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Vanderbilt astronomers among NASA’s TESS Mission team to discover a rare newly formed planet

by Jun. 24, 2020, 10:09 AM

Stars mapped out by Vanderbilt astronomers for exploration by NASA’s Transiting Exoplanet Survey Satellite (TESS) mission and recently decommissioned Spitzer Space Telescope have led to the discovery of AU Mic b, a newly formed Neptune-like exoplanet located a relatively short 31.9 light-years away.

The exoplanet is named in connection with the star it orbits, AU Microscopii, referred to as AU Mic. AU Mic is known as a “touchstone system”, a star close enough to be used to study the formation and evolution of stars and planets. These touchstone systems also allow astronomers to measure the composition of the planets’ atmospheres to see if they may be habitable — and thus a possible interplanetary destination for future human generations. The M dwarf star is approximately 22 million years old – 150 times younger than our Sun – and is found in the southern constellation Microscopium (that’s Greek for the microscope).

The article entitled, “A planet within the debris disk around the pre-main-sequence star AU Microscopii” was published in the journal Nature on June 24.

“Discovering and confirming the existence of AU Mic b was a profound experience,” said the co-author Keivan Stassun, Stevenson Professor of Physics and Astronomy and co-investigator of the TESS mission.

photo of Keivan Stassun
Keivan Stassun (Vanderbilt University/John Russell)

“Astronomers have long surmised that planets must form around their parent stars, out of the gas and dust leftover from the formation of the star itself. And for a long time, we’ve known of star systems that possess one of the pieces of the puzzle—lots of young stars surrounded by gas and dust, and lots of older stars encircled by planets—but here we have an extremely rare case that puts all the pieces together: A young star encircled by planets within the gas and dust from which they formed.”

Dax Feliz, a Ph.D. student in Stassun’s lab and a co-author of the study, contributed key expertise honed from working with massive amounts of data from the TESS telescope over the past two years. “There were multiple, very strong stellar flares that the team had to remove from the data to be sure that the planet was truly there. The discovery tells us that TESS can help us discover yet unknown information about a neighboring stellar system that we’ve come to know well,” said Feliz.

The mission is managed by NASA’s Goddard Space Flight Center and the master star catalog that the mission uses for targeting is maintained by a data visualization system developed through Vanderbilt’s Frist Center for Autism and Innovation. Vanderbilt is a member of a tight global network of universities, research institutes and observatories researching collected data. In periods of 27 days, TESS captures images of the endless sky. Researchers use the images to monitor the brightness of the stars, tracking for regular changes that might indicate a planet is passing through. Typically, two transits confirm the existence of a planet but due to the use of the Spitzer Space Telescope, the researchers were able to measure a total of three transits to absolutely confirm the existence and orbital period of AU Mic b.

AU Mic b orbits AU Mic in just over eight days and has a mass like Neptune’s, less than 58 times that of Earth. This calculation was made based on international observations from the European Southern Observatory in Chile and the W. M. Keck Observatory and NASA’s InfraRed Telescope Facility at the summit of Maunakea, a culturally significant landmark within the indigenous Hawaiian community.

According to a release Thomas Barclay, the paper’s co-author and an associate project scientist for TESS at NASA’s Goddard Space Flight Center, “AU Mic b formed far from the star and migrated inward to its current orbit, something that can happen as planets interact gravitationally with a gas disk or with other planets.” Its formation and path are being compared to exoplanets and stars with similar properties to help astronomers understand how planets develop and travel.

(NASA-JPL/Caltech)

To truly illustrate the excitement of this finding, AU Mic b joins the Jet Propulsion Laboratory’s (JPL) Galaxy of Horrors poster series. The series portrays exoplanets in classic “scary movie” themed posters and are available to the public for high-resolution download.

This is not the end of TESS data helping astronomers to identify new planets near AU Mic. According to the release the paper’s lead author Peter Plavchan, an assistant professor of physics and astronomy at George Mason who co-mentored Feliz through the Fisk-Vanderbilt Masters-to-Ph.D. Bridge Program, teased that “there is an additional candidate transit event seen in the TESS data. We are continuing to monitor the star with precise radial velocity measurements, so stay tuned.”

The research was supported by grants from NASA, the National Science Foundation, the Mount Cuba Astronomical Foundation and George Mason University start-up funds among others. Funding for the TESS mission is provided by NASA’s Science Mission directorate.

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