Pictured above are the orbits of the over 1,000 known Potentially Hazardous Asteroids (PHAs). These documented tumbling boulders of rock and ice are over 140 meters across and will pass within 7.5 million kilometers of Earth -- about 20 times the distance to the Moon. Although none of them will strike the Earth in the next 100 years -- not all PHAs have been discovered, and past 100 years, many orbits become hard to predict.
A new planet was discovered that is similar to Earth in size and composition, meaning it has a rocky surface and an iron core. But that is where similarities end. This twin, named Kepler-78b, has an orbit so close to its parent star, that the surface is about 2,000 degrees hotter than Earth's. The planet's orbit around the star takes only 8.5 hours, instead Earth's 12 month orbit. Located 400 light years away from Earth in the constellation Cyngus, this hellish Earth shouldn't exist. For a planet only 20% larger than Earth with such a small orbit, astronomers can't figure out how it was formed.