1 Ceres – Readying to Image the “First Asteroid”

The day that the Dawn spacecraft first entered 1 Ceres orbit, 6MAR2015 Credit: NASA

Soon, I’ll make my first attempt to image the first asteroid discovered by humans.

In 1778, Johann Elert Bode first suggested an undiscovered planet could exist between the orbits of Mars and Jupiter. Bode observed that there was a regular pattern in orbits of the known planets, except for a large gap between Mars and Jupiter.

Bode’s empirical formula for the planets’ average distances from the Sun (or semi-major axes, a) was: 

a = ([0,3,6,12,24,48,96]+4)/10

The formula predicted a missing planet at a distance of 2.8 AU from the Sun, between Mars and Jupiter:

Mercury: a=0.4 predicted, a=0.39 actual

Venus: a=0.7 predicted, a=0.72 actual

Earth: a=1.0 predicted, a=1.00 actual

Mars: a=1.6 predicted, a=1.52 actual

Missing: a=2.8 predicted

Jupiter: a=5.2 predicted, a=5.20 actual

Saturn: a=10.0 predicted, a=9.54 actual

In 1800, a group of 24 experienced astronomers, dubbed the “Celestial Police,” begin a methodical search for the expected planet. Ceres was discovered by Giuseppe Piazzi from Palermo, Sicily on 1 January 1801. Piazzi only observed Ceres for a month before it was lost in the Sun’s glare.

Ceres would be visible again, but after many months, it would be difficult to predict its exact position. Fortunately, the mathematician Carl Friedrich Gauss, then just 24 years old, developed an efficient method of orbit determination. He predicted the path of Ceres, and astronomers recovered it near the predicted position in December, 1801.

It was originally considered a planet, but was reclassified as an asteroid in the 1850s after many other objects in similar orbits were discovered.

Now, it is known to be a 940 km wide dwarf planet, the only one within Neptune’s orbit; similar to Pluto. This is only recent knowledge (2015). It is the 25th largest known object in our Solar System. Dawn data provides evidence for a permafrosted surface topping a frozen ocean.

Between the orbits of Mars and Jupiter is a mysterious dwarf planet called Ceres. Its surface is dark and muddy, but has hundreds of patches of bright material. The salt-covered dome and other bright features in Occator Crater are so reflective that they looked like flashlights in distant images. NASA’s Dawn spacecraft got a close look, and pointed scientists to the idea that liquid brine has come up from the interior of Ceres, forming the Occator dome and other bright features. Ceres’ crust also contains a significant amount of ice. Astrobiologist Britney Schmidt discusses the implications, as well as her fieldwork in Antarctica.

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