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As of Oct. 14, 2016 there were 3533 planets in the Extrasolar Planets Encyclopedia. In October 1995 there was only one known extrasolar planet (exoplanet) known to be orbiting a sunlike star. That was 51 Pegasi b, about 50 light years away in the constellation Pegasus.

51 Peg b was a breakthrough in astronomical research, but it was also an unsettling surprise. The planet is about the size of Jupiter, but orbiting closer to its star than Mercury does to the Sun. Its year is about four days long. This was simply impossible according to our understanding of Solar System formation at the time.

Other such planets have been discovered since then, and they're known as hot Jupiters.

Infographic profile of 51 Peg b

And just think of all the planets here now, but still undiscovered!

Proxima Centauri b is the closest known exoplanet to our Solar System. Based on the data collected so far, it seems to be terrestrial and located in the habitable zone of the star Proxima Centauri. Astronomers can get very excited about such findings, but there isn't enough data even to determine the planet's mass let alone its size, surface features, composition and habitability. [Artist's impression. Credit: ESO/M. Kornmesser]

Based on what we know so far, researchers point out that there are many possibilities for Proxima b. It could be a rocky planet with small amounts of liquid water on one side and frozen water on the other. It could have a liquid ocean on the side facing its star and a dark side covered by ice. Or perhaps it's like Mercury, rocky with a large metallic core. Could it be an ocean planet covered by a 200-km deep ocean? Or have a rocky core covered with a 3000-km thick layer of ice? [Artist's depiction of an waterworld. Credit: David A. Aguilar (CfA)]

More about Proxima Centauri b

TRAPPIST-1 is a dwarf star in the constellation Aquarius. NASA's Spitzer Space Telescope has found 7 Earth-sized planets orbiting it 40 light years away.

All of the planets are closer to the star than Mercury is to the Sun, which may not seem very habitable at first sight. However the star is an ultra-cool dwarf and its habitable zone is much closer to it than the Sun's habitable zone. It's cool enough for liquid water to survive on planets orbiting quite close.

The planets are also close to each other. According to NASA,

Google was very quick with a Google doodle to celebrate the 7-planet discovery.

More about some of the names submitted at Public tries to name 7 new planets after Nasa discovery- with chaotic results.

The Solar System has just one star, and we'd assumed that most stars were single. It was a surprise to learn that double stars, triple stars and other multiple systems were at least as common as singlets. But surely stars like this wouldn't have planets? The complicated gravitational dynamics would eject planets from the system.

Echoing Luke Skywalker's home Tatooine from Star Wars, there was surprise at the first discovery of a planet in a double-star system. But last year a team led by the University of Arizona discovered a planet in a triple star system. It takes over 500 years to complete one orbit. For a quarter of the orbit it would be in nearly constant daylight. Then for the rest of the year it would have a “night-side and day-side with a unique triple sunset and sunrise each day.” The planet is a giant one, bigger than Jupiter.