“Historically, our assumption has been that the region around Jupiter is fairly empty, cleaned out by the giant planet’s gravity, but our results teach us that there is a region that is constantly being fed,” said Kathryn Volk at the University of Arizona Lunar and Planetary Laboratory in 2019 about a constant source of new objects that may help explain the surprising rate of icy body impacts with Jupiter, such as the Shoemaker-Levy 9 event in 1994 when over twenty fragments of comet that collided with Jupiter were observed by astronomers at hundreds of observatories around the world.
In July of 2009 Shoemaker-Levy was followed by a comet or asteroid that gouged a Pacific-Ocean sized hole in the gas giant. Both epic events have been found to arrive from an orbital region just beyond Jupiter that acts as a “comet gateway.”
New Simulation that Tracks Evolution of Planetary Systems Over Several Billion Years
This week, an international group of astronomers, led by Martin Schlecker of the Max Planck Institute for Astronomy, has found that the arrangement of rocky, gaseous and icy planets in alien planetary systems beyond our Solar System is apparently not random, and depends on only a few initial conditions, based on a new simulation that tracks the evolution of planetary systems over several billion years.
Planetary systems around sun-like stars, which produce in their inner regions super-Earths with low water and gas content, very often form a planet comparable to our Jupiter on an outer orbit that deflect potentially dangerous asteroids and comets on their orbits into the zone of rocky planets in a way that reduces the number of catastrophic collisions. A conjecture that has been hotly debated.
Has Jupiter Played an Important Role in the Evolution of Life on Earth?
Scientists suspect that the planet Jupiter played an important role in the development of life on Earth, raising the question whether such a combination of planets is rather random, or whether it is a common result of the formation of planetary systems.
In contrast, a 2016 simulation study published in Astrobiology suggested that the “Jupiter as shield” concept, implying that the planet shields Earth from comet impacts was not true, rather Jupiter’s most important role in fostering the development of life on Earth was just the opposite — delivering the volatile materials from the outer Solar System needed for life to form, and the previously underestimated role that Saturn may have also played in the evolution of life on Earth.
Scientists from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, the University of Bern and the University of Arizona have now found strong evidence that rocky planets similar to Earth occur conspicuously often together with a Jupiter-like planet that is in a wide orbit.
“We call such gas giants cold Jupiters. They grow at a distance from the central star, where water exists in the form of ice,” explains Schlecker, who led the study. The Earth-like planets studied are so-called dry super-Earths, i.e., rocky planets larger and more massive than the Earth, which have only a thin atmosphere and hardly any water or ice that populate the inner, i.e., temperate zone of the planetary systems and are very similar to the Earth except for their size.
Earth –a “Dry” Planet
“Also, the Earth is, despite the enormous oceans and the polar regions, with a volume fraction for water of only 0.12% is altogether a dry planet,” adds Schlecker.
To find a cold Jupiter together with an ice-rich super-Earth in the inner region is therefore almost impossible. Furthermore, dense, extended gas envelopes are mainly found in massive super-Earths.
Simulations of 1000 Planetary Systems
These conclusions are based on a statistical evaluation of new simulations of 1000 planetary systems that are evolving in a protoplanetary disk around a sun-like star. These simulations are the latest achievement in a long-standing collaboration between the University of Bern and MPIA to study the origins of planets from a theoretical perspective. Starting from random initial conditions, e.g., for the masses of gas and solid matter, the size of the disk and the positions of the seed cells of new planets, the scientists tracked the life cycle of these systems over several billion years.
“During the simulations, the planetary embryos collected material, grew into planets, changed their orbits, collided or were ejected from the system,” Christoph Mordasini from the University of Bern and co-author of the research paper describes the simulated processes. The simulated planetary systems eventually had planets of different sizes, masses and compositions on different orbits around the central star.
“Such simulations support the investigation of exoplanetary systems,” says Hubert Klahr, head of the working group on the theory of planet formation at MPIA, “since planets like cold Jupiters require a lot of time to orbit their mother star on their wide orbits.” This makes it difficult to find them through observation, so the search for exoplanets does not realistically reflect the actual composition of planetary systems. Astronomers are more likely to find high-mass planets in close orbits around low-mass stars. “Simulations, on the other hand, are in principle independent of such limitations.”
“We wanted to verify a surprising finding following observations made in recent years that planetary systems with a cold Jupiter almost always contain a super-Earth,” says Schlecker. Conversely, about 30% of all planetary systems in which super-Earths are formed also appear to have a cold Jupiter. It would be plausible to expect that massive planets are more likely to disrupt planetary systems during their formation in such a way that the formation of other planets is hindered. However, these cold Jupiters seem to be sufficiently far away from the interiors, so that their influence on the development seems to be rather small.
However, the evaluation of the simulated planetary systems could not confirm this trend. Only one-third of all cold Jupiters was accompanied by at least one super-Earth. Furthermore, astronomers found a cold Jupiter in only 10% of all synthetic planetary systems with super-Earths. Thus, the simulations show that both super-Earths and cold Jupiters are only slightly more likely to occur together in a planetary system than if they appeared alone.
NextGen Telescopes Will Provide Verification
However, it will only be possible to verify this concept with powerful telescopes such as the Extremely Large Telescope (ELT) of the European Southern Observatory or the James Webb Space Telescope (JWST). Both are expected to be operational within this decade. “Theoretical predictions must be able to fail in the face of empirical experience,” Schlecker demands. “With the next-generation instruments that are about to be deployed, we will be able to test whether our model will hold up or whether we have to go back to the drawing boards.”
In principle, this result could also apply to such dry rocky planets, which have roughly the size and the mass of the Earth. So, it might not be a coincidence that the solar system contains a planet like Jupiter as well as Earth.
Source: M. Schlecker et al. The New Generation Planetary Population Synthesis (NGPPS). III. Warm super-Earths and cold Jupiters: A weak occurrence correlation, but with a strong architecture-composition link, Astronomy & Astrophysics (2020). DOI: 10.1051/0004-6361/202038554
The Daily Galaxy, Sam Cabot, via Max Planck Institute for Astronomy
Image at top of page: this view of Jupiter’s Great Red Spot and turbulent southern hemisphere was captured by NASA’s Juno spacecraft as it performed a close pass of the gas giant planet on February 12, 2019. NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill