On October 19th, 2017, astronomers were astounded to learn that an interstellar object (named ‘Oumuamua) flew by Earth on its way out of the Solar System. Years later, astronomers are still debating what this object was – a comet fragment, a hydrogen iceberg, or an extraterrestrial solar sail? What’s more, the arrival of 2I/Borisov two years later showed how interstellar objects (ISOs) regularly enter our Solar System (some even stay!)

It’s little wonder then why proposals are in place to design missions that could rendezvous with an interstellar object the next time one passes by. One such mission is Project Lyra, a concept proposed by researchers from the Initiative for Interstellar Studies (i4is). Recently, an international team led from the I4IS drafted a White Paper that was submitted to the 2023-2032 Planetary Science and Astrobiology Decadal Survey.

The team behind the paper, titled “Interstellar Now! Missions to and Sample Returns from Nearby Interstellar Objects” was led by Andreas Hein and Marshall Eubanks of i4is and Space Initiatives Inc. They were joined by associates from the Paris Observatory, the Florida Institute of Technology (FIT), the Institute of Theory and Computation (ITC), the Technical University of Munich (TUM) and the FH Aachen University of Applied Sciences.

Established by the NASA Authorization Acts of 2005 and 2008, the National Academies began conducting the Decadal Surveys for the purpose of reviewing proposals for space-based missions, ground-based facilities, infrastructure, and supporting research that will help advance the cause of space exploration and planetary science in the coming decade.

The 2023 – 2032 Decadal Survey is expected to be a momentous event, with proposals for missions that will allow us to learn a great deal more about the Universe we live in. A particularly hot topic right now is exoplanets, the study of which has exploded in recent years. So far, 4,201 have been confirmed, the vast majority within the last decade, while another 5,481 candidates await confirmation.

As Hein and his colleagues indicate in their paper, the introduction of next-generation ground-based and space-based telescopes in the coming years will provide astronomers with opportunities to directly image exoplanets and characterize their atmospheres like never before. Unfortunately, getting truly deep insights into distant planets and determining if life actually thrives there requires that we study them up close.

Alas, sending missions to other star systems is extremely expensive and time-consuming. As Andrea Hein and colleagues explained to Universe -Today via email:

“Observing exoplanets from Earth will certainly improve in the future and we may be able to say if some forms of life exist on them. But this will not substitute for going there and looking at them from a close distance. The main limitation is that exoplanetary systems are incredibly far away.

“The next stellar system, the Alpha Centauri system is 4.3 light-years away… Now, the farthest object humanity has ever sent into deep space, the Voyager probes, are currently just about 150 m away. To go there, we need some new breakthrough technology.”

One such idea is Breakthrough Starshot, a proposal to send a tiny spacecraft to Alpha Centauri using a lightsail and a powerful laser array. Prof. Manasvi Lingam – an assistant professor at FIT, a researcher with the ITC, and a co-author on the paper – has co-authored numerous studies on the subject along with Prof. Abraham Loeb (founder of the ITC and Chair of the Breakthrough Starshot Advisory Committee).

However, as Lingam, Heir, and their colleagues explained, these types of spacecraft are not going to be launched until sometime in the 2050s, according to the most recent estimates. With a travel time of about 20 years, this means that the earliest data to be received from these will probes will not come until the 2070s. And given the size of the probes and their instruments, the data is likely to be limited.

However, the presence of ISOs in our Solar System offers a means for studying extrasolar planets and their systems without having to endure the aforementioned challenges and limitations. In their paper, Hein and his colleagues showed through a series of analyses that visiting these objects with tiny spacecraft as they pass through the Solar System is entirely feasible.

Their analyses reiterate arguments originally put forward in 2017 shortly after ‘Oumuamua passed through the Solar System, and again in 2019 with the arrival of 2I/Borisov. In these studies, the i4is team proposed mounting a mission known that is similar in concept to Starshot (Project Lyra) and calls for a lightweight spacecraft and lightsail propelled by lasers. As Heir and his colleagues illustrated:

“The basic principle of going to an ISO is: If the prophet cannot go to the mountain, let the mountain come to the prophet. ISOs are objects which may have been ejected from exoplanetary systems for various reasons and they are flying through our solar system. ISOs are like ‘manna from deep heaven’. This is the equivalent of a traveling zoo. You can observe and visit a large variety of these objects from very different origins without the need of going to the star systems of their origin.”

In their paper, the team explored three types of mission profiles that could be mounted using today’s technology. These included flybys, rendezvous, and sample return missions. In terms of flybys, which would be similar to what the New Horizon‘s spacecraft performed with Pluto and Arrokoth, the spacecraft wouldn’t decelerate and would gather images and data as it flew past the ISO.

