So in what sense is the gas cloud not a part of the planet? It surrounds the planet and is gravitationally bound to it. Wouldn’t you have to say that the planet simply has, due to high temperature, an extended atmosphere?

The modelling indicates a dust cloud, not a gas cloud. If so it probably originates from collisions between objects orbiting the planet, rather than being an extension of the planet’s atmosphere. Such a satellite swarm would be a more massive analogue to the irregular satellite systems around the giant planets of our solar system. See Kennedy & Wyatt (2011) “Collisional evolution of irregular satellite swarms: detectable dust around Solar system and extrasolar planets”

On the other hand, it’s wonderful that a government organisation can have such a great sense of humour!

It would be interesting if it turned out the cloud didn’t surround the planet, but orbited it like a moon. I doubt that’s possible, because of tidal effects, but it could explain misreadings of velocity.

I love the modification of the Goddard credit at the end of the video.

Click to Annatarenate

Click to Gorthaurenate

Click to Necromancenate

How’s that for sailing away into the geeky blue yonder? For going above and beyond the call of geek duty? For reaching back for a little something extra on my geek fastball?

Not bad, although that first one might be better as Celebrimborenate, as Celebrimbor was one of the elven smiths who learned the art of ring-making from Annatar (and also, coincidentally, drew the signs in Ithildin on Narvi’s west door to Moria).

And was your reference to Saruman an allusion to his status as a kind of satellite of Sauron?

You can use the first two stars in the front of the Great Square of Pegasus, Markab (Alpha) and Scheat (Beta) as pointers and follow the line upwards (or downwards*) till you get to the first reasonably bright star which will be it.

* For clarity – that’s upwards in the southern hemisphere but downwards in that upside down northern hemisphere!

Fomalhaut (& the rest of Piscis Austrinus, the Southern Fish constellation plus Aquarius, Pisces and more) is on the side towards the ecliptic and away from Andromeda.

October is a good month for viewing Pegasus and Messier 31 and the Andromeda galaxy’s companions.

Guess many (most?) folks reading this will already know but if you wish to see Fomalhaut in the night sky – latitude, weather and time permitting -here’s a hopefully handy tip :

You can use the first two stars in the front of the Great Square of Pegasus, Markab (Alpha) and Scheat (Beta) as pointers and follow the line upwards (or downwards) till you get to the first reasonably bright star which will be it. Unless one of the planets has moved across the line in Aquarius or Pisces! (Not happening now or for ages I think.)

The two “back leg” stars of the Square of Pegasus btw (Algenib and Alpheratz /Sirrah) lead similarly to Beta Ceti – Diphda or Deneb Kaitos.

I think the disagreement here is just semantics. My point is simply that neither paper is published in refereed literature, the sense that we use when we say something is ‘published’. Certainly I never think of an article a colleague or I post on the arxiv or on a webpage or on FB, etc to be “published” until it is actually published: as in ‘published in a journal’.

-”Which is exactly what the second paper is saying, so to claim that it “completely hand-waves” this away is somewhat disingenuous.”

The reason I call it hand-waving is that the paper estimates how often these collisions occur that may (or may not) produce a detectable dust cloud but doesn’t squarely face how short-lived such an unbound dust cloud is and thus process the fact that such a fleeting event is unlikely to be witnessed/an unlikely explanation.

- “They actually do state that the location at Fomalhaut b should be lower – your characterisation of this as that they “mistakenly derive” the wrong rate appears to be a misrepresentation. ”

No. The rate they quote is roughly “one collision every century”. That rate is explicitly derived from their estimate for the mass of the disk ring for collisions *in the ring* and thus describing it as such is not a misrepresentation. It does not tell you the collision rate at the location of Fomalhaut b, where there is no evidence for a belt of debris material. The alternative is that the collision may have happened elsewhere but the debris cloud just now finds its way to Fomalhaut b’s location: that is but a small subset of possible collision outcomes.

Also, the following statement “Even if the rate at the Fomalhaut b position may be lower, given the approximations of our model the rate is high enough to make such a ∼ 50year-old event plausible.” doesn’t follow: in their derivation, the collision rate scales as the mass of the disk squared. So a factor of 10 reduction in the local mass of planetesimals (a highly conservative inference if the ALMA map is a good tracer of the parent bodies’ locations) yields a factor of ~ 100 reduction in the collision rate at that location. Sure, it is plausible (in fact, almost guaranteed) that at some point in Fomalhaut’s history there were 50 km objects colliding in its debris ring. But that does not mean it is plausible that it just happens to be happening now and where there is no detectable debris ring, instead of where there is such material.

- “however I do not consider this conclusion to be certain at the current time, nor am I a particular fan of somewhat hyperbolic press releases giving the impression that these ongoing debates have been firmly resolved.”

Certainly agree. 1210.6620 is far more measured than the media reports imply, and the press/Twitter is just really getting carried away. Fomalhaut b’s status is far from certain and probably will be for a very, very long time.

- neither paper has been ‘published’ but both have been made public.

Actually being made public is exactly what “published” means – I never claimed it was published in a peer-reviewed scientific journal. And in any case in these current times of “science by press release” it certainly seems that an arXiv publication is more than enough to go on to justify calling in the press.

As explained in the first paper (and apparently ‘declared to be true’ but not detailed in the discovery paper), the dust from any such collision would shear out extremely fast compared to the lifetime of the star (~450 Myr according to the most recent estimate from Mamajek (2012)) and other mechanisms would completely remove the dust in a likewise rapid timeframe. In other words, we would have to be catching this collision ‘just now’.

Which is exactly what the second paper is saying, so to claim that it “completely hand-waves” this away is somewhat disingenuous.

Furthermore, the second authors mistakenly derive the collision rate appropriate for planetesimals *within* the dust belt while Fomalhaut b is located well outside of it.

They actually do state that the location at Fomalhaut b should be lower – your characterisation of this as that they “mistakenly derive” the wrong rate appears to be a misrepresentation. Furthermore a ring-crossing orbit is not ruled out with the current data (even the 1210.6620 paper notes this), so we could perhaps consider that the collision occurred within the belt.

To be clear here: I am certainly in favour of the planet hypothesis, however I do not consider this conclusion to be certain at the current time, nor am I a particular fan of somewhat hyperbolic press releases giving the impression that these ongoing debates have been firmly resolved.