Ceres: the dwarf planet in the asteroid belt


Ceres is the largest object in the asteroid belt that falls in between Mars and Jupiter. It is also the only Dwarf planet that lies within the orbit of Neptune.

” The cosmos is within us. We are made of star stuff. We are a way for the universe to know itself”

– Carl Sagan


It was identified as a Dwarf planet in 2006 due to the fact that it was bigger and also very different from its neighbors

Ceres and Vesta

Coming to the size, Ceres has a radius of 476 km (296 miles). To compare, the Earth’s radius is 6,378 km (3,963 miles). That makes it more than 13 times the radius of Ceres.

The surface of Ceres is covered with countless, very small craters. But it is surprising that none of them are larger than 280 km (175 miles) across.

Surprising because given the location and the lifetime (4.5 billion years) of Ceres, it stands in between the asteroid belt, so logically Ceres should have experienced thousands of hits by asteroids that are substantial in size. The reason this could happen is only if ice or other low-density material like salt happens to be just below its surface. This would smooth out its surface over time.


The story of the discovery of Ceres is pretty interesting.

It all started in 1772 with a German Astronomer Johann Elert Bode.

Bode in 1766 had proposed a hypothesis that became very famous. It was called the Titus-Bode Law. According to this law, as you extend outwards from the sun, each planet will be approximately twice as far from the sun as the one before.

Titus-Bode Law
KrishnavedalaTitus-Bode lawCC BY-SA 3.0

But there was one problem. There was a huge gap between Mars and Jupiter that seem to not obey this hypothesis.

So Bode suggested that there has to be an undiscovered planet with a radius of approximately 2.8 astronomical units that lied between Mars and Jupiter.

After the discovery of Uranus and Saturn which both happened to obey the hypothesis, it grew stronger.

So by now most believed the Titus-Bode law to be true and began the search for the unknown planet.

Then came Franz Xaver von Zach a Hungarian astronomer. He gathered a team of 24 astronomers. He called them – CELESTIAL POLICE. Their job was to find the predicted planet that lied in between Mars and Jupiter according to Bode’s hypothesis.

It was unfortunate that they never discovered the planet, but instead, they ended up finding a huge number of asteroids in the region.

But here comes the twist.

Giuseppe Piazzi, an Italian Catholic priest, mathematician, and astronomer. He was also selected for the search of Ceres.

On 1st January 1801, Piazzi discovered Ceres. And this was before he even received the invitation to join the search.

He was actually searching for something else (the 87th star of the catalog of the Zodiacal stars of Nicolas-Louis de Lacaille). But as he saw, he found a moving object in the sky. He first thought it was a comet.

On 24th January 1801, Piazzi made declared his discovery in letters to Barnaba Oriani and Johann Elert Bode.

He sent his final ‘Complete Observations’ to Bode, Oriani, and Jerome Lalande in April.

His observations were published in the September 1801 issue of the Monatliche Correspondenz.

Now it was time for his observations to be confirmed by pointing the telescopes towards the predicted path.

But there was one problem!

It had almost been 9 – 10 months since Piazzi first observed Ceres. And by now, it had already displaced from that position in the sky and was now too close to the Sun. This made it difficult for astronomers to track it.

It was predicted though that by December 1801, Ceres would be visible again.

But till then it would have been very late, due to the fact that it would get very difficult to tell its position in the sky. In other words, Ceres will be lost.

So in order to recover Ceres, Johann Carl Friedrich Gauss, a German mathematician and a physicist who was just 24 then, devised a method that would help determine the orbit of Ceres.

After he predicted the path of Ceres, referring through his observations, Heinrich W. M. Olbers and Von Zach found Ceres.


The name Ceres comes from ‘Cerere Ferdinandea’, suggested by Piazzi. Here, Cerere in Italian is the Roman God of agriculture and Ferdinandea – is King Ferdinand.


It is believed that Ceres was formed along with the rest of the solar system, which was about 4.5 billion years ago.

It was around 4 billion years ago that Ceres found its path in the asteroid belt along with thousands of other wanderers (asteroids).

Many scientists describe Ceres as an embryonic planet. What does that mean?

Well, it means that Ceres had started to form a planet but because of some reason, it couldn’t be one.

What reasons you ask?

