope, which is operated
by the Association of Universities for Research in Astronomy
under NASA contract NAS 5-26555. These observations are
associated with program programs 12169 and 12474. Some
of the data presented herein were obtained at the W. M. Keck
Observatory, which is operated as a scientific partnership
among the California Institute of Technology, the University
of California, and NASA. The Observatory was made possible
by the generous financial support of the W. M. Keck
Foundation. J.F. acknowledges support from the UK Science
and Technology Facilities Council in the form of an Ernest
Rutherford Fellowship (ST/J003344/1). The research leading
to these results has received funding from the European Research
Council under the European Union’s Seventh Framework
Programme (FP/2007-2013)/ERC Grant Agreement no. 267697
(WDTracer). B.T.G. was supported in part by the UK Science and
Technology Facilities Council (ST/I001719/1). Keck telescope time
for program 2011B-0554 was granted by NOAO through the
Telescope System Instrumentation Program, funded by NSF.
Supplementary Materials
www.sciencemag.org/content/342/6155/218/suppl/DC1
Materials and Methods
Fig. S1
Tables S1 and S2
References (36, 37)
22 April 2013; accepted 15 August 2013
10.1126/science.1239447
Femtosecond Visualization
of Lattice Dynamics in
Shock-Compressed Matter
D. Milathianaki,1
* S. Boutet,1
G. J. Williams,1
A. Higginbotham,2
D. Ratner,1
A. E. Gleason,3
M. Messerschmidt,1
M. M. Seibert,1,4
D. C. Swift,5
P. Hering,1
J. Robinson,1
W. E. White,1
J. S. Wark2
The ultrafast evolution of microstructure is key to understanding high-pressure and strain-rate
phenomena. However, the visualization of lattice dynamics at scales commensurate with those
of atomistic simulations has been challenging. Here, we report femtosecond x-ray diffraction
measurements unveiling the response of copper to laser shock-compression at peak normal elastic
stresses of ~73 gigapascals (GPa) and strain rates of 109
per second. We capture the evolution
of the lattice from a one-dimensional (1D) elastic to a 3D plastically relaxed state within a few tens
of picoseconds, after reaching shear stresses of 18 GPa. Our in situ high-precision measurement of
material strength at spatial (<1 micrometer) and temporal (<50 picoseconds) scales provides
a direct comparison with multimillion-atom molecular dynamics simulations.
T
he distinct properties of materials at high-
pressure and/or strain-rate conditions lead
to a broad range of phenomena in fields
such as high-energy-density physics (1), Earth
and planetary sciences (2, 3), aerospace engi-
neering (4), and materials science (5, 6). For the
latter, a predictive understanding and control
of mechanical properties, enabled by the di-
rect comparison of experiments with large-scale
atomistic simulations, is the ultimate goal. Where-
as the bulk material behavior can be inferred
by macroscopic measurements (7, 8), key infor-
mation on the mechanical properties requires
knowledge of the physics embedded at the
lattice level. Such knowledge has traditionally
been obtained via nanosecond-resolution x-ray
11 OCTOBER 2013 VOL 342 SCIENCE www.sciencemag.org220
REPORTS
5. www.sciencemag.org/content/342/6155/218/suppl/DC1
Supplementary Materials for
Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor
Planet
J. Farihi,* B. T. Gänsicke, D. Koester
*Corresponding author. E-mail: jfarihi@ast.cam.ac.uk
Published 11 October 2013, Science 342, 218 (2013)
DOI: 10.1126/science.1239447
This PDF file includes:
Materials and Methods
Fig. S1
Tables S1 and S2
References
6. Supporting Online Material for
Evidence for Water in the Rocky Debris
of Disrupted Extrasolar Minor Planets
J. Farihi1,4∗
, B. T. G¨ansicke2
, D. Koester3
1
Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK
2
Department of Physics, University of Warwick, Coventry CV5 7AL, UK
3
Institut f¨ur Theoretische Physik und Astrophysik, University of Kiel, 24098 Kiel, Germany
4
STFC Ernest Rutherford Fellow
∗
To whom correspondence should be addressed; E-mail: jfarihi@ast.cam.ac.uk
We describe here in detail the observations and analyses supporting the main paper, specifically
the spectroscopy of the metal-enriched white dwarf atmosphere and the analytical link to the
elemental abundances of the infalling planetary debris.
