Is there another planet in our solar system?

That is Gor, from the book, Chronicles of Gor, Tarnsmen of Gor, Etc

Although it is a good series of books, it is fiction, sorry.

Really? Why are people always telling me dumb things!

Planet X was thought to exist (or at least be plausible) until Voyager 2 data was used to gain a more accurate mass for Neptune. With that JPL recalculated Neptunes gravitational effect on Uranus and the discrepancies attributed to Planet X vanished. Since then further probe trajectories have not found any discrepancies that would suggest the existence of Planet X.

Actually, this idea is much older than that series of fiction books. The idea of a Counter-Earth was first proposed by the philosopher Philolaus in ancient Greece (around 400 BCE).

Oh good. Now I don’t feel so stupid for thinking it might be possible.

From Wikipedia article at @PhiNotPi‘s post:

Any planetary sized body at Earth’s L3 point should have been visible by the NASA STEREO coronagraphs during the first half of 2007…Given the sensitivity of STEREO’s COR2 coronagraph, anything larger than 100 kilometres (62 mi) in diameter should have been detected.

In other words, there’s evidence against the existence of counter-Earth.

The concept of another planet on the exact other side of the Sun was also used in the SciFi film “Doppelganger”, which later became known as “Journey To The Far Side Of The Sun”.
However, NASA did check: nothing there, or really well cloaked.

@Skaggfacemutt The question is, why are you beleiving those dumb things right away. If you have even a little doubt, research it first. Even if you dont, you can learn more about it.

For a huge list of cultural references, see the Wikipedia page Fictional Planets of the Solar System.

Nope. There are so many interplanetary probes and satellites in various orbits around the sun they would have seen it many years a go. Here is a picture from Voyager taken in 1990 of Earth, Venus and our Sun. It easily had the capability to find anything out there.
The Spitzer and Kepler telescopes are in Earth trailing orbits around the sun. SOHO was placed in Halo orbit in 1996. They’d see it.
That story is fiction. Clever fiction.

There is a theory that our Sun has a sister star, forming a binary star system.

Another??

There’s at least eight others.

@Crashsequence2012 I assume you mean 7, since the demotion of Pluto.

@XOIIO I didn’t believe it at all – just wanted to hear what everyone else thought about the possibility. Believe me, I am the farthest thing from gullible – if anything I am the world’s biggest skeptic. In fact, I dismiss so many things, that is one of the reasons I ran this question by all of you.

@ayls_billones Nice find. I’ve done some more research, and Here is the Wikipedia article(dwarf_planet) on the dwarf planet, now called Eris. It is bigger than Pluto, but its discovery actually helped to lead to the downgrading of that planet, Pluto, and others, to “dwarf planets” instead of planets.

Also, according to the article, that Eris is not 97 times farther from the sun compared to Pluto, but 97 times farther from the sun compared to Earth. It is about 2.5 times farther away from the sun than Pluto.