What We Have Learned from our First Two Interstellar Visitors, and the Possibility of Fast Reactive Missions for Future Exploration

The discovery of the first interstellar object, 1I/`Oumuamua, passing through the solar system in 2017 has provoked intense, sustained interest. 1I was accessible to ground based telescopes for less than a month, and a little longer from space. After this brief observing period its characteristics were quite different from what was expected from the first interstellar object (ISO) which was expected to look like a comet. Incorporating a diverse range of scientific disciplines including galactic, stellar, and planetary dynamics, planetesimal formation, tidal disruption, shape modeling, and the nature and evolution of comets this one discovery has really energized a new interdisciplinary awareness in the study of planet formation. This is because ISOs enable the close up study of material from other planetary systems, allowing us to assess similarities and differences in the chemistry and physical processes driving planetary growth in other planetary systems. The second ISO, 2I/Borisov, was discovered less than 2 years after the first, much sooner than expected, and has characteristics which are very different from 1I. The Rubin Telescope it will greatly increase the ISO discovery rate. An ideal way to characterize an ISO would be through in-situ exploration with a space mission. NASA's competed mission calls are not compatible with missions that are responsive to new discoveries, where there is no target at the time they are proposed. Two approaches have been suggested to explore these targets: spacecraft in storage, ready to launch following target discovery and spacecraft in standby orbit, as is being done by ESA's Comet Interceptor mission. When the target is unknown at the time of spacecraft development there are a number of implications regarding the definition of basic spacecraft capability (e.g., delta-V) and payload. This talk will summarize what is known about the first ISOs and discuss the strategies for follow-up and coordination of observations of these objects in the era of the 2020's with the availability of 30-m class telescopes, new space-infrared facilities, and explore what the requirements would be for in-situ exploration with a mission