Chemistry of White Dwarf Planets —“Basically Earth-like”
The NASA/ESA Hubble Space Telescope has found signs of Earth-like planets in an unlikely place: the atmospheres of a pair of burnt-out stars in a nearby star cluster. The white dwarf stars are being polluted by debris from asteroid-like objects falling onto them. This discovery suggests that rocky planet assembly is common in clusters, say researchers.
The stars, known as white dwarfs — small, dim remnants of stars once like the Sun — reside 150 light-years away in the Hyadesstar cluster, in the constellation of Taurus (The Bull). The cluster is relatively young, at only 625 million years old.
Astronomers believe that all stars formed in clusters. However, searches for planets in these clusters have not been fruitful — of the roughly 800 exoplanets known, only four are known to orbit stars in clusters. This scarcity may be due to the nature of the cluster stars, which are young and active, producing stellar flares and other outbursts that make it difficult to study them in detail.
The two “polluted” Hyades white dwarfs are part of a search of planetary debris around more than 100 white dwarfs, led by Boris Gänsicke of the University of Warwick, United Kingdom. Using computer models of white dwarf atmospheres, Detlev Koester from the University of Kiel in Germany is determining the abundances of various elements that can be traced to planets in the COS data.
Hubble’s spectroscopic observations identified silicon in the atmospheres of two white dwarfs, a major ingredient of the rocky material that forms Earth and other terrestrial planets in the Solar System. This silicon may have come from asteroids that were shredded by the white dwarfs’ gravity when they veered too close to the stars. The rocky debris likely formed a ring around the dead stars, which then funnelled the material inwards.
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