It is a good time to try to observe the dwarf planet Ceres as it is just past opposition and is located between the constellations Cetus and Pisces. The clear sky clocks don’t look favourable over the next few days but if the clouds part then take a look towards the south about 30 degrees above the horizon around midnight. If it remains cloudy read on to learn more about the Ceres.
Ceres is, by far, the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Like Pluto, Ceres was originally classified as a planet shortly after it was discovered in 1801 by Italian astronomer Giuseppe Piazzi. It was “demoted” to an asteroid (“star-like” object) by William Herschel in 1802, and was classified, along with Pluto, as a dwarf planet in 2006.
NASA’s Dawn spacecraft went into orbit around Ceres in March 2015. Images from Dawn, as it approached Ceres highlighted bright white spots, within the Occator Crater whose composition puzzled scientists. Recent studies of spectroscopy data sent back by Dawn have indicated the presence of ammonia-rich clays. This suggests that Ceres may have formed in the Kuiper belt, past Neptune, and migrated inward as ammonia-bearing salts have been detected in the outer solar system such in the geysers of Enceladus (a moon of Saturn). Other studies conclude that recent geologic activity was probably involved in the creation of the bright spots.
In Sept 2016, NASA scientists released a paper in Science that claims that Ahuna Mons is the strongest evidence yet for the existence of ice volcanoes. Cryovolcanoes are similar to regular volcanoes except they spurt out a mixture of salt and water rather than lava. The ejected salty water freezes and creates an icy dome at the top, which, for the NASA scientists is one of the telltale signs that Ahuna Mons is a cryovolcano.
Ahuna Mons appears to be quite young. It likely formed in the last 200 million years or so. In contrast, Ceres probably formed about 4.6 billion years ago like the rest of the solar system.
The heating process that leads to this cryovolcanism is not clear – Ceres doesn’t experience tidal heating; its insides are not heated by another object’s powerful gravitational pull as Ceres never gets close enough to a giant planet. So Ceres is again similar to Pluto in that the energy driving cryovolcanism must come from the dwarf planet’s internal heat, likely the heat left over from its long-ago formation along with some contribution from radioactive decay.
Other interesting facts:
- Ceres was the first object considered to be an asteroid.
- Plumes of water vapour shooting up from Ceres’ surface were observed by the Herschel Space Telescope.
- Ceres accounts for one-third of the mass in the asteroid belt yet it is still the smallest dwarf planet.
- Ceres is the only dwarf planet with no moons.