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Tuesday September 17, 2019
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Cosmic Trip

U-M physics professor David Gerdes took a detour to the Kuiper Belt.

by Patrick Dunn

From the July, 2019 issue

Gerdes is one of numerous scientists from countries including Spain, Brazil, and Switzerland working on the multi-year Dark Energy Survey (DES). Using a special camera mounted on a thirteen-foot Chilean telescope, they've created what Gerdes describes as "a time-lapse movie of how the universe has changed over the last six billion years." He says the Milky Way galaxy is "like an irritating foreground object" to most of his collaborators on the project; they're more concerned with how the mysterious "dark energy" far beyond it is influencing the universe's expansion.

The survey's data collection period began in 2012 and ended this January, and Gerdes says it will take about two years to finish analyzing all the data. But he says the results so far have been "a little disappointing." Instead of new insights, they've validated "the simplest story you could tell about why the universe" is expanding, in keeping with concepts Albert Einstein introduced in his 1915 theory of relativity. "Unfortunately, it was not a major surprise," Gerdes says.

But Gerdes found myriad surprises as he studied DES data a little closer to home--relatively speaking. Analyzing DES findings in the Kuiper Belt between Neptune and the edge of our solar system, Gerdes and his students have discovered several hundred new objects and a dwarf planet.

To Gerdes's chagrin, his main funder, the U.S. Department of Energy, was uninterested in these smaller-scale studies, so he had to seek new grants from NASA and the National Science Foundation to continue his work. "I decided that I enjoyed this so much that I would rather break up with my funding agency than break up with my science," he says.

Working with what astronomers call trans-Neptunian objects--objects farther from the Sun than Neptune--Gerdes has been drawn into the discussion about the possibility of a ninth planet. (Pluto, which formerly held that title, was downgraded to a dwarf planet in 2006.) He says "the real prize" would be to find a planet-sized body "lurking

...continued below...

in our data set somewhere"--but he says he's "something of a Planet Nine skeptic." He notes that there's not enough matter that far from the Sun to make a planet. He also doubts that a planet created closer to the Sun could somehow have gotten ejected to the outer reaches of the solar system. "I'd be lying if I told you I wasn't dying to discover the ninth planet," Gerdes says. "... But nature doesn't have to do what we want."

Although they're unlikely to grab the national headlines that discovering a ninth planet would, the Kuiper Belt still holds endless discoveries for Gerdes and his team. He says his students can still "just go into our data" and "find new objects" in an area that scientists still know very little about.

"There are interesting open questions that are not fundamental questions about the nature of the universe, but they're really cool," Gerdes says. "They are, in a sense, fundamental questions about the origin of our own home."     (end of article)

[Originally published in July, 2019.]


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