After defending his doctoral dissertation on modeling interstellar objects on Monday, June 30, Matthew Hopkins intended to take a well-deserved vacation. But it seems the universe had other plans for him.
The next day, the Atlas Terrestrial-impact Last Alert System (ATLAS) telescope in Rio Hurtado, Chile, detected a mysterious object whizzing toward the Sun. The first observations showed that it came from outside our solar system, potentially becoming the third discovery of an interstellar object in history. Astronomers from all over the world, including Hopkins, sprang into action to try to gather as much data as possible about this wandering space rock. On Thursday, July 3, the International Astronomical Union’s Minor Planet Center confirmed that the interstellar object is indeed traveling through our cosmos, naming it 3I/ATLAS. Now Hopkins and his colleagues believe they know where it came from.
“This is very exciting!” Hopkins, a PhD student in astrophysics at the University of Oxford, told IFLScience. “I’ve been waiting to compare my predictions with the new data for four years, and 3I/ATLAS is already giving us new insights into this fascinating population spanning the galaxy.”
Thanks to previous observations, astronomers have learned a lot about 3I/ATLAS. It is the largest and brightest interstellar object, according to Space.com. Experts are almost certain that this is a comet that is rushing through our solar system at incredibly high speeds. At the time of its discovery, the object was traveling at 137,000 miles per hour (221,000 kilometers per hour), and it will accelerate as it approaches the Sun. 3I/ATLAS is much larger than the two interstellar objects that came before it: Comet Oumuamua and Comet 2I/Borisov. According to preliminary estimates, it could be 6 to 19 miles (10 to 30 kilometers) wide. Don’t worry, there is no chance that this space rock will collide with our planet, but it will safely approach the Earth on October 30.
Initial spectroscopy showed that 3I/ATLAS has a redder color than typical solar system comets, similar to some trans-Neptunian objects – small planets orbiting the Sun outside Neptune’s orbit, or tiny icy celestial bodies located between Jupiter and Neptune called centaurs. Another study conducted photometric observations of the object, which showed that it is similar in color to some comets in the solar system, but noticeably bluer than Oumuamua and 2I/Borisov.
Together, these early findings paint a vivid picture of our solar system’s latest visitor, but figuring out where this comet came from is just as important as figuring out what it looks like. Interstellar objects like this one are “pristine, primordial remnants of the planet-forming process in other planetary systems,” writes Darryl Seligman, an assistant professor of physics and astronomy at Michigan State University, in an article for The Conversation. Understanding the origin of 3I/ATLAS will allow astronomers to extrapolate information about how planets form in this alien star system.
To this end, Hopkins and his colleagues analyzed 3I/ATLAS using the Outaouais-Oxford model. This new model integrates data from the European Space Agency’s (ESA) Gaia Observatory with models of protoplanetary disk chemistry and galactic dynamics to predict the distribution of velocities, ages, and compositions among the population of interstellar objects in our cosmic neighborhood. Hopkins and several of his co-authors have contributed to the development of the Outagami-Oxford.
Their findings, which are now available on the arXiv preprint server and have not yet been peer-reviewed, suggest that 3I/ATLAS originates from a specific part of the Milky Way galactic disk. This is a disk-like component of our galaxy that contains stars, gas, and dust and rotates in a circular coplanar motion around the center of the galaxy. According to the Hopkins study, 3I/ATLAS probably comes from the thick part of the disk, which contains about 10% of the Milky Way’s stellar mass. These stars are usually much older than those in the thin disk of the galaxy.
“Studying their chemistry and dynamics will deepen our understanding of how planetesimals form and evolve in the Milky Way disk, and how such objects respond to the potential of the Milky Way,” the study says. Planetesimals are smaller celestial bodies, such as asteroids or comets, that serve as building blocks for planets.
“[Comet 3I/ATLAS] probably comes from an old star in a thick disk, and we think it’s been around longer than the solar system,” study co-author Chris Lintott, a professor of astrophysics at Oxford, told IFLScience. “There’s a two-thirds chance it’s more than 7 billion [years old], and that explains its color.” If confirmed, it would be the first known interstellar object to visit this distinct galactic population.
To test their hypothesis, the researchers will closely monitor 3I/ATLAS as it approaches the Sun. Old stars tend to form water-rich interstellar objects, Lintott explained. If this comet comes from a thick disk, it should produce a lot of cometary activity, which occurs when surface ice heats up and goes directly from solid to gas. Meanwhile, astronomers around the world will continue to get to know the third interstellar visitor to our galaxy.
