Ceres (dwarf planet)

Ceres is a special kind of space object called a dwarf planet. It lives in the asteroid belt, a region between the planets Mars and Jupiter. Ceres was the first asteroid ever found. A scientist named Giuseppe Piazzi discovered it on January 1, 1801, from an observatory in Sicily.

Ceres is not very big—about a quarter the width of our Moon. Because it is small and far away, it is usually too faint to see without a telescope. We didn’t know much about its surface until a NASA spacecraft called Dawn flew close to Ceres in 2015.

Dawn showed that Ceres has a surface made of water ice and minerals. It may also have a hidden ocean of liquid water inside. Sometimes, salty water flows to the surface and creates icy volcanoes. This makes Ceres the closest active icy volcano world to the Sun. It also has a very thin atmosphere made of water vapor that comes and goes from different places on its surface.

History

Discovery

In the 1700s, some scientists thought there might be a hidden planet between the orbits of Mars and Jupiter. In 1772, a German astronomer named Johann Elert Bode used a special math rule to guess where this planet might be. In 1800, a group of astronomers began searching for this missing planet.

On January 1, 1801, an astronomer named Giuseppe Piazzi in Sicily discovered a moving object that looked like a star. He realized it was something new and shared his findings with other scientists. By the end of 1801, the object moved too close to the Sun to see clearly. A mathematician named Carl Friedrich Gauss used math to predict where to look again, and in December 1801, astronomers found the object near Gauss's prediction.

Name and symbol

Piazzi wanted to name the object Ceres Ferdinandea, after the Roman goddess of farming and his king. But other countries did not like the second part, so it was dropped. The name Ceres was chosen after the Roman goddess. The symbol for Ceres looked like a sickle, a tool tied to the goddess's symbols.

Classification

At first, Ceres was thought to be a planet. But as more similar objects were found nearby, scientists began calling them asteroids. In 2006, after much discussion, Ceres was called a dwarf planet because it shares its space with many other asteroids and is not the only big object there. Some scientists still think of Ceres as a planet because of its size and shape. Today, Ceres is known as both a dwarf planet and an asteroid.

Orbit

Ceres travels around the Sun in a path between the planets Mars and Jupiter, right in the middle of the asteroid belt. It takes about 4.6 Earth years to complete one trip around the Sun. Ceres's path is tilted a little compared to Earth's path, at an angle of 10.6°, which is more than Mercury but less than Pluto. Its path is also slightly stretched out, or elongated.

Ceres does not belong to a group of asteroids called an asteroid family, likely because it contains a lot of ice. Smaller asteroids with ice would have disappeared over time. Ceres was once thought to be part of a group called the Gefion family, but it was later found to have a different makeup and is not from the same origin as those asteroids.

Resonances

Objects in the asteroid belt usually do not get pulled into special patterns, or resonances, with each other because they are small and far apart. However, Ceres can sometimes pull other asteroids into temporary patterns for very long periods — from a few hundred thousand years to over two million years. About fifty such asteroids have been found. Ceres is nearly in step with another asteroid called Pallas, but not close enough for this to matter over very long times.

Rotation and axial tilt

Ceres takes about 9 hours and 4 minutes to spin once, which is called its day. Scientists use a special crater called Kait to mark the starting point for measuring this spin.

Ceres leans just a little bit, with an axial tilt of 4 degrees. This small tilt means some craters near the poles stay in shadow all the time. These shadowy spots might trap water ice, much like what happens on the Moon and Mercury. A spacecraft called Dawn found that Ceres's north pole points toward a specific spot in the sky, which helps explain why its seasons are very mild today. In the past, the pull of Jupiter and Saturn caused Ceres's tilt to change between 2 and 20 degrees, leading to bigger seasons. The last big change in seasons happened about 14,000 years ago. Craters that stay dark even when Ceres leans the most might hold onto water ice from long ago.

prime meridian cold traps what occurs on the Moon Mercury Dawn Delta Draconis

Geology

Main articles: Geology of Ceres and List of geological features on Ceres

Ceres is the largest object in the main asteroid belt between Mars and Jupiter. It is made of materials similar to some meteorites found on Earth and has a round shape. Scientists think Ceres has a mixture of rock and water ice inside.

Ceres makes up a big part of the mass of the asteroid belt and is the only dwarf planet close to Earth’s orbit. It might have a small core of rock, but its inside is still a mystery. We don’t know if it has a magnetic field because the spacecraft that studied it did not have the right tools to check.

