Ceres, a dwarf planet first discovered by Giuseppe Piazzi (Italian astronomer) in 1801, is known to be the most water-rich body in our inner solar system. According to scientists, Ceres is composed of ice, water, salts, and organics, which has led to a belief that the planet has great potential for extraterrestrial life and future human habitability.

History and Discovery of planet Ceres

The word “Ceres” in ancient Roman religion refers to the goddess of agriculture. Planet Ceres is located in the asteroid belt which marks the boundary between terrestrial planets and giant planets of our solar system. Ceres is the only object in the asteroid belt large enough (950 km in diameter) to be called a dwarf planet. Other large mass objects (asteroids) with a mean diameter of less than 600 km in the region are VestaPallas, and Hygiea.

In the month of January 1801, a catholic priest and astronomer – Giuseppe Piazzi discovered planet Ceres. Piazzi initially thought Ceres could be a comet, but after 24 careful observations he announced the discovery as “something better than a comet.” The announcement came on 24 January 1801, and the results were published in Monatliche Correspondenz. Classification of Ceres has changed over time, it was initially thought to be a missing planet by the astronomer Johann E. Bode in 1801. Ceres was considered to be a planet for the next 50 years but later on, was demoted to an asteroid, as the precise definition of a planet was not formulated until 2006.

In 2006, the debate in the Astronomy community surrounding Pluto sparked an interest in Ceres and its reclassification. The definition of planet and the differentiation between planets and dwarf planets was established by the International Astronomical Union (IAU) that Ceres along with Pluto, Eris, Makemake, and Haumea are dwarf planets.

Comparison of planet Earth, Moon, and dwarf planet Ceres
Image Credit: Gregory H. Revera, NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Dawn – a spacecraft in search of planet Ceres

Dawn is a retired NASA space probe launched in September 2007 with an objective of studying 2 objects in the asteroid belts; dwarf planet Ceres and asteroid Vesta. Dawn was retired on 1 November 2018 and it is currently in an uncontrolled orbit around the dwarf planet Ceres. NASA’s Dawn mission had to be retired because it ran out of hydrazine fuel, which led to a loss of communication, as the probe wasn’t able to point its antennas towards the Earth.

The space probe traveled about 4.3 billion miles (6.9 billion kilometers) with the help of ion engines, acquiring 172 GB of scientific data and 100,000 images. In July 2011, Dawn arrived at Vesta and in March 2015 it reached Ceres, making it the only space mission to orbit 2 destinations in a single journey. Dawn spacecraft successfully collected high-resolution gamma-ray and neutron data, images, infrared spectra and gravity data from an altitude as low as 22 miles (35 kilometers). The total cost for the Dawn program was US$500 million out of which $370 million was used to build and launch the spacecraft and $130 million for 11 years of operation and data analysis. 

Dawn mission fulfilled its original objectives at Ceres in 2016 and gathered data related to global shape, mean density, elemental composition, surface morphology, mineralogy, regional gravity, and topography. 

Nasa's Dawn mission facts and figures
Image Credit: NASA/JPL-Caltech

Geology and Geomorphology of planet Ceres

Ceres originated 4.5 billion years ago along with the rest of the solar system. Planet Ceres is also referred to as an “embryonic planet” meaning that it started to form but didn’t quite finish due to Jupiter’s strong gravitational pull.

Ceres is similar to terrestrial planets (Mars, Earth, Mercury, and Venus) as compared to its neighboring asteroids, but it is much less dense. The interior of Ceres consists of layers that aren’t as clearly defined, having a solid crust (ammonium/magnesium bearing phyllosilicates, carbonates, organics, and clathrates). Meanwhile, the upper mantle is hypothesized to have water ice and pore fluid (brine) and the lower mantle might contain aqueously altered rocks.

Ceres is suspected to have as much as 25% water, which means that it might have more water than Earth. Ceres has a solid crust with large salt deposits, these salts aren’t like table salt (sodium chloride) but instead are made of different minerals like magnesium sulfate.

Internal structure of planet Ceres
Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

The surface of Ceres is covered in countless small, young craters, but none are larger than 280 km (175 miles) in diameter. This is surprising, as the dwarf planet must have been hit by numerous large asteroids during its 4.5 billion-year lifetime. Lack of craters might be due to the existence of ice layers in its sub-surface, as the surface features (crater impacts) could smooth out over time if ice or another lower-density material (salt) exists below the surface.

Hydrothermal activity resulting from cryovolcanoes (ice volcanoes) might have removed large craters from the surface. There is another explanation which says that there are regions within surface craters on Ceres that are always in shadow. It’s possible that without direct sunlight, these “cold traps” could have water ice stored in them for long periods of time.

Surface features of planet Ceres
Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Ceres has a very thin atmosphere, studies suggest evidence of water vapor. The vapor may be generated from cryovolcanic eruptions due to internal heat, pressurization of the subsurface ocean due to overlying ice layers on surface or sublimation (solid to gas conversion) of ice near the surface. After studying Ceres, planetary geoscientists have concluded that the dwarf planet might not have a magnetosphere.

