Rounding out my exoplanet week, I have, in my humble opinion, saved the best for last. This last story from Eos’ exoplanet issue looks at some wild and weird planets, including zombies and my favorite, puffballs.

I spoke yesterday about planets that got a second chance of life, orbiting pulsars. These are also called zombie planets. It’s hard to believe a planet can exist in orbit around a pulsar, which is a rapidly spinning neutron star that emits huge pulses of energy on the regular. You can time a clock by these pulses. Add in a planet, which tugs on the star gravitationally, and that timing gets slightly altered. And then we know there’s a planet there.

Here’s what’s even wilder to me. The timing of pulsars is so precise that we could detect the gravitational tug of something as small as an asteroid. But we don’t. This means these zombie planets are rare. So why say they got a second chance? Well, pulsars come after a supernova of the star, and supernovae are pretty destructive. It’s unlikely a planet orbiting a star that went supernova could survive. These zombie planets may have formed from the leftover debris of the system or even from any destroyed companion stars, like a white dwarf. Once the star has gone supernova, all that debris forms a disk around the pulsar, and like any regular protoplanetary disk, planets form. And now we have zombie planets. At least they aren’t going for our brains, am I right?

Finally, I am going to end this week talking about cotton candy planets. I have a friend from university who researches these, and I’m so proud of the work she has done, so that’s perhaps why these are close to my heart. She’s mentioned in the Eos article, too!

You’ve heard of hot Jupiters — gas giant planets orbiting close in to their stars so that they’re super hot. Sometimes, the atmosphere around these planets can get puffed up from the heat. That’s not what’s happened with the super-puff planets, though. Those worlds are much, much cooler. Three such planets were found in orbit around Kepler-51, and the mechanism making them puff up must be something other than heat.

Maybe, since Kepler-51 is a fairly young star, the planets are still puffed up from the internal heat of their formation. Or they formed really quickly, grabbing tons of gas from the protoplanetary disk. It’s even possible that they may not be all that puffy, which would be a disappointment to me, but could be the result of high hazy layers or wide bands of rings making the planets appear larger than they actually are.

What makes Kepler-51’s super-puffs even more unusual is that they are close to their star while most other known super-puffs are the most distant planets in their systems. That would mean these planets have to form far out and migrate inward. Or maybe they just have to end up far enough away to hold on to their massive atmospheres. Or some combination. As my friend Jessica Libby-Roberts said: There is still a lot to be done in this area.

I look forward to finding out where this research goes in the coming years.

More Information

Oddballs of the Exoplanet Realm (Eos)