Apex domains cannot have CNAME records.
Question and response
Question
dig static.theplanet.com. NS
Answer
static.theplanet.com. 4 NS ns1.softlayer.net.
static.theplanet.com. 4 NS ns2.softlayer.net.
Authority
The response has no authority records.
Additional
ns1.softlayer.net. 4 A 67.228.254.24
ns2.softlayer.net. 4 A 67.228.255.25
ns1.softlayer.net. 4 AAAA 2607:f0d0:0:15:1:0:0:1
ns2.softlayer.net. 4 AAAA 2607:f0d0:0:15:2:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0