Dr Anderson and his team considered some of the proposed modifications to gravity, and found that any adjustment to explain the anomalous acceleration would conflict with the observed orbits of the planets.

ECONOMIST: A space oddity

Each of the two planets orbits a different star in the Beehive Cluster, which consists of about 1, 000 stars located between 520 and 610 light years away.

FORBES: Astronomers Find Planets Within A Cluster Of Stars

Near-Earth objects are asteroids or comets, believed to be remnants from the formation of the planets, whose orbits brings them close to the Earth.

BBC: Asteroid impact centre site selected

This would make sense if short-period comets started off in the Kuiper belt and were nudged into closer orbits around the sun by the gravity of the most distant of the giant planets, Neptune.

ECONOMIST: Unbuckling the Kuiper belt

These slight pulls cause regular variations in the planets' orbits, affecting the timing of their transits.

MSN: Kepler telescope adds 41 planets to its list - Technology & science - Space - Space.com | NBC News

The simulations also showed that rocky planets known as Hot Earths often form inside the orbits of Hot Jupiters.

BBC: NEWS | Science/Nature | Earth-like planets may be common

Such asteroids would rapidly have adopted orbits that cut across those of the inner planets, including Earth.

ECONOMIST: Asteroid impacts

Each one, Vogt said, is like a Rorschach test for the theorists, offering plenty of ways to look at this brand-new material and many new thoughts on the origins of the stars, their planets, their orbits and their life spans.

CNN: Astronomers spy new neighbors outside solar system

But at the same time, what we started to understand about the formation process, we thought there would indeed be a lot of these orbits of giant planets spiraling inward after they're born and things that give you, for instance, hot Jupiters.

NPR: What Makes Our Solar System Special?