Daily Archives: October 13th, 2010

Does Gliese 581g Exist?

The excitement last month surrounding the discovery of a possible life supporting planet in the nearby Gliese 581 red dwarf system raised the expectations of meeting neighbors.

Many scenarios were discussed on the InnerTubes, one including a possible laser light message from closeby to the area in which the possible planet is at.

But there is a problem with this scenario; there hasn’t been any confirmation the planet actually exists, let alone any proof of possible intelligent life flashing semaphore signals at us:


The planets in the Gliese 581 system were discovered using spectroscopic radial velocity measurements. Planets ‘tug’ on the star they orbit, causing it to shift in position (stars and planets actually orbit a common center of mass). By measuring the star’s movement in the sky, astronomers can figure out what sort of planets are orbiting it. Multi-planet systems create a complicated signal, and astronomers must tease out the spectral lines to figure out what represents a planet, and what is just “noise” – shifts in the star light not caused by an orbiting planet. Astronomers have developed various ways to reduce such noise in their telescopic observations, but it still creates a level of uncertainty in detecting extrasolar planets.

The Geneva team plugged the HARPS data on Gliese 581 into computer models to check on the odds the signal was the result of noise, rather than evidence of the habitable planet ‘g’ as claimed by the Lick-Carnegie team.

“Simulations on the real data have shown that the probability that such a signal is just produced ‘by chance’ out of the noise is not negligible, of the order of several percents,” Pepe said. “Under these conditions we cannot confirm the presence of the announced planet Gliese 581 g.”

Pepe noted that while he did not speak at the IAU meeting about Gliese 581 f, the other potential planet in this system announced by the Lick-Carnegie team, the HARPS data calls that planet into question as well.

“We haven’t made a detailed analysis yet, but at first glance no statistically significant signal [for planet f] is emerging from our data set,” he said.

Gliese 581 is already one of the most intriguing solar systems known, with four planets confirmed orbiting the star. The addition of the potentially habitable planet ‘g’ would make the system the go-to place in the search for alien life, but more work needs to be done to either confirm or refute the planet’s existence.

“I would say the detection was less than comfortably secure, even in the original Vogt et al. paper — the paper was carefully worded, as opposed to what was in some media reports,” said Ray Jayawardhana, a University of Toronto astronomer who was not involved in either study. “Of course, it’s not easy to definitively rule out something, but the HARPS evidence is at least raising some doubts.”

I think some time reserved on the Kepler satellite would be in order here. That would answer a lot of questions concerning whether this planet exists or not.

It might even answer this laser signal business also.

I think it’s bunk, it’s sounds too much like a modern day “War of the Worlds” scenario.

But it’s not a good idea to poo-poo Hawking’s opinions about ETIs just yet.

Doubt Cast on Existence of Habitable Alien World