Wellesley Team Discovers Possible Planet in Research
with Hubble Space Telescope
Mass.— This past summer, Wellesley College student researchers and their advisor Kim McLeod, Wellesley's Theresa Mall Mullarkey associate professor of astronomy, worked with a Penn State University team to discover a mystery object — a planetary-mass companion to a brown dwarf in the constellation Taurus.
"Brown dwarfs are nature's 'almost stars,'" said McLeod, "gassy bodies that aren't quite hot enough in their cores to fuse hydrogen."
The Wellesley College research team, from left to right: Associate Professor of Astronomy Kim McLeod and students Ijeoma Ekeh, Jaclyn Payne and Allison Youngblood.
The companion, possibly a planet, was discovered as part of a Hubble Space Telescope project to investigate brown dwarf formation. The mystery object turns out to have between five and ten times the mass of Jupiter, the biggest planet in our solar system. The work, "Discovery of a Planetary-Mass Companion to a Brown Dwarf in Taurus," by Penn State University's Kamen Todorov and Kevin Luhman and McLeod will be published in the May 1 issue of the Astrophysical Journal Letters.
"Whether this object should be called a 'planet' is up for discussion, as it doesn't fit neatly into our current theories of planet formation," McLeod said. "Most people have a good sense of what a planet is: it orbits a star, is big enough to have become spherical, and – this last bit thanks to the Pluto debate – is enough of a gravitational bully to have cleared out other objects from its orbital path."
To astronomers, planets also form from the "circumstellar disk" of gas that accumulates around a star as the star itself is forming. However, according to theoretical models, it takes a while for a planet to build up to masses bigger than Jupiter. The Taurus mystery object poses a problem for these models, as the whole region is only about a million years old — very young by stellar standards and not nearly old enough for such a big planet to have formed from a circumstellar disk.
"One alternative explanation is that the object formed from its own disk of matter, separate from but next to the one that formed its bigger brown dwarf companion," McLeod said. "In that case, it wouldn't quite do to call it a planet, contrary to the case for the hackneyed duck: it walks like a duck (orbits something bigger) and quacks like a duck (has the same mass) but didn't come from a duck's egg (the big object's disk)."
McLeod notes that it is very unusual for undergraduates to work directly on Hubble Space Telescope data. However, three Wellesley students and one from Colgate did just that.
Wellesley senior Allison Youngblood did the initial processing of the data last spring as an independent study project. She is going on to graduate school in astronomy in the fall.
Then in the summer a trio of students, Wellesley Davis Scholar Jaclyn Payne, Wellesley sophomore Ijeoma Ekeh and Colgate junior Steven Mohammed, worked to analyze the data.
"One was a master at being able to cut to the heart of turgid Hubble documentation and had the people skills to put together a great talk, one had the astronomy background to be able to put the discovery into context and the software skills to make the analysis more efficient, and the third had the physics background to do the calculations for the interpretation," McLeod said. "The trio discovered the mystery object independently from the Penn State team members."
Since 1875, Wellesley College has been a leader in providing an excellent liberal arts education for women who will make a difference in the world. Its 500-acre campus near Boston is home to 2,300 undergraduate students from all 50 states and 75 countries.