1 Summary of the Observations and Datasets
GD 61 exhibits infrared excess consistent with circumstellar dust orbiting within its Roche limit
(26), and bears the unambiguous signature of debris accretion via its metal-polluted atmosphere.
The white dwarf was observed with the Cosmic Origins Spectrograph (COS) during Hubble
Space Telescope Cycle 19 on 2012 January 28. The ultraviolet spectra were obtained with a
total exposure time of 1600 s (split between two FP-POS positions) using the G130M grating
and a central wavelength setting at 1291 ˚A, covering 1130−1435 ˚A at R ≈ 18 000. The COS
data were processed and calibrated with CALCOS 2.15.6, and are shown in Figure S1. Optical
1
7. spectroscopy of GD61 was obtained on 2011 October 24 with the Keck II Telescope and the
Echelle Spectrograph and Imager (36, ESI) in echelle mode, effectively covering 3900−9200 Å
at R 13 000. The spectra were obtained in a series of 16 exposures of 900 s each, for a total
exposure time of 4 hr, and reduced using standard tasks in IRAF1
.
2 Derivation of Photospheric and Debris Abundances
Elemental abundances for GD61 were derived from the COS and ESI data by fitting white dwarf
atmospheric models (37) to the observed spectra. For these calculations, Teff = 17 280 K and
log g = 8.20 are adopted, based on a published analysis of low-resolution optical spectra (24).
The resulting photospheric abundances and upper limits are listed in Table S1 together with
previous measurements from the Far Ultraviolet Spectroscopic Explorer (24, FUSE) and Keck I
HIRES (26). Notably, all heavy element abundances agree well, despite being derived using
separate instruments and with multiple absorption lines across distinct wavelength regimes.
The transformation between the heavy element abundances in the white dwarf
atmospheres and those within the infalling planetary debris are calculated assuming a steady
state balance between accretion and diffusion. An early (or build-up) phase of accretion is
theoretically possible in GD61, but this is unlikely (see main paper). Importantly, in this case an
early phase would imply a larger oxygen excess and H2O fraction, and therefore the more
conservative, and most probable, assumption is made.
For white dwarfs with significant convection zones like GD61, the atmospheric mass
fraction Xz of heavy element z is related to its accretion rate zM via
z cvz zz tX MM (S1)
___________________________________
1
IRAF is distributed by the National Optical Astronomy Observatories, which are operated by the
Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science
Foundation.
2
8. where tz is the sinking timescale for the element and Mcvz is the mass of the stellar convection
zone. The mass fraction is determined from the model atmosphere fits and the sinking timescale
is known from white dwarf diffusion calculations (5). In essence, Equation S1 states that the
accretion rate of element z equals its rate of depletion as it settles below the mixing layer. The
ratio of two heavy elements within the debris (and hence parent body) is either the ratio of their
respective accretion rates in the steady state, or the ratio of their atmospheric mass fractions in
the early phase, and related by
˙Mz1
˙Mz2
=
Xz1
Xz2
×
tz2
tz1
(S2)
Table S2 lists the relevant quantities of GD 61 for the key elements that determine the total
oxygen budget of the debris. The steady state metal abundances relative to oxygen are taken
from the fourth column. The sinking timescales for GD 61 have been updated following a
correction in the theoretical calculations2
, and they are somewhat different than those presented
in a previous analysis (26). Notably, this correction has strengthened the case for an oxygen
excess in GD 61.
3 Evaluation of Oxygen Excess and Uncertainties
The method for calculating the overall oxygen budget is as follows. We begin with the columns
in Table S2, and in particular the identify the total oxygen budget with: 1) its mass accretion
rate for the steady state or 2) its mass within the stellar convection zone for the early phase.
