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Wednesday, September 23, 2020

Explained: Dwarf planet Ceres is now an ‘ocean world’. What does this mean?

There are five dwarf planets in our Solar System. The most famous is Pluto. The other four, in order of size, are Eris, Makemake, Haumea and Ceres.

By: Explained Desk | New Delhi | Updated: August 18, 2020 9:10:53 am
Ceres, Ceres NASA, dwarf planets, how many dwarf planets, what is ocean world, NASA dawn mission, express explained, indian expressScientists have determined that Ceres has a brine reservoir located about 40 km deep and which is hundreds of miles wide. (Photo: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Researchers have shed new light on the dwarf planet Ceres, which lies in the asteroid belt between Mars and Jupiter and is also the largest object in that belt. Ceres now has the status of an “ocean world”, after scientists analysed data collected by NASA’s Dawn spacecraft. Their findings have been published as a series of papers in the journals Nature Astronomy, Nature Communications and Nature Geoscience.

What is a dwarf planet?

There are officially five dwarf planets in our Solar System. The most famous is Pluto, downgraded from the status of a planet in 2006. The other four, in order of size, are Eris, Makemake, Haumea and Ceres. The sixth claimant for a dwarf planet is Hygiea, which so far has been taken to be an asteroid.

Last year, using observations made through the European Space Organisation’s SPHERE instrument at the Very Large Telescope (VLT), astronomers found that Hygiea may possibly be a dwarf planet since it satisfied the four criteria set by the International Astronomical Union (IAU) for a celestial body to be called a dwarf planet.

These four criteria are – that the body orbits around the Sun, it is not a moon, has not cleared the neighbourhood around its orbit (which means it is not the dominant body in its orbit around the Sun and this is what differentiates a planet from a dwarf planet) and has enough mass for its gravity to pull it into a roughly spherical shape.

Ceres exploration in the past

The dwarf planet was first spotted by Giuseppe Piazzi in 1801, who assumed that Ceres was the missing planet between Mars and Jupiter. It was classified as a dwarf planet in 2006 and is the first dwarf planet to be orbited by a spacecraft. In 2015, NASA’s Dawn reached it to study its surface, composition and history.

Dawn was launched in 2007 and visited Vesta and Ceres. In 2015, it went into the orbit around Ceres and the information it collected reinforced the idea that dwarf planets could have hosted oceans over a significant part of their history. The mission concluded in 2018.

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Why do researchers study Ceres?

Scientists are interested in this dwarf planet because it hosts the possibility of having water, something that many other planets do not have. Therefore, scientists look for signs of life on Ceres, a possibility that has also maintained scientists’ interest in the planet Mars, whose atmosphere was once warm enough to allow water to flow through it.

The possibility of the presence of water on celestial bodies makes them more intriguing for scientists since “almost everywhere we find water on Earth, we find life,” as NASA puts it.

Another reason why scientists are interested in the dwarf planet Ceres is because studying it can give insights about the formation of the Solar System since it is considered to be a fossil from that time.

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What does it mean to be an ‘ocean world’?

Ceres, NASA has said, “is a crucial piece of the ocean worlds puzzle”. “With a crust that mixes ice, salts, rock-forming minerals and other materials, Ceres looks to be a remnant “ocean world,” wearing the chemistry of its old ocean and records of the interaction on its surface.” Scientists are interested in exploring ocean worlds because they may support life.

The observations from Dawn suggest the presence of briny liquid water under Ceres’s surface. Before the mission ended in October 2018, the spacecraft dipped to less than 35 km above the surface of the dwarf planet, due to which it was able to collect data in a higher resolution.

Now, by analysing this data, which was collected at the end of the mission, scientists have determined that Ceres has a brine reservoir located about 40 km deep and which is hundreds of miles wide, making the dwarf planet, “water rich”.

Significantly, in the papers, scientists note that an ocean world in Ceres was not expected, since it is too far away from the Sun and is too small to have radioactive materials to keep the oceans liquid for most of the dwarf planet’s history. “Ceres can then be added to the rather short list of bodies for which we know the interior structure at high resolution, and the only ocean world to date (bar Earth),” the scientists note.

There are other dwarf planets and moons in our solar system where oceans exist, including the moons of Saturn and Jupiter.

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