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    Sunspots Might Be Fooling Us Into Seeing Distant Earth-like Planets
    By News Staff | July 5th 2014 02:30 PM | 1 comment | Print | E-mail | Track Comments

    Astronomers search for exoplanets by measuring shifts in the pattern of a star's spectrum - the different wavelengths of radiation that it emits as light.

    These "Doppler shifts" result from subtle changes in the star's velocity caused by the gravitational tugs of orbiting planets, but Doppler shifts of a star's absorption lines can also result from magnetic events like sunspots originating within the star itself -- giving false clues of a planet that does not actually exist.

    "In the search for low-mass planets,"  said Suvrath Mahadevan, an assistant professor of astronomy and astrophysics at Penn State and a coauthor of a new research paper om the issue, "accounting for the subtle signature of a magnetics events in the star is as important as obtaining the highest possible Doppler precision."


    Due to this discovery, a research team has found that some signals suspected to be coming from two planets orbiting the star at a distance where liquid water could potentially exist, actually are coming from events inside the star itself, not from so-called "Goldilocks planets" where conditions are just right for supporting life. 

    "This result is exciting because it explains, for the first time, all the previous and somewhat conflicting observations of the intriguing dwarf star Gliese 581, a faint star with less mass than our Sun that is just 20 light years from Earth," said lead author Paul Robertson, a postdoctoral fellow at Penn State. As a result of this research, the planets now confirmed to be orbiting this dwarf star total exactly three.


    Detections about 
    red dwarf star Gliese 581
    , made with the Doppler technique, were published in scientific papers from 2004 to 2014 and put some of the claimed planets in or near the star's habitable zone, where it might be possible for life as we know it to exist. Blue indicates detections of candidate planets in the just-right region inside or near the habitable zone, where liquid water could exist. Orange indicates detections in the too-hot region that is too close to the star. Green indicates detections in the too-cold region farther away from the star and outside the habitable zone. Credit: NASA/Penn State University

    "We also have proven that some of the other controversial signals are not coming from two additional proposed Goldilocks planets in the star's habitable zone, but instead are coming from activity within the star itself," said Mahadevan. None of the three remaining planets, whose existence the research confirms, are solidly inside this star system's habitable zone, where liquid water could exist on a rocky planet like Earth.

    The research team made its discovery by analyzing Doppler shifts in existing spectroscopic observations of  Gliese 581 obtained with the ESO HARPS and Keck HIRES spectrographs. The Doppler shifts that the scientists focused on were the ones most sensitive to magnetic activity. Using careful analyses and techniques, they boosted the signals of the three innermost planets around the star, but "the signals attributed to the existence of the two controversial planets disappeared, becoming indistinguishable from measurement noise," Mahadevan said. "The disappearance of these two signals after correcting for the star's activity indicates that these signals in the original data must have been produced by the activity and rotation of the star itself, not by the presence of these two suspected planets.


    "Our improved detection of the real planets in this system gives us confidence that we are now beginning to sufficiently eliminate Doppler signals from stellar activity to discover new, habitable exoplanets, even when they are hidden beneath stellar noise, said Robertson. "While it is unfortunate to find that two such promising planets do not exist, we feel that the results of this study will ultimately lead to more Earth-like planets.".

    The size of each planet in this figure corresponds to its minimum mass. Some simplifications have been made for illustrative purposes. The refereed literature provides a complete history of the scientific publications relevant to this star and its planets.

    Older stars such as Gliese 581, an "M dwarf" star in the constellation Libra about one-third the mass of our Sun, have until now been considered highly attractive targets in the search for extraterrestrial life because they are generally less active and so are better targets for Doppler observations. "The new result from our research highlights a source of astrophysical noise even with old M dwarfs because the harmonics of the star's rotation can be in the same range as that of its habitable zone, raising the risk of false detections of nonexistent planets," Mahadevan said. "Higher-precision analysis for discovering Earth-like planets using spectrographs will be increasingly more necessary as next-generation spectrographs with the higher Doppler precision needed for detecting important subtle signatures come on line this decade -- like the Habitable Zone Planet Finder (HPF) that our team now is developing at Penn State." A description of this research is available on the Habitable Zone Planet Finder blog http://hpf.psu.edu


    Published in Science. Source: Penn State

    Comments

    Michael Martinez
    Here is little bit of nit-pickery, not really directed at you.  This has been boiling up inside of me for a couple of years.  The actual source for this story is science.penn.edu and the article can be found here.  The article neglects to mention which two planets are no longer deemed to be real.  I think it may be Gliese 581e and Gliese 581g.  What drives me nuts about these press releases coming out of universities is that they often fail to mention really interesting stuff which most lay people won't know, such as:

    • Which hemisphere you have to be in to see a star (even if only through a telescope)  
    • How far from the Solar System a star is  
    • Which planets hanging around a star are actually being discussed  
    • Which galaxy a particular dwarf galaxy may be associated with  
    • How far from the Milky Way a galaxy or dwarf galaxy may be  
    • Which direction (Earth-side, far-side, above, below) from the Milky Way a (dwarf) galaxy lies  
    I get the sense that the people who write these articles are either publicists who don't know that much about the science or scientists who have lost touch with the fact that most people don't know the names and locations of all the stars, or what is going on with these stars.

    Sure, people can search Bing and Google for more information but that takes time out of my day.  And the search engines are REALLY BAD at organizing usable information.  They either show you Wikipedia articles (which may or may not be trustworthy -- how is a lay person to know?) or they show you endless variations on the same badly written or incomplete articles.

    And this is true for every branch of academic research, not just the astronomical sciences.  New medicines are announced making comparisons with existing medicines identified only by their chemical names (which may be due to trademark issues); archaeological discoveries are announced without explaining to the armchair traveler that such-and-such city now lies in modern STATE about Xteen miles/kilometers east/west/north/south of MODERN CITY; and so forth.

    Finding good information about academic research on the Internet is a nightmare because most writers assume they are writing for an informed audience when, in fact, they are informing a LAZY audience that will take their information, replicate it, use it to update hundreds if not thousands of Wikis and Wiki-like sites, and write sensational headlines around interesting quotes that leave out every possible detail that would provide some meaningful context to people who don't know what is going on.

    And worse, the Penn State Science article has a broken link, which when I tried to report it to their Site Administrator led me to ANOTHER broken link.

    Modern science has to learn to communicate well when talking to the masses.  The Internet is incapable of fixing that problem.