Free Astronomy Magazine September-October 2016

SPACE CHRONICLES Erik Petigura, a post- doctoral scholar in planetary science and a coauthor of the study. “The newborn planet K2-33b will help us understand how planets form, which is important for understanding the processes that led to the formation of the Earth and even- tually the origin of life.” When stars form, they are encircled by dense regions of gas and dust called pro- toplanetary disks, from which planets form. By the time a young star is a few million years old, this disk has largely dissipated and planet forma- tion is mostly complete. The star or- bited by K2-33b has a small amount of disk material left, indicated by observations from NASA's Spitzer space telescope, indicating that it is in the final stages of dissipating. “Astronomers know star formation orbit around its host star in about five days. This implies that it is 20 times closer to its star than Earth is to the Sun. K2-33b is a large planet like the gas giants in our solar system. In our solar system these giant planets are all far from the Sun. As it turns out, the proximity of the giant planet K2-33b to its star is not too out of the ordinary for planets in our galaxy — many have been discovered close in, often completing an orbit around their parent star in weeks or even days. The explanation for this is that large planets can be formed far from their star and migrate inward over time. The position of K2-33b so close to its parent star at such an early age implies that if migration occurred, it must have occurred quickly. Alternatively, the planet could be evidence against the migration the- ory, suggesting that giant planets can in fact form close in to their stars. K2-33b is fully formed, but it may still evolve over time. The next step is to measure the planet's mass and determine its density. These mea- surements will offer insights into the planet's fate later in life — wheth- er it will stay roughly the same size or if it will cool and contract. “In the last 20 years, we have learn- ed that Nature can produce a stag- gering diversity of planets — from planets that orbit two stars to plan- ets that complete a full orbit every few hours,” Petigura concluded. “We have much to learn, and K2- 33b is giving us new clues .” T his image shows the K2-33 system, and its planet K2-33b, compared to our own solar system. The planet has a five-day orbit, whereas Mercury orbits our sun in 88 days. The planet is also nearly 10 times closer to its star than Mercury is to the sun. [NASA/JPL-Caltech] has just completed in this region, called Upper Scorpius, because rough- ly a quarter of the stars still have bright protoplanetary disks,” David said. “The remainder of stars in the region do not have such disks, so we reasoned that planet formation must be nearly complete for these stars, and there would be a good chance of finding young exoplanets around them.” K2-33b, like many other exoplanets, was detect- ed due to the periodic dimming in the central star's light as the planet passes in front of it. By studying the fre- quency of dips in the star's light and measur- ing by how much the light dimmed, the team was able to determine the size and orbital pe- riod of the planet. K2-33b is “a remarkable world,” Petigura said. The exoplanet, which is about six times the size of Earth, or about 50 percent larger than Nep- tune, makes a complete W hen a planet such as K2-33b passes in front of its host star, it blocks some of the star's light. Observing this periodic dimming, called a transit, from continual monitoring of a star's brightness, allows astronomers to detect planets outside our solar system with a high degree of certainty. This Neptune-sized planet orbits a star that is between five and 10 million years old. In addition to the plan- et, the star hosts a disk of planetary debris, seen as a bright ring encircling the star. [NASA/JPL-Caltech] n