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The Arecibo Observatory in Puerto Rico, used by Alex Wolszczan in his co-discovery of the first exoplanets in 1992. Credit: NAIC Arecibo Observatory, a facility of the NSF

Worlds Beyond

The extraordinary revolution of exoplanet science
3 November 2020

In the beginning, there were astronomers with terrestrial telescopes; then came Kepler—NASA’s groundbreaking planet-hunting space telescope—and with it, a new era of astronomical discovery.

Before Kepler, those astronomers made a myriad of amazing discoveries, among them the first known exoplanets—two frozen worlds orbiting a dead star in the constellation Virgo—and the first exoplanet known to orbit a sunlike star. In fact, in the 17 years that followed that initial discovery, those same scientists discovered hundreds of exoplanets. 

Then Kepler was sent into orbit and the real deluge began: early on, a rocky, Earth-sized exoplanet (Kepler-10b); then, an Earth-sized exoplanet (Kepler-186f) orbiting in its host star's habitable zone; and the discoveries just kept pouring in. Within a span of less than three decades, our understanding of the worlds that exist outside our own solar system expanded by many orders of magnitude—from literally nothing to the certain knowledge that there is an innumerable multitude of worlds out there that potentially could sustain life.


An artist's illustration of NASA's Kepler space telescope. Credit: NASA/Ames Research Center/W. Stenzel/D. Rutter
This illustration depicts NASA's Kepler space telescope against a backdrop of planets. Kepler leaves a legacy of more than 2,600 planet discoveries from outside our solar system, many of which could be promising places for life. Credit: NASA/Ames Research Center/W. Stenzel/D. Rutter


Those first known exoplanets—circling a pulsar 2,300 light years from the Sun—were, in fact, co-discovered in 1992 by Penn State's Alex Wolszczan, then at Cornell University. And Kepler-186f, the first known Earth-sized exoplanet orbiting in a habitable zone, was discovered in 2014 by a team of scientists that included Penn State's Eric Ford. Wolszczan went on to found and direct the Center for Exoplanets and Habitable Worlds at Penn State, of which Ford is now director, and which has since become the home of a number of prominent exoplanet scientists who continue to lead and shape their field.

Kepler’s Legacy

To put the growth of exoplanet science pre- and post-Kepler in context, in the 17 years between that first exoplanet discovery by Wolszczan and the launch of the Kepler space telescope, astronomers confirmed the existence of 340 worlds outside our solar system. In just over half that amount of time, roughly nine and a half years of observations with Kepler—from March 6, 2009, to October 30, 2018—they confirmed the existence of nearly 2,700 more exoplanets. 

In all, Kepler surveyed more than half a million stars, and one of NASA's recent analyses of the Kepler data concluded that "20 to 50 percent of the stars visible in the night sky are likely to have small, possibly rocky, planets similar in size to Earth, and located within the habitable zone of their parent stars. That means they’re located at distances from their parent stars where liquid water, a vital ingredient to life as we know it, might pool on the planet surface."

And Kepler’s impact extends well beyond what it was able to observe in its nearly 10 years of operation. K2—the spacecraft’s second mission, initiated after a severe malfunction in its targeting and stabilization system—discovered a number of promising candidates for follow-up observations and future missions. Since Kepler’s retirement, the number of confirmed exoplanets has risen to nearly 4,000 (3,890 at last count), and NASA's newest planet-hunting space telescope—the Transiting Exoplanet Survey Satellite, also known as TESS—is now leading the way with another 81 confirmed exoplanets and nearly 2,400 candidates discovered since its launch in July 2018.

The Next Generation

Looking even further, beyond TESS, a number of NASA's next-generation flagship missions—flown by its costliest and most capable science spacecraft—are being designed specifically, if not exclusively, with exoplanet science in mind: among them, the James Webb Space Telescope, the Nancy Grace Roman Space Telescope, and the Habitable Exoplanet Observatory (HabEx) and Large UV/Optical/IR Surveyor (LUVOIR) mission concepts. Here again, Penn State researchers in the Eberly College of Science are at the fore, with Rebekah Dawson serving on the Science and Technology Definition Team for the LUVOIR mission concept. 

