Planet-Devouring Star Reveals Possible Limestone Crumbs (SDSSJ1043+0855 )

Extrordinary if it's real...

http://www.keckobservatory.org/recent/entry/planet_devouring_star_reveals_possible_limestone_crumbs

A group of researchers using the W. M. Keck Observatory have discovered a planet-like body that may have been encrusted in limestone and is having its surface layers devoured by its deceased host star. In addition to extending a relatively new method of determining the chemical composition of planets to examine their internal structure, the team found that the rocky material being accreted by the star could be comprised of minerals that are typically associated with marine life processes here on Earth

Link to Centauri-dreams :
http://www.centauri-dreams.org/?p=35816

An alien apocalypse. Oops.

Many skepticism in the coment section of Centauri Dreams...

The abstract, as presented in the AAS meeting:

Quote :

We present spectroscopic observations of the dust- and gas-enshrouded, polluted white dwarf star SDSSJ104341.53+085558.2 (hereafter SDSSJ1043). Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet spectra combined with deep Keck HIRES optical spectroscopy reveal the elements C, O, Mg, Al, Si, P, S, Ca, Fe, and Ni and enable useful limits for Sc, Ti, V, Cr, and Mn in the photosphere of SDSSJ1043. From this suite of elements we determine that the parent body being accreted by SDSSJ1043 is dry, rocky, and iron-poor. Synthesizing all available heavily-polluted white dwarf measurements, we find a trend in the Fe/Mg vs Fe/Si abundance ratio-space suggestive of whether accreted material originates from the inner or outer regions of a rocky body; we use this trend to identify the material being accreted by SDSSJ1043 as likely to have come from the outermost layers of a differentiated object. Enhanced levels of Ca and C in this object can be explained by the presence of significant amounts of calcium-carbonate and, if definitive, could be suggestive of a world with a crust rich in limestone.

Quote :

Many skepticism in the coment section of Centauri Dreams...

Don't they refuse to believe anything at face value, though?

Moreover everyone seemed to have jumped to the conclusion that the authors indicate it is biological (they didn't), then patted themselves on the back for wonkily deconstructing what information is given in the press release. What good does disassembling something do if you cannot build something else from it?

It is probably unwise to make comments without seeing the entire paper, but from what has been presented I would say that the conclusions seem reasonable. Calcium carbonate is a fairly simple compound, so a CaCO₃-rich lithosphere is not unimaginable (perhaps for a more carbon-rich planet than Earth). Though not necessarily biological, on Earth calcium carbonate is strongly associated with marine processes, so one must wonder if this applies in the general case.

A paper about this star from another group:

Another one grinds the dust: Variability of the planetary debris disc at the white dwarf SDSS J104341.53+085558.2

Quote :

We report nine years of optical spectroscopy of the metal-polluted white dwarf SDSS J104341.53+085558.2, which presents morphological variations of the line profiles of the 8600 Å Ca II triplet emission from the gaseous component of its debris disc. Similar changes in the shape of the Ca II triplet have also been observed in two other systems that host a gaseous disc, and are likely related to the same mechanism. We report the Mg, Si, and Ca abundances of the debris detected in the photosphere of SDSS J1043+0855, place upper limits on O and Fe, and derive an accretion rate of (2.5 - 12) x 10⁸ g/s, consistent with those found in other systems with detected debris discs. The Mg/Si ratio and the upper limit on the Fe/Si ratio of the accreted material broadly agree with those found for the crust of the Earth. We also review the range of variability observed among white dwarfs with planetary debris discs.

The observations are less intensive than what the Keck group results are made out to be, but they do at least find that the material composition is more planet-like than asteroid-like.

Here's the preprint:

Does a Differentiated, Carbonate-Rich, Rocky Object Pollute the White Dwarf SDSSJ104341.53+085558.2?

Quote :

We present spectroscopic observations of the dust- and gas-enshrouded, polluted, single white dwarf star SDSSJ104341.53+085558.2 (hereafter SDSSJ1043+0855). Hubble Space Telescope Cosmic Origins Spectrograph far-ultraviolet spectra combined with deep Keck HIRES optical spectroscopy reveal the elements C, O, Mg, Al, Si, P, S, Ca, Fe, and Ni and enable useful limits for Sc, Ti, V, Cr, and Mn in the photosphere of SDSSJ1043+0855. From this suite of elements we determine that the parent body being accreted by SDSSJ1043+0855 is similar to the silicate Moon or the outer layers of Earth in that it is rocky and iron-poor. Combining this with comparison to other heavily polluted white dwarf stars, we are able to identify the material being accreted by SDSSJ1043+0855 as likely to have come from the outermost layers of a differentiated object. Furthermore, we present evidence that some polluted white dwarfs (including SDSSJ1043+0855) allow us to examine the structure of differentiated extrasolar rocky bodies. Enhanced levels of carbon in the body polluting SDSSJ1043+0855 relative to the Earth-Moon system can be explained with a model where a significant amount of the accreted rocky minerals took the form of carbonates; specifically, through this model the accreted material could be up to 9% calcium-carbonate by mass.

The authors fairly strongly support a water-based origin for a high calcium carbonate content, so this can be interpreted as indirect evidence for water on a terrestrial ex-planet.