We calculate the fraction of oxygen that can be absorbed as CO2 based on the upper limit for
carbon, and subtract this from the total available. Next, we perform a similar calculation for the
mass of oxygen in MgO, Al2O3, Si2, CaO, and FeO based on their detections or upper limits,
again subtracting these from the budget. After accounting for all the major oxygen carriers, any
remaining mass is considered excess.
2
http://www1.astrophysik.uni-kiel.de/~koester/astrophysics/astrophysics.html
3
9. The collective data for GD 61 is robust and comprehensive, comprising four instruments
with each probing distinct wavelength regions and containing multiple transitions for each ele-
ment from the far-ultraviolet to the red optical region. The uncertainties in the metal abundances
of this white dwarf are given as 3σ adopted values in the last column of Table S1. Using a brute
force approach, all 128 possible combinations of abundance values are calculated for C, O, Mg,
Al, Si, Ca, Fe where the abundance values N(X)/N(He) take on each of the values x ± δx.
Evaluating all possible permutations, the dispersion in the resulting oxygen excesses values
(0.068) results in a 6.1σ confidence for the case of steady state accretion.
References and Notes
1. N. M. Batalha, et al., Astrophys. J. 729, 27 (2011)
2. F. Fressin, et al., Nature 482, 195 (2012)
3. D. K. Sing, et al., Mon. Not. R. Ast. Soc. 416, 1443 (2011)
4. C. M. Lisse, et al., Astrophys. J. 747, 93 (2012)
5. D. Koester, Astron. Astrophys. 498, 517 (2009)
6. B. Zuckerman, D. Koester, I. N.Reid, M. H¨unsch, Astrophys. J. 596, 477 (2003)
7. D. Koester, D. Wilken, Astron. Astrophys. 453, 1051 (2006)
8. J. Farihi, M. A. Barstow, S. Redfield, P. Dufour, N. C. Hambly, Mon. Not. R. Ast. Soc. 404,
2123 (2010)
9. M. Jura, J. Farihi, B. Zuckerman, Astron. J. 137, 3191 (2009)
10. W. T. Reach, M. J. Kuchner, T. von Hippel, A. Burrows, F. Mullally, M. Kilic, D. E. Winget,
Astrophys. J. 635, L161 (2005)
4
10. Figure S1. The normalized COS spectra of GD 61 (grey), together with the best fitting model
spectra (red). Interstellar absorption features are indicated by vertical grey dashed lines, and
are blueshifted with respect to the photospheric features by 40 km s−1
. Geocoronal airglow of
O I at 1302.2, 1304.9, and 1306.0 ˚A can contaminate COS spectra to some degree, and typical
airglow line profiles are shown in the middle panel scaled to an arbitrary flux.
7
11. Table S1. Elemental Abundances N(X)/N(He) in GD 61
Ultraviolet Optical
Element COS FUSE ESI HIRES Adopted
Detections:
H −3.70 (0.10) −4.00 (0.10) −3.98 (0.10) −3.89 (0.15)
O −6.00 (0.15) −5.80 (0.20) −5.75 (0.20) −5.95 (0.13)
Mg −6.50 (0.30) −6.74 (0.10) −6.65 (0.18) −6.69 (0.14)
Si −6.82 (0.12) −6.70 (0.20) −6.85 (0.10) −6.85 (0.09) −6.82 (0.11)
S −8.00 (0.20) −8.00 (0.20)
Ca −7.77 (0.06) −7.90 (0.19) −7.90 (0.19)
Fe −7.60 (0.30) −7.60 (0.20) −7.60 (0.20)
Upper limits:
C −9.10 −8.80
N −8.00
Na −6.80
P −8.70
Al −7.80 −7.20
Ti −8.60
Sc −8.20
Cr −8.00
Fe −7.50
Ni −8.80
8
12. Table S2. Atmospheric and Debris Properties for Key Trace Elements in GD 61
Early Phase Steady State
Element tdiff XzMcvz
a ˙Mz
(105
yr) (1021
g) (108
g s−1
)
H ∞ 5.755
C 1.730 < 0.001 < 0.001
O 1.706 0.802 1.489
Mg 1.808 0.222 0.389
Al 1.735 < 0.019 < 0.035
Si 1.438 0.190 0.419
S 0.952 0.014 0.048
Ca 0.782 0.023 0.091
Fe 0.855 0.063 0.232
Total Z 1.332 2.704
Note. The metal-to-metal ratios within the planetary debris for the early phase and steady state
regimes are derived directly from the values in the third and fourth columns respectively.
a
The third column is the mass of each element residing in the convection zone of GD 61, and
their total (excluding hydrogen) represents a minimum mass for the parent body due to the
continual sinking of metals.
