It's only been 18 years since the first direct observation of planets outside the Solar System. That (very significant moment) happened in 2004.

The truth is that we do not know much about the other planets in the universe, only that there are likely billions of billions of them. There are so numerous, that it is highly probable that self replicating molecules have arisen many, many times on these planets as they have on Earth.

What lies on these worlds, in terms of their landscapes and forms of life, may lie the truest expressions of complexity and beauty in the universe. They may contain atmospheric wonders, such as volcano ash laced with supermassive lightening storms. They may contain storms so fierce that they would strip the flesh from your bones, and rain so acidic that it melts what remains. They may contain mountains higher than the width of most countries. They may contain basic forms of life; molecules that have discovered how to gather resources for their own replication. They may contain inter-species empires that span entire star systems, or they may contain their ruins. But many are likely beyond our imaginations to conceive, locked as they are on a single planet. They are distant new worlds, and perhaps there will one day be a new frontier interacts with these planets that may have a history as deep and as rich as our own.

We have detected mere thousands, many of which are very large as large planets are the easiest to detect. We detect hundreds more every year, but as yet there are no signs of life.

There are and would be some truly spectacular planets, both inside and outside our solar system.

There are endless vistas of planets.

Artist’s impression (and exaggerated view) of the exoplanets orbiting stars


Types of planets

Periodic table of planets

The *Periodic Table of Exoplanets* divides most of the known exoplanets into six mass/size and three temperatures groups for visualization purposes (18 categories total). Exoplanets in the Hot Zone are too close of their parent star to have liquid water. Those in the Warm 'Habitable' Zone have the right distance for liquid water given the right size and atmosphere. Water can only exist as ice for those in the Cold Zone. Miniterrans are low mass bodies most likely spherical and without atmospheres, similar to Mercury and the Moon. Subterrans are comparable to Mars, Terrans to Earth and Venus, and Superterrans are a transition group between terrans and neptunians. Neptunians are similar in mass to Neptune and Uranus, and Jovians to Jupiter and Saturn, or larger. Not all bodies stated in the objects count in the title are classified in the table due to unknown stellar or planetary parameters. Those potentially habitable are described with more details in the Habitable Exoplanet Catalog (HEC).


Figure 1. Current confirmed exoplanets classified into eighteen thermal-mass categories. The number of exoplanets in each category is shown in the center of each frame and as a percent in the lower left. The diagram also shows the number of multiple stellar systems (top right). The most abundant objects of the confirmed exoplanets are hot jovians. RE = Earth radii, ME = Earth masses. CREDIT: PHL @ UPR Arecibo.


Figure 2.Current** **NASA Kepler exoplanets candidates classified into eighteen thermal-size categories. The number of exoplanets in each category is shown in the center of each frame and as a percent in the lower left. The number of those already confirmed are shown in the lower right. The diagram also shows the number of multiple stellar systems (top right). The most abundant objects of the Kepler exoplanets are hot terran and superterrans. RE = Earth radii. CREDIT: PHL @ UPR Arecibo.


Figure 3.Current Solar System spherical objects (with mass over 10-5 Earth masses) including planets, dwarf-planets, and moons classified into eighteen thermal-mass categories. The number of objects in each category is shown in the center of each frame and as a percent in the lower left. The diagram helps as a base for comparison with the tables for exoplanets (figure 1 and 2). The most abundant objects of the Solar System are cold miniterrans (dwarf-planets and moons). RE = Earth radii, ME = Earth masses. CREDIT: PHL @ UPR Arecibo.

  • Figure 4.** Simple summary of the number of confirmed exoplanets in each planet category. CREDIT: PHL @ UPR Arecibo.

Nearest exoplanets


Reddit community, [A Visualization of the Closest Star Systems that Contain Planets in the Habitable Zone, and Their Distances from Earth [OC]](

Habitatable exoplanets


Another list


How far we’ve looked


That's fine. Baby steps.

Estimates on how many

There are more living worlds out there as there are songs on Earth. The entire song of Earth is just one. That's how broad we have to set our horizons.

Imagine if around many planets throughout the universe there were self replicating bundles of atoms with systems that they have built to sustain themselves (biology) but also in relation to each other (society).

Roughly one out of every 37 to one out of every 70 sunlike stars in the sky might harbor an alien Earth, a new study reveals.

These findings hint that billions of Earthlike planets might exist in our galaxy, researchers added.

