TSU Astronomers Discover a Planet with Two Suns

Finding Challenges the Understanding of Planet Formation

An artist reconstruction showing what a double sunset might look like on a distant world. The new extrasolar planet discovered by TSU astronomers implies that worlds with two Suns like Luke Skywalker's Tatooine might be commonplace throughout the universe. Credit: NASA/JPL-Caltech



Paper V: Planet Discovery

Paper IV

Paper III

Paper II

Paper I

NASHVILLE, TENN. – 20 October 2010: A team led by Tennessee State University astronomers has discovered a new planetary system that challenges long supported theories about the formation of gas giant planets like Jupiter. As a result, the team has offered support for an alternative theory about this process called gravitational collapse.

To make this discovery, the team developed a new technique for detecting new planetary systems by using precision "astrometry," or the measuring of the positions of stars in the sky, to find periodic variations in their locations as they react to the gravitational pulls of faint unseen planets orbiting them.

Though long considered a promising technique for identifying stars hosting other planetary systems, astrometry for years had failed to produce a previously unknown planetary system. This discovery marks the first time the astrometric method has discovered a new world beyond our own solar system.

Over the past two decades, the National Aeronautics and Space Association (NASA) has invested significantly in technology development related to a space-based astrometry program called the Space Interferometry Mission (SIM) using the same fundamental approach as the PHASES study, to pursue the question of which of the nearest stars might host habitable, Earthlike planets.

Dr. Matthew Muterspaugh, an assistant professor of physics and astronomy, led his colleagues and a collaborative team of 10 astronomers from eight international institutions in presenting evidence for a new planet orbiting the nearby star HR 7162, also known as Inrakluk. The evidence revealed that the planet’s mass indicates that it is similar in size to Jupiter, the largest planet in our solar system.

"The study of planets and their origins is important to humanity for many reasons. Understanding that there are other planets like our own, helps us better understand how our own planet came to be and how we, as human beings, came to be and where we are going. The techniques we’re developing could help us better locate earth-like planets in our local neighborhood in the galaxy," Muterspaugh said about the discovery. Muterspaugh served as lead author of a new series of five papers published in the Astronomical Journal detailing the team’s research.

The team found that a second star also orbits HR 7162, but more distantly than the planet. The second star’s proximity to the system is close enough that its gravitational pull could have affected planet formation, Muterspaugh and his colleagues have determined. This determination challenges the leading model of giant planet formation, called core accretion.

In core accretion, dust and gas particles circling a young star cling together and slowly become larger, forming rocks, boulders and eventually the rocky cores of planets. The process of creating rocks from dust clinging together requires millions of years to form Jupiter-like planets.

According to models of the system’s evolution, the second star's gravity in the HR 7162 system should have disrupted the planet-forming gas and dust from the system in just thousands of years and should have removed it from the system. That a planet exists in spite of the gravity predictions challenges core accretion as the singular model for gas giant planet formation.

The team’s gravitational collapse theory offers an alternative method of forming giant planets. In this theory, overly dense regions of the gas and dust cloud circling the star develop enough gravitational attraction within themselves to rapidly pull together into giant planets.

Simulations show these regions can collapse rapidly, well within the few thousand years that the planet forming materials would have survived in HR 7162 before being ejected from the system by the second star.

Some studies suggest that binary star systems produce more overdense regions in their gas and dust clouds, because of the turbulent gravitational environment the two stars create, enhancing the odds of giant planet formation by this mechanism.