On July 14th, 2015, the New Horizons mission made history when it became the first robotic spacecraft to conduct a flyby of Pluto. On December 31st, 2018, it made history again by being the first spacecraft to rendezvous with a Kuiper Belt Object (KBO) – Ultima Thule (2014 MU69). In addition, the Voyager 2 probe recently joined its sister probe (Voyager 1) in interstellar space.
Given these accomplishments, it is understandable that proposals for interstellar missions are once again being considered. But what would such a mission entail, and is it even worth it? Kelvin F. Long, the co-founder of the Initiative for Interstellar Studies (i4iS) and a major proponent of interstellar flight, recently published a paper that supports the idea of sending robotic missions to nearby star systems to conduct in-situ reconnaissance.
The paper, titled “Interstellar Probes: The Benefits to Astronomy and Astrophysics“, recently appeared online. The paper summarizes material that Long will be presenting at the 47th IAA Symposium on Future Space Astronomy and Solar-System Science Missions – which is part of the 70th International Astronautical Congress – on Oct. 10th, 2019; specifically, the session dealing with Space Agency Strategies and Plans.
To begin, Long outlines how astronomy/astrophysics (particularly where space telescopes have been involved) and space exploration using robotic probes have had a profound impact on our species. As he explained to Universe Today via email:
“The astronomical endeavor has opened up our horizons of knowledge on the origin and evolution of the Solar System, galaxy and the wider Universe. It is an activity that humans have conducted for arguably tens of thousands of years as we looked towards the stars, and they encouraged our curiosity. We could never touch the stars, but we could look at them, and instrumentation gave us the potential to look at them even closer. Then, the discovery of the electromagnetic spectrum helped us to understand the Universe in a way we had never done before.”
At present, humanity’s efforts to study planets and celestial bodies directly have been confined entirely to the Solar System. The farthest robotic missions have traveled (the Voyager 1 and 2 space probes) have been to the outer edge of the heliopause, the boundary between our Solar System and the interstellar medium.
All of these missions have taught us a great deal about planetary formation, the history and evolution of our Solar System, and about planet Earth itself. And in recent decades, the deployment of missions like Hubble, Spitzer, Chandra, Kepler, and the Transiting Exoplanet Survey Satellite (TESS) have revealed thousands of planets beyond our Solar System.
Naturally, this has led to renewed interest in mounting missions that would be able to explore extrasolar planets directly. In the same way that missions like MESSENGER, Juno, Dawn, and New Horizons have explored Mercury, Jupiter, Ceres and Vesta, and Pluto, respectively, these missions would be responsible for bridging the interstellar divide and beaming back images and data of distant planets.
“[S]o the question is are we content to merely look at them from afar or would we like to go there?” said Long. “Space probes offer a clear advantage over long-range remote sensing, which is the potential for direct in-situ scientific investigations from orbit or even on the surface. In a universe where the Earth and even our solar system is reduced to a mere pale blue dot among the void, we would be crazy not to one day try.”
But of course, the prospect of exploring other solar systems presents some major difficulties, not the least of which is cost. To put it in perspective, the Apollo program cost an estimated $25.4 billion USD, which works out to $143.7 billion when adjusted for inflation. Sending a ship to another star is therefore like to run into the trillions.
But as Long explained, all of these challenges can be summarized into two categories. The first addresses the fact that we lack the necessary technological maturity:
“Like all spacecraft, an interstellar space probe would need power, propulsion and other systems to achieve its mission and successfully reach its target and acquire its data. Building spacecraft that can go fast enough to accomplish the journey to the nearest stars in a reasonable human life time and also powering those propulsion systems, is not easy, and exceeds the performance of any technology we have ever launched into space to date by several orders of magnitude. Yet, the basic principles upon which how those machines would operate, from a physics and engineering perspective, are well understood. It merely requires a focused program of effort to make this possible.”
As we addressed in a previous post, it would take an incredibly long time to venture to even the nearest star. Using existing technology, it would take a spacecraft anywhere from 19,000 to 81,000 years to reach Alpha Centauri. Even using nuclear propulsion (a feasible but not yet tested technology), it would still take 1000 years to get there.
