4,470 research outputs found
An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect
Planets like the Earth cannot form unless elements heavier than helium are
available. These heavy elements, or `metals', were not produced in the big
bang. They result from fusion inside stars and have been gradually building up
over the lifetime of the Universe. Recent observations indicate that the
presence of giant extrasolar planets at small distances from their host stars,
is strongly correlated with high metallicity of the host stars. The presence of
these close-orbiting giants is incompatible with the existence of earth-like
planets. Thus, there may be a Goldilocks selection effect: with too little
metallicity, earths are unable to form for lack of material, with too much
metallicity giant planets destroy earths. Here I quantify these effects and
obtain the probability, as a function of metallicity, for a stellar system to
harbour an earth-like planet. I combine this probability with current estimates
of the star formation rate and of the gradual build up of metals in the
Universe to obtain an estimate of the age distribution of earth-like planets in
the Universe. The analysis done here indicates that three quarters of the
earth-like planets in the Universe are older than the Earth and that their
average age is 1.8 +/- 0.9 billion years older than the Earth. If life forms
readily on earth-like planets - as suggested by the rapid appearance of life on
Earth - this analysis gives us an age distribution for life on such planets and
a rare clue about how we compare to other life which may inhabit the Universe.Comment: 13 pages, 2 figures, minor revisions to conform to accepted Icarus
version, in pres
Is the Pre-WMAP CMB Data Self-consistent?
Although individual observational groups vigorously test their data sets for
systematic errors, the pre-WMAP CMB observational data set has not yet been
collectively tested. Under the assumption that the concordance model is the
correct model, we have explored residuals of the observational data with
respect to this model to see if any patterns emerge that can be identified with
systematic errors. We found no significant trends associated with frequency,
frequency channels, calibration source, pointing uncertainty, instrument type,
platform and altitude. We did find some evidence at the ~ 1 to ~ 2 sigma level
for trends associated with angular scale (l range) and absolute galactic
latitude. The slope of the trend in galactic latitude is consistent with low
level galactic contamination. The residuals with respect to l may indicate that
the concordance model used here needs slight modification. See Griffiths &
Lineweaver (2003) for more detail.Comment: 8 pages, 4 figures, to be published in the proceedings of "The Cosmic
Microwave Background and its Polarization", New Astronomy Reviews, (eds. S.
Hanany and K.A. Olive
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