Ceres (dwarf planet) facts for kids
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Ceres as imaged by Dawn, May 2015. Two bright spots dot its surface; the bright crater at right is Haulani, while the bright spot at left is the floor of the crater Oxo
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| Discovery | |||||||||
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| Discovered by | Giuseppe Piazzi | ||||||||
| Discovery date | 1 January 1801 | ||||||||
| Designations | |||||||||
| MPC designation | 1 Ceres | ||||||||
| Pronunciation | /ˈsɪəriːz/, SEER-eez | ||||||||
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Named after
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Cerēs | ||||||||
| Adjectives | Cererian, -ean (/sɪˈrɪəriən/) | ||||||||
| Orbital characteristics | |||||||||
| Epoch 21 January 2022 (JD 2459600.5) | |||||||||
| Aphelion | 2.98 AU (446 million km) | ||||||||
| Perihelion | 2.55 AU (381 million km) | ||||||||
| 2.77 AU (414 million km) | |||||||||
| Eccentricity | 0.0785 | ||||||||
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Average orbital speed
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17.9 km/s | ||||||||
| 291.4° | |||||||||
| Inclination |
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| 80.3° | |||||||||
| 7 December 2022 | |||||||||
| 73.6° | |||||||||
| Satellites | None | ||||||||
| Proper orbital elements | |||||||||
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Proper semi-major axis
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2.77 AU | ||||||||
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Proper eccentricity
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0.116 | ||||||||
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Proper inclination
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9.65° | ||||||||
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Proper mean motion
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78.2 deg / yr | ||||||||
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Proper orbital period
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4.60358 yr (1681.458 d) |
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Precession of perihelion
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54.1 arcsec / yr | ||||||||
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Precession of the ascending node
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−59.2 arcsec / yr | ||||||||
| Physical characteristics | |||||||||
| Dimensions | (966.2 × 962.0 × 891.8) ± 0.2 km |
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Mean radius
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469.7±0.1 km | ||||||||
| 2,772,368 km2 | |||||||||
| Volume | 434,000,000 km3 | ||||||||
| Mass | |||||||||
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Mean density
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2.1616±0.0025 g/cm3 | ||||||||
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Equatorial surface gravity
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0.284 m/s2 (0.0290 g0) | ||||||||
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Moment of inertia factor
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0.36±0.15 (estimate) | ||||||||
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Equatorial escape velocity
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0.516 km/s 1141 mph | ||||||||
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Sidereal rotation period
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9.074170±0.000001 h | ||||||||
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Equatorial rotation velocity
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92.61 m/s | ||||||||
| ≈4° | |||||||||
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North pole right ascension
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291.42744° | ||||||||
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North pole declination
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66.76033° | ||||||||
| 0.090±0.0033 (V-band) | |||||||||
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| C | |||||||||
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| 3.34 | |||||||||
| 0.854″ to 0.339″ | |||||||||
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Ceres (also known as 1 Ceres) is a dwarf planet located in the main asteroid belt. This belt is found between the orbits of Mars and Jupiter. Ceres was the very first asteroid ever found.
It was discovered on January 1, 1801, by Giuseppe Piazzi in Sicily. At first, people thought it was a new planet. Later, it was reclassified as an asteroid, and then as a dwarf planet. Ceres is special because it's the only dwarf planet that isn't located beyond Neptune's orbit.
Ceres is about a quarter the size of Earth's Moon. Because it's so small, it's too faint to see with just your eyes. You need a telescope to spot it, even when it's closest to Earth. Scientists didn't know much about Ceres until the NASA spacecraft Dawn arrived in 2015.
The Dawn mission found that Ceres's surface is a mix of water ice and minerals like carbonates and clay. Data from gravity measurements suggest Ceres has layers, like a muddy (ice-rock) mantle and a stronger crust with some ice. Even though Ceres probably doesn't have a big ocean of liquid water inside, salty water (brine) can still flow through its outer layers. This brine can reach the surface, forming cryovolcanoes like Ahuna Mons. This makes Ceres the closest known active cryovolcano to the Sun. Ceres also has a very thin, temporary atmosphere made of water vapor. This vapor comes from specific spots on its surface.
Contents
History of Ceres
How Ceres Was Discovered
For many years, astronomers believed there might be a hidden planet between Mars and Jupiter. This idea came from a mathematical rule called the Titius–Bode law. This law seemed to predict where planets should be, but it had a gap between Mars and Jupiter. It suggested another planet should exist about 420 million kilometers from the Sun.
In 1800, a group of astronomers, sometimes called the "celestial police", started a careful search for this missing planet. While they didn't find Ceres, they later discovered other asteroids like Pallas and Vesta.
