system
Given the following post, respond as if you're commenting on Reddit:
human
How has the understanding of exoplanets changed since the first were detected in 1988?
gpt
Among various discoveries:

* Exoplanets seem to be very common for many types of stars - other than failing to detect planets due to technological limitations, just about everywhere we've looked for planets, we've found them. We've even observed what are believed to be the remains of destroyed planets around white dwarfs, the dead remnants of stars.
* Planets can exist both much closer and much further from their stars than we see in the Solar System. The discovery of "hot Jupiters" (and then hot Saturns, hot Neptunes, hot Super-Earths...) came as quite a surprise, and their formation mechanism is still an open question.
* Planets come in all shapes and sizes. Whilst there is quite a gap in size between Earth and Neptune in the Solar System, we've found plenty of planets with intermediate masses and radii. There is still debate as to whether these are Super-Earths, Mini-Neptunes, or an entirely different type of planet.
* Exoplanet atmospheres are also diverse. We've seen clear atmospheres, hazy atmospheres, thick cloud decks, no atmospheres, atmospheres visibly being boiled off by a star - again, attempting to describe these variations and work out what types of clouds exist are hot topics in research.
* Multi-planet systems are common, especially for rocky planets. Once again, a feature that is unlike the solar system is how close some of the known planets are to one another - theoretical work implies that they are about as close as they can be without disastrously affecting each other's orbits.