In the post-Kepler era, it's not just space telescopes that scientists are using to identify and confirm exoplanet candidates; Earth-based instruments continue to serve important functions, and Penn State scientists are leading here, as well. One of the world's premier exoplanet-hunting facilities, the Hobby-Eberly Telescope at McDonald Observatory, owes its revolutionary concept to Larry Ramsey and Daniel Weedman. And Suvrath Mahadevan has designed two of the world's best spectrographs, used to detect exoplanets and assess their potential habitability by analyzing the light from their host stars: the Habitable Zone Planet Finder (HPF) spectrograph on the Hobby-Eberly Telescope and the NEID spectrograph on the WIYN Telescope at Kitt Peak National Observatory.


The Hobby-Eberly Telescope. Credit: Penn State
The Hobby-Eberly Telescope—a revolutionary concept invented by Penn State's Larry Ramsey and Daniel Weedman—was the world's largest optical telescope at the time of its commissioning in 1997. Today, it is the third largest, and with the addition of the Habitable Zone Planet Finder—designed by Penn State's Suvrath Mahadevan—is now one of the world's premier exoplanet-hunting facilities. Credit: Penn State


Mahadevan also leads Penn State's partnership in the Sloan Digital Sky Surveys, whose several telescopes—the New Mexico State University 1-Meter Telescope and Sloan Foundation 2.5-Meter Telescope at Apache Point Observatory and the Irénée du Pont Telescope at Las Campanas Observatory in Chile—are among the preeminent Earth-based instruments in operation today. And Jason Wright leads the University's partnership in MINERVA—yet another top exoplanet science facility, at the Fred Lawrence Whipple Observatory.

More Penn State Science

Eberly researchers are also key players in several other areas of exoplanet science. 

In the realm of peer pedagogy and research facilitation, Penn State has hosted two of the exoplanet science community's three workshops since 2010 on extremely precise radial velocities—one of the methods used to detect exoplanets, and the one responsible for the vast majority of exoplanet discoveries—which have drawn experts from across the country and around the world. 

Toward addressing the issues inherent to big data, the University has deployed a cutting-edge supercomputer cluster—the Cyber-Laboratory for Astronomy, Materials, and Physics (CyberLAMP)—which will process the astounding quantities of data generated by Penn State’s exoplanet scientists. In 2016, the University was awarded more than $900,000 by the National Science Foundation to launch this effort, which is also being utilized by other scientific collaborations worldwide, including the Nobel Prize–winning LIGO Scientific Collaboration.

And at the nexus of science and government policy, in 2018 Fabienne Bastien was selected to serve on the National Academies of Sciences, Engineering, and Medicine’s Committee on Exoplanet Science Strategy, tasked with proposing to NASA what its scientific priorities should be for the next decade of exoplanet science. The committee's report definitively set the stage for Penn State to continue leading in a number of vital areas and initiatives.

In the spring of 2019, the Center for Exoplanets and Habitable Worlds marked its 10-year anniversary with a celebration of “the extraordinary progress in exoplanet science over the past decade and the long journey that has led to Penn State emerging as one of the world’s leading centers for exoplanet research and education.”

With such an illustrious history, and much on the horizon to warrant excitement, it’s a stellar view in all directions from this tiny corner of the universe that we call Happy Valley.

Hero image (at top): The Arecibo Observatory in Puerto Rico, used by Penn State's Alex Wolszczan (then at Cornell) in his co-discovery of the first exoplanets in 1992. At that time, Arecibo was the world's largest single-dish radio telescope. Today, it is surpassed in its class only by the Five-hundred-meter Aperture Spherical Radio Telescope (FAST), in China's Guizhou Province. Image credit: NAIC Arecibo Observatory, a facility of the NSF