I'm always fascinated with the way the media handle nearby stars and the planets that may orbit them, especially as our inventory of confirmed planets continues to grow. A recent National Geographic television special is a case in point. The show's graphics were superb, its narration gripping. But how puzzling to run into a fundamental misunderstanding about our nearest stellar neighbors.
In "Journey to the Edge of the Universe," putative travelers have moved out through the Solar System, passing (an ingenious touch) the various probes and artifacts we humans have scattered from Mercury out to the Kuiper Belt. As we move to the nearest stars, we pass what is obviously the red dwarf Proxima Centauri and make for the binaries Centauri A and B. Describing them, the narrator says, "Not one but three stars, spinning around each other locked in a celestial standoff, each star's gravity attracting the other, their blazing orbital speed keeping them apart."
And then this: "Get between them and we'd be vaporized."
Not a chance. We don't yet know whether there are planets around Centauri A or B. But we do know that there are stable orbits around these stars, and that both of them could have planets in the habitable zone, where liquid water can flow on the surface. Their mean separation is 23 AU. There is, in other words, plenty of room between Centauri A and B for a spacecraft to move without danger of being vaporized. I feel like I'm nitpicking given the intense effort that went into this production, but it seems important to clear up misconceptions that are widely distributed.
As with the show's treatment of Gliese 581 c. The National Geographic special shows the planet as a living world of continents and oceans, and indeed, the discovery announcement made it appear that 581 c was squarely in the habitable zone of this tiny red dwarf. But almost every subsequent study has shown this to be deeply unlikely - conditions on Gliese 581 c are probably much more like Venus than Earth. Moreover, although the show depicted the planet as rotating, so that the day/night terminator continued to shift, it's much more likely that this planet is tidally locked to its primary, one side always facing the star.
So, the initial euphoria about Gliese 581 c being "Earthlike" quickly gave way to skepticism. Indeed, if there is a habitable planet in the GL 581 system, it may (just possibly) be GL 581 d. If the media continue to get it wrong, let's hope science gets it right.
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this page last updated 4 July 2009
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