9
13. References and Notes
1. N. M. Batalha, W. J. Borucki, S. T. Bryson, L. A. Buchhave, D. A. Caldwell, J. Christensen-
Dalsgaard, D. Ciardi, E. W. Dunham, F. Fressin, T. N. Gautier, R. L. Gilliland, M. R.
Haas, S. B. Howell, J. M. Jenkins, H. Kjeldsen, D. G. Koch, D. W. Latham, J. J. Lissauer,
G. W. Marcy, J. F. Rowe, D. D. Sasselov, S. Seager, J. H. Steffen, G. Torres, G. S. Basri,
T. M. Brown, D. Charbonneau, J. Christiansen, B. Clarke, W. D. Cochran, A. Dupree, D.
C. Fabrycky, D. Fischer, E. B. Ford, J. Fortney, F. R. Girouard, M. J. Holman, J.
Johnson, H. Isaacson, T. C. Klaus, P. Machalek, A. V. Moorehead, R. C. Morehead, D.
Ragozzine, P. Tenenbaum, J. Twicken, S. Quinn, J. VanCleve, L. M. Walkowicz, W. F.
Welsh, E. Devore, A. Gould, Kepler’s first rocky planet: Kepler-10b. Astrophys. J. 729,
27 (2011). doi:10.1088/0004-637X/729/1/27
2. F. Fressin, G. Torres, J. F. Rowe, D. Charbonneau, L. A. Rogers, S. Ballard, N. M. Batalha,
W. J. Borucki, S. T. Bryson, L. A. Buchhave, D. R. Ciardi, J. M. Désert, C. D. Dressing,
D. C. Fabrycky, E. B. Ford, T. N. Gautier 3rd, C. E. Henze, M. J. Holman, A. Howard, S.
B. Howell, J. M. Jenkins, D. G. Koch, D. W. Latham, J. J. Lissauer, G. W. Marcy, S. N.
Quinn, D. Ragozzine, D. D. Sasselov, S. Seager, T. Barclay, F. Mullally, S. E. Seader, M.
Still, J. D. Twicken, S. E. Thompson, K. Uddin, Two Earth-sized planets orbiting Kepler-
20. Nature 482, 195–198 (2012). doi:10.1038/nature10780 Medline
3. D. K. Sing, F. Pont, S. Aigrain, D. Charbonneau, J.-M. Désert, N. Gibson, R. Gilliland, W.
Hayek, G. Henry, H. Knutson, A. L. des Etangs, T. Mazeh, A. Shporer, Hubble Space
Telescope transmission spectroscopy of the exoplanet HD 189733b: High-altitude
atmospheric haze in the optical and near-ultraviolet with STIS. Mon. Not. R. Astron. Soc.
416, 1443–1455 (2011). doi:10.1111/j.1365-2966.2011.19142.x
4. C. M. Lisse, M. C. Wyatt, C. H. Chen, A. Morlok, D. M. Watson, P. Manoj, P. Sheehan, T. M.
Currie, P. Thebault, M. L. Sitko, Spitzer evidence for a late-heavy bombardment and the
formation of ureilites in η Corvi at ∼1 Gyr. Astrophys. J. 747, 93 (2012).
doi:10.1088/0004-637X/747/2/93
5. D. Koester, Accretion and diffusion in white dwarfs. Astron. Astrophys. 498, 517–525 (2009).
doi:10.1051/0004-6361/200811468
14. 6. B. Zuckerman, D. Koester, I. N. Reid, M. Hünsch, Metal lines in DA white dwarfs. Astrophys.
