Image Caption: An artist’s impression of a massive asteroid belt in orbit around a star. The new work with SDSS data shows that similar rubble around many white dwarfs contaminates these stars with rocky material and water. Credit: NASA-JPL / Caltech / T. Pyle (SSC). Full size version
An international team of astronomers have discovered compelling evidence that rocky planets are commonplace in our Galaxy. Leicester University scientist and lead researcher Dr Jay Farihi surveyed white dwarfs, the compact remnants of stars that were once like our Sun, and found that many show signs of contamination by heavier elements and possibly even water, improving the prospects for extraterrestrial life. On Tuesday 13th April Dr Farihi will present his results at the RAS National Astronomy Meeting (NAM 2010) in Glasgow.
White dwarf stars are the endpoint of stellar evolution for the vast majority (>90%) of all stars in the Milky Way, including our Sun. Because they should have essentially pure hydrogen or pure helium atmospheres, if heavier elements (in astronomy described as ‘metals’, examples including calcium, magnesium and iron) are found then these must be external pollutants. For decades, it was believed that the interstellar medium, the tenuous gas between the stars, was the source of metals in these polluted white dwarfs.
Farihi and his team used data from the Sloan Digital Sky Survey (SDSS), a project that aims to survey the sky in infrared light, imaging more than 100 million objects and following up 1 million of these by obtaining their spectrum (dispersing the light by colour).
By examining the positions, motions and spectra of the white dwarfs identified in the SDSS, Farihi and his team show that this is no longer a viable theory. Instead, rocky planetary debris is almost certainly the culprit in most or all cases.
The new work indicates that at least 3% and perhaps as much as 20% of all white dwarfs are contaminated in this way, with the debris most likely in the form of rocky minor planets with a total mass of about that of a 140 km diameter asteroid.
This implies that a similar proportion of stars like our Sun, as well as stars that are a little more massive like Vega and Fomalhaut, build terrestrial planetary systems. Astronomers are thus playing the role of celestial archaeologists by studying the 'ruins' of rocky planets and or their building blocks.
The scientists also measured the composition of the contaminating planetary debris through its chemical signature which stands out in the otherwise pure atmosphere of the white dwarfs.
Excitingly, it appears a significant fraction of these stars are polluted with material that contained water, with important implications for the frequency of habitable planets around other stars. If internal water is present in a substantial fraction of asteroids around other stars, like those that contaminated the white dwarfs, it is conceivable that at least simple life may be common throughout the Galaxy.
Dr Farihi comments: “In our own Solar System with at least one watery, habitable planet, the asteroid belt - the leftover building blocks of the terrestrial planets - is several percent water by mass. From our study of white dwarfs, it appears there are basic similarities found among asteroid-like objects around other stars; hence it is likely a fraction of these white dwarfs once harbored watery planets, and possibly life.”
Dr Jay Farihi
University of Leicester
Tel: +44 (0)116 252 3577
Mob: +44 (0)779 449 2697
E-mail: jf123@star.le.ac.uk
NAM 2010 Press Office (12th – 16th April only)
Room G358
Gilbert Scott Building
University of Glasgow.
Tel: +44 (0)141 330 7409, +44 (0)141 330 7410, +44 (0)141 330 7411
Dr Robert Massey
Press and Policy Officer
Royal Astronomical Society
Mob: +44 (0)794 124 8035
E-mail: rm@ras.org.uk
Anita Heward
Press Officer
Royal Astronomical Society
Mob: +44 (0)7756 034 243
E-mail: anitaheward@btopenworld.com
FURTHER INFORMATION
The results will appear in the journal Monthly Notices of the Royal Astronomical Society. A preprint of the paper can be seen at http://arxiv.org/abs/1001.5025
NOTES FOR EDITORS
The RAS National Astronomy Meeting 2010 will take place from 12-16th April at the University of Glasgow. The conference is held in conjunction with the UK Solar Physics (UKSP) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST) meetings. NAM2010 (www.astro.gla.ac.uk/nam2010/) is principally sponsored by the Royal Astronomical Society (RAS) and the University of Glasgow.”