Ceres consists of several geomorphic features, including; impact craters, domes, fractures, mounds, groves, etc. The famous surficial feature on Ceres is a mons (planetary mountain) named Ahuna Mons. Ahuna Mons is a cryovolcano and the largest mountain in the dwarf planet Ceres with an average height of 13,500 feet (approx. 4000 meters) estimated to be formed 70 to 240 million years ago.

NASA’s Dawn mission shows Ceres in false-color renderings, highlighting differences in surface materials.

Astrobiology and potential habitability

Scientists are keen to examine the possibility of past or current life on planet Ceres along with its potential for human habitability. In a research paper published in Astrobiology journal, planetary scientists analyze several key aspects of Ceres, including; the existence and nature of liquids on Ceres, active and passive geologic activity on the planet, the evolution of chemical and physical conditions in its ocean, and possible origin of organics on the planet.

Two lines of evidence for the presence of liquid in planet Ceres is currently available. The first one relates to the presence of a weaker sub-surface layer below the crust – upper mantle, which can hold pore fluid in conjunction with phyllosilicates. The second is related to the formation of Ahuna Mons cryovolcano, which could have been fed by a deep brine reservoir.

Scientists studying the Ceres discovered a patch of ice that has increased in size over time. Meanwhile, a separate research team found carbon-rich minerals on the surface of Ceres that do not last long, suggesting that water has a powerful presence on the dwarf planet.

There are two kinds of volcanism in our solar system; in the first type, magma (molten rocks) erupts from the subsurface and reaches the surface in the form of lava, examples include planet Earth and Io moon’s volcanism. The second type of volcanism is called cryovolcanism, in which large plumes of frozen water erupt to the surface, examples include moons like Europa and Enceladus.

Previous studies have shown that Ceres could have a mixture of both kinds of volcanism, a hybrid between the inner (rocky) solar system and outer (icy) solar system. Volcanism at Ceres is driven by water and could cause an eruption of rocks, salts and heated materials, like mud oozing out to the surface from cracks and fissures.

The surface of Ceres consists of bright spots on its surface which have been identified as sodium carbonate, a salt found in the bottom of the Earth’s oceans. As no crashing asteroid could have brought this salt on Ceres, it is postulated that sodium carbonate rose to the surface of Ceres, which hints geologic activity.

Evidence of bioessential elements in sub-surface liquid water (brines) suggests that Ceres may have been habitable at some point in its past. Bacteria are known to survive in temperate ranges of 261 and 395 Kelvin (-12 and 122 Celsius) and 100 MPa (Megapascal) pressure. This kind of pressure exists in the outer 170 to 220 km on Ceres, thermal modeling indicates at these depths and temperatures in the above range could have existed on the planet for most of its history. These regions are deprived of sunlight so for lifeforms to exist, energy from chemical sources is necessary. This chemical energy could have been provided by a geologic process known as serpentinization, which could have been started by asteroid impacts and radiolysis/photolysis process.

Scientists believe that if life was ever-present on Ceres, its signs could still be detected today. “Organic compound candidates that might have survived till the present day on Ceres to help in identifying potential biosignatures,” said Julie C. Rogez, a planetary geophysicist at NASA/JPL in a recent research article.

Many lipid biomarkers are stable on billion-year timescales, while other compounds such as biological amino acids are stable on shorter geologic timescale when submerged in ice. Nucleic acid chains are recoverable only up to about 1 Ma (million years ago) from ice and permafrost. As the dwarf planet does not contain an Earth-like atmosphere, the lifetime of all potential chemical biosignatures in near-surface material could be significantly further reduced due to the impact of harmful radiation.

The evidence retrieved from NASA’s Dawn mission has helped scientists to confirm that planet Ceres once had availability of water, organics, energy sources, and might still have today. Future exploration of planet Ceres could help to define the relationship between liquid water and environmental factors that could have combined to make Ceres a habitable planet. Meanwhile, in addition to space exploration, scientists believe that laboratory scaled experimentation and modeling could also help in learning more about its dynamics and potential to support life.

Interesting facts about planet Ceres

Which dwarf planet is located in the asteroid belt?

Ceres is the only dwarf planet located in the asteroid belt (inner solar system), encompassing one-third of all the mass found in the asteroid belt.

What is cerium (element) named after?

Cerium, a rare-earth element discovered in 1803, was named after the dwarf planet Ceres.

Does ceres have any moons or rings?

Ceres does not have any moons or rings, and scientists believe that it also lacks a magnetosphere.

How far is Ceres from the sun?

Ceres is located 2.8 Astronomical Units away from the Sun which is why it receives sunlight in about 22 minutes.

How thick is the Ceres’s mantle?

Ceres’s mantle is about 100 km thick, which could consist of 200 million cubic km of water, more than all the freshwater on Earth.

How long does Ceres take to orbit the sun?

Ceres takes 1,682 Earth days (4.6 Earth years), to make one trip around the sun. As Ceres orbits the sun, it completes one rotation every 9 hours, making its day length one of the shortest in the solar system.

CITE THIS ARTICLE: "A strange dwarf planet Ceres & its astrobiological significance," in Geoscience Daily, April 2, 2020, https://geosciencedaily.com/space/strange-dwarf-planet-ceres/.