J. 596, 477–495 (2003). doi:10.1086/377492
7. Astronomers use the term ―metal‖ when referring to elements heavier than helium.
8. D. Koester, D. Wilken, The accretion-diffusion scenario for metals in cool white dwarfs.
Astron. Astrophys. 453, 1051–1057 (2006). doi:10.1051/0004-6361:20064843
9. J. Farihi, M. A. Barstow, S. Redfield, P. Dufour, N. C. Hambly, Mon. Not. R. Astron. Soc.
404, 2123 (2010).
10. M. Jura, J. Farihi, B. Zuckerman, Six white dwarfs with circumstellar silicates. Astron. J.
137, 3191–3197 (2009). doi:10.1088/0004-6256/137/2/3191
11. W. T. Reach, M. J. Kuchner, T. von Hippel, A. Burrows, F. Mullally, M. Kilic, D. E. Winget,
The dust cloud around the white dwarf G29-38. Astrophys. J. 635, L161–L164 (2005).
doi:10.1086/499561
12. B. T. Gänsicke, T. R. Marsh, J. Southworth, A. Rebassa-Mansergas, A gaseous metal disk
around a white dwarf. Science 314, 1908–1910 (2006). doi:10.1126/science.1135033
Medline
13. J. H. Debes, K. J. Walsh, C. Stark, The link between planetary systems, dusty white dwarfs,
and metal-polluted white dwarfs. Astrophys. J. 747, 148 (2012). doi:10.1088/0004-
637X/747/2/148
14. J. Farihi, B. T. Gänsicke, P. R. Steele, J. Girven, M. R. Burleigh, E. Breedt, D. Koester, A
trio of metal-rich dust and gas discs found orbiting candidate white dwarfs with K -band
excess. Mon. Not. R. Astron. Soc. 421, 1635–1643 (2012). doi:10.1111/j.1365-
2966.2012.20421.x
15. J. Farihi, M. Jura, J. E. Lee, B. Zuckerman, Strengthening the case for asteroidal accretion:
Evidence for subtle and diverse disks at white dwarfs. Astrophys. J. 714, 1386–1397
(2010). doi:10.1088/0004-637X/714/2/1386
16. S. Xu, M. Jura, Spitzer observations of white dwarfs: The missing planetary debris around
DZ stars. Astrophys. J. 745, 88 (2012). doi:10.1088/0004-637X/745/1/88
15. 17. J. Girven, C. S. Brinkworth, J. Farihi, B. T. Gänsicke, D. W. Hoard, T. R. Marsh, D. Koester,
Constraints on the lifetimes of disks resulting from tidally destroyed rocky planetary
bodies. Astrophys. J. 749, 154 (2012). doi:10.1088/0004-637X/749/2/154
18. J. Farihi, M. Jura, B. Zuckerman, Infrared signatures of disrupted minor planets at white
dwarfs. Astrophys. J. 694, 805–819 (2009). doi:10.1088/0004-637X/694/2/805
19. M. Jura, J. Farihi, B. Zuckerman, Externally polluted white dwarfs with dust disks.
Astrophys. J. 663, 1285–1290 (2007). doi:10.1086/518767
20. M. Jura, A tidally disrupted asteroid around the white dwarf G29-38. Astrophys. J. 584, L91–
L94 (2003). doi:10.1086/374036
21. B. Zuckerman, D. Koester, C. Melis, B. M. S. Hansen, M. Jura, The chemical composition of
an extrasolar minor planet. Astrophys. J. 671, 872–877 (2007). doi:10.1086/522223
22. M. Jura, M. Muno, J. Farihi, B. Zuckerman, X-ray and infrared observations of two
externally polluted white dwarfs. Astrophys. J. 699, 1473–1479 (2009).
doi:10.1088/0004-637X/699/2/1473
23. D. Koester, R. Napiwotzki, B. Voss, D. Homeier, D. Reimers, HS 0146+1847—a DAZB
white dwarf of very unusual composition. Astron. Astrophys. 439, 317–321 (2005).
