The solar system formed quickly

• Radioactive dating of rocks from the Earth, Moon, Mars & meteorites is in agreement

• The planets formed from the solar nebula at an age of roughly 4.6 billion years ago

• The remnants of the solar nebula were then cleared out of the solar system, halting planet building – how?
  • Radiation pressure (light)
  • The solar wind (ionized hydrogen, flowing off the Sun at 250 miles per second)
  • Planet sweeping
  • Gravity boosting (ejection from the solar system)
  • Could we harness any of these forces, to travel through the stars?

Solar sails, large but light mirrors propelled through space by sunlight. [NMSU, S. Smith]

There are also planets around other stars (extrasolar planets)! We have discovered more than five thousand so far, and more candidates are under study!

Most are gas giants like Jupiter, so massive and orbiting at such small radii that they perturb the orbits of their parent stars.

A few hundred, however, seem more like Earth. These rocky bodies orbit their parent stars within the Goldilocks zone, neither so hot that all water has evaporated away, nor so cold that it is all locked up as ice, but just right, with balmy temperatures that could support liquid water, and perhaps host life.

• NASA's Kepler spacecraft is one of our best planet finders.
• The Trappist-1 star system may support an amazing seven Earthlike planets!