In a world dominated by short-term thinking, we tend to be driven by media cycles. That makes the coverage of science, among other subjects, problematic. Science operates through the analysis of detail as various minds subject a problem to hypotheses that can be tested experimentally. In other words, good science often takes time, which is why situations like the Gliese 581c story can be so frustrating.
Announce a habitable planet around another star and the media love you. Spend months and (if needed) years subjecting the habitability question to analysis and you’re not on the public radar. Many scientists have come to question whether Gliese 581c is remotely habitable; some even argue for habitability for the next planet out, Gliese 581d. We’re still trying to weigh the data, and such deliberate processes aren’t the sort of thing to replace the latest Hollywood starlet scandals on CNN.
The good scientist ignores media vagaries and proceeds with the painstaking details. The hunt for better tools for analysis is unceasing. Take the so-called Rossiter effect. It shows up in radial velocity data during a planetary transit, causing a distortion that seems to indicate a radial velocity shift. But there is no change in the velocity of the star being studied — the Rossiter effect only mimics such a change. The transiting planet has, in other words, meddled with the light being studied.
William F. Welsh and Jerome Orosz (San Diego State University) want to know whether this radial velocity ‘anomaly’ can be used to detect an Earth-like planet. After all, they point out, in the case of a terrestrial body orbiting beyond 0.5 AU, the amplitude of the Rossiter effect can be larger than the radial velocity of the host star’s orbit. The two astronomers simulated Rossiter effect signals and threw in observational noise to study the question. Could a useful signal be extracted from the noise of periodic star pulsations and other stellar variables?
The results aren’t encouraging for planets of Earth’s radius. But it does appear that the Rossiter effect could snare a slightly larger planet, especially as we move up to two Earth radii. Here’s the gist:
While using the Rossiter eﬀect for discovering an Earth-like planet is certainly not competitive with the photometric technique (due to the vast multiplexing advantage wide-ﬁeld photometry has), the Rossiter eﬀect can used to provide an important conﬁrmation of potential warm Earth-like planets. Since many of the most interesting transits that will be seen by the Kepler Mission will also be the most challenging, an independent conﬁrmation of the transit via spectroscopy of the Rossiter effect may prove to be very helpful.
So what we’re dealing with here is a technique that can help us confirm the detection of a planet found by other methods. As Gliese 581c demonstrates, the more tools at our disposal to make such confirmations, the sooner we’ll be able to reach definitive conclusions. Such painstaking science rarely makes the headlines, but papers like this wind up leading to tools for scientists working at levels of detail that were once unimaginable. Further work will demonstrate the Rossiter effect’s viability, but looking for ways to extend our planet-hunting reach will doubtless yield the methods we’ll need to better understand what Kepler gives us.
The paper is Welsh and Orosz, “On Using the Rossiter Effect to Detect Terrestrial Planets,” Transiting Extrasolar Planets Workshop, ASP Conf. Ser. Vol 366, 2007; Eds. A. Afonso, D. Weldrake and Th. Henning, p. 176 (abstract).