Earth's Twin

THE EIGHT PLANETS of our Solar System aren’t the only ones we’ve ever had — they’re merely the survivors.

But that doesn’t mean the other planets were destroyed. Earth may have a long-lost sibling somewhere in interstellar space. At least one rocky planet, around the same mass as Mars, may have been booted out of the early Solar System.

These are just some of the findings compiled in a recent review paper in the Annual Review of Astronomy and Astrophysics, taking a look at the mysterious third zone of our Solar System, those points past Neptune and out into interstellar space.

Today, the planets in our Solar System are neatly sorted by size and composition:

• The four rocky inner planets orbit in the space between the Sun and the Asteroid Belt
• The outer Solar System is the realm of giants — Jupiter, Saturn, Uranus, and Neptune — which gathered enormous masses of gas and ice around their rocky cores
• Beyond Uranus and Neptune lies the realm of the dwarf planets, like Pluto, Eris, Sedna, and their even smaller neighbors, whether dwarf planet or comet

And that’s a little strange. As if something is missing.

“It seems unlikely that Nature created four giant planet cores, but then nothing else larger than dwarf planets in the outer Solar System,” planetary scientists Brett Gladman of the University of British Columbia and Kathryn Volk of the University of Arizona write in the review.  READ MORE