As you know, Ceres falls right in between Mars and Jupiter. So, in the early stages of its formation, gravitational perturbations from Jupiter prevented Ceres from gathering more material to become a planet.


Ceres is said to have a very thin atmosphere that comprises water vapor.

This water vapor may be a result of the ice volcanoes.

Also, a possibility is that it could be a result of sublimation. Surface water is unstable at distances less than 5 AU from the sun. And since Ceres is 2.8 AU away from the sun, it is highly possible that it is subjected to direct solar radiation.

Moreover, Dawn (spacecraft) in 2017 had confirmed that the transient atmosphere on Ceres appeared to have a link to the solar activity.

In other words, the ice on Ceres is subjected to sublimation when energetic particles from the sun hit the exposed ice in the craters.

Visiting Ceres

The Dawn spacecraft was launched to study Vesta (the second largest world in the asteroid belt) and Ceres on 27th 2007.

Dawn spacecraft
Dawn spacecraft

It all started in the 1990s when NASA had just begun with its Discovery program. The aim of this program was to have low – cost scientific missions.

It was in 1996 when the team suggested the exploration of the asteroid belt.

Unfortunately, there were some problems regarding the funding and the mission got delayed for some years.

The spacecraft was propelled using 3 Xenon ion thrusters that were derived from NSTAR technology which was used by the Deep Space 1 spacecraft. It used them one at a time.

The ion thrusters have a specific impulse of 3,100 s and produce a thrust of 90mN.

It was on 3rd May 2011 that Dawn reached its first location, 1.2 million km from Vesta.

It Orbited Vesta for 13 months.

After that, Dawn used its ion thrusters to depart for Ceres. On 6th March 2015, the spacecraft reached Ceres.

The instruments on the spacecraft included a gamma-ray and neutron detector, a framing camera, and a visual and an infrared spectrometer.

Dawn took images of Ceres at near – Hubble resolution.

It gave Ceres’s shape and its elemental Composition.

Images credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

For more sightseeing please visit here

Things Dawn made clear
  1. Dawn clearly showed us that location was the key as to how the early system organized and evolved.
  2. Strengthened the idea that not just icy moons, but even dwarf planets could have hosted oceans during a large part of their history and also potentially still do.
  3. Found organics at Ceres and made us curious to study more on the little world.
  4. Made it clear that Ceres was, or possibly recently was geologically active.


Ceres is 2.8 AU away from the sun (1 AU = 149597871 km).


One year on Ceres is 1,682 days long. That is 4.6 Earth years. Imagine if we lived there our birthdays would come once in 4.6 years. That would be so sad.  


The dwarf planet doesn’t experience any seasons. This comes down to the fact that its axis of rotation is tilted by just 4 degrees. That is negligible as compared to the 23.5-degree axis tilt of the Earth.


Though the layers of Ceres aren’t quite clearly defined, Ceres is probably said to have a solid core followed by a mantle of water ice.

Ceres Interior
Ceres Interior

The shallow subsurface is no more than 30% – 40% ice in volume and the rest 60% – 70% is rock, salts, and clathrates.

The crust is mostly rocky and dusty with a large number of salt deposits. These salts on Ceres aren’t like the ones we find on Earth – table salt (sodium chloride) but instead they are made of different minerals like magnesium sulfate.


Amongst other celestial objects like Jupiter’s moon – Europa, Saturn’s moon – Enceladus, Mars, etc. Ceres too is suspected to harbor life.

And why not, Ceres is believed to contain more water than here on Earth. And where there is water, there is a good chance of finding life.

Of course, it won’t be as evolved as us. But there is a chance that there could be small microbes, similar to bacteria.

But till now there is no evidence that can support this.


Ceres is the largest object in the asteroid belt

It was discovered on January 1st, 1801 by Giuseppe Piazzi

It was formed around 4.5 billion years ago.

Has a very thin atmosphere that comprises water vapor.

Ceres is 2.8 AU away from the sun.

One year on Ceres is 4.6 Earth years long.

We would love to hear from you, which is your favorite dwarf planet?


Sahil Asolkar

writer and co-founder

Sahil Asolkar is a writer, poet, and shows a good interest in astronomy. His work can be seen in the articles he writes for Astronomiac.

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