Across the Universe: Spotting Ceres

This column first ran in The Tablet in March 2015

Ceres was the first body found in the region between Mars and Jupiter now called the Asteroid Belt. In the late 1700s Titius and Bode had noted a pattern in planet positions that suggested there should be a planet in the gap between Mars and Jupiter; on New Year’s Day of 1801, Father Giuseppi Piazzi found Ceres from his observatory in Sicily.

Bode's Law appears in the footnote on page 635 of his book of astronomy, Anleitung zur Kenntniss des gestirnten Himmels ("Manual for Knowing the Starry Sky") as seen in the Vatican Observatory copy here.

They expected a planet, so that’s what they called Ceres – though William Herschel, who had just discovered the gas giant Uranus, sniffed that such a tiny dot of light was neither planet nor star (Latin, “aster”) but a mere “asteroid.” Only fifty years later, when a number of other such small bodies had been found, did Ceres and the other asteroids get “demoted” to the status of “minor planet.” (And later work showed that the Titius-Bode pattern which predicted a planet at Ceres’ position was actually just a coincidence of numbers, not a reliable law.)

A mere 950 km in diameter, Ceres is indeed small – even Pluto’s diameter is two and a half times bigger and more than 15 times its volume – but it’s still by far the biggest object in the asteroid belt. It’s nearly twice the diameter and six times the volume of Vesta. We can measure its gravity’s tiny pull on Mars to estimate its mass, and we can just make it out as a disk in our biggest telescopes to get its diameter and volume, so we know it has a density somewhere between water and rock. We also know that, for its size, it reflects little light; its surface must be almost jet black, like a dark meteorite.

Indeed, this small size and dim surface made Ceres seem for many years a dull subject for study. But in 2006, when Pluto and other similarly-sized objects out beyond Neptune were recognized as a separate family of bodies called Dwarf Planets, it seemed reasonable to add Ceres to their number. So once again Ceres was re-classified. (Unlike Pluto, Ceres doesn’t have a vocal fan club so its repeated reclassifications have gone mostly unnoticed by the general public.)

A few years ago the Hubble telescope observed Ceres’ blurry disk to be slightly flattened. With a little fancy math (and some assumptions) you can compare the flattening with the spin rate to conclude that, unlike rubble-pile asteroids, Ceres was a solid body compressed by its own gravity, with a dense core. That implied its upper regions were full of low density stuff, probably ice, below a dust-covered surface. This idea gained traction when Esa’s Heschel Space Telescope, looking for water in our galaxy, stumbled on a detection of a plume of water from Ceres itself.

Dawn, approaching Ceres earlier this year, added the final touch: the discovery of two small white spots that many scientists are suggesting might be bits of ice poking through its dusty crust. Now we’re speculating that this fresh ice may indicate liquid water – and life? – inside this body, once thought so dull and uninteresting.

Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, contains the brightest area on Ceres. 
Dawn's close-up view reveals a dome in a smooth-walled pit in the bright center of the crater. A separate figure shows the bright spots in a mosaic of two Dawn images taken using a shorter exposure time to show details within the bright features that are overexposed, or nearly so, in the full mosaic. The images used to make these mosaics were taken from Dawn's low-altitude mapping orbit (LAMO), 240 miles (385 kilometers) above Ceres. Credit: NASA


But we’ve only just arrived; it is far too early to jump to conclusions. Planet or asteroid or dwarf? Black meteorite, dusty ice ball, or a home for life? If we’ve learned any lesson from Ceres, it’s to take in what it shows you with an open mind, rather than assume you know it all ahead of time, and only see what you expect to see.

That would be like worrying over the empty Tomb, without noticing the Gardener standing beside you.

(Most recently, organic material has been found on the surface of Ceres; for the latest Ceres information, check out the Dawn website.)

Br. Guy Consolmagno

About Br. Guy Consolmagno

Brother Guy Consolmagno SJ is Director of the the Vatican Observatory and President of the Vatican Observatory Foundation. A native of Detroit, Michigan, he earned undergraduate and masters' degrees from MIT, and a Ph. D. in Planetary Science from the University of Arizona; he was a postdoctoral research fellow at Harvard and MIT, served in the US Peace Corps (Kenya), and taught university physics at Lafayette College before entering the Jesuits in 1989.

At the Vatican Observatory since 1993, his research explores connections between meteorites, asteroids, and the evolution of small solar system bodies, observing Kuiper Belt comets with the Vatican's 1.8 meter telescope in Arizona, and applying his measure of meteorite physical properties to understanding asteroid origins and structure. Along with more than 200 scientific publications, he is the author of a number of popular books including Turn Left at Orion (with Dan Davis), and most recently Would You Baptize an Extraterrestial? (with Father Paul Mueller, SJ). He also has hosted science programs for BBC Radio 4, been interviewed in numerous documentary films, appeared on The Colbert Report, and for more than ten years he has written a monthly science column for the British Catholic magazine, The Tablet.

Dr. Consolmagno's work has taken him to every continent on Earth; for example, in 1996 he spent six weeks collecting meteorites with a NASA team on the blue ice regions of East Antarctica. He has served on the governing boards of the Meteoritical Society; the American Astronomical Society Division for Planetary Sciences (of which he was chair in 2006-2007); and IAU Commission 16 (Planets and Satellites). In 2000, the small bodies nomenclature committee of the IAU named an asteroid, 4597 Consolmagno, in recognition of his work. In 2014 he received the Carl Sagan Medal from the American Astronomical Society Division for Planetary Sciences for excellence in public communication in planetary sciences.

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Across the Universe: Spotting Ceres — 1 Comment

  1. A faithful reader writes: “I stumble and fumble about a lot of sky-definition… I thought a meteorite was one of those sky-things that actually had landed on Earth. But reading today’s post on the tags to attach to Ceres, there’s a suggestion ‘…Black meteorite…’ Did I have a wrong or incomplete understanding of Meteorite?”

    No… it was an ambiguity on my part. At the end I wanted to mention the thought that the surface material of Ceres might be the same material as is found in black meteorites. The Tablet has a pretty strict word limit and sometimes, squeezing out the last few words, I would also squeeze out any clarity that those words might have added. Sorry!

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