The universe is awash in planets. As of this writing, there are 3,989 exoplanets (planets outside of our solar system) that have been confirmed by astronomers. Several thousand more have been detected, but await confirmation. The online Exoplanet Encyclopedia keeps tabs of exoplanet discoveries, and it must be updated quite often. The number of planets known will likely be larger by the time you read this.
Over the past few years we have discovered exoplanets at an average rate of over two per day! It appears that on average every star has five or six planets, perhaps more. With current telescopic detectors we can only discover those that are the largest — most of them larger than the Earth. As telescopes improve, we can expect to find many more, and smaller, exoplanets.
Most of these planets have been discovered over the past few years with the NASA Kepler Space Telescope. That telescope was recently retired. A somewhat different space telescope, known as TESS (Transiting Exoplanet Survey Satellite), is now in space and is focused on finding planets around the brightest nearby stars. TESS may find as many as 20,000 planets during its projected two-year mission lifetime!
The number of planets in the universe is truly staggering! Our galaxy has about 400 billion stars. That is very roughly 10 times the number of people that have lived on Earth. And there are well over 400 billion galaxies that can be seen in the visible universe. That means that there are more planets than the number of grains of sand on all the beaches on Earth. There are more planets than the total number of heartbeats of all the people that have ever lived on Earth.
And the types of planets that are being discovered truly boggle the imagination! There are planets that are mostly water. There are planets that are mostly metal. There are rocky planets like the Earth but that are over 10 times as massive. There are planets that have two suns in their skies, and there are planets that have four suns in their skies.
There are planets where the same side of the planet always faces its star, and it is so hot that the surface is covered with molten magma, and the atmosphere is vaporized rock. But it is so cold on the night side that when the hot air blows around to that side it “snows” rock snowflakes. There is even one planet that appears to have a large fraction of elemental carbon, which as everyone knows that at super high pressure is diamond — a “diamond world.”
The closest star beyond our solar system (Proxima Centauri) has a planet just a bit larger than the Earth. There is one system (TRAPPIST-1) a little farther away than Proxima Centauri that has seven nearly Earth-sized planets, three of which are probably about the same temperature as the Earth and have a large amount of water. Over 50 planets have been found that are about the same size and have the same temperature as the Earth, which means liquid water is stable on them. They may be habitable, at least for the most common life form that exists on Earth — bacteria.
And all of these exoplanets may be just the tip of the iceberg. There appear to be vast numbers of planets that float around between the stars. These are sometimes called “rogue worlds” or worlds that have no sun. These exoplanets are dark to the visible light that our eyes see. But they may not necessarily be cold inside. Many may have subsurface oceans of water like that which Europa — a moon of Jupiter has under a crust of ice. Europa has several times more liquid water than in all the oceans of Earth combined.
Is there life on any of these exoplanets? We really have no idea. But we have found that the requirements for life — liquid water, carbon and other raw materials, and usable energy — probably exist on numerous planets and moons.
Completely apart from the question of life elsewhere, it is sometimes good simply to pause and reflect on our amazing Earth and the truly, truly incredible universe we inhabit.
Michael Summers is a professor of planetary science and astronomy at George Mason University.
The views and opinions expressed in this commentary are those of the author and do not reflect the official position of The Daily Caller.