Space is littered with cosmic wanderers. Some are stars booted from the grip of a companion they once had. Others are rogue comets and asteroids on runaway trajectories with nowhere to go and no one chasing them. We typically call those interstellar objects. Then there are mysterious fragments booted from their solar system by the explosive culmination of their stars’ lives. That’s what Garrett Levine at Yale University is looking for.
"At the end of a star's lifetime, it's losing mass, and everything's going haywire in its system," Levine tells Inverse. "Some stuff might fall onto the star, and some might leave the system, and it's the latter we're looking at."
These fragments are called jurads (named for the late astronomer Michael Jura), and short of using god-like powers to shatter a planet light years away and peer inside, they’re the best way to get even a glimpse of how planets form in distant star systems, and if they’re chemically like any of the planets in our Solar System. To find these jurads, Levine and his colleagues are using one of the most ambitious projects in astronomy: the Legacy Survey of Space and Time (LSST). This program will use the Vera C. Rubin Observatory in Chile (whose potential with the group’s research is what Levine calls the “scientific opportunity of a lifetime”), to image the entire visible sky for an unparalleled survey of what is lurking in and beyond our Solar System. If the researchers can spot a jurad, astronomers around the world can point a telescope at it, and this might reveal the secrets of how planets form beyond our Solar System.
Cosmic Backyards is an Inverse series that explores the cutting-edge research looking into the depths of the cosmos. This work is pushing the boundaries of our understanding of the universe, and our place in it.
Tracing an Interloper
In 2017, a mysterious object swept through our Solar System. Called ‘Oumuamua, its trajectory showed that it came from outside our Solar System, and was on its way back out. While debate After 'Oumuamua's discovery, astronomers speculated about the existence of another kind of object from exoplanetary systems. Researchers call these objects jurads and they are most often icy bodies like comets, but potentially asteroids or fragments of planets pushed to the outskirts of their star’s system. They seem to roam freely around the galaxy after their home stars died and their gravity weakened as they subsequently lost mass.
The comets and asteroids of our Solar System are ancient leftovers of the processes that gave birth to Earth and its sibling worlds, and so can shed light on our Solar System's ancient history. Interstellar objects could similarly shed light on the formation of exoplanets and, "originating from varied environments, can not only reveal how common or unique our Solar System is, but also how comets change over time," Dennis Bodewits, an astrophysicist at Auburn University in Alabama who is not affiliated with Levine’s research, tells Inverse.
Whereas a typical interstellar object could have been flung out of its home star system at any time — comets are flung out of our own Solar System regularly — jurads are fragments that are flung out upon the death of their star.
The Vera C. Rubin Observatory will open its eyes to the night skies in 2024. As data pours in, the telescope could catch a jurad flying in.
"It's a really incredible opportunity to gain crucial information about extrasolar systems," study co-author Aster Taylor, an astrophysicist at the University of Michigan, tells Inverse. "Interstellar objects, including jurads, are basically our only chance to take samples from another stellar system. It's hard to express how exciting that is for me, as an astrophysicist."
All in all, investigating objects from another star helps address the "big and general question that many astronomers would like to answer — whether our Solar System is typical, an outlier, or in-between," Levine says. "There are many ways to attack this question, and our study is one example."
It Works On Paper
To figure out if they could find jurads with the Rubin Observatory, Levine and company first modeled Oort Clouds, the giant swarms of icy rocks around stars where comets are usually believed to originate. (The research was outlined in a recent study in the Planetary Science Journal.) They estimated how many objects that Oort Clouds around stars about one to eight times the Sun's mass might release in their end stages. They also modeled if astronomers would be able to tell if an object came from before or after a star’s death.
When our Sun and roughly 97 percent of all stars die, all that will be left is their core, and this leftover object is called a white dwarf. Previous research suggested that each white dwarf is expected to kick out up to an Earth's amount of mass.
They found that it was possible to distinguish jurads from objects kicked out before a star died. As stars reach their ends, they grow bright and blast out gusts of gas. This can drive off hyper-volatile molecules such as carbon monoxide, and stellar winds could deposit dust that covers the entire jurad surface, they say.
However, LSST is currently expected to only discover about 15 interstellar objects over the course of its roughly 10-year observational campaign. As such, given what scientists currently know about exoplanetary systems, Levine and his colleagues say it's not impossible but not likely that LSST will detect a jurad.
Still, Pedro Bernardinelli, an astrophysicist at the University of Washington in Seattle who was not involved in the work, notes there are many uncertainties with analyses of this kind. "This is not a problem with the work — it is rather a problem with our understanding of planetary formation, and how similar or not our own Solar System is to others," he notes. As such, "I would not take as a prophecy that LSST will never find such objects."
But LSST isn’t the only hope: Other missions with a chance at discovering interstellar interlopers include the Near-Earth Object Surveyor, the Nancy Grace Roman Space Telescope, and the Transiting Exoplanet Survey Satellite, and future research can estimate how well they might detect jurads, Levine says. The James Webb Space Telescope may also detect volatile compounds streaming off interstellar bodies, Bodewits says.
"It's a very exciting time to be in astronomy and astrophysics," Levine says. "We're at a point where we've answered a lot of questions, but like all good fields of science, once we've answered a question, usually two or three more pop up."
