Scientific American is a serious magazine, so it should pay close attention to its writers’ use of language.  Here’s a quotation from an article posted on its web site this morning:

According to new research posted on the preprint server arXiv.org, the visitor is tumbling willy-nilly rather than smoothly rotating on its axis.

Nola Taylor Redd, Scientific American, 13 December 2017.

Willy-nilly is a survival from archaic English, “will I, nill I” (or “will he, nill he”), meaning, “Whether I want to (or he wants to) or not.”

The writer seems to have meant something like “helter-skelter”, or “higgledy-piggledy”  (or, in the words of the researchers, “in an excited rotational state undergoing Non-Principal Axis (NPA) rotation . . . .”).

In the same article:

The researchers . . . state in their paper “1I/‘Oumuamua was likely set tumbling within its parent planetary system, and will remain tumbling well after it has left ours.”

That is arguably correct, but at best it’s bad style. Remain means to stay in one place or state, not to persist in an action. The researchers mean that it will keep tumbling, or continue tumbling.  Remain just sounds more sciency than keep, I guess.