Ceres

In 1596, Kepler claimed that the planetary orbits would only follow “God’s design” if there were two more planets: one between Mars and Jupiter and one between Mercury and Venus. Later folks came up with the Titius–Bode law This says that for each n there should be a planet whose distance from the Sun is

times the distance between the Earth and Sun.

• For n = 0 we get Venus. • For n = 1 we get Earth. • For n = 2 we get Mars. • For n = 3 we get… NOTHING??? • For n = 4 we get Jupiter. • For n = 5 we get Saturn. • For n = 6, this rule correctly predicted the location of another planet: Uranus.

So, starting in 1800, a team of twenty-four astronomers called the “celestial police” looked between Mars and Jupiter. And in 1801 one of them, a priest named Giuseppe Piazzi, found an object in the right place! Later, other members of the celestial police found other asteroids in a belt between Mars and Jupiter. But the first to be found was the biggest: Ceres.

In 2015, the human race sent a probe called Dawn to investigate Ceres. And it found something wonderful.

The surface of Ceres is a mix of ice and hydrated minerals like carbonates and even clay! If you haven’t thought much about clay, let me just say that most clay on Earth is produced by the erosion of rocks by water. In fact I even read somewhere that most clay was formed after the rise of lichens and plants, since they’re so good at breaking down rock.

Ceres probably doesn’t have an internal ocean of liquid water like Jupiter’s moon Europa. But it seems that brine still flows through its outer mantle and reaches the surface!

Here is one artist’s image, from NASA:

A new paper argues that Ceres contains a lot of ice, and was once an ocean-covered world. This was formerly thought impossible. One of authors, Mike Sori, says:

We think that there’s lots of water-ice near Ceres surface, and that it gets gradually less icy as you go deeper and deeper. People used to think that if Ceres was very icy, the craters would deform quickly over time, like glaciers flowing on Earth, or like gooey flowing honey. However, we’ve shown through our simulations that ice can be much stronger in conditions on Ceres than previously predicted if you mix in just a little bit of solid rock.

Here’s the paper:

• I. F. Pamerleau, M. M. Sori and J. E. C. Scully, An ancient and impure frozen ocean on Ceres implied by its ice-rich crust, Nature Astronomy (2024).

And here’s where I got that quote:

• Cheryl Pierce, Asteroid Ceres is a former ocean world that slowly formed into a giant, murky icy orb, Phys.Org, September 28, 2024.

By the way, did you notice something funny about the Titius–Bode law? I left out Mercury! You get Mercury’s orbit if you set n = -∞. This means Kepler was sort of right, but also sort of wrong. If you allow negative integers n, the Titius–Bode law predicts an infinite sequence of planets between Mercury and Venus, with smaller and smaller orbits whose radii approaches that of Mercury.

Also by the way, most astrophysicist aren’t fully convinced by any of the theories put forth for why the Titius–Bode law should work. For more, try this:

• Wikipedia, Titius–Bode law: theoretical explanations.