Thursday, October 14, 2010

Gliese 581g: Then Again, Maybe So

"Astronomer Stands By Discovery of Alien Planet Gliese 581g Amid Doubts" (October 13, 2010)

"Despite the doubts raised recently over the existence of the potentially habitable alien world Gliese 581g, the planet's co-discoverer is standing behind his find.

"Steven Vogt, leader of the team that detected Gliese 581g, said he respects the work of the researchers who questioned the planet's existence yesterday (Oct. 12). He said he cannot comment on the scientists' results, since he hasn't seen their data.

"But he has confidence in his own team's conclusions...."

This isn't the curious case of the peculiar signal that cropped up recently. (October 11, 2010) This is a more run-on-the-mill 'we're not so sure' situation about whether or not Gliese 581f and g are really there. (October 13, 2010)

Several groups of scientists analyzing the same set of data to see it they all get the same (or similar) results is pretty much business-as-usual in the scientific community. It's sort like having someone proofread what you've written.

This time, though, the bunch that couldn't find Gliese 581g and f weren't using quite the same data. That got the Lemming's attention.

Back to the article:

"...Since then, the discovery has received a lot of attention, from both the media and other researchers. One group of astronomers, led by Michel Mayor of the Geneva Observatory in Switzerland, performed a follow-up investigation in an attempt to confirm the existence of Gliese 581g. [FAQ: 12 Questions (and Answers) on Planet Gliese 581g]

"At an astronomy conference this week in Torino, Italy, the Swiss team announced that it could not confirm Gliese 581g or 581f, another planet Vogt's team discovered in the same system. Though the researchers did not refute the existence of either planet, they did confirm the other four previously found around the star.

"Vogt said he wasn't overly surprised to hear the news, since the two newfound planets' signals were quite weak.

"Similar methods, different results

"Both research teams used similar methods - scrutinizing the parent star Gliese 581's movement, looking for the telltale gravitational tug of orbiting planets. And both teams analyzed some of the same data.

"Vogt's team looked at 119 measurements made by the HARPS instrument on the La Silla telescope at the European Southern Observatory in Chile, as well as 142 measurements from the HIRES instrument on the Keck I telescope at Hawaii's Keck Observatory.

"The Swiss team analyzed those same 119 HARPS measurements, and they looked at 60 additional HARPS observations as well. Vogt said those 60 new measurements could lead to a maximum potential detection sensitivity gain of only 23 percent or so, assuming all the new data points are useful and non-redundant.

"The Swiss team didn't investigate any of the Keck data, however - a fact Vogt finds puzzling, especially since his team concluded that both the HARPS and HIRES measurements had to be combined to reliably detect all six planets orbiting Gliese 581...."

It looks to the Lemming as if the Swiss team has said that, since by ignoring 119 measurements they were able to not-find Gliese 581g and f - the planets aren't there. Maybe this is unfair, but that sounds a little like proving that someone isn't there, by taking a picture of the person with a cap over the lens.

Maybe the Swiss team didn't like the Keck data. Maybe they had a reason for not liking it.

Whatever's going on: It doesn't look like the Gliese 581 planetary system is going to be a boring topic for quite a while - at least, not among folks who are interested in planets circling other stars.

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