HMC world over 75AU from it's parent star, is that unusual?

baqar79 · Nov 23, 2017

I was doing some exploration looking for interesting Henry Draper catalogue stars (stars starting with HD in their name), and came across this undiscovered system:

If you go out a little over 1000LY from the bubble you can find a few untagged giants, but this was the first time I've seen a body orbit so distant from it's star; and furthermore it isn't an ice planet/gas giant, but a HMC world.
AspX well lit compared to dark planet:

Finally the planet without the AspX, showing it's distant sun over 75AU (37,000Ls) away at the top, middle of the picture (lots of small dots around it which I think are the planets that are much closer in):

Perhaps these aren't all that unusual, but it was the first time I've come across (and noticed) a planet like this. The next planet in is a lot closer to it's star at only 7.4AU.

Aura Lorell · Nov 23, 2017

The 323 KLs showed in the system map are measured from the entry star not the B star that is also 320+ KLs from the entry star. I've seen all kinds of planets in all kinds of distances from their star, from 20 Ls to over 20 KLs. How far was this one from it's parent star?

baqar79 · Nov 23, 2017

While this planet is 320+ KLs from the primary A star in this system, it is also ~37 KLs (75AU) from the secondary B star as well (Semi major axis in the tool tip on the left).

The next planet in is much closer to the B star at only 7.4AU, and it is a rocky ice planet. This HMC world also seems to have volcanism as well, despite being 10x further out. It's not a particularly stunning find, but It seemed a little unusual to me.

That second star also had 2 Ammonia worlds; so when I approached the weirdly distant planet, I half expected to see the Thargoid equivalent of a Death Star

Aura Lorell · Nov 23, 2017

That far out I'd have expected an icy planet rather than an HMC. I don't know if this is rare or not, however. Thinking about it this may well be a hand-authored system. Perhaps someone with more knowledge in either the stellar forge or astrophysics/astronomy or both could comment.

Zieman · Nov 23, 2017

Aura Lorell said:
That far out I'd have expected an icy planet rather than an HMC. I don't know if this is rare or not, however. Thinking about it this may well be a hand-authored system. Perhaps someone with more knowledge in either the stellar forge or astrophysics/astronomy or both could comment.

HMC being the furthest planet isn't really a rare thing in E: D. Not very common, but not very rare either.

Allitnil · Nov 23, 2017

In my experience, a semi-major axis of 75 AU is pretty rare for any planetary body although the records are much greater - over 700 AU for an HMC (!)

If you look at http://www.elitegalaxyonline.com/portfolio/longest-semi-major-axis-terrestrial-planets/ and filter for HMCs then this find would be the 22nd biggest. That would count as rare for me [up]

Ian Doncaster · Nov 23, 2017

Zieman said:
HMC being the furthest planet isn't really a rare thing in E: D. Not very common, but not very rare either.

My guess is that these are supposed to have been captured from another system. Quite often the outermost planet of the system is in an unusual orbit compared with the rest.

Sapyx · Nov 23, 2017

It's not common, but not extraordinarily rare either. As the above poster stated, these are "rogue planets" modelled by the stellar forge, interstellar wanderers that have been captured or native planets that have been flung into deep, usually highly eccentric orbits. This one is odd in having a nearly circular orbit.

These "cold heavy metal planets" usually have hydrogen/helium/neon atmospheres, like this one does.

Redfox · Nov 23, 2017

Did a quick check on EDDB (https://eddb.io/body) and there the 75.5 AU are at around rank 150 out of 2.1 million HMC.

I have doubts if that's really an indication of rarety or rather of CMDRs not being willing to invest the time to get out there 'just' for a HMC.

Anyway, nicely spotted and obviously not sth common. +1

baqar79 · Nov 23, 2017

Allitnil said:
In my experience, a semi-major axis of 75 AU is pretty rare for any planetary body although the records are much greater - over 700 AU for an HMC (!)

If you look at http://www.elitegalaxyonline.com/portfolio/longest-semi-major-axis-terrestrial-planets/ and filter for HMCs then this find would be the 22nd biggest. That would count as rare for me [up]

700AU wow!

Thanks, it was the most interesting and unusual find for me of the night, so I'll probably keep my eyes open for other bodies like it.