If the public seems more interested in spaceflight as a vehicle for streaming TV dramas, the reality of both the Europa Clipper liftoff and the astounding ‘catch’ of SpaceX’s Starship booster may kindle a bit more interest in exploring nearby space. When I say ‘nearby,’ bear in mind that on this site the term refers to the entire Solar System, as we routinely discuss technologies that may one day make travel to far more distant targets possible. But to get there, we need public engagement, and who could fail to be thrilled by a returning space booster landing as if in a 1950’s SF movie?

Europa may itself offer another boost if Europa Clipper’s science return is anything like what it promises to be. Closing to 15 kilometers from the surface and making 49 passes over the icy ocean world, the spacecraft may give us further evidence that outer system moons can be venues for life. We also have the European Space Agency’s Jupiter Icy Moons Explorer (JUICE), which will study Europa, Callisto and, in a spectacular move, end up orbiting Ganymede for extended close-up observations.

Image: Europa Clipper begins its journey. Credit: SpaceX.

JUICE gets to Jupiter in July of 2031, while Europa Clipper starts its flybys in the same year, though arriving in 2030. As a measure of how tricky it can be to get to these destinations, both craft make flybys of other worlds, returning in fact to the Earth for some of these. Europa Clipper’s journey will be marked by gravity assists from Mars in February of 2025 and Earth in December 2026. JUICE has already performed one Earth/Moon flyby and will make a flyby of Venus (August, 2025) followed by two Earth flybys (September 2026 and January 2029). A long and winding road indeed!

Speaking of flybys, it’s interesting to note that we have two cometary appearances this month. Comet C/2023 A3 (Tsuchinshan-ATLAS) and C/2024 S1 (ATLAS) are both likely to be visible in October, with the latter closest to Earth on October 24 as it swings toward Sol where it will likely disintegrate. The former should make an appearance in the western sky just after sunset before growing fainter in the latter part of the month. C/2023 A3 appears to be an Oort Cloud object, or long period comet, with an orbital period of some 80,000 years. Short-period comets (Halley’s Comet is one of these) have much shorter orbits, with Halley’s showing up every 76 years.

I find the Oort Cloud a fascinating subject, for it’s based on deduction and not observation. Astronomer James Wray (Georgia Tech), writing in The Conversation, makes the point that while we can’t directly image this vast collection of comets, likely numbering in the hundreds of billions, we can estimate that it extends possibly as far as halfway to the Alpha Centauri system. That’s an intriguing thought, for it means our cometary cloud may intermingle with an equivalent cloud (if one exists) from the Centauri stars. The space covered by our first interstellar probes is not vacant, though the distances between individual objects would still be vast. On the other hand, if the theory that the Oort Cloud formed because of interactions with the giant planets, it’s possible that in the absence of such planets (still not demonstrated), Centauri A and B may not have formed such a cloud.

Wray makes the case that long-period comets are conceivably our greatest planetary threat, outranking near Earth asteroids in degree of danger since an incoming Oort object would likely not be spotted until well inside the planetary system, giving us little time to react. ‘Oumuamua, after all (not an Oort object) was discovered after its closest approach to Earth.

Cometary flybys of our Sun will always be cherished for their visual appeal as ices evaporate and a tail forms, and a collision course with Earth is a highly unlikely scenario, but it’s always best to consider the prospects. Wray puts it this way:

One way to prepare for these objects is to better understand their basic properties, including their size and composition. Toward this end, my colleagues and I work to characterize new long-period comets. The largest known one, Bernardinelli–Bernstein, discovered just three years ago, is roughly 75 miles (120 kilometers) across. Most known comets are much smaller, from one to a few miles, and some smaller ones are too faint for us to see. But newer telescopes are helping. In particular, the Rubin Observatory’s decade-long Legacy Survey of Space and Time, starting up in 2025, may double the list of known Oort Cloud comets, which now stands at about 4,500.

The European Space Agency’s Comet Interceptor mission, scheduled for launch later in this decade, should offer an option for intercepting an Oort Cloud comet when one appears, making it possible to learn more about these objects in terms of their composition and possible role in the delivery of volatiles to the inner system. Oort comets are tricky because their wide orbits mean gravitational influences from other stars can nudge one into a solar close pass without any prior warning. An incoming long-period comet, writes Wray, might offer mere weeks or days to prepare any defense measures we have in place. Even so, the odds of an impact are extremely low.

Image: A stunning return. The Starship booster comes home. Credit: SpaceX.

All this is by way of hoping public interest in space will be quickened both by recent mission successes, ongoing exploration of possible sources of life, and the appearance of the occasional comet. The startling SpaceX success with Starship’s ‘catch’ underlines that technological advances, like comets, can seem to come out of nowhere when we’re not paying attention. I’m thinking back to the science fiction I read as a kid and realizing that watching Starship’s booster descend was right out of Astounding Stories. Heinlein would have loved it, and indeed foreshadowed what unfolded on Sunday.

As SpaceX communications manager Dan Huot put it: “What we just saw, that looked like magic.”