Our Planets Found: Ceres (Planet 7.5)

When found:
January 1, 1801.

By who:
Giuseppe Piazzi.

Description:
Ceres is the largest object in the asteroid belt between Mars and Jupiter and the only dwarf planet in the inner Solar System.

Discovered in 1801, it was initially hailed as the eighth planet, fulfilling predictions from the Titius-Bode law about a missing body between Mars and Jupiter.

For about 50 years, it was classified as a planet alongside the then-known worlds. However, the discovery of numerous similar objects in the asteroid belt during the early to mid-1800s led astronomers to reclassify Ceres as the first and largest asteroid, a status it held for over a century as the belt was understood to contain remnants of a failed planet formation. This changed again in 2006, when the International Astronomical Union (IAU) established a formal definition of a "planet" that required an object to clear its orbital neighborhood of other debris—a criterion Ceres does not meet due to sharing its orbit with thousands of asteroids.

As a result, it was reclassified as a dwarf planet, joining Pluto, Eris, Haumea, and Makemake in this category, recognizing its spherical shape and geological complexity while distinguishing it from the eight classical planets.

With a diameter of about 940 km, it has a rocky core, an icy mantle that may contain briny water, and a dusty crust with salt deposits and craters.

Distance from Earth:
Closest distance: approximately 146 million miles.

Length of Year & Day:
Year: 1,682 Earth days (about 4.6 years).
Day: 9 hours.

Interesting fact:
Ceres may harbor a subsurface layer of liquid briny water, and its bright spots are reflective salt deposits from water that has seeped to the surface, raising questions about potential signs of past or present microbial life.

Like its Finder:
Like Giuseppe Piazzi, a Catholic priest and astronomer who meticulously cataloged stars and founded observatories, Ceres stands as a bridge between the rocky inner planets and the icy outer worlds, nurturing hidden reservoirs of water like a quiet guardian of potential life.