Asteroid belt archives – universe today
According to current estimates, there could be as many as 100 billion planets in the Milky Way alone. Unfortunately, finding evidence for these planets is difficult and time consuming work. For the most part, astronomers are forced to rely on indirect methods that measure dips in a star’s luminosity (the transit method) Doppler measurements of the star’s own motion (the radial velocity method) .
Direct imaging is very difficult due to the cancellation effect of stars, where their luminosity makes it difficult to detect planets orbiting them. Fortunately, a new study by Caltech’s Infrared Processing and Analysis Center (IPAC) has determined that there may be a shortcut to finding exoplanets using direct imaging. The solution, they claim, is to look for systems with a circumstellar debris disk, as they are sure to have at least one giant planet.
The study, titled “A Direct Imaging Survey of Spitzer Detected Debris Disks: Occurrence of Giant Planets in Dusty Systems”, was recently published in The Astronomical Journal. Tiffany Meshkat, Associate Research Scientist at IPAC / Caltech, was the lead author of the study, which she conducted while working at NASA’s Jet Propulsion Laboratory as a postdoctoral researcher.
For the purposes of this study, Dr Meshkat and his colleagues looked at data from 130 different single star systems with debris disks, which they then compared to 277 stars that do not appear to host disks. These stars were all observed by NASA’s Spitzer Space Telescope and were all relatively young (less than a billion years old). Of these 130 systems, 100 had already been studied in order to find exoplanets.
Dr Meshkat and his team then tracked the remaining 30 systems using data from the WM Keck Observatory in Hawaii and the European Southern Observatory (ESO) Very Large Telescope (VLT) in Chile. Although they did not detect any new planets in these systems, their examinations made it possible to characterize the abundance of planets in systems with disks.
What they found is that young stars with debris disks are more likely to also have giant exoplanets with wide orbits than those without. These planets were also likely to be five times the mass of Jupiter, making them âsuper-Jupitersâ. As Dr Meshkat explained in a recent NASA press release, this study will come in handy when the time comes for exoplanet hunters to select their targets:
âOur research is important to know how future missions will plan which stars to observe. Many planets discovered by direct imaging were in systems with debris disks, and we now know that dust could be an indicator of undiscovered worlds. “
This study, which was the largest examination of stars with dusty debris disks, also provided the best evidence to date that giant planets are responsible for controlling debris disks. While the research has not directly addressed why the presence of a giant planet would cause debris discs to form, the authors say their findings are consistent with predictions that debris discs are the product of giant planets stirring. and causing dust collisions.
In other words, they believe that the gravity of a giant planet would cause the planestimals to collide, thus preventing them from forming additional planets. As study co-author Dimitri Mawet, who is also a principal investigator at JPL, explained:
âWe may not find small planets in these systems because, very early on, these massive bodies destroyed the building blocks. rocky planets, sending them crashing into each other at high speed instead of smoothly combining.
In the solar system, giant planets create a sort of debris belt. For example, between Mars and Jupiter you have the main asteroid belt, while beyond Neptune is the Kuiper belt. Many of the systems examined in this study also have two belts, although they are significantly younger than the solar system’s own belts – about 1 billion years compared to 4.5 billion years.
One of the systems examined in the study was Beta Pictoris, a system that has a debris disk, comets, and a confirmed exoplanet. This planet, designated Beta Pictoris b, which has 7 Jupiter masses and orbits the star at a distance of 9 AU – nine times the distance between Earth and the Sun. This system has been directly imaged by astronomers in the past using ground-based telescopes.
Interestingly, astronomers predicted the existence of this exoplanet long before it was confirmed, based on the presence and structure of the system’s debris disk. Another system that was investigated was HR8799, a system with a debris disc that has two prominent dust belts. In such systems, the presence of more giant planets is inferred from the need to maintain these dust belts.
This is believed to be the case for our own solar system, where 4 billion years ago, giant planets diverted passing comets towards the Sun. This culminated in the Late Heavy Bombardment, where the inner planets were subjected to countless impacts that are still visible today. Scientists also believe that it was during this time that the migrations of Jupiter, Saturn, Uranus, and Neptune deflected dust and small bodies to form the Kuiper Belt and Asteroid Belt.
Dr Meshkat and his team also noted that the systems they examined contained significantly more dust than our solar system, which could be attributed to their age differences. In the case of systems that are about 1 billion years old, the increased presence of dust could be the result of the colliding of small bodies that have not yet formed larger bodies. From this it can be inferred that our solar system was once much dustier.
However, the authors note that it’s also possible that the systems they’ve observed – which have a giant planet and a debris disk – may contain more planets that simply haven’t been discovered yet. Ultimately, they concede that more data is needed before these results can be considered conclusive. But in the meantime, this study could serve as a guide for where to find exoplanets.
As Karl Stapelfeldt, chief scientist at NASA’s Office of the Exoplanet Exploration Program and co-author of the study, said:
“By showing astronomers where future missions such as NASA’s James Webb Space Telescope stand their best chance of finding giant exoplanets, this research paves the way for future discoveries.”
Additionally, this study could help shed light on our own understanding of how the solar system has evolved over billions of years. For some time now, astronomers have questioned whether or not planets like Jupiter migrated to their current positions and how this affected the evolution of the solar system. And the debate continues on how the main belt formed (i.e. empty or full).
Last but not least, it could inform future studies, allowing astronomers to know which star systems are developing in the same direction as ours billions of years ago. Wherever star systems have debris disks, they induce the presence of a particularly massive gas giant. And when they have a disk with two prominent dust belts, they can deduce that it will also become a system containing many planets and and two belts.
Further reading: NASA, The Journal of Astrophysics