doi:10.1051/0004-6361:20053058
24. P. E. Tremblay, P. Bergeron, The ratio of helium‐ to hydrogen‐atmosphere white dwarfs:
Direct evidence for convective mixing. Astrophys. J. 672, 1144–1152 (2008).
doi:10.1086/524134
25. S. Desharnais, F. Wesemael, P. Chayer, J. W. Kruk, R. A. Saffer, FUSE observations of
heavy elements in the photospheres of cool DB white dwarfs. Astrophys. J. 672, 540–552
(2008). doi:10.1086/523699
26. M. Jura, S. Xu, The survival of water within extrasolar minor planets. Astron. J. 140, 1129–
1136 (2010). doi:10.1088/0004-6256/140/5/1129
27. J. Farihi, C. S. Brinkworth, B. T. Gänsicke, T. R. Marsh, J. Girven, D. W. Hoard, B. Klein,
D. Koester, Possible signs of water and differentiation in a rocky exoplanetary body.
Astrophys. J. 728, L8 (2011). doi:10.1088/2041-8205/728/1/L8
16. 28. B. T. Gänsicke, D. Koester, J. Farihi, J. Girven, S. G. Parsons, E. Breedt, The chemical
diversity of exo-terrestrial planetary debris around white dwarfs. Mon. Not. R. Astron.
Soc. 424, 333–347 (2012). doi:10.1111/j.1365-2966.2012.21201.x
29. B. Klein, M. Jura, D. Koester, B. Zuckerman, C. Melis, Chemical abundances in the
externally polluted white dwarf GD 40: Evidence of a rocky extrasolar minor planet.
Astrophys. J. 709, 950–962 (2010). doi:10.1088/0004-637X/709/2/950
30. M. Jura, Pollution of single white dwarfs by accretion of many small asteroids. Astron. J.
135, 1785–1792 (2008). doi:10.1088/0004-6256/135/5/1785
31. J. Farihi, B. Zuckerman, E. E. Becklin, Spitzer IRAC observations of white dwarfs. I. Warm
dust at metal-rich degenerates. Astrophys. J. 674, 431–446 (2008). doi:10.1086/521715
32. C. T. Russell, C. A. Raymond, A. Coradini, H. Y. McSween, M. T. Zuber, A. Nathues, M. C.
De Sanctis, R. Jaumann, A. S. Konopliv, F. Preusker, S. W. Asmar, R. S. Park, R.
Gaskell, H. U. Keller, S. Mottola, T. Roatsch, J. E. Scully, D. E. Smith, P. Tricarico, M.
J. Toplis, U. R. Christensen, W. C. Feldman, D. J. Lawrence, T. J. McCoy, T. H.
Prettyman, R. C. Reedy, M. E. Sykes, T. N. Titus, Dawn at Vesta: Testing the
protoplanetary paradigm. Science 336, 684–686 (2012). doi:10.1126/science.1219381
Medline
33. A. S. Rivkin, E. S. Howell, F. Vilas, L. A. Lebofsky, in Asteroids III, W. F. Bottke Jr., A.
Cellino, P. Paolicchi, R. P. Binzel, Eds. (Univ. of Arizona Press, Tucson, 2002), pp. 235–
253.
34. P. C. Thomas, J. W. Parker, L. A. McFadden, C. T. Russell, S. A. Stern, M. V. Sykes, E. F.
Young, Differentiation of the asteroid Ceres as revealed by its shape. Nature 437, 224–
226 (2005). doi:10.1038/nature03938 Medline
35. C. Visscher, B. Fegley Jr., Chemistry of impact-generated silicate melt-vapor debris disks.
Astrophys. J. 767, L12 (2013). doi:10.1088/2041-8205/767/1/L12
36. A. I. Sheinis, M. Bolte, H. W. Epps, R. I. Kibrick, J. S. Miller, M. V. Radovan, B. C.
Bigelow, B. M. Sutin, ESI, a new Keck Observatory echellette spectrograph and imager.
Proc. Astron. Soc. Pac. 114, 851–865 (2002). doi:10.1086/341706
37. D. Koester, Mem. Soc. Astron. Ital. 81, 921 (2010).