SOLAR SYSTEM

Detailed explanation-1: -Thanks to Rosetta and Philae, scientists discovered that the ratio of heavy water (water made from deuterium) to “regular” water (made from regular old hydrogen) on comets was different than that on Earth, suggesting that, at most, 10% of Earth’s water could have originated on a comet.

Detailed explanation-2: -Astronomers once thought comets, such as Halley’s Comet (top), could be the source of Earth’s water. But the amount of heavy water (D2O) these icy bodies carry doesn’t match the amount found on Earth.

Detailed explanation-3: -In contrast, comets come from the outer solar system and contain lots of water-ice and other volatiles.

Detailed explanation-4: -Meteorites are shards that have broken off of larger objects such as comets or asteroids, and it is thought that asteroids and comets from the outer reaches of the solar system may have left water on nascent Earth after impact.

Detailed explanation-5: -Asteroids are made up of rock and iron like the four planets closest to our sun, but they are much smaller. All the asteroids put together would be smaller than our moon. Asteroids are different from comets, which are mostly rock and ice. Comets have tails.

Detailed explanation-6: -As space rocks bombarded Mars during its first 100 million years, they brought water-enough to form a planet-wide, 300-meter-deep ocean, researchers say. The team examined meteorites that had come to Earth from Mars in order to estimate how much water reached the early Red Planet.