Scientists were recently left scratching their heads after a "potentially disruptive" solar storm smashed into Earth without warning.

The surprise solar storm hit Earth just before midnight UTC June 25 and continued throughout most of June 26, according to Spaceweather.com (opens in new tab).

Related: Ancient solar storm smashed Earth at the wrong part of the sun's cycle — and scientists are concerned .

Scientists initially suspected coronal mass ejection (CME) caused the freak storm — a large burp of plasma with an embedded magnetic field that is belched out from a sun spot — but they couldn’t tell if it had occurred on the Earthside or farside of the sun, according to Spaceweather.com. .

However, experts now blame a much rarer co-rotating interaction region (CIR) of the sun; these are "transition zones between slow- and fast-moving streams of solar wind," according to Spaceweather.com.

The solar wind that blasted Earth on June 25 and 26 peaked at around 1.57 million miles per hour (2.52 million kilometers per hour), which is consistent with other CIRs in the past, according to Spaceweather.com.

The surprise solar storm hit Earth less than a week after a giant sunspot, known as AR3038, doubled in size over a 24-hour period and reached a maximum diameter more than 2.5 times the size of Earth.

Scientists don't know if the gargantuan sunspot and the solar storm are connected. .

—An 'Internet apocalypse' could ride to Earth with the next solar storm, new research warns.

Because scientists initially believed the recent solar storm could have been caused by a farside CME, they predicted that the unusual auroras could last until June 29