However, they also make allowances for an impactor, a small sub-probe that crashes into a body to create a plume that can then be collected and studied by the spacecraft. Examining these particles or light generated from the impact with a spectrometer would reveal secrets about its composition. This is similar to what NASA and India did with their Lunar Crater Observation and Sensing Satellite (LCROSS) and the Chandrayaan-1 probe.

Next up, there’s the possibility of a rendezvous mission, which the team indicates is more challenging from a technical standpoint, but offers numerous scientific advantages. Said the team:

“A rendezvous mission is more sophisticated, as it requires that the spacecraft is decelerated to land or orbit the ISO… A rendezvous mission has the advantage that the spacecraft has more time to observe the object. It can collect samples from its surface and take pictures from various angles.”

Last, there the possibility of a sample-return mission, which would leverage technologies and expertise from a number of missions launched in the past two decades. This includes NASA’s Stardust comet sample-return mission – the first mission of its kind to rendezvous with a comet (Wild 2) and returned samples to Earth by 2006 – and the more recent OSIRIS-REx and Hayabusa/Hayabusa2 missions.

Hein and his colleagues also pointed out how missions to ISOs have the advantage of being possible using existing technologies. Specific examples include launch vehicles like SpaceX’s Falcon Heavy, the heatshield technology used by NASA’s Parker Solar Probe, and standard chemical propellants. That’s just the tip of the iceberg, said Lingam, since there are many technologies not currently in use, but which are feasible nonetheless:

“There are three broad classes of technologies delineated in our paper. The first is good ‘ol fashioned chemical rockets, but they are primarily suitable for flyby missions, which are anticipated to yield relatively limited scientific information. The second is solar electric propulsion, which is more convenient for rendezvous missions permitting in-situ analyses. The third has not yet been fully realized – nuclear thermal propulsion – although it remains within the reach of current technology. Its real attractiveness stems from the expectation that it could permit sample return missions to Earth.”

A small caveat is that astronomers will have a very hard time determining where an ISO originally came from as a result of perturbations in their trajectories. It’s also limited by the fact that any missions we mount will be restricted to objects that were ejected from their system in such a way that the laws of physics and the interstellar medium were able to deposit it in our Solar System.

However, difficult does not mean it’s impossible, as researchers demonstrated with both ‘Oumuamua and 2I/Borisov. Based on what was observed from both ISOs, researchers were able to postulate a great deal about the kinds of environments they are likely to have formed in (even if they were unable to pinpoint their home systems).

Regardless of the challenges and limitations, sending missions to inspect them (and maybe return samples) will reveal a wealth of data about ISOs. As Hein and his colleagues summarized:

“From the astrophysical and astrochemical standpoints, they would enable us to understand the various mechanisms by which these objects are formed and ejected, the chemical composition of other planetary systems and how they differ from our own, the galactic history of ISO formation, and the interactions of ISOs with the interstellar medium and galactic cosmic rays during their journey. They will also shed light on the inventory and abundances of prebiotic molecules inherent in these objects. In the highly optimistic scenario, they might even reveal traces of extinct (or extant) life in the form of molecular biosignatures.”

Hein and his colleagues are hardly alone in their appraisal, which is why multiple space agencies are looking for low-cost, rapid-deployment spacecraft concepts that could rendezvous with ISOs. One such concept is the ESA’s ‘Comet Interceptor’, a “fast-class” mission that could be sent to space and be ready to intercept an ISO once it enters our system.

Earlier this year, it was announced that the NASA Innovative Advanced Concepts (NIAC) Program had awarded Phase I funding to a team from MIT that’s working on a dynamic orbital slingshot. This idea is the brainchild of Richard Linares, an assistant professor in the Department of Aeronautics and Astronautics (AeroAstro) at MIT, who proposed this slingshot as a way of letting a spacecraft catch up to an ISO so they can study it up close.

Similar missions could be mounted to objects that are orbiting within our System, as previous studies have shown that thousands of ISOs could have been captured by our Solar System over time that are still here. Its also been suggested that ISOs currently in our cosmic backyard could be identified and studied once the Vera Rubin Observatory comes online – formerly known as the Large Synoptic Survey Telescope (LSST).

The payoffs for this research go beyond learning what conditions are like in other star systems. If theories regarding galactic panspermia via interstellar objects are true, we may discover how life (or the necessary ingredients to get it started) is transported throughout the galaxy. If any objects we find turn out to be interstellar probes, missions to ISOs will finally resolve the age-old burning question: “Are we alone in the Universe?“

Looking to the next decade, it’s obvious that we stand to learn a great deal more about the Solar System, exoplanets, our galaxy, and the Universe as a whole. Thanks to next-generation observatories, robotic spacecraft, and humanity’s long-awaited return to the Moon, there is no shortage of opportunities to grow our knowledge of the cosmos and our place in it.

Further Reading: arXiv