How Planets Are Formed: Researchers Look to Exoplanets for Answers

The longest government shutdown in the history of the United States is affecting the nation’s space research. NASA’s Johnson Space Center union employees protested yesterday outside the gates of the space center, demanding that the government stops the resulting furloughs that financially hurt 800,000 federal employees and their families.  


More than 3,000 employees of the Houston center and almost 17,000 NASA employees nationwide currently do not know when their work will resume. The toll is apparent: in the past week, the main camera on NASA’s Hubble Space Telescope broke – the same camera that provided humanities with images of stars, galaxies and deep sky surveys. 


New technologies – such as NASA’s James Webb Space Telescope set to launch in 2021 – are essential to discoveries in astronomy, such as the most recent discovery of disintegrating planets that could offer insight into what worlds are made of by measuring the minerals of the galaxy. The scientists working on disintegrating planet can proceed only if the James Webb telescope is launched on time.  


One such disintegrating world is the super Mercury-size planet that is orbiting its parent star, KIC 12557548, at a distance that’s just twice the diameter of the star. The surface temperature of the planet is estimated to be 1815.6 degrees Celsius. 


The extreme temperatures cause the planets to dissolve. "The atmosphere is just rock vapor," says Eva Bodman, an exoplanet researcher at Arizona State University and the author of a research paper on disintegrating planets published in the Astronomical Journal. "It's the sheer heat of the planet that's pushing off this rock vapor atmosphere." 


Another is Kepler-1520b, discovered in 2012, when scientists studying data gathered by the NASA's Kepler space telescope found signs of a world disintegrating by heat and pressure. It is estimated to have the surface temperature of 4,200 degrees Celsius on the side that faces the star it orbits. It is so close to its host star that the orbit is completed in a little more than half a day. Because of this orbit, the exoplanet is locked in gravitational stability, meaning one half of it is always facing the star, causing it to turn into a mass of molten rock and magma seas, exposing the planet’s interior.  


The slowly disappearing planet could provide insight into how planets are formed in the galaxy 2,000 light-years from Earth. "The composition in an exoplanet system could be substantially different from the solar system," says Bodman. 

Thousands of exoplanets discovered by Kepler have shown astronomers that our solar system differs significantly from other planets orbiting the stars.  


In this case, Bodman wanted to determine if it was possible to measure the composition of a small, rocky, disintegrating exoplanet by studying its debris. However, the problem she faced was that the ground-based telescopes aren’t sensitive enough to track the debris. She expects the James Webb Telescope, designed specifically for the study of exoplanets, to identify the ingredients. 


"Webb would be able to measure the relative abundances of different minerals," Bodman says. "From that, we can infer the geochemistry of the interior of these planets was before they started disintegrating."  


The disintegration process takes place when the radiation of the stars pushes against the planet’s atmospheres, creating a tail of debris. NASA’s Hubble Space Telescope has identified hydrogen and helium in the atmospheres of exoplanets, but the rocky material in planet disintegration is beyond Hubble’s reach. James Webb is expected to provide more answers, capturing new wavelengths and materials such as carbon, quartz and iron, and answering astronomers’ questions about what happens inside the distant worlds.

"If we were able to detect any of these features, we could say with some certainty what these rocky bodies are made off," says Knicole Colon, a research astrophysicist at NASA's Goddard Space Flight Center in Maryland who has studied the disintegrating planet K2-22. "That could definitely be very informative for understanding rocky exoplanets in general." 


While the exact mechanism for planet formation is unknown, scientists believe that planets are formed by a process called accretion, in which clouds of dust and gas left after the birth of a star come together to form larger and larger objects. As the gas giants grow more massive, they attract more gas, forming their atmospheres. Discovering what exactly is on the interiors of the planets would help scientists better understand the first steps in planet formation. 


"There's no reason that the solar system should be different from exoplanets, and vice versa," Colon says. "We're all planets, so we all formed in possibly similar ways. Understanding these planets is another step in the process to the bigger picture." 

Bodman adds that even if they are formed in a similar fashion, the planets themselves may look quite differently. "The composition in an exoplanet system could be substantially different from the solar system," she says. 


Only a few disintegrating planets have been found – probably because of their short lifetime. Bodman and Colon agree that it’s likely there is another disintegrating exoplanet or two in the Kepler data. The recently launched Transiting Exoplanet Survey Satellite (TESS) has already found hundreds of planets, providing scientists with more data. 


And with the Webb telescope, exoplanet composition will give scientists an unprecedented look at their interiors – perhaps even their cores. "In theory, we could know more about these exoplanets than even about the Earth, and definitely more than the other planets in the solar system," Bodman says. 


While the science is moving forward, the logistical questions remain: if the federal government continues much longer, will the pace of discoveries slow down, and will the launch of the James Webb telescope stay on track for 2021?

Photo credit: NASA