Ice cap on Venus!

[timwetherell]

OK I admit, I'm click bating just a little with that title  But on a few occasions recently when I've been observing Venus I've noticed a light feature towards the north pole of the planet. Obviously it's not ice! (Venus is roasting hot and you'd never see the surface through the clouds anyway) But it does look like a white cap perhaps with a darker band below. I was wondering if anyone else had ever seen this? I'm thinking 3 possible explanations (You'll note lunacy is not among them, though clearly it can't be entirely discounted  )

(1) Some sort of polar cloud vortex ?

(2) The atmospheric dispersion creates a slight blue fringe at that end of Venus and that somehow leads to the illusion of a bright spot ?

(3) A combination of air ripples (seeing) and some sort of psychological predisposition to "expect" a feature there. Perhaps rather like the Ashen light which may be a predisposition based on our experience of earthshine on the Moon (though it may be a real physical phenomenon too - the jury's still out as far as I know) ?

I had a go at photographing it with a DSLR (I'm not an expert astrophotographer!) and it's certainly not as clear in the photo as it appeared in the eyepiece but perhaps there's a hint of it - though not much of one!

As an interesting aside, I came across this 1968 paper that does appear to suggest the presence of physical ice on venus - Just shows how far we've come in our understanding of Venus since then! http://science.sciencemag.org/content/159/3819/1097

[StarSapling]

Over the last couple of weeks of observing Venus, I have been noticing what I call bright cusp caps at both cusps.  The southern cusp cap appears to be about twice the size of the northern one, and both cusp caps appear to have dusky borders.  But this is Venus and I'm never 100% certain of what I'm seeing.

[Moonshane]

I agree Tim

I have been seeing similar recently but have never been confident enough to 'tick it'.

Mike has been sketching this sort of thing for a while.

 

[timwetherell]

57 minutes ago, StarSapling said:

Over the last couple of weeks of observing Venus, I have been noticing what I call bright cusp caps at both cusps.  The southern cusp cap appears to be about twice the size of the northern one, and both cusp caps appear to have dusky borders.  But this is Venus and I'm never 100% certain of what I'm seeing.

That's really interesting! I was just out observing a couple of hours ago and i saw something at the southern end too. I've either never seen it before or never noticed it but tonight observing around 3.30pm before sunset, there does indeed appear to be something similar at the southern end and as you say, it's larger. 

Could still be an atmospheric illusion, rather than anything physical on venus but that really cool that a few of us have noticed it

This was my sketch from this evening with my 7" refractror. I tried taking some photos too but haven't had chance to process them yet.

[timwetherell]

57 minutes ago, Moonshane said:

I agree Tim

I have been seeing similar recently but have never been confident enough to 'tick it'.

Mike has been sketching this sort of thing for a while.

 

Just had a look at Mike's sketches (which are beautiful by the way) and yes, there do indeed appear to be lighter bits at the poles.

Like you say, one can never be 100% sure with Venus but it's an interesting phenomenon!

[John]

There is a known effect that is observed from time on Venus called Cusp Caps. Paul Abel and others note, sketch and image them here on a Japanese observing site:

http://alpo-j.asahikawa-med.ac.jp/kk15/v150611z.htm

[John]

Also worth having a look at this BAA page:

https://www.britastro.org/node/4939

[timwetherell]

1 hour ago, John said:

Also worth having a look at this BAA page:

https://www.britastro.org/node/4939

Great reference! I'll look forward to reading and absorbing all that info. From an quick initial glance at the sketches there, it does indeed look like cusp caps are a "thing"  

 

[timwetherell]

This is the best of my photos from yesterday and I think it does show at least the southern cusp cap

 

[John]

Thats a really good photo of a really tricky target Tim

I can see a brightened area around the southern cusp area in that image as well.

[spaceboy]

I'd seen the same phenomenon the other evening while observing using a green #58 filter. I put it down to white cloud and the sun reflecting off it. I know Venus is pretty much covered in "cloud" but it's mostly darker cloud where the sun would not reflect the same. I see similar brightening on Mars when there is cloud / dust storms. The ice caps are still easy to make out but the brighter cloud could be easily mistaken for ice otherwise.