Asteroid Ceres has been promoted to dwarf planet

There is a disturbance in the symmetry of the solar system. Between the orbits of Jupiter and Mars there should be a planet. Instead, there is a belt of rubble, big rocks, little rocks, and lots of dust. In 1801 Giuseppe Piazzi discovered Ceres, in one of those fortuitous accidents that litter the history of science, (apparently he was looking for a star) and surmised, not unreasonably,  that this was the missing planet. However, several other largish planet-like bodies were discovered some years later, all having similar orbits to Ceres. By 1850 so many objects had been discovered that Alexander von Humboldt coined the term Asteroid Belt, and by 1863 Ceres and its cousins were recognised as asteroids.

The asteroid count as of 25 September 2019 was 796,990! Expect this number to increase.

In 2006 Pluto was demoted to dwarf planet by the International Astronomical Union, but on the upside Ceres’ status improved setting it apart from all the other asteroids – it became a dwarf planet. According to the IAU, a dwarf planet “… is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite”.

Ceres is now regarded as an embryonic or proto-planet, one that began accreting 4.6 billion years ago but kind of lost interest; perhaps it liked its neighbours. Continue reading →