Apex domains cannot have CNAME records.
Question and response
Question
dig d8.85ae.static.theplanet.com. NS
Answer
d8.85ae.static.theplanet.com. 1 NS ns4.arpa.networklayer.com.
d8.85ae.static.theplanet.com. 1 NS ns3.arpa.networklayer.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0