Astronomers have found a tenth planet, larger than Pluto and nearly three times farther from the Sun as Pluto is today. Temporarily designated 2003 UB313, the new planet is the most distant object yet seen in the solar system, 97 times farther from the Sun than the Earth is.

Explanation: The four common Planet Surface Processes are: Cratering, Volcanoes, Erosion, and Weathering (chemical and physical).

Planetary differentiation, therefore, refers to the processes that cause an essentially homogeneous accreted body that is made up of primordial solar material to become separated into layers having different chemical and/or physical properties.

impact cratering

The Short Answer: A planet is round because of gravity. A planet’s gravity pulls equally from all sides. Gravity pulls from the center to the edges like the spokes of a bicycle wheel. This makes the overall shape of a planet a sphere, which is a three-dimensional circle.

Smaller asteroids are generally not round. This is because small asteroids have very weak gravitational pulls, meaning they cannot pull all the material surrounding them towards their center equally. Therefore, unlike planets, these small asteroids are not spherical and round.

Smaller bodies like asteroids lack the mass—and thus the gravity—to pull their rocky surfaces into a spherical shape. The rocks resist the weak gravitational tug and retain the lumpy-looking, potato or dumbbell shapes we see in asteroid photos from spacecraft or Earth-based radar observations.

Most of them live in the main asteroid belt—a region between the orbits of Mars and Jupiter. Some asteroids go in front of and behind Jupiter. They are called Trojans. Asteroids that come close to Earth are called Near Earth Objects, NEOs for short.

All of the planets are round because of gravity. When our Solar System was forming, gravity gathered billions of pieces of gas and dust into clumps which grew larger and larger to become the planets. The force of the collision of these pieces caused the newly forming planets to become hot and molten.

Planets are round because their gravitational field acts as though it originates from the center of the body and pulls everything toward it. The only way to get all the mass as close to planet’s center of gravity as possible is to form a sphere. The technical name for this process is “isostatic adjustment.”

The gravitational force of a planet’s mass pulls all of its material toward the center, smoothing out any jarring non-roundness. Many of the smaller bodies of the solar system are not round because their gravity is not enough to smooth out their shape.

oblate spheroid

The Earth is an irregularly shaped ellipsoid. While the Earth appears to be round when viewed from the vantage point of space, it is actually closer to an ellipsoid.

Venus is the brightest object in the sky after the Sun and the Moon, and sometimes looks like a bright star in the morning or evening sky. The planet is a little smaller than Earth, and is similar to Earth inside. We can’t see the surface of Venus from Earth, because it is covered with thick clouds.

There are eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Instead, it is classified as a dwarf planet. Other dwarf planets include Ceres, Haumea, Makemake, and Eris.

According to the International Astronomical Union, the organization charged with naming all celestial bodies and deciding on their statuses, Pluto is still not an official planet in our solar system. Soon after Pluto was discovered in 1930, it was designated a planet, the ninth in our solar system.

Pluto’s reddish brown color on the other hand is believed to be created when cosmic rays and ultraviolet light from the Sun interact with the methane in Pluto’s atmosphere and on its surface. The tholins formed in Pluto’s atmosphere eventually fall to its surface, staining the dwarf planet in “gunk” of a reddish hue.

It is irrelevant that Pluto’s surface temperature is extremely low, because any internal ocean would be warm enough for life. This could not be life depending on sunlight for its energy, like most life on Earth, and it would have to survive on the probably very meagre chemical energy available within Pluto.

NATIONAL HARBOR, MARYLAND—Researchers on NASA’s New Horizons mission have discovered evidence on Pluto for what appears to be two cryovolcanoes—volcanoes built out of frozen ice that once oozed molten ice from the inside of the dwarf planet.

A whiff of ammonia in reddish ices on Pluto may be evidence of recent geological activity on the dwarf planet, with liquid water spewing out from Pluto’s depths like molten lava would on Earth, a new study finds.

Pluto a Breathable Planet? Although there turned out to be more carbon monoxide than expected, the gas makes up just a small part of Pluto’s overall atmosphere, which is mostly nitrogen, like Earth’s. (Related: “Saturn Moon Has Oxygen Atmosphere.”)