These new calculations are based in data from the Kepler space telescope, which in February wowed the globe by revealing more than 1,200 possible alien worlds, including 68 potentially Earth-size planets. The spacecraft does so by looking for the dimming that occurs when a world transits or moves in front of a star.

Scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., focused on roughly Earth-size planets within the habitable zones of their stars — that is, orbits where liquid water can exist on the surfaces of those worlds. [The Strangest Alien Planets]

After the researchers analyzed the four months of data in this initial batch of readings from Kepler, they determined that 1.4 to 2.7 percent of all sunlike stars are expected to have Earthlike planets — ones that are between 0.8 and two times Earth's diameter and within the habitable zones of their stars.

"This means there are a lot of Earth analogs out there — two billion in the Milky Way galaxy," researcher Joseph Catanzarite, an astronomer at NASA's Jet Propulsion Laboratory, told "With that large a number, there's a good chance life and maybe even intelligent life might exist on some of those planets. And that's just our galaxy alone — there are 50 billion other galaxies."

After three to four years of Kepler data are investigated, the scientists predict a total of 12 Earthlike worlds will be found. Four of these have already been seen in the four months of data released so far, they added. Kepler mission scientists have estimated that, altogether, there could be 50 billion planets in the Milky Way, though not all would be Earth-size worlds within the habitable zone of their local stars. [NASA's Kepler Telescope By-The-Numbers]

When it comes to the 100 nearest sunlike stars within a few dozen light years, these findings suggest that only about two might have Earthlike worlds. Still, Catanzarite did note that red dwarfs might host Earthlike planets as well, and that such stars are far more common than sunlike stars.

Although researchers will find it much harder to detect an Earth-size planet transiting in front of dim red dwarfs, scientists are currently trying to detect such planets around these stars by the gravitational tugs they would exert on each other.

"I'd expect to hear one day about habitable Earth analogs around these stars," Catanzarite said.

Catanzarite and his colleague Michael Shao detailed their findings online March 8 in a paper submitted to the Astrophysical Journal.

Material patterns

Metals generally sink to the centre of objects

Then rocks, then liquids, then gasses, all according to density.


Material cycles

  • Long lasting cycles of different kinds of materials may be the foundation of complexity. It just comes down to the vast amounts of matter endlessly churning away through the forces of nature.
  • See the material cycles of Earth in the introduction section of Earth.

Weather emerges with an energy source

David Deamer, First Life: Discovering the Connections between Stars, Cells, and How Life Began

Weather emerges when a source of energy (sunlight) interacts with vast masses if gas (the atmosphere) and water (the ocean) [I'd say 'liquid'].

Chemical reactions are those processes by which changes occur in the electronic structure of atoms and molecules such that new compounds with new properties are produced.

A physical process typically chances the energy content of a system, but does not alter the electronic structure of its components.

Escape velocities of gasses


Rocky Planets

  • Only the thin 'skin' of a rocky planet is solid. Even thinner is the vapour above it. The vast majority of the planet is churning magma.
  • The crust is a TINY layer on top of what is really a massive molten ball.
  • There's not ALL that much water on Earth. It just skims the top, which forms our oceans and lakes.

Gas giants are still mostly hydrogen at different densities, plus a rocky core.


If a planet is too rocky:

They become gas giants.

43 points · 12 hours ago

In general, anything that naturally forms will at some point become so heavy that it starts forming an atmosphere of hydrogen and helium. This causes a progress where most of the planet's mass ends up being hydrogen and helium, which turns it into an ice giant (like Uranus and Neptunus) or a gas giant (like Jupiter).

15 points · 11 hours ago

Yeah - the problem isn't about a rocky planet getting too big, it's about a very large rock not becoming gassy, too. Jupiter itself may have a very large, rocky core, too - 20x the size of Earth. Or at least, a core made of of heavier elements that have been exposed to extreme pressure and temperature and can't really be called 'rocks' any more, but may have been once.

The overall issue, though, is that there's a LOT of hydrogen and helium compared to everything else. What makes Earth rocky is the abundance of iron, silicon, magnesium, and others that compose minerals. But they're outnumbered by hydrogen alone by a factor of 10,000:1 or more, on the scale of the solar system. So you need a way to not only get a bunch of rocks together, but have the atmosphere blow away.

With the larger gravity of a bigger world, it's much harder to lose the ga