When the interstellar object (ISO) Oumuamua appeared in our Solar System in 2017, it generated a lot of interest. The need to learn more about this was great, but unfortunately, there was no way to actually do so. It came and went, and we wondered what it was made of and where it came from. Then in 2019 comet ISO Borisov came for a brief visit, and again we were left wondering about it.
There are likely to be more of these ISOs crossing our Solar System. There has been talk of having missions ready to visit one of these interstellar visitors in the future, but for that to happen, we need advance notice of their arrival. Could the Vera Rubin Observatory tell us early enough?
No mission leaves the launch pad without detailed planning, and detailed planning depends on observations. Earth-based observations laid the foundation for our forays into the Solar System. NASA missions like OSIRIS-REx, Lucy and Psyche are simply impossible without detailed ground observations paving the way.
One of our most powerful and unique observatories will soon begin operating, the Vera Rubin Observatory. Its main activity will be the Legacy Survey of Space and Time (LSST). LSST will image our Solar System in much greater detail than ever before, and will do so continuously for a decade. The wealth of data flowing from these observations will be a huge boon for mission planning and will likely inspire missions we haven’t yet dreamed of.
VRO’s Legacy Space and Time Survey is based on the observatory’s 8.4-meter wide-angle primary mirror and its ability to change targets in just five seconds. Attached to it is the world’s largest digital camera, a 3.2 gigapixel behemoth. The VRO will image the entire available night sky every few nights.
LSST aims to detect transients such as supernovae and gamma-ray bursts. It will also study dark energy and dark matter and map the Milky Way. But it will also map small objects in our Solar System, such as near-Earth asteroids (NEA) and Kuiper Belt objects (KBOs).
“Nothing will come close to the depth of Rubin’s research and the level of characterization we will get for Solar System objects,” said Siegfried Eggl, assistant professor at the University of Illinois Urbana-Champaign and leader of the Inner Solar System Working Group within the Rubin/LSST Solar System Scientific Collaboration. “It’s fascinating that we have the ability to visit interesting objects and observe them up close. But to do this we need to know that they exist and where they are. This is what Rubin will tell us.”
It is difficult to overstate how VRO and its LSST will advance our understanding of the Solar System. There are other survey telescopes, such as Pan-STARRS (Panoramic Survey Telescope and Rapid Response System). Pan-STARRS has detected a large number of astronomical transients. Its function is to detect them and alert astronomers so that other telescopes can observe them.
Pan-STARRS is based on two telescopes with 1.8-meter mirrors and is our most effective detector of Near-Earth Objects (NEOs), but once VRO is operational it will be relegated to a distant second place.
Interestingly, VRO will also detect ISOs. In a 2023 paper, researchers estimated that VRO will detect up to 70 interstellar objects every year. If the VRO can see them early enough, it could give us time to launch a mission for one of them.
“Rubin is able to give us the preparation time needed to launch a mission to intercept an interstellar object,” Eggl said. “That’s a synergy that’s unique to Rubin and unique to the times we live in.”
It is unclear how many ISOs visit our Solar System each year and will be detectable. While some researchers suggest the VRO could detect 70 per year, others say the number will be lower. VRO is not magic. Objects that are very dark and/or move very quickly may escape detection. But it seems certain that LSST will detect some ISOs. It can even discern patterns in their trajectories that make it easier to detect more of them.
As our knowledge of ISOs grows, the desire to visit one will grow with it. The appearance of Oumuamua and Borisov shows that opportunities will continue to arise. There are already preliminary plans on how to visit one.
ESA’s Comet Interceptor is designed to visit a long-period comet. The Interceptor mission has three spacecraft, and each one will study the comet from a different angle, providing a 3D view. Early warning is critical to the Comet Interceptor mission, and ESA specifically mentions LSST as enabling the mission, alerting us to an appropriate target soon.
But the target doesn’t have to be a comet. It could be anything traveling through the interior of the Solar System.
The unique thing about the Comet Interceptor is that it will already be lying in wait for its target. After launch, it will travel to the Sun-Earth Lagrange 2 (L2) point. It will enter a halo orbit and await further instructions. ESA can wait until the VRO detects a desirable target on the correct trajectory and can activate the Comet Interceptor.
NASA’s Lucy mission shows how advanced knowledge of objects in the Solar System enables powerful missions. Lucy relies on accurate observations of Solar System objects and will visit several asteroids traveling through the Solar System’s interior, using Earth as a gravitational aid on three separate occasions. Detailed knowledge of the Solar System inspired and enabled Lucy’s mission.
Comet Interceptor, or another similar mission, will not need such a complex path. But like Lucy, it will be based on insightful observations, something the VRO and LSST will provide in great depth.
LSST won’t just enable missions like the Comet Interceptor. This will inspire new ones that we cannot yet imagine. This is because we still don’t know what the Research will reveal. It can reveal regions of objects that behave in ways we haven’t seen before, or types of grouped objects that have remained invisible.
“If you think of Rubin looking at a beach, you will see millions and millions of individual grains of sand that together make up the entire beach,” said Eggl, “There could be an area of yellow sand, or black volcanic sand, and a space mission to an object in that region could investigate what makes it different. We often don’t know what is strange or interesting unless we know the context in which it is found. With our current telescopes, we have essentially been looking at the big rocks on the beach,” says Eggl, “but Rubin will zoom in on the finer grains of sand.”
The Jupiter Trojan asteroids that Lucy will visit are a good example of this. This type of asteroid was predicted to exist in the 1770s, but the first one was not seen until more than a century later. Even then, no one was sure it was actually a Trojan asteroid until nearly another century had passed. Now, astronomers know there are thousands of them.
Similarly, our knowledge of ISOs could become much more complete when LSST comes into operation. A whole new window for ISOs could open. Astronomers can discern patterns in their trajectories and composition that lead to a new understanding of their origins. If Comet Interceptor or a similar mission is sent to one of them, we will learn more about how planetary systems form, including our own.
Not everything in our Solar System formed where we see it today. Some bodies have been captured, such as Neptune’s moon Triton, which is likely a captured Kuiper Belt object. Astronomers think it is highly likely that some of the objects in our Solar System are captured ISOs. VRO and the missions it inspires could identify these objects.
New observations lead to new questions and new missions designed to answer them. This is an old pattern in our quest to understand nature.
Who knows what the VRO will see and what future missions its discoveries will lead to?