Giuseppe Piazzi, a priest and astronomer in Sicily, found Ceres on January 1, 1801. He was looking for a star but noticed a moving, star-like object instead. He first thought it was a comet. Piazzi watched Ceres for several weeks. He announced his discovery, saying it might be "something better than a comet" because it moved so slowly and steadily.
After Piazzi's discovery, Ceres moved too close to the Sun to be seen. It was hard to predict where it would reappear. A young mathematician named Carl Friedrich Gauss developed a new method to calculate its path. Thanks to his work, Ceres was found again on December 31, 1801, by astronomers Franz von Zach and Heinrich Olbers. Ceres's position fit the Titius–Bode law almost perfectly.
Early estimates of Ceres's size varied greatly. In the 1970s, new methods helped scientists measure its diameter more accurately. They found it was about 939 kilometers across.
Naming Ceres
Piazzi wanted to name his discovery Ceres Ferdinandea. Ceres was for the Roman goddess of agriculture, who had her oldest temple in Sicily. Ferdinandea was to honor King Ferdinand III of Sicily. However, other countries didn't like the "Ferdinandea" part, so it was dropped. Astronomers eventually agreed on the name Ceres.
The element Cerium, discovered in 1803, was also named after Ceres. The old symbol for Ceres, still used in astrology, looks like a sickle. This was a symbol of the goddess Ceres.
How Ceres Is Classified
Ceres's classification has changed several times. For over 50 years, Ceres was listed as a planet in astronomy books. But as more objects were found in the asteroid belt, astronomers realized these were a new type of object. In 1802, William Herschel called them asteroids, meaning "star-like".
By the 1860s, astronomers understood that major planets and asteroids were different. In 2006, the International Astronomical Union (IAU) created a clear definition for a "planet". A planet must:
- Be round because of its own gravity.
- Orbit a star.
- Have "cleared the neighborhood" around its orbit. This means it's the main object in its orbital path.
Ceres meets the first two points, but it doesn't clear its neighborhood. It shares its orbit with thousands of other asteroids. It only makes up about 40% of the asteroid belt's total mass. Because of this, Ceres was classified as a dwarf planet.
There's still some confusion about whether Ceres is also an asteroid. NASA sometimes says Vesta is the largest asteroid. However, the IAU's Minor Planet Center lists Ceres as both an asteroid and a dwarf planet.
Ceres's Orbit
Ceres orbits the Sun between Mars and Jupiter, in the middle of the asteroid belt. One year on Ceres (its orbital period) lasts about 4.6 Earth years.
Compared to Earth, Ceres's orbit is moderately tilted. Its orbital inclination is 10.6 degrees. This is more tilted than Mercury's orbit (7 degrees) but less than Pluto's (17 degrees). Ceres's orbit is also slightly oval-shaped, with an orbital eccentricity of 0.08. This is similar to Mars's orbit.
Ceres is not part of an asteroid family. Asteroid families are groups of asteroids that formed from the same collision. Ceres is likely too icy to be part of such a family. Smaller icy bodies would have evaporated over time.
Rotation and Tilt
A day on Ceres (its rotation period) lasts about 9 hours and 4 minutes. Ceres has a small axial tilt of about 4 degrees. This means its poles don't get much direct sunlight. Because of this, some craters in its polar regions are always in shadow. These "cold traps" can collect water ice over time, similar to what happens on the Moon and Mercury.
The Dawn spacecraft confirmed Ceres's axial tilt. This small tilt means Ceres doesn't have strong seasonal changes in sunlight. However, Jupiter and Saturn's gravity have caused Ceres's tilt to shift over millions of years. In the past, its tilt ranged from 2 to 20 degrees, meaning it did experience seasonal changes. Craters that stayed shadowed during these periods are most likely to hold onto water ice.
Ceres's Geology
Ceres is the largest object in the main asteroid belt. It's classified as a C-type or carbon-rich asteroid. It's shaped like a slightly flattened sphere, wider at its equator than at its poles. Measurements from the Dawn spacecraft show its average diameter is about 939 kilometers.
Ceres's density suggests that about a quarter of its mass is water ice. It makes up 40% of the total mass of the asteroid belt. However, it's still much smaller than Earth's Moon. Ceres is almost round due to its own gravity, a state called hydrostatic equilibrium. Scientists believe Ceres does not have a magnetic field.
Ceres's Surface
What Ceres Is Made Of
The surface of Ceres is mostly the same everywhere. It's rich in carbonates and clay minerals that have been changed by water. The amount of water ice in its surface material (regolith) varies. There's more ice near the poles and less near the equator.
Studies have found graphite, sulfur, and sulfur dioxide on Ceres's surface. Graphite likely comes from space weathering on older surfaces. Sulfur and sulfur dioxide are gases that would normally escape quickly. Their presence suggests recent geological activity.
