This is entertaining. He also coauthored a paper below on using photon 
sails to perform this probing.

LC

https://arxiv.org/abs/2004.14192  
Searching for a Black Hole in the Outer Solar System
Edward Witten 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Witten%2C+E>

There are hints of a novel object ("Planet 9") with a mass 5−10 M⊕ in the 
outer Solar System, at a distance of order 500 AU. If it is a relatively 
conventional planet, it can be found in telescopic searches. Alternatively, 
it has been suggested that this body might be a primordial black hole 
(PBH). In that case, conventional searches will fail. A possible 
alternative is to probe the gravitational field of this object using small, 
laser-launched spacecraft, like the ones envisioned in the Breakthrough 
Starshot project. With a velocity of order .001 c, such spacecraft can 
reach Planet 9 roughly a decade after launch and can discover it if they 
can report timing measurements accurate to 10−5 seconds back to Earth.

Comments: 4 pp, additional references
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); High Energy 
Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
Cite as: arXiv:2004.14192 <https://arxiv.org/abs/2004.14192> [astro-ph.EP]
  (or arXiv:2004.14192v2 <https://arxiv.org/abs/2004.14192v2> [astro-ph.EP] for 
this version)


https://arxiv.org/abs/2005.12336  

Exploration of the outer solar system with fast and small sailcraft
Slava G. Turyshev 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Turyshev%2C+S+G>
, Peter Klupar 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Klupar%2C+P>, 
Abraham 
Loeb <https://arxiv.org/search/astro-ph?searchtype=author&query=Loeb%2C+A>, 
Zachary 
Manchester 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Manchester%2C+Z>
, Kevin Parkin 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Parkin%2C+K>, Edward 
Witten 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Witten%2C+E>, S. 
Pete Worden 
<https://arxiv.org/search/astro-ph?searchtype=author&query=Worden%2C+S+P>

Two new interplanetary technologies have advanced in the past decade to the 
point where they may enable exciting, affordable missions that reach 
further and faster deep into the outer regions of our solar system: (i) 
small and capable interplanetary spacecraft and (ii) light-driven sails. 
Combination of these two technologies could drastically reduce travel times 
within the solar system. We discuss a new paradigm that involves small and 
fast moving sailcraft that could enable exploration of distant regions of 
the solar system much sooner and faster than previously considered. We 
present some of the exciting science objectives for these miniaturized 
intelligent space systems that could lead to transformational advancements 
in the space sciences.

Comments: A White Paper to the National Academy of Sciences Planetary 
Science and Astrobiology Decadal Survey 2023-2032. 13 pages, 5 figures and 
2 tables
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth 
and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics 
(astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)
Cite as: arXiv:2005.12336 <https://arxiv.org/abs/2005.12336> [astro-ph.IM]
  (or arXiv:2005.12336v1 <https://arxiv.org/abs/2005.12336v1> [astro-ph.IM] for 
this version)

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