Surface

Composition

The surface of Ceres looks the same everywhere and contains materials changed by water, like clays. There is also water ice, especially near the poles.

Pictures from space telescopes show carbon, sulfur, and other materials on the surface. Some areas have dark spots that might be organic materials, like those found in coal. These materials suggest Ceres formed in cold areas far from the Sun.

Craters

Ceres has many craters, but fewer big ones than expected. The biggest crater, Kerwan Basin, is about 284 kilometers across. The craters tell us about the history of impacts in the solar system.

Tectonic features

Though Ceres does not have moving plates like Earth, some lines on its surface might be from stretching or cracking.

Cryovolcanism

Main article: Bright spots on Ceres

Ceres has a mountain called Ahuna Mons that might be a place where icy mud flowed onto the surface long ago. There are also bright spots on Ceres, possibly from salty water that came up from below and dried out.

Internal structure

The inside of Ceres is active because of water ice and salty water. Ceres is mostly made of rock and water ice, with a lot of water deep inside.

The surface of Ceres can support big craters, meaning the outer layer is strong. Scientists have different ideas about what’s inside Ceres, but they agree it’s a mix of rock and ice in various amounts.

Exosphere

In 2017, the spacecraft Dawn found that Ceres has a thin, temporary atmosphere made of water vapor. Signs of this atmosphere were first seen in early 2014 when the Herschel Space Observatory noticed small areas on Ceres releasing water vapor. These areas are very small, about 60 kilometers wide, and release a lot of water molecules every second.

Scientists think the water vapor might come from ice on Ceres's surface turning directly into gas, or from small volcanic-like eruptions inside Ceres. The water vapor doesn’t stay long and can escape quickly. The Dawn spacecraft also showed that Ceres can change particles from the Sun's wind, possibly because of its thin atmosphere of water vapor. This atmosphere is constantly being made again as water escapes from below the surface and from ice exposed by impacts or solar activity.

Origin and evolution

Ceres is a very old object that formed about 4.56 billion years ago. It is one of only three big objects left from that time in the inner part of our Solar System. Scientists think Ceres may have formed farther out, between the orbits of Jupiter and Saturn, before moving to its current place.

Early in its history, Ceres may have had enough heat to create a rocky center and an icy outer layer, possibly even a liquid ocean. However, later impacts might have mixed things up. Ceres has fewer large craters than expected, which suggests its surface has changed over time. There is also evidence that chemical reactions happened at higher temperatures, pointing to past activity inside Ceres. Even though it is small, Ceres still shows signs that its inside has shaped its surface over time.

Habitability

Ceres has a lot of water, more than any other body in the inner Solar System except Earth. This water, mixed with salt, might create places where tiny life could live. Even though Ceres doesn’t get heated by the gravity of a larger planet like some other worlds do, it’s close enough to the Sun and has materials that could keep water liquid deep inside for a very long time.

Scientists have found materials that are important for life, like carbon, hydrogen, oxygen, and nitrogen, on Ceres. These could help create the building blocks for life, even though we haven’t found everything yet.

Observation and exploration

Observation

When Ceres is closest to Earth, it can appear very dim but might be seen with special binoculars on a very clear night. Only one other asteroid, Vesta, can sometimes appear just as bright.

In 1984, Ceres passed in front of a star, helping scientists learn more about its size and shape. In 1995, the Hubble Space Telescope took images of Ceres, and in 2002, very powerful ground telescopes captured more detailed pictures.

Dawn mission

Main article: Dawn (spacecraft)

In the 1990s, NASA planned a mission to explore the asteroid belt. The Dawn spacecraft was launched in 2007 and was the first to visit both Vesta and Ceres. It reached Ceres in March 2015.

Dawn carried instruments to study Ceres’s shape and surface. As it moved closer to Ceres, it took pictures showing craters and bright spots. Dawn orbited Ceres at different heights to learn more about the dwarf planet. In 2015, scientists announced that Ceres had features that looked like frozen volcanoes.

In June 2018, Dawn came as close as 35 km to Ceres’s surface before running out of fuel and ending its mission in November 2018.

Future missions

In 2020, a team from Europe suggested a mission to collect samples from Ceres’s surface. China is also planning a mission to bring samples from Ceres back to Earth in the 2020s.