On October 19, 2017, the first interstellar object ever discovered flew past Earth on its way out of the solar system. Less than two years later, a second object was discovered, an easily identifiable interstellar comet called 2I / Borisov. The appearance of these two objects confirmed previous theoretical work that concluded that interstellar objects (ISOs) regularly enter our solar system.
How often this happens has since been the subject of extensive research. According to a new study by researchers from the Interstellar Studies Initiative (i4is), approximately 7 ISOs enter our solar system every year and follow predictable orbits while they are here. This research could allow us to send a spaceship to rendezvous with one of these objects in the near future.
The research describing these results was carried out by several researchers from i4is, a non-profit organization dedicated to making interstellar flight a reality in the near future. They were joined by researchers from the Florida Institute of Technology, the Harvard Institute for Theory and Computation (ITC), the University of Texas at Austin, the Technical University of Munich and the Observatoire de Paris.
Oumuamua as it appeared on the night of October 29th with the William Herschel telescope. Queen’s University Belfast / William Herschel Telescope
The investigation of ‘Oumuamua in October 2017 sparked a revolution in astronomy and the study of celestial objects. Not only was this an object that had formed in another star system, but its arrival and discovery implied a large population of such objects. The discovery of 2I / Borisov in 2019 confirmed what many astronomers already suspected – that ISOs are regularly entering our solar system.
Marshall Eubanks is not only a physicist at i4is (and lead author of the study), but also the chief scientist of Space Initiatives Inc. and CEO of Asteroid Initiatives LLC. As he emailed Universe Today, the discovery of ‘Oumuamua and 2I / Borisov is significant in ways that should not be underestimated:
“[J]Just by proving their existence, it has had a profound impact, creating a field of study almost out of nowhere (an area that funding agencies are only just beginning to recognize). Interstellar objects offer us the opportunity to study Exobodies decades before the earliest possible missions to the nearest stars like Proxima Centauri and literally touch them in the future. “
This led to several suggestions for missions that might meet with future ISOs discovered through our system. One such proposal was Project Lyra, which researchers at the i4is shared in a 2017 study (with support from Asteroid Initiatives LLC). There’s also ESA’s Comet Interceptor mission, which they plan to launch in 2029 to meet with a long-time comet.
Artist’s impression of the interstellar object Oumuamua, which is outgassed when it leaves our solar system. Photo credit: ESA / Hubble, NASA, ESO, M. Kornmesser
“We started working on potential interstellar object missions in 2017, right after the discovery of ‘Oumuamua, and initially focused more on the hunt for that particular object, as opposed to Seligman & Laughlin who focused on ISOs that will be in the future could be discovered. Said Eubanks. “The Comet Interceptor mission would fall into a similar category (build-and-wait).”
Given that ISOs were formed in another star system, the ability to study them up close would give scientists a glimpse into the conditions prevailing there. In fact, studying ISOs is the next best thing to send interstellar probes to neighboring star systems. Of course, any such mission poses many technical challenges, not to mention the need for advance warning. As Eubanks explained:
“There are two basic types of missions here: plan and wait or start and wait missions like the ESA Comet Interceptor and car chases as would be required to reach 1I / ‘Oumuamua. It’s very unlikely that car chases can clash with a retreating ISO – these will almost certainly be limited to quick flyby. Rendezvous missions, missions that match speeds and circling or landing the ISO must be warned in advance. “
To illustrate, when astronomers first became aware of Oumuamua, the object was already closest to the Sun (also known as the perihelion passage) and passed Earth. Because of this, observers only had 11 days to make observations when they left the solar system and were out of the range of their instruments.
Artist’s impression of 2I / Borisov beyond our solar system. Photo credit: NRAO / AUI / NSF, S. Dagnello
In the case of 2I / Borisov, amateur astronomer and telescope manufacturer Gennadiy Borisov saw it on August 30, 2019, about three months before it reached perihelion (December 8, 2019). In order for future missions to meet with them, it is imperative to know as much as possible about how often ISOs are arriving and how fast they are traveling.
For their study, Eubanks and his colleagues tried to better restrict these two variables. To do this, they first considered how the speed of an interstellar object is affected by the local state of rest (LSR) – the mean movement of stars, gas and dust in the Milky Way near the Sun:
“We assume that ISOs originate from or are formed with stars and their planetary systems and that, after they are alone, they have the same galactic dynamics as stars. We use the two well-known ISOs 1I / ‘Oumuamua and 2I / Borisov, as well as the efficiency of past and current astronomical surveys to estimate the number of these objects in the galaxy, and star velocity estimates from the Gaia mission to estimate velocity propagation should be expected. “
What they found was that in an average year, the solar system would be visited by up to 7 ISOs that are asteroid-like. Meanwhile, objects like 2I / Borisov (comets) are rarer and appear about every 10 to 20 years. They further found that many of these objects would move at speeds greater than that of ‘Oumuamua – which was moving at over 16 miles per second before and after picking up lift from the sun.
Swarm of laser sail spacecraft leaving the solar system. Photo credit: Adrian Mann
Knowing these parameters will help scientists prepare for possible rendezvous missions with ISOs. Eubanks and his colleagues discussed this in more detail in an earlier study: “Interstellar Now! Missions to explore nearby interstellar objects. “As reported by Universe Today at the time of publication, the study looked at a wider range of potential ISOs and the feasibility of achieving them.
In the meantime, this latest study provides basic information to aid in the planning and execution of these missions. In addition to the Lyra project and ESA’s Comet Interceptor, there are numerous proposals for spacecraft that could meet with interstellar objects (or even make the interstellar journey itself).
This includes Project Dragonfly, a small spaceship and laser sail that was the subject of a concept design study conducted in 2013 by the Initiative for Interstellar Studies (i4iS). Another is Breakthrough Starshot, a concept by Yuri Milner and Breakthrough Initiatives that also calls for a tiny spaceship with a light sail and a powerful laser array to be sent to Alpha Centauri.
This proposal was formulated in recent years by Prof. Abraham Loeb and Prof. Manasvi Lingam. While Leob is the founder of the ITC and chairman of the Starshot Advisory Committee, Lingham is a longtime researcher of the ITC and co-author of “Interstellar Now!” and this newest paper. These concepts are proposed not only interstellar, but also as a possible method of “hunting for objects” that enter our solar system.
One way or another, we will soon be peaking in other star systems! And knowing how to intercept and study the objects that they regularly get in our way is a good start!
Further reading: arXiv
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