Physicists Research Close Encounters of the Interstellar Kind

Researchers at Carnegie Mellon University and Harvard University have an idea for exploring the outer reaches of space: Look close to Earth.

"It's very difficult for us to travel out of the solar system, so let's explore what comes to us instead," said Hy Trac, associate professor of physics.

Trac, Diptajyoti "Dipto" Mukherjee, a doctoral student in Carnegie Mellon's McWilliams Center for Cosmology; and Amir Siraj and Abraham Loeb, both of Harvard University, have new research suggesting that interstellar objects (ISO) exist within our solar system and could be captured by Earth's gravity or Jupiter.

Mukherjee studies how gravity influences objects, and that can be applied to interstellar objects as well. He works on dynamical problems where objects influence each other through gravity, and he has developed and worked with many of the numerical tools.

"We were interested in interstellar objects and did simulations to see what might be out there," Trac said.

While Mukherjee's primary work relates to gravitational waves and cosmological phenomena such as black holes, the tools to track smaller scale objects is the same.

"Newtonian gravity works the same everywhere," Mukherjee said. "We had this idea that, what if the code that we used to simulate things in smaller scales and that formed part of the motivation of what why we wanted to do this."

Excitement around interstellar objects has increased in recent years. An object known as Oumuamua — its formal name 1I/2017 U1 — was spotted in 2017 from Haleakalā Observatory in Hawaii. Racing through space at of 87 km per second, it was too fast to have originated in the solar system. A second object, a comet called Borisov, was identified in 2019 to also be interstellar in origin. Two meteoroids, CNEOS 2014-01-08 (IM1) and CNEOS 2017-03-09, which produced fireballs detected by satellites, have since been hypothesized to be from beyond the reaches of the solar system as well.

The Harvard researchers have been tracking the paths of the objects, and this summer Loeb found spherules in places consistent with the simulated trajectory of the meteoroid impact in the Pacific Ocean.

"People have been tinkering with this idea that we will detect more objects with new telescopes such as the Vera Rubin going up," Mukherjee said.

The Vera C. Rubin Observatory is being constructed in northern Chile and will be the site for the Legacy Survey of Space and Time (LSST), of which Carnegie Mellon and the University of Washington are creating new software platforms to analyze large astronomical datasets generated by the upcoming Legacy Survey of Space and Time.

While confirmed interstellar objects within our solar system are still rare, the discovery of these and others suggest that they can be captured by planets' gravity and kept in orbit, Mukherjee said, who is first author on a paper published by the Monthly Notices of the Royal Astronomical Society.

Mukherjee built and ran some hundred billion simulations using the Vera computing cluster at the Pittsburgh Super Computing Center. The simulation indicated that there should be hundreds of thousands of interstellar objects in the solar system. Some of them come within the vicinity of orbits of planets like Jupiter and Earth, which could have hundreds of thousands of objects in near Earth orbit where most are less than 1 meter in diameter.

"A key part in projects like this is trying to detect how and where these objects are," Mukherjee said. "We want to better understand what orbits these lie on with more accurate simulations."

Knowing more about these objects has important implications for learning about the formation of the solar system or extrasolar systems, but they can be difficult to identify because they don't reflect as much light as other objects that originate from the solar system, like asteroids and comets.

"We may be able to use machine learning to identify ISOs amongst solar system bodies. But it's like finding a needle in a haystack. Once we find one nearby, we could try to land a probe on it like we have done with asteroids," Trac said.

This research was supported by the McWilliams Center and NASA.