The man who discovered the first planet outside of our solar system has now discovered the first planet eaten up by its sun. AAAS Fellow Alex Wolszczan, an Evan Pugh Professor of Astronomy and Astrophysics at Penn State University, along with an international team of astronomers, has found evidence of a planet being destroyed by an expanding "red giant," a star in the later stages of its life.
The astronomers were using the Hobby-Eberly Telescope to study the star known as BD+48 740, which is 11 times larger than our Sun, when they discovered two key pieces of evidence of the planet's destruction: the highly unusual elliptical orbit of the star's remaining planet, and the presence of lithium in the star, which occurs in only rare circumstances—in this case, by the absorption of a planet. The unusual orbit of the remaining planet was likely caused when it received a burst of energy as the ill-fated planet plummeted into the star and was destroyed.
Wolszczan spoke with AAASMC about the discovery and about the continued discovery of exoplanets since the first one he co-discovered in 1992.
AAASMC: What is the significance of finding a planet that has been destroyed by its own star, and is this our fate billions of years in the future?
Alex Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State University: This provides us with observational evidence of the details of the planet destruction process. It improves the completeness of our understanding of the evolution of planetary systems as their stars change over time.
Such findings are also important for astrobiologists, who think about the evolution of life on timescales comparable to the stellar ages. Just think about a civilization that reaches our level of understanding of the Universe, only to find out that, in a few generations, their star will begin to die. What would they do?
AAASMC: Do we have any guesses as to how long the "planet-eating" process takes? Outside of the telltale highly elliptical orbit, how long are effects such as the lithium signature detectable?
Wolszczan: This process is like an eye blink compared to the timespan of stellar evolution: just about 100,000 years.
AAASMC: In 1992, you co-discovered the first planet outside of our solar system, orbiting a pulsar. Since then, over 700 exoplanets have been discovered. How much do we know (or can we speculate) about these planets? Do any look like they could be Class M planets, capable of supporting life as we know it?
Wolszczan: One crucial thing we have learned is the fantastic, totally unsuspected diversity of planetary systems. Our solar system is just one of the many possible realizations of planetary architectures. We have also learned that the lower the mass of a planet, the more of them are out there. So, finding Earth-like "rocks" in habitable zones (HZs) of their stars shouldn't be that hard. And, in fact, some have been found already. Planets in HZs of M-dwarfs, capable of supporting life as we know it, have also been found. Of course, life on a planet tidally locked to its star, as in the case of the Earth-Moon system, could be quite different from our experience.
AAASMC: The Kepler spacecraft has identified over 2,000 planetary candidates. How much farther in the future do you think it will be when we discover signs of extraterrestrial life?
Wolszczan: It looks like we are going to end up with a sizable list of planets in HZs of their stars, but we will not yet have the instrumentation that is needed to detect and study the so-called "biomarkers" in planetary atmospheres. Hopefully, there will be enough funding available to support building such instruments.
AAASMC: You were the first to discover a planet outside of our solar system, and you are the first to discover a planet that has been swallowed up by its star. What's next on the horizon? What else are you searching for?
Wolszczan: Well, we have been also looking for ways to detect magnetic fields of exoplanets. This is not only important for our understanding of the internal structure of exoplanets, but such detections would also tell us a lot about planetary habitability. For example, our Earth sits nicely in the Sun's HZ, but that very Sun would kill us if the Earth's magnetic shield against the solar wind of lethal particles suddenly disappeared.