More views on exoplanet terminology



In cleaning off my desk this morning, I unearthed the August 12 issue of Science, which contained yet another paper about a new exoplanet discovery (K. Wagner et al, “Direct imaging of a Jovian exoplanet within a triple-star system”).

Also in this issue was a lovely Perspective on the Wagner et al paper, “Making sense of the exoplanet zoo,” by astrophysicist Rebecca Oppenheimer at the American Museum of Natural History. Following up on my post of September 7, I though I’d share some of her thoughts.

“The single most certain statement about” exoplanets is “expect the unexpected,” she says. I certainly agree. As to the newly discovered Jovian exoplanet in a tripl0-star system, Oppenheimer observes, “Many such solitary objects…are being discovered routinely. All are different from each other, straining current classification schemes.”

She mentions another star, HD 41004, “that exhibits the ‘unexpected’ and draws into question what constitutes a solar system.” HD 41004 is “somewhat smaller than the Sun, with an object 2.5 times as massive as Jupiter on an orbit slightly more than Earth’s about the Sun. In addition, another star orbiting HD 41004, at the equivalent of Uranus’s orbit, has a substellar object orbiting it with about 20 times the mass of Jupiter.” “So,” she asks, “is our labeling of HD 41004 as a ‘solar system’ accurate?”

As I noted in yesterday’s post, Oppenheimer notes, “categorizing is an age-old practice in scientific thought.” However, she comments, “after 22 years of working on substellar objects, I suspect that” the labels now used to sort them may have lost their utility in advancing knowledge. Labels can become obfuscating terms.”

Hear hear.

“With fascinating discoveries, such as Wagner et al’s…and the thousands of objects intermediate between it and stars, what we know is that they consistently fail to conform to the stellar classification system intrinsic to the history of astrophysics. In such a confusing situation, the best we can do is rethink the basic assumptions,” Oppenheimer says. (Pardon me for such extensive quoting, but her piece is so well written….) She cites a paper by Chen and Kipping ( that proposes a new nomenclature: “Jovian, Neptunian, and Terran worlds. Whether this scheme will certainly be debated, but it is a fresh alternative to the confusing terms in use today.”

Finally, she notes – wisely, I think – “Perhaps it is too early to define classes of objects” in the universe. To do so may obscure their commonalities and differences, urging overspecialization in the study of objects assumed to be unrelated because of thought-constraining labels.”

Thank you, Dr. Oppenheimer!

The University of Surrey put out a press release today about newly published research that “has shone light on a globular cluster of stars that could host several hundred black holes, a phenomenon that until recently was thought impossible.” A September 7 press release from the Carnegie Institution for Science reports, “Dwarf galaxies are enigmas wrapped in riddles. Although they are the smallest galaxies, they represent some of the biggest mysteries about our universe. While many dwarf galaxies surround our own Milky Way, there seem to be far too few of them compared with standard cosmological models, which raises a lot of questions about the nature of dark matter and its role in galaxy formation.” Every day I read of new research findings about things we didn’t know existed or didn’t believe could exist. It’s what gets me up in the morning….

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