Space exploration – to the far end of the Solar System? Maybe, or maybe not.

Steph P. Bianchini March 7, 2014 3 Comments

2015 NASA budget – as disclosed in these day by the White House – (http://www.space.com/24911-nasa-2015-budget-highlights.html) – amounts at $17.5 billion to NASA, about $200 million less than 2014 but still enough for one thing or two. Especially if some private commercial companies can help here and there. (And that seems by now not so far-fetched, especially if you talk about corporations of the kind of Space X and Orbital Science: http://tinyurl.com/n32tshm).

What is included in 2015 NASA plans ? Obviously enough, the necessary funding to keep the International Space Station on its orbit (it is hoped to last until 2024); and on the wish-list a mission to Jupiter’s promising moon Europa,  which many scientists regard as our Solar System’s best bet to host life beyond Earth. (And yes, Mars is still there too. How surprising, isn’t it? )

(Credits: SPACE.com; NASA)

But what about the rest of the Solar System? A good look at the space exploration feasibility studies repository (http://www.nap.edu/reports/13117/appendix_g.html) will show a far more interesting, and ambitious, list. 

There are well-established objects of interest  – the already mentioned Mars and Europa, but also Io and Ganymede, to keep at Jupiter. And Saturn’s moon Titan, of course, another favourite in the search for extra-terrestrial life. But there are also some more bizarre targets, like the mysterious TNOs. 

What is a Trans-Neptunian object (TNO), anyway? With this definition, scientists refer to any object in the Solar System orbiting at a greater average distance than Neptune. After Pluto’s discovery in 1930, over 1200 have now been identified so far, including the so-called Plutoids, dwarf planets smaller than Mercury, and yet “having enough mass to become spherical under their own gravity.“ http://www.spaceanswers.com/solar-system/2044/what-are-trans-neptunian-objects/#sthash.glUk7IeC.dpuf). TNOs are collectively defined as bodies populating the Kuiper Belt, and which are believed to retain the most pristine and least altered material of the solar system (Fornasier,S. et al. 2013. TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of 9 bright targets at 70–500 micron, available at:http://arxiv.org/abs/1305.0449)

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Chiron, the principal target of one of the feasibility studies for NASA missions (NASA App G 22_Chiron_Orbiter.pdf available from: http://www.nap.edu/reports/13117/appendix_g.html) is one of them. (While the most famous, it was not even the first one to be discovered. As a matter of fact, the first centaur to be ever found out was 944 Hidalgo in 1920, even if they were not not recognized as a distinct population until the discovery of Chiron, as late as 1977. To date, the largest known centaur is 10199 Chariklo, discovered in 1997 and that, with 260 km in diameter, is only as big as a mid-sized main-belt asteroid).

To be fair, part of the interest for the TNOs comes to the fact that many of the nearby stars similar to the Sun are surrounded by disks of dust that are thought to be derived from collisions between comets – thus similar to the ones of the Kuiper Belt. Any knowledge gathered from the Kuiper Belt to stellar dust disks suggests that the inner boundary exhibited by some disks may be an indication of the existence of planets (National Research Council. 1998., Exploring the Trans-Neptunian Solar System. Washington, DC: The National Academies Press, http://www.nap.edu/catalog.php?record_id=6080).

Even today, not a lot is known about the TNOs in general, and Chiron in specific, is known. Furthermore, talking specifically about Chiron, even among these categories this celestial body presents a characteristic that put it aside all the others and attracts specific interest: in addition of having an eccentric orbit, it also displays an intermittent cometary behaviour, even if this specific aspect is erratic and difficult to model. (This is also one of the reasons these class of object has attracted the name of Centaurs, mythological creatures between horses and men. Horner, J.; Evans, N.W.; Bailey, M. E. 2004. “Simulations of the Population of Centaurs I: The Bulk Statistics”, Monthly Notices of the Royal Astronomical Society 354 (3): 798–810. arXiv:astro-ph/0407400). This also means that a flyby mission to Chiron, like the ones that have already explored other planets in the solar system, won’t even be enough to understand its secrets: in order to gather the required amount of information, the spacecraft will need to orbit the dwarf planet for a period not inferior to three years – thus posing by itself a total new set of technical challenges.

Based on these considerations, a case has been made regarding the feasibility of a mission orbiting the Centaur Object Chiron, by using the state of art of NASA’s available technology. The New Frontier cost range situated it around US $ 800 M, also outlining 5 scenarios, focusing in particular on the alternative propulsion systems and trajectories needed to send the spacecraft over there. The main problem that the feasibility study highlighted lies in the fact that the most affordable systems – the chemical and the solar electricity propulsion ones – are not able to deliver the full set of equipment necessary for the studies, while the other three, especially the radioisotope system, while technically more suitable, are too expensive. Other simulations, assessing the different duration of the cruise stages until Chiron and the gravitational assist from Jupiter or Saturn orbit are also being evaluated. Other problem is related to the transfer of information – given the distance from Earth and the fact that any system will have to survive between 11-13 years of cruise time before reaching its target. According to the findings of the feasibility study, an Earth-based high-power laser beacon may be required. The kind of information that will be retrieved will obviously be of a more limited quantity and variety compared to other missions planned to other, nearer celestial bodies, but this is a non avoidable limitation considering distance and technical challenges of the mission.

As an additional bonus, the mission will have the opportunity to extend data collection to other celestial bodies, first of all other Centaurs like Okyrhoe and Echeclus that are closer to Earth. If cleared to go, the target launch date will range between 2015 and 2025.

It is evident that the cost-opportunity of these kind of missions will have to be carefully evaluated, especially considered the dwindling funds available for space missions. With the kind of budget allocated in 2015, Chiron mission is not going to take off anytime soon (and with some good reasons, some many argue). The most sensible choice would likely be to wait for the first results coming from the New Horizons’ mission in 2015 http://www.nasa.gov/mission_pages/newhorizons/main/#.Uxo5px_mgUQ) .

(Credit: NASA)

Launched in 2006, it is due to explore Pluto for the first time https://www.youtube.com/watch?v=_LBJz4TxG0I) and then, subject to extension from NASA, keeping up its investigation of other TNOs, including Chiron.  But don’t hold your breath.