Debris disks may be signposts of giant exoplanets
Within the expanse of our beautiful Milky Way Galaxy, there are estimated to be billions of extra-solar planets (a.k.a. “exoplanets”). In recent years, astronomers have used telescopes on land as well as in space to locate and observe exoplanets. The vastness of space, combined with the inherent brightness of stars and the much smaller size and dimness of the planets that orbit them, makes finding and observing them an incredibly difficult task to achieve.
An international group of researchers have released a paper in The Astronomical Journal that may make looking for large, Jupiter-type exoplanets somewhat easier.
The paper suggests that when astronomers are looking for these giant exoplanets, they should concentrate on looking at young star systems that have debris disks around them. Young stars that are from a few million to one billion years old and appear to have a disk of dust and debris orbiting them may be the best place to look for giant exoplanets.
Researchers looked at 130 single-star systems that the Spitzer Space Telescope had determined to have debris disks around them and compared them to 277 stellar systems that appeared not to have debris disks, making this the largest study to observe stars with debris disks.
Of the 130 stars with known debris disks, 100 had been previously observed and scanned for exoplanets. The research group followed up on the 30 that had not been already seen using the Keck Observatory in Hawaii and the European Southern Observatory’s, or ESO‘s, Very Large Telescope (VLT) in Chile using adaptive optics and coronography to visualize the star systems.
Tiffany Meshkat – the lead author of the paper and a postdoctoral researcher at NASA’s Jet Propulsion Laboratory (JPL) as well as an assistant research scientist at IPAC/Caltech, both in Pasadena, California – said: “Our research is important for how future missions will plan which stars to observe. Many planets that have been found through direct imaging have been in systems that had debris disks, and now we know the dust could be indicators of undiscovered worlds.”
Even though the group did not detect any additional exoplanets in the 30 previous unobserved systems, the observations they made provided supplementary data that helped to characterize the abundance of planets in systems with debris disks.
Marta Bryan, a graduate student at Caltech, performed the analysis of the data and found that long-period giant planets were nine times more common around stars with debris disks than around those without them.
When researchers observed star systems containing debris disks with giant exoplanets in distant orbits, they noted that the star systems had similar dual dust disks analogous to the Solar System’s two zones – the asteroid belt (between Mars and Jupiter) and the Kuiper Belt (beyond the orbit of Neptune).
The Kuiper Belt, which contains Pluto and thousands of other icy objects beyond the orbit of Neptune, also appears to exist in many of these systems. Jupiter, the most massive planet in the Solar System, strongly influences the region between it and Mars, whereas Neptune does the same for the Kuiper Belt.
“It’s possible we don’t find small planets in these systems because, early on, these massive bodies destroyed the building blocks of rocky planets, sending them smashing into each other at high speeds instead of gently combining,” said Caltech associate professor of astronomy co-author Dimitri Mawet, who is also a JPL senior research scientist.
There are many reasons why giant exoplanets are easier to detect than the small more rocky terrestrial planets, so it is entirely possible that star systems with giant exoplanets in distant orbits may also contain minor, rocky planets that simply haven’t been detected yet.
The study did not resolve why the giant exoplanets seem to be found more often around stars with debris disks. However, it is possible that the gravitational influence of such massive bodies, each at least five times more massive than Jupiter in this study, could cause small bodies within their gravitational influence to collide and become pulverized rather than accreting to form new planetesimals.
Beta Pictoris (above right image) is one such example of a star system that has been directly imaged with a debris disk as well as containing a comet and a confirmed exoplanet that was predicted to be there before it had even been imaged based on the presence of its dust-laden circumstellar disk.
LEFT: Debris Disk around star HR 8799. Credit: NASA / JPL-Caltech / K. Su (Univ. of Arizona). RIGHT: HR 8799 system with four orbiting exoplanets. Credit: Jason Wang and Christian Marois
In the case of HR 8799 (above two images) – a system of four giant planets – the system contains two distinct circumstellar disks instead of a single debris disk. The giant planets nudge comets in toward the system’s star, as was the case in the Solar System during the Late Heavy Bombardment about 4 billion years ago. During this period, the giant planets within the Solar System migrated in toward the Sun and then out again until they settled into the orbits they maintain today.
“By showing astronomers where future missions such as NASA’s James Webb Space Telescope have their best chance to find giant exoplanets, this research paves the way to future discoveries,” said chief scientist of NASA’s Exoplanet Exploration Program Office and study co-author Karl Stapelfeldt of JPL.
A native of the Greater Los Angeles area, Ocean McIntyre's writing is focused primarily on science (STEM and STEAM) education and public outreach. McIntyre is a NASA/JPL Solar System Ambassador as well as holding memberships with The Planetary Society, Los Angeles Astronomical Society, and is a founding member of SafePlaceForSpace.org. McIntyre is currently studying astrophysics and planetary science with additional interests in astrobiology, cosmology and directed energy propulsion technology. With SpaceFlight Insider seeking to expand the amount of science articles it produces, McIntyre was a welcomed addition to our growing team.