Sounds like he's talking about the Aether Theory without actually
mentioning the Aether here.

Technology Review: Blogs: arXiv blog: The Clue That Could Explain The
Fly-By Anomalies
"Last year, we looked at an idea from Stephen Adler at Princeton
University, that suggested the change in velocity could caused by
collisions between the spacecraft and particles of dark matter. Adler
even calculated the kind of distribution of dark matter particles that
would explain the observed changes in velocity--a kind of halo of them
around Earth. "
http://www.technologyreview.com/blog/arxiv/24232/?a=f

Yousuf Khan