| Evolution in the News - August 2014 |
| by Do-While Jones |
Two habitable planets discovered outside our solar system have been un-discovered.
It isn’t just the “truth” about dinosaurs that change on a daily basis—planets do too!
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Two planets considered among the most promising for life outside the solar system don’t exist, scientists report July 3 in Science. The signals embedded in starlight that were attributed to the planets may instead have been caused by the changing magnetic activity of their star, Gliese 581. 1 |
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Some of the first exoplanets identified as candidates for habitable worlds turn out to be mirages conjured up by magnetism on their host star. Earlier studies looked at tiny changes in the motion of the star Gliese 581 and concluded that at least five planets must circle it. Of these, two planets, dubbed GJ 581d and GJ 581g, were thought to be at a distance that would allow liquid water to exist on their surface. But a team led by Paul Robertson of Pennsylvania State University in University Park studied emissions from hydrogen in the star's spectrum and discovered magnetic disturbances within Gliese 581. These magnetic changes, as they rotate around the star, mimic the signal an exoplanet would produce, and probably misled the earlier researchers. 2 |
Both reference a very technical report in the journal, Science, in which the authors said,
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We assert that the periodic RV [Doppler Radial Velocity] signal at 66 days is an artifact induced by the stellar rotation rather than an exoplanet. … GJ 581d [planet “d” circling star Gliese 581] and (the now less widely believed to exist) GJ 581 g [planet “g” circling star Gliese 581] were considered to be among the first exoplanets likely to host habitable environments if they were rocky. … Although GJ 581 may still be dynamically capable of accommodating terrestrial-mass planets in its HZ [Habitale Zone], we see no evidence at this time for additional planets in the activity-corrected residuals around our three-planet model [which does not include planets d and g]. 3 |
The story began in 2007 with this report in the respected journal, Science.
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For the first time, astronomers have found an Earth-like planet that could be habitable. Like an oasis in space, the rocky world, possibly covered with oceans, orbits a puny red dwarf star just over 20 light-years away in the constellation Libra. … the new planet, found by Stéphane Udry of Geneva Observatory in Switzerland and his colleagues, orbits right in the habitable zone of its mother star, Gliese 581, where temperatures are between 0° and 40°C. 4 |
It was reported by a peer-reviewed journal, as absolute fact, not only that the planet had been discovered, but also what temperature it was. Now that the planet has been un-discovered, one has to question the temperature readings, too.
These two planets are not the only planets that might not exist to have been described in the technical literature.
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Several promising exoplanets have been cast into doubt in the past. The gassy giant Fomalhaut b, for instance, was hailed as one of the first exoplanets to have its picture taken – but it may be nothing more than a blob of dust. And the closest Earth-sized world to us, Alpha Centauri Bb, could just be noise in the data. 5 |
Let me make it perfectly clear that I personally believe that it is highly unlikely that out of all of the stars in the Universe, our Sun is the only star than has planets orbiting it. In fact, I suspect that there are only a few (if any) stars in the Universe which DON’T have planets orbiting them. It seems likely to me that if whatever process (natural or supernatural) is responsible for creating the Universe created one star (our Sun) with planets around it, it would also create planets around most (or all) of the other stars.
So, I believe there are lots of planets out there orbiting other stars. BUT I don’t believe any of them have actually been detected (or will be in the near future).
Nobody has actually seen a star—astronomers have just seen starlight. Sometimes they see very slight changes in color, presumably due to a Doppler shift, presumably caused by a star being wobbled by the presence of one or more heavy planets orbiting it. Sometimes they see very slight changes in intensity, presumably caused by a big planet moving between us and the star, eclipsing some of the starlight.
After working for decades on weapons designed to detect the position of targets based on radiation from them in the visible, infrared, ultraviolet, and microwave spectrum, I know from experience that one can’t trust very subtle measurements.
After living for decades in the Mojave Desert, I know from experience that long-distance optical observations of mountains can fool you. I’ve often seen mountains wiggle like Jell-O on hot summer afternoons. But, when I hike up those mountains I discover that they are hard as rock (because they are rock). The air between me and a distant mountain distorts the light coming from the mountain making it appear to move.
Who knows what gravitational or magnetic fields are swirling around in the vast space that separates us from the stars making them twinkle, like the Earth’s atmosphere makes them twinkle. The fact that starlight appears to twinkle does not mean that there are planets orbiting them.
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So should astronomers – and the media, New Scientist included – be more cautious next time they trumpet an exoplanet haul? For instance, many announcements come with eye-catching artists' impressions, but only a handful of worlds have been directly photographed, and they show up as tiny pin-pricks of light. Most exoplanets are revealed only as subtle variations in the light from their star. "I spend my days looking at squiggles on a graph," says Robertson. "But a lot of science is publically funded, and the taxpayers who contribute to that deserve a return on their investment. I wouldn't say we should shy away from artist impressions or anything that helps us communicate the results of our work to the public." 6 |
Taxpayers deserve to be told the truth—not fanciful stories that will make them feel good about funding non-scientific “research.”
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Footnotes:
1
Grant, Science News, 9 August 2014, “Habital planet’s reality questioned”, https://www.sciencenews.org/article/exoplanets-once-trumpeted-life-friendly-may-not-exist
2
Nature, 10 July 2014, “The exoplanets that were not”, Page 128, http://www.nature.com/nature/journal/v511/n7508/full/511128b.html
3
Robertson, et al., Science, 25 July 2014, “Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581”, pp. 440-444, https://www.science.org/doi/10.1126/science.1253253
4
Schilling, Science, 27 April 2007, “Habitable, But Not Much Like Home”, p. 528, https://www.science.org/doi/10.1126/science.316.5824.528b
5
Aron, New Scientist, 3 July 2014, “First life-friendly exoplanet may not exist after all”, http://www.newscientist.com/article/dn25842-first-lifefriendly-exoplanet-may-not-exist-after-all.html
6
ibid.