Scientists also found organic compounds in some craters, like Ernutet. Most of Ceres's surface is rich in carbon, making up about 20% of its mass. This is much higher than in meteorites found on Earth. This chemistry suggests Ceres formed in a very cold environment, possibly beyond Jupiter's orbit. It gathered material rich in carbon and water, which could be good for organic chemistry.
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Black-and-white photographic map of Ceres, centred on 180° longitude, with official nomenclature (September 2017)
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Ceres, polar regions (November 2015): North (left); south (right). The south pole is in shadow. "Ysolo Mons" has since been renamed "Yamor Mons."
Craters on Ceres
The Dawn mission showed that Ceres has many craters. However, it has fewer large craters than scientists expected. The largest confirmed crater, Kerwan Basin, is 284 kilometers wide. The likely reason for fewer large craters is that Ceres's icy crust slowly flattens out big impacts over time.
Ceres's north pole has more craters than its equator. Some large, shallow basins with worn-down edges are probably old, eroded craters. The biggest of these is Vendimia Planitia, which is 800 kilometers across.
Dawn also saw over 4,400 boulders larger than 105 meters on Ceres's surface. These boulders likely formed from impacts and are found near craters. Boulders on Ceres break down quickly due to temperature changes and meteorite impacts. They are estimated to last only about 150 million years.
Cryovolcanoes on Ceres
Ceres has one very noticeable mountain called Ahuna Mons. This mountain appears to be a cryovolcano, which is a volcano that erupts icy, watery material instead of molten rock. It has few craters, suggesting it's relatively young, perhaps 240 million years old.
Scientists think Ahuna Mons formed from a mix of salty water and rock that pushed up from inside Ceres. It's located roughly opposite the Kerwan Basin. The impact that created Kerwan might have sent shockwaves through Ceres, causing the icy, muddy material to erupt onto the surface.
Computer simulations suggest that cryovolcanoes on Ceres slowly flatten out over hundreds of millions of years. Scientists have found 22 features that could be old, flattened cryovolcanoes. Models suggest that, on average, one cryovolcano forms on Ceres every 50 million years.
Hundreds of bright spots have been seen by Dawn. The brightest ones are in the middle of Occator Crater, which is 80 kilometers wide. The brightest spot is called Cerealia Facula. A haze sometimes appears above Cerealia, suggesting that ice is sublimating (turning directly into gas) or that gas is escaping. In March 2016, Dawn found clear evidence of water ice on the surface of Oxo crater.
In 2015, NASA scientists suggested the bright spots might be a type of salt from evaporated brine, like magnesium sulfate. These spots were also linked to ammonia-rich clays. In 2017, further studies showed the bright areas contained a lot of sodium carbonate. In August 2020, NASA confirmed that Ceres is rich in water. It has a deep reservoir of brine that comes to the surface in many places, creating these bright spots.
Inside Ceres
Ceres's active geology is driven by ice and salty water. Scientists estimate that Ceres is about 50% water by volume. Its largest craters are several kilometers deep. This suggests that Ceres's outer layer is much stronger than pure water ice. It's likely a mix of silicates, salts, and methane clathrates, with no more than 30% water ice.
Gravity measurements from Dawn have led to different ideas about Ceres's inside. One idea is a three-layer model:
- An outer crust, about 40 kilometers thick, made of ice, salts, and minerals.
- A middle layer, about 60 kilometers thick, of muddy brine and rock.
- An inner muddy "mantle" of hydrated rock.
It's not clear if Ceres has a liquid core or a dense metal core. However, the low density in the center suggests it might still have about 10% empty space (porosity).
Ceres's Atmosphere
In 2017, Dawn confirmed that Ceres has a temporary atmosphere of water vapor. Earlier, in 2014, the Herschel Space Observatory had detected small areas on Ceres releasing water vapor. These areas were no more than 60 kilometers wide. Each released about 3 kilograms of water per second.
Scientists think this vapor comes from ice sublimating (turning directly into gas) on the surface. It could also come from cryovolcanic eruptions caused by heat inside Ceres. Or, it might be from a subsurface ocean that is being squeezed. In 2015, Ceres was added to a list of "active asteroids" because of this activity.
Water ice on the surface of Ceres is not stable when it's close to the Sun. It's expected to turn into gas if exposed to sunlight. Solar flares can also cause exposed ice patches to release water molecules. Water ice can move from deep inside Ceres to the surface, but it escapes quickly.
Dawn's instruments showed that Ceres speeds up electrons from the solar wind. This likely happens when the solar wind hits Ceres's thin water vapor atmosphere. Ceres's thin atmosphere is constantly refilled. This happens through impacts exposing water ice, water ice moving through the porous crust, and solar activity.
How Ceres Formed and Changed
Ceres is a surviving protoplanet. This means it's a very early planet that formed 4.56 billion years ago. Along with Pallas and Vesta, it's one of only three such objects left in the inner Solar System. Other protoplanets either joined to form larger planets, were shattered, or were pushed out by Jupiter.
