Last week, astronomers announced the discovery of DeeDee, a possible dwarf planet. That name—dwarf planet—means it is like Pluto: Massive enough to assume a spherical shape due to its own gravitational force, but not quite big enough to control the region of space it inhabits. And it too circles the sun, but from much, much farther away than Pluto. A single orbit takes 1,100 years, making DeeDee the second-most distant dwarf astronomers have ever discovered.
The Internet's scientific diaspora got excited for DeeDee. New worlds, even tiny ones, are special. But eventually, they won't seem so. Scientifically, DeeDee is mainly important as a data point—an addition to a growing catalog of similar objects. And—like a census—as the catalog grows, the individuals listed therein will become less interesting. Which might sound sad but is actually a sign that astronomy is succeeding. Dwarf planets were only created as a class a decade ago, and it's only a matter of time before you don't care that somebody found a new one.
When University of Michigan astronomer David Gerdes began the research that would eventually yield this big rock that might be a small planet, his goal was (and still is) larger. He wanted to use data from a dark-energy survey to find “trans-Neptunian objects”---anything orbiting beyond Neptune that is neither a planet proper nor a comet. He started combing through observations from a Chile-based instrument called the Dark Energy Camera.
The camera, as you might guess, is meant to study dark energy. But, says Gerdes, “fundamentally, what we’re doing is making a big, detailed map.” And in that map, Gerdes’s team looked for points of light that moved from night to night. This suggests they are small objects orbiting the Sun, rather than huge, bright objects moving incredibly fast through some distant part of the universe.
In an initial search of just one percent of the survey’s sky area, they found five new trans-Neptunian objects. And with that proof of concept, they decided to expand, searching a couple thousand square degrees of sky. (If you extend your arm all the way, the tip of your pinkie covers approximately one square degree of sky.) That larger patch contained a few hundred candidates. One of which stood out: 2014 UZ22, affectionately called DeeDee for “distant dwarf.”
Gerdes and his team spotted DeeDee when it was more than 90 astronomical units away—90 times the average distance from Earth to the Sun. To show up from that far away, it had to either be small and very shiny, or big and less reflective. Given those parameters, DeeDee is somewhere between 350 kilometers (very shiny) and 1,200 kilometers across (pretty dull). New, still-in-process data from the ALMA telescope in Chile, which can detect infrared light, should help pin down the dwarf's size and shininess.
That’s all fantastic. But what’s most fantastic: Dwarf planets like DeeDee are becoming more and more discoverable, in general.
Scientists didn't demote Pluto to dwarf planet out of spite. They were matching it to its context. When more powerful telescopes showed them more of the outer solar system, they realized Pluto was one of many icy, rocky bodies lurking far from the Sun. In 2004, astronomers discovered Sedna, about 40 percent as wide as Pluto.
A year later, they found Eris, an object bigger than Pluto. The name—Greek goddess of strife and discord—was appropriate. Instead of turning Eris into the 10th planet, astronomers at the contentious 2006 International Astronomical Union conference created a new category of thing: the dwarf planet. Pluto and Eris both became that thing.
Today, the International Astronomical Union recognizes five dwarf planets---Pluto, Eris, Ceres, Haumea, and Makemake. Mike Brown, the self-described “Pluto-killer,” claims six more objects are “nearly certainly” dwarf planets. His site lists almost 1,000 more, with dwarf planet statuses ranging from “highly likely” to “possibly." So while finding a new potential dwarf like DeeDee is laudable, its addition to the catalog is now just that: an addition to the catalog.
This move from curiosity to category is not a thing to be mourned, which Gerdes would agree with (after all, he found the one while searching for the many). A lone object could be an outlier. But with a bunch, scientists can study the population; conclusions become generalizable. It’s why a government takes a census instead of publishing 350 million individual biographies. It’s why a medical trial doesn’t just recruit one poor participant. In transitioning to something that can be measured in aggregate, dwarf planets join pretty much every other astronomical object ever.
How many stars can you name? How many galaxies? “[The] saying has been ‘In astronomy, one is a pet rock, 10 a solid statistical sample,’” says astronomer William Keel.
Just last week, scientists announced that the universe contains 10 times as many galaxies as they previously thought---up from around 200 billion to 2 trillion. To do that, they didn’t actually have to discover billions of new galaxies: They looked deeply into the sky and extrapolated. Scientists know enough about galaxies, and know of enough galaxies, to deal in math.
Astronomical objects---from space rocks to star systems---are most notable as individuals when scientists weren’t expecting them and have to scramble to explain. That scramble usually means finding more examples, reaching “solid statistical sample” status, and then doing statistical science.
Alone, DeeDee is a shiny thing far, far away. Combined with other dwarfs and trans-Neptunian objects, it can help reconstruct the recipe from which the solar system was baked. DeeDee, Pluto, Haumea, Makemake, Ceres, and all the future dwarf planets that will get only number-names are the solar system’s leftover ingredients. They and their smaller companions are the dusting of sugar and flour left on the counter after the dough has accreted into cookies.
“[They] are kind of the primordial globs of stuff that formed the rest of the planets,” says Gerdes, “and so by studying them and how they’re distributed and what their sizes and compositions are, and the dynamics of their orbits, we can learn about that primordial solar nebula out of which we and the other planets coalesced.”
Still, the surprises aren’t done. Scientists will inevitably find dwarfs and subdwarfs that will make them go, “Huh.” And they'll have a meeting, and that meeting will have a bunch of arguments, and eventually they will agree to create new subclasses to explain and contain these new, weird little worlds.
DeeDee, Gerdes says, is delightful in its own right. But it’s also tautological proof: Because they found DeeDee, they can find more stuff like DeeDee, more Makemakes, more Plutos. And those objects—all the spilled flour and sugar—might someday reveal the solar system’s secrets.
