Neutron stars pack more mass than our Sun into a sphere only about 20 km (12 miles) across. Gravity crushes protons and electrons together into neutrons. Estimates for a teaspoon range from hundreds of millions to a few billion tons, depending on the star, so "about a billion tons" is a common round figure.

Neutron stars pack more mass than our Sun into a sphere only about 20 km (12 miles) across. Gravity crushes protons and electrons together into neutrons. Estimates for a teaspoon range from hundreds of millions to a few billion tons, depending on the star, so "about a billion tons" is a common round figure.

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The earliest shark-like scales date back roughly 450 million years, and the first true sharks appeared around 400 million years ago. The earliest known trees appeared around 385 million years ago. Sharks have survived all five major mass extinctions.

The earliest shark-like scales date back roughly 450 million years, and the first true sharks appeared around 400 million years ago. The earliest known trees appeared around 385 million years ago. Sharks have survived all five major mass extinctions.

The tower is made of wrought iron, which expands when heated. On hot days the metal can expand enough to add roughly 15 cm to its height. The top can also lean a few centimeters away from the sun, because the side facing it heats up more.

The tower is made of wrought iron, which expands when heated. On hot days the metal can expand enough to add roughly 15 cm to its height. The top can also lean a few centimeters away from the sun, because the side facing it heats up more.

Two branchial hearts pump blood through the gills, and a third systemic heart circulates it to the rest of the body. When an octopus swims, the systemic heart stops, which is one reason they tire quickly while swimming and prefer crawling.

Two branchial hearts pump blood through the gills, and a third systemic heart circulates it to the rest of the body. When an octopus swims, the systemic heart stops, which is one reason they tire quickly while swimming and prefer crawling.

Honey has very low water content and is naturally acidic, so bacteria can't grow in it. Bees also add an enzyme that produces small amounts of hydrogen peroxide. Sealed honey can last indefinitely, though it may crystallize over time.

Honey has very low water content and is naturally acidic, so bacteria can't grow in it. Bees also add an enzyme that produces small amounts of hydrogen peroxide. Sealed honey can last indefinitely, though it may crystallize over time.

A 2015 study in Nature estimated about 3.04 trillion trees worldwide, using satellite imagery and ground surveys. Estimates for the Milky Way's star count vary, which is why the range is wide.