The second major issue, according to Long, is the lack of political will. At present, planet Earth is facing multiple problems, the largest of which are overpopulation, poverty, and climate change. These problems, combined, essentially mean that humanity will have to see to the needs of billions’ more people while at the same dealing with diminishing resources.
“Given competing problems on Earth, it is felt that there is no justification today to approve the expenditure of such missions,” said Long. “Obviously, the discovery of an exoplanet with potentially interesting biology may change this. There is the potential for the private sector to attempt such missions, but these are likely in the future, since most private efforts are focused on the Moon and Mars.”
The one exception to this, Long explains, is Breakthrough Initiatives’ Project Starshot, which aims to send a gram-scale probe to Proxima Centauri in just 20 years. This would be possible by using a light sail, which would be accelerated by lasers to relativistic speeds of up to 60,000 km/s (37,282 mps), or 20% the speed of light.
A similar mission concept is known as Project Dragonfly, a concept being developed by an international team of scientists by Tobias Häfner. Interestingly enough, this proposal was born of the same conceptual design study that inspired Starshot – which was hosted by Initiative for Interstellar Studies (i4iS) in 2013.
Like Starshot, the Dragonfly concept call for a laser-driven light sail that would tow a spacecraft up to relativistic speeds. However, Dragonfly spacecraft would be significantly heavier than a gram-scale probe, which would allow for more scientific instruments to be included. The spacecraft would also be slowed by a magnetic sail upon arrival.
While missions like these are likely to cost in the vicinity of $100 billion to develop, Long certainly feels that this in the realm of affordability given the potential payoffs. Speaking of payoffs, an interstellar mission would have plenty, all of which would be enlightening and exciting. As Long said:
“The opportunity to conduct close up observations of other stellar systems would give us a much better understanding about how our own Solar System formed and also the nature of stars, galaxies and exotic phenomena like black holes, dark matter and dark energy. It could also give us better predictions for the potential for life evolving systems.”
There’s also the possibility that space probes conducting interstellar voyages at relativistic speeds will discover new physics. At present, scientists understand the Universe in terms of quantum mechanics (the behavior of matter at the subatomic level) and General Relativity (matter at the largest of scales – stars systems, galaxies, superclusters, etc.).
To date, all attempts at finding a Grand Unified Theory (GUT) – aka. a Theory of Everything (TOE) – that would merge these two schools of thought have failed. Long asserts that scientific missions to other star systems could very well provide a new synthesis, which would help us learn a great deal more about how the Universe functions as a whole.
But of course, no talk of payoffs would be complete without mentioning the biggest one of all: finding life! Even if it was just a colony of microbes, the scientific implications would be immense. As for the implications of finding an intelligent species, the implications would be immeasurable. It would also resolve the timeless question of whether or not humanity is alone in the Universe.
“Finding intelligent life would be a game changer, since if we were to make contact with such a species and share our knowledge with each other, this will have a profound effect on our sciences but also our personal philosophies,” said Long. “This is important when considering the age old question of human origins.”
But of course, a lot needs to happen before any such missions could be contemplated. For starters, the technological requirements, even for a technically-feasible concept like Starshot, need to be addressed well in advance. As will all the potential risks associated with interstellar flight at relativistic speeds.
But above all, we will need to know ahead of time where to send these missions in order to maximize the scientific return on our investment. This is where traditional astronomy and astrophysics will play a big role. As Long explained:
Before any missions are launched at other stars systems, it will be necessary to first characterize the scientific value of visiting those systems before hand, which will require the long-range astronomical observing platforms. Then, once the probes have been launched, they will also help to calibrate our measurements of the cosmic distance scale, which will also help to improve our astronomical instruments. It is clear therefore that any species that aspires to be enlightened about the Universe and its place in it, should embrace both forms of inquire since they enhance each other.
It may be many decades before humanity is prepared to commit the time, energy and resources to an interstellar mission. Or it may simply be a matter of years before existing proposals have all the technical and logistical issues worked out. Either way, when an interstellar mission is mounted, it will be a momentous and extremely historic event.
And when it begins to send back data from the nearest star systems, it will be an event unparalleled in history. Aside from the necessary advances in technology, all that is needed is the will to make the crucial investments happen.
Further Reading: arXiv