Celestia Forums

.ssc code for the HR 8799 system, orbits are set up to be face-on and circular (this is the likely configuration according to Marois et al. 2008) and mean anomalies are calculated using the positions given for 2008 Aug 12. Probably could do slightly better by doing a best fit to all of the observed positions but I'm leaving that for now. Gives quite a good match to the images shown in the press releases.

EDIT: the .ssc file is in the add-on in my next post.

Fomalhaut b would be trickier to model because the system is not being observed face-on, the orbit is likely eccentric and there doesn't seem to be a convenient table of values for the positions available.

I've modelled Fomalhaut b by making its orbit apsidally-aligned with the dust disk, and setting up the mean anomaly to match the position angle in 2006. I've also added the possible circumplanetary disc. Because of the 400 K temperature from modelling I have rendered it as a class III planet. Parameters based on Kalas et al. (2008).

This add-on also includes the HR 8799 system as described in my previous post.

(I should mention that I have not attempted to model the circumstellar dust disks themselves)

Very nice! Looking forward to downloading this when I get home!
And what a wonderful discovery. These aren't the first images of exoplanets though, but the image of Fomalhaut b is the first visible light image of an exoplanet. The rest have been IR.

That's very nice, ajtribick. Thanks.
I've added a disk to Fomalhaut in my copy of Celestia, but they are so different in scale I can't get them to display together yet. So here's a cut-n-paste job.

Thanks! As for the Fomalhaut dust disc, the inner edge is around 133 AU, the width is 25 AU. The planet shouldn't go through the disc.

(What's incredible is that the mass of the Fomalhaut dust disc at these distances is consistent with the planet Fomalhaut b forming in situ, while the models for the formation of our solar system predict that Uranus and Neptune had to be formed further in than their current positions... makes you wonder what kind of gigantic planets lurk closer to the star)

I thought (from the images in the news) that there was a thinner dust disk that stretched nearly to the star- but it seems that the main disk - an 'eccentric' disk to boot- is outside of the planet.

This planet formed way, way further out than anything in our solar system- from disk instability perhaps, like a little star, rather than from core accretion like our planets.

Not entirely sure about that - there's a whole bunch of scattered light all over the place which makes it difficult to see what's going on with regard to dust interior to the ring.

I've changed the dimensions of the dust ring, so that the planet now orbits in (nearly) dust-free space. That makes it easier to see them both together. Here's an image of the new version-

I've added a few streaks in Gimp to suggest individual moonets orbiting in the dust, following the lead of the official NASA artist's impression
http://en.wikipedia.org/wiki/Image:Fomalhaut_planet.jpg
which is probably too colourful...
I'm still trying to adjust the orbit of the dust ring, so that it orbits with the planet, so I can't pretend that it is accurate. Not yet anyway.

How did you add the disk aroud the star, ive been trying to do that but no success so far?

Wow, I absolutely love the appearance of Fomalhaut, how did you accomplish this?

Basically I cheated.

The dust disk is just a transparent png on a billboard; I made a really thin billboard, then duplicated it so that it appears just above and below the plane of the planet's orbit. There is a useful tool in Gimp called 'whirl and pinch' which can make ring-shaped blurs.

The star is acheived using Gimp- the 'supernova' effect. It would be nice if Celestia could produce such effects- but for illustration purposes, a bit of post-work in Gimp can do all sorts of nice things.

Oh right, i thought you managed to place a ring around the star in celestia.
Ive tried creating rings (really large rings around a few Au's) around a small planet inside the target star but even then the rings fail to appear.

Ring display appears to be linked to the angular diameter of the parent planet - if you use the add-on I posted you will find that as you move away from Fomalhaut b the rings disappear abruptly.

I've noticed that too.
The planet, without the rings, is a very dim object- perhaps the image that has been obtained of this world is mostly an image of the ring system - either that or the planet is whiter than Venus.

zhar2 wrote:Oh right, i thought you managed to place a ring around the star in celestia.
Ive tried creating rings (really large rings around a few Au's) around a small planet inside the target star but even then the rings fail to appear.

I tried doing that but with a planet. I wanted two ring systems for a planet and have them perpendicular to each other. The rings for the planet within a planet would not appear.

ajtribick wrote:Ring display appears to be linked to the angular diameter of the parent planet - if you use the add-on I posted you will find that as you move away from Fomalhaut b the rings disappear abruptly.

Yes, could it be that theres a limit in celestia for the displau of rings to a certain range of distance?, my intention was to use rings to create dust disks around stars to accompany a asteroid belt.

I've put rings around stars before, by embedding an emissive True planet in their centres, and the ring worked great. So I've a little bit of experience with this.

The ring's suddenly disappearing isn't based on distance, but rather the angular size of the planet. Make a 15 AU-radius planet with a 100 AU-radius ring, give the planet a mesh that doesn't exist, and there you go, just a ring, a rather large ring that can be seen for quite some distance. Only issue is clicking on the star and actually selecting the planet instead. One thing I haven't tried is making the planetary radius > 1 ly. It might be completely unselectable from within the system then.

Celestia v1.6 has the SSC option
Clickable false

selden wrote:Celestia v1.6 has the SSC option
Clickable false

Well that would certainly make things easier.