Mining the Heavens: Astronomers Could Spot Asteroid Prospects

By Sarah Lewin, Staff Writer, Space.com | June 12, 2017 07:00am ET

NEW YORK — Harvard astrophysicist Martin Elvis would like to see astronomers take on a crucial role for future asteroid mining: as astronomical prospectors scoping out the next big catch.

Elvis discussed his dream for applied astronomy June 4 here at the Dawn of Private Spaceflight Science Symposium. Efficient asteroid mining would jump-start a space economy and bring down costs for exploration and space science, guiding humans into a modern space age, he said.

"My basic goal is just to revolutionize our exploration of the solar system, of the universe," Elvis said at the conference.

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The need for speed in Near-Earth Asteroid characterization

J.L. Galache, C.L. Beeson, K.K. McLeod, M. Elvis

Minor Planet Center, Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
School of Physics & Astronomy, University of Southampton, Southampton, Hampshire SO171BJ, UK
Whitin Observatory, Wellesley College, Wellesley, MA 02481, USA
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

We have used Minor Planet Center (MPC) data and tools to explore the discovery circumstances and properties of the currently known population of over 10,000 NEAs, and to quantify the challenges for follow-up from ground-based optical telescopes. The increasing rate of discovery has grown to ∼1000/year as surveys have become more sensitive, by 1 mag every ∼7.5 years. However, discoveries of large (H≤22) NEAs have remained stable at ∼365/year over the past decade, at which rate the 2005 Congressional mandate to find 90% of 140 m NEAs will not be met before 2030 (at least a decade late). Meanwhile, characterization is falling farther behind: Fewer than 10% of NEAs are well characterized in terms of size, rotation periods, and spectral composition, and at the current rates of follow-up it will take about a century to determine them even for the known population. Over 60% of NEAs have an orbital uncertainty parameter, U≥4, making reacquisition more than a year following discovery difficult; for H>22 this fraction is over 90%. We argue that rapid follow-up will be essential to characterize newly discovered NEAs. Most new NEAs are found within 0.5 mag of their peak brightness and fade quickly, typically by 0.5/3.5/5 mag after 1/4/6 weeks. About 80% have synodic periods of <3 years that would bring them close to Earth several times per decade. However follow-up observations on subsequent apparitions will be difficult or impossible for the bulk of new discoveries, as these will be smaller (H>22) NEAs that tend to return 100× fainter. We show that for characterization to keep pace with discovery would require: quick (within days) visible spectroscopy with a dedicated  telescope; long-arc (months) astrometry, to be used also for phase curves, with a  telescope; and fast-cadence (<min) light curves obtained rapidly (within days) with a  telescope. For the already-known large (H≤22) NEAs that tend to return to similar brightness, subsequent-apparition spectroscopy, astrometry, and photometry could be done with 1–2 m telescopes.

How Many Assay Probes to Find One Ore-­bearing Asteroid?

Martin Elvis and Thomas Esty

Harvard-Smithsonian Center for Astrophysics, USA

Harvard University, USA

The number of ore‐bearing asteroids could well be small and remote telescopic techniques are inadequate to identify such asteroids confidently. Finding an asteroid that can be profitably mined requires proximate observations from assay probes. Here we use a simple statistical approach to estimate the number of assay probes, Nassay, needed to find at least one ore-­‐bearing asteroid at a high confidence (90%, 95%, 99%). We present results for a wide range of values of the probability of an asteroid being rich in the resource of interest, Prich. We find that Nassay depends strongly on Prich, for likely values of Prich (<0.5). For a plausible value of Prich~0.1 then to obtain 90% confidence that at least one ore-­‐bearing asteroid is found, Nassay = 22, and for 99% confidence Nassay = 44. A factor two increase in Prich roughly halves Nassay, while even for Prich~0.5 , Nassay (90%) = 4. Hence any improvement in asteroid characterization prior to sending probes to its proximity would be an effective way to cost-­‐effectively search for valuable resources among the asteroids. Some possibilities for doing so are briefly discussed. 

How many ore-bearing asteroids?

Dr. Martin Elvis

Harvard-Smithsonian Center for Astrophysics, HEAD, 60 Garden Street, Cambridge, MA 02138, United States

A simple formalism is presented to assess how many asteroids contain ore, i.e., commercially profitable material, and not merely a high concentration of a resource. I apply this formalism to two resource cases: platinum group metals (PGMs) and water. Assuming for now that only Ni–Fe asteroids are of interest for PGMs, then 1% of NEOs are rich in PGMs. The dearth of ultra-low delta-v (o4.5 km s!1) NEOs larger than 100 m diameter reduces the ore-bearing fraction to only "1 in 2000 NEOs. As 100 m diameter NEOs are needed to have a value ZUS$1B and the population of near-Earth objects (NEOs) larger than 100 m diameter is "20,000 (Mainzer et al., 2011) the total population of PGM ore-bearing NEOs is roughly 10. I stress that this is a conservative and highly uncertain value. For example, an order of magnitude increase in PGM ore-bearing NEOs occurs if delta-v can be as large as 5.7 km s!1.Water ore for utilization in space is likely to be found in "1/1100 NEOs. NEOs as small as 18 m diameter can be water-ore-bodies because of the high richness of water ("20%) expected in "25% of carbonaceous asteroids, bringing the number of water-ore-bearing NEOs to "9000 out of the 10 million NEOs of this size. These small NEOs are, however, hard to find with present surveys. There will be "18 water-ore-bearing NEOs 4100 m diameter.
 These estimates are at present highly imprecise and sensitive to small changes, especially in the maximum delta-v allowed. Nonetheless the low values found here mean that much improved determinations of each of the terms of the formalism are urgently needed. If better estimates still find small numbers of ore-bearing NEOs then thorough surveys for NEA discovery and, especially, characterization are needed.
 Strategies for the two classes are likely to be different.

Astronomical Prospecting: A Necessary Precursor to Asteorid Mining

Dr. Martin Elvis

Harvard-Smithsonian Center for Astrophysics, USA, melvis@cfa.harvard.edu

 

Ore-bearing, i.e. potentially profitable, asteroids are rare, roughly 1 in 660, or 1 in 66 if low delta-v asteroids are preselected. Prospecting for ore-bearing asteroids will be a multi-step process, as for mineral resources on Earth. Even at 1 in 66, roughly 100 asteroids must be sampled to find at least one ore-bearing one, if a 5% chance of finding none is accepted. Even at moderate “NewSpace” prices, the total cost of 100 interplanetary in situ asteroid prospecting probes likely becomes prohibitive. Fortunately, remote prospecting using astronomical techniques to sieve the near-Earth asteroid population can change the odds to about 1 in 4. This reduces the number of probes required by an order of magnitude. Hence professional quality astronomical prospecting is a business necessity for any asteroid mining venture. Some of the details of how to go about astronomical prospecting are discussed.

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