Even though Ceres is now in the asteroid belt, its makeup suggests it didn't form there. It seems it formed between Jupiter and Saturn's orbits. Then, as Jupiter moved outward, Ceres was pulled into the asteroid belt. Finding ammonia salts in Occator Crater supports this idea. Ammonia is much more common in the outer Solar System.
Ceres's early development depended on heat sources. These included energy from impacts and the decay of radioactive materials. This heat might have been enough to separate Ceres into a rocky core and an icy mantle. It might even have had a liquid water ocean soon after it formed. If it had an ocean, it should have left an icy layer under the surface when it froze. But Dawn found no evidence of such a layer. This suggests Ceres's original crust was broken up by later impacts. These impacts would have mixed the ice with salts and rocky material.
Ceres has surprisingly few large craters. This suggests that its icy material and cryovolcanism have smoothed out older features. The presence of clays and carbonates means chemical reactions happened at temperatures above 50 degrees Celsius. This is consistent with hot water activity inside Ceres.
Ceres has become less geologically active over time. Its surface is now mostly covered in impact craters. However, Dawn showed that internal processes have continued to shape Ceres's surface. This was a surprise, as scientists thought Ceres's small size would have stopped internal activity early on.
Is Ceres Habitable?
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Ceres isn't discussed as much as Mars or Europa for potential life. However, it has the most water of any body in the inner Solar System besides Earth. The likely pockets of brine (salty water) under its surface could be places where microbial life could exist.
Unlike Europa, Ceres doesn't get heat from tidal forces. But it's close enough to the Sun and has enough long-lasting radioactive materials to keep liquid water under its surface for long periods. The discovery of organic compounds and water mixed with carbon on its surface could create conditions good for organic chemistry. Ceres has carbon, hydrogen, oxygen, and nitrogen. Phosphorus hasn't been found yet, and sulfur was detected by Hubble but not by Dawn.
Observing and Exploring Ceres
How We Observe Ceres
When Ceres is closest to Earth and the Sun, it can be bright enough to see with binoculars. It's usually too dim to see with just your eyes, unless the sky is very dark.
In 1984, astronomers watched Ceres pass in front of a star. This event, called an occultation, helped them measure its size and shape more accurately. In 1995, the Hubble Space Telescope took ultraviolet images of Ceres. In 2002, the Keck Observatory took infrared images using special technology.
Before the Dawn mission, only a few surface features on Ceres were clearly seen. Hubble images in 1995 showed a dark spot, nicknamed "Piazzi." Later, Hubble images in 2003 and 2004 showed eleven features. Dawn eventually showed that "Piazzi" was a dark area in Vendimia Planitia.
The Dawn Mission
The Dawn mission was part of NASA's plan for low-cost science missions. Dawn was launched on September 27, 2007. It was the first spacecraft to visit both Vesta and Ceres.
Dawn first orbited Vesta for 13 months. Then, it used its special ion engine to travel to Ceres. It successfully entered orbit around Ceres on March 6, 2015.
The spacecraft had cameras, a visual and infrared spectrometer, and a gamma-ray and neutron detector. These tools helped scientists study Ceres's shape and what it's made of. As Dawn approached Ceres in January 2015, it took its first close-up images. These images showed impact craters and a small bright spot.
Dawn studied Ceres from different heights. It started at 13,500 kilometers, then moved closer to 4,400 kilometers, then 1,470 kilometers, and finally to 375 kilometers. In October 2015, NASA released a true-color picture of Ceres from Dawn. The mission was extended in 2017 to allow for even closer orbits.
Dawn quickly found signs of cryovolcanism. In February 2015, two bright spots were seen inside a crater. This led to ideas about cryovolcanoes or gas escaping. In September 2016, scientists said that Ahuna Mons was strong proof of cryovolcanic features on Ceres. In May 2015, NASA released a higher-resolution image showing that the bright spots were made of many smaller spots.
In December 2015, NASA scientists reported that the bright spots might be a type of salt from evaporated brine. These spots were also linked to ammonia-rich clays. In June 2016, studies showed the bright areas contained a lot of sodium carbonate. This suggested that recent geological activity created the bright spots.
From June to October 2018, Dawn orbited Ceres very closely. The Dawn mission ended on November 1, 2018, when the spacecraft ran out of fuel.
Future Missions to Ceres
In 2020, a team from the European Space Agency (ESA) suggested a mission concept called Calathus Mission. This mission would go to Occator Crater to collect samples of the bright carbonate spots and dark organic materials. These samples would then be brought back to Earth. The China National Space Administration is also planning a sample-return mission to Ceres for the 2020s.
See also
In Spanish: Ceres (planeta enano) para niños
- List of exceptional asteroids
- List of Solar System objects by size
- List of former planets
