Knowing where to point our future planet-hunter telescopes in space is crucial, because we’ll want to maximize observing time for the most likely stellar candidates. There are various ways to narrow the list, but one involves the study of existing spectroscopic data. Charles Lineweaver (Australian National University) calls it a ‘poor man’s technique,’ an inexpensive way to look at the elements within stars and calculate from their abundance the kind of planets that may have formed in that system.
The differences between the rocky terrestrial planets in our own Solar System and the outer gas giants are instructive. We can assume that planets form from the same raw materials as the stars they orbit. But the inner planets lack volatile gases like hydrogen and helium compared to the Sun, while maintaining the same abundances of heavier elements like silica and iron. The latter don’t vaporise easily in warmer inner orbits.
So a star heavy in iron is likely circled by inner planets abundant in the same element. The kind of elements involve may tell a fascinating tale. Lineweaver told Australia National Broadcasting’s Science Online that the ratio of carbon to oxygen, for example, could predict the formation of vastly different kinds of planets. Here’s a quote from the article:
“As the planetary disc cools, carbon and oxygen combine to form carbon monoxide, which gets blown away. If there is more oxygen than carbon, the oxygen that’s left combines with everything else and you’ll end up with a rocky planet like Earth… But if there’s more carbon, it combines with silica and magnesium and iron and you end up with all sorts of weird carbide planets that may have a diamond core.”
Hence a kind of element mapping may take place: The ratio of carbon to oxygen being higher near the center of the galaxy, such diamond carbide planets may be more abundant there. In any case, we have spectroscopic data in great quantity for nearby worlds we’ll be examining with future planet-finder missions. An upcoming Lineweaver paper will go into detail about how predictive the abundances of these elements may be.
Hi Paul
Carbon-rich planets is such a cool idea. I can imagine huge amounts of amorphous carbonia in place of the high-pressure Ice phases we get in Ice Giants, or planets with oceans of carbon dioxide. Super-critical carbon dioxide has also been suggested as a medium for life. With a bit of water around we could get layers of water on top of deep layers of carbon dioxide – two oceans kept separate by their density. Alternatively with less oxygen and more hydrogen the planets could be covered in hydrocarbons – oil. Oceans of crude.
Better not tell Exxon about that one.
I always thought that stellar characteristics would determine planetary system composition, in particular metallicity and stellar mass. ‘Knowing the mother is knowing the children’.
But it is very interesting to see that become more specific for different elements. I am looking forward to the day that planetary systems can be predicted and modeled in detail on the basis of stellar element composition.
Astrometric effects of solar-like magnetic activity in late-type stars and their relevance for the detection of extrasolar planets
Authors: A. F. Lanza, C. De Martino, M. Rodono’
(Submitted on 20 Jun 2007)
Abstract: Using a simple model based on the characteristics of sunspots and faculae in solar active regions, the effects of surface brightness inhomogeneities on the position of the photocentre of the disk of a solar-like, magnetically active star, are studied. A general law is introduced, giving the maximum amplitude of the photocentre excursion produced by a distribution of active regions with a given surface filling factor. The consequences for the detection of extrasolar planets by means of the astrometric method are investigated with some applications to forthcoming space missions, such as GAIA and SIM, as well as to ground-based interferometric measurements. Spurious detections of extrasolar planets can indeed be caused by activity-induced photocentre oscillations, requiring a simultaneous monitoring of the optical flux and a determination of the rotation period and of the level of activity of the target stars for an appropriate discrimination.
Comments: 17 pages, 6 figures, accepted by New Astronomy
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0706.2942v1 [astro-ph]
Submission history
From: Antonino Francesco Lanza [view email]
[v1] Wed, 20 Jun 2007 09:28:27 GMT (42kb)
http://arxiv.org/abs/0706.2942
Astronomers are First to Successfully Predict Extra-Solar Planet
http://www.spaceref.com/news/viewpr.nl.html?pid=24463
“Astronomers, including one at The University of Arizona,
have successfully predicted the existence of an unknown
planet, the first since Neptune was predicted in the 1840s.
This planet, however, is outside our own solar system,
circling a star a little more than 200 light years from Earth.”
Parent Stars of Extrasolar Planets. IX. Lithium Abundances
Authors: Guillermo Gonzalez
(Submitted on 4 Feb 2008)
Abstract: We compare the Li abundances of a sample of stars with planets discovered with the Doppler method to a sample of stars without detected planets. We prepared the samples by combining the Li abundances reported in several recent studies in a consistent way. Our results confirm recent claims that the Li abundances of stars with planets are smaller than those of stars without planets near the solar temperature. We also find that the vsini and $R^{‘}_{\rm HK}$ anomalies correlate with the Li abundance anomalies. These results suggest that planet formation processes have altered the rotation and Li abundances of stars that host Doppler detected planets. We encourage others to test these findings with additional observations of Li in stars with temperatures between 5600 and 6200 K.
Comments: 8 pages, 9 figures; accepted for publication in MNRAS
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0802.0434v1 [astro-ph]
Submission history
From: Guillermo Gonzalez [view email]
[v1] Mon, 4 Feb 2008 15:19:04 GMT (146kb,D)
http://arxiv.org/abs/0802.0434