Gliese 581g: astronomical speculation?

12 10 2010

<<This is the first draft of an article I wrote for “The Mark”. Due to the real time dispute over Gliese 581g and whether it actually exists, I rewrote the submitted article. However, I think the issue of Vogt’s speculation deserves a forum… So here is my original discussion.>>

Last week saw the announcement by a US-based team of researchers that a potentially habitable planet around another star had been discovered. The obscurely named Gliese 581g sits at just the right distance–in the so-called habitable zone–from its star to possibly have liquid water on its surface. Think Goldilocks: not to cold, not too hot, but just right.

Gliese 581g is actually the 6th planet reported in the Gliese 581 (the star) system. All the planets are packed in close to the star as well. You can see an image of the system <here>. In fact, Gliese 581g takes only 37 days to orbit its parent star. Thus in Gliese 581g “years”, you ‘re ten times older than Earth years.

It’s incredibly difficult to see planets around other stars. Think of trying to see a glow worm infront of 100 of the world’s brightest lighthouses.  Such “direct imaging” techniques are in their infancy, although Canadian’s are leading the way. But so far 460 of the 492 planets we’ve discovered have been found using one “indirect” technique in particular, rather unromantically known as the “radial velocity method”.

The mutual attraction between planets and stars makes both of them move around a common point, the so-called barycentre of the system. For the planet, it takes a big orbit. For the star the size of the orbit is very small – inside the star itself: the star looks like it “wobbles”. But the motion is still large enough for us to detect with high precision measurements. The finest speed we can measure over such enormous distances is about that of walking pace, a few metres per second.

But if a number of planets orbit around a star all the different tugs act together. The motion of the star thus becomes very complex. While we have analysis techniques to separate each of the tugs, you need good data and lots of it. In Gliese 581g’s case it took observations over 11 years and combined data from Hawaii and Chile. All in all, this detection is a triumph of careful measurements and painstaking analysis.

“Is there life on other planets?” Is a question the 20th century considered philosophical, in the 21st century it should be answerable.

But when lead author Stephen Vogt commented last week that he was “100% certain” there was life on the newly discovered planet, eyes rolled. There was no need for hype. Gliese 581g is amazing on its own merits. People started to get on a bandwagon criticising Vogt. I found myself wondering had he been egged on by journalists for “the quote”.

Then just a couple of days ago I was emailed a transcript of an interview by Marc Kuchner with the highly reknowned producer of documentaries for PBS, Dana Berry. One section in the interview immediately made me think of Vogt’s comment:

“DB: Don’t be afraid to speculate and imagine on camera. There are many cases when I get someone who won’t guide me into the possibilities of a certain subject by defaulting to, “well, we don’t know,” or “I’m not the expert on that subject…” So I’m forced to ask the question in different ways, and sometimes I still can’t get past “the facade.” This happens because sometimes scientists are fearful that their credibility is on the line. A TV interview is not a peer-reviewed paper, so my advice is don’t be afraid to open up. Dream, speculate, and share your excitement, tell me what it means, tell me why you think its A and not B, and tellme who subscribes to B and what you think of that group. In other words, be a human.

I’m very sympathetic to Berry’s concerns about how scientists communicate on TV, but your credibility is on the line, as Vogt has discovered. The vast majority of science is tax-payer funded. Speaking out in popular programs is exactly where your credibility matters most. Speculation is context dependent and frequently highly qualified. But the act of editing can easily make five interesting words become a soundbite without qualification.

Everyone loves to dream and to ponder what might be possible. Some of the best science comes from the beginning “What if..?” But as science becomes more and more important to society, the need for integrity becomes absolutely critical. Fortunately for astronomy, hype doesn’t really lead to any serious ramifications. But when it comes to global warming, well that’s another story.

My optimistic hope is that in 30 years we’ll know whether Vogt’s speculation is right. It will take a lot of money and technological brilliance, but designs for telescopes capable of measuring the atmospheres of other planets already exist. Perhaps the most well known among professional astronomers is the Terrestrial Planet Finder. An immensely ambitious design that would see five space craft flying together in formation to make a giant telescope, it would allow us to measure with precision we can only dream of today. Right now it’s on hold. TPF is simply too expensive and too risky for the current economic climate.

Watch that space.




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