The Hot Neptune Desert
We're living in one of the most exciting times in astronomy, finally able to detect exoplanets, we're able to challenge the old theories, assumptions about how planets are created and find themselves where they are today.
Originally, the only planetary system we knew of was our own, so theories such as the Cigar theory (small planets - large planets - mid size planets - small planets) were entirely based on what we saw in our system, so you could imagine the confusion when the first planets we found were hot Jupiter planets orbiting the host star in less than a day in some cases.
One of the new kinds of planets we've found are sub Neptune (planets larger than Earth but smaller than Neptune/Uranus) and Hot Neptunes. These kind of planets not seen in our own system continue to challenge our own models of how planets may come to be.
Take TOI-1853 b, orbiting TOI-1853 found by TESS and sitting 544 light years from Earth in the constellation of Boötes. The TESS data showed it to be 3.46 times the size of Earth, a little smaller than Neptune, but with an orbit 50 times closer to the Star than Earth, it was a good Hot Neptune candidate.
So the team of astronomers observed the star to see what mass effect the planet was having, and the surprise was, it was 73 times more massive than Earth, similar to Saturn, but being much smaller, clearly this planet is made of much denser materials than expected.
Such planets challenge how we think planets are created, the density makes it the most dense Neptune planet detected so far, and has spawned a number of assumptions in how it could have come to be, maybe it was a much larger Jupiter type planet in a eccentric orbit, and each time it came close to the star, it would lose atmosphere, eventually leaving behind a much more dense rocky core, and ultimately setting in a more circular orbit, or maybe it was two super Earth's that collided early in the stars life and created a monster rocky planet. The rarity of these planets has led to the "Hot Neptune Desert" description, we simply don't see many of them out there, which is why they are so interesting.
Our observations challenge our theories, and what we're finding is that the process of planetary creation is more chaotic and unique to each system. That's exciting, because when we first set out to the stars, every single star is likely to bring us unique surprises.
