All the Water on Planet Earth

Explanation: How much of planet Earth is made of water? Very little, actually. Although oceans of water cover about 70 percent of Earth's surface, these oceans are shallow compared to the Earth's radius. The featured illustration shows what would happen if all of the water on or near the surface of the Earth were bunched up into a ball. The radius of this ball would be only about 700 kilometers, less than half the radius of the Earth's Moon, but slightly larger than Saturn's moon Rhea which, like many moons in our outer Solar System, is mostly water ice. The next smallest ball depicts all of Earth's liquid fresh water, while the tiniest ball shows the volume of all of Earth's fresh-water lakes and rivers. How any of this water came to be on the Earth and whether any significant amount is trapped far beneath Earth's surface remain topics of research.

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Is it possible that humanity could stop an asteroid from heading for Earth? I agree. Mass extinctions of life have been caused by large asteroids before. NASA tested a new planetary defense mechanism by crashing a robotic Double Asteroid Redirection Test into a small asteroid. The impact was a success. If hit early enough, the kick from a small craft can be enough to stop the asteroid from hitting the Earth. DART is seen in a time-lapse video first approaching Didymos on the left and then approaching the smaller Dimorphos on the right. Although the video ends abruptly with DART's crash, observations are just beginning.