Dynamics of Cats

...as pointed out to me by Dunkleosteus in the comments.

Greg at systemic has the full story

This is a good one, with all the ingredients - and the competition aspect also.
Teaches us to a) read astro-ph when it comes in at night, not the next morning and b) always follow up your hot RV detections with systematic transit surveys.

So, what have we got this time?

Gliese 436b - an 23 Earth mass planet around a nearby M star (0.44 times the mass of the Sun). It has a 2.6 day orbital period - it is hot.
And they have a transit detection (so it is nead edge-on) and it is large, planet radius of about 25,000 km (about 4 times that of the Earth).
Original discovery was 3 years ago by the California team, by radial velocity variability.

So, it is low density - which implies high gas and volatile content.

There have been several "hot Neptunes" found recently around low mass stars, and some discussion in the community about whether they formed in situ (from compact dense debris disks) or formed further out past the "ice line" and migrated in to their current orbits, much like the "hot Jupiters" are thought to have done around more massive stars.
If the former, they'd be dense and small, composed of iron and refractory silicates. If the latter, they'd be gas and ice rich and relatively low density - with a rocky/metal core surrounded by a layer of ice and gas.
For a variety of reasons I was firmly in the second camp, but the people in the first camp had some good arguments, so we waiter for data.

And here it is. It is icy hot!

Now for the surprise. It has a significant eccentricity of 0.16!
That is impossible, of course. Hot planets must be circular, the time scale for tides to circularize the orbits is ridiclously short. Except of course for HAT-2 and maybe the HD189733 hot Jovians that is...

Oh, and the host star is low metallicity - about 1/2 that of the Sun...

Greg discusses the eccentricity issue in detail, but basically the only plausible explanation is that there is another planet close in that is strongly perturbing this one, and the whole system must be undergoing secular evolution - that Neptune is toast, gonna burn in not too many giga years (haven't run the numbers for how quickly any likely companion interaction will push it in - unless of course there is a corotation barrier or something keeping it out).

Just keeps getting better.