Amanda Kooser/CNET

After being closed for 10 days following a sudden and unexplained evacuation, the Sunspot Solar Observatory in New Mexico is set to reopen on Monday.

The observatory on Sacramento Peak, which overlooks the nearby White Sands Missile Range, was cleared along with the local post office and a handful of nearby residences, following a visit from the FBI earlier this month. No explanation for the evacuation was given to the observatory's employees or to local law enforcement.

"The Association of Universities for Research in Astronomy (AURA) who manages the facility is addressing a security issue at this time," AURA spokesperson Shari Lifson said in an emailed statement last week.

The FBI has not yet responded to a request for further information.

The lack of details led to a flurry of speculation and conspiracy theories. The internet wanted answers to whether the federal government was trying to cover up evidence of aliens or imminent solar flares.

On Sunday, Lifson sent out a follow-up release that would appear to rule out any such out-of-this-world explanation.

"AURA has been cooperating with an on-going law enforcement investigation of criminal activity that occurred at Sacramento Peak," reads the statement. "During this time, we became concerned that a suspect in the investigation potentially posed a threat to the safety of local staff and residents... AURA determined that moving the small number of on-site staff and residents off the mountain was the most prudent and effective action to ensure their safety."

The lack of information on the closure of the observatory was necessary for safety reasons, according to the statement.

"We recognize that the lack of communications while the facility was vacated was concerning and frustrating for some. However, our desire to provide additional information had to be balanced against the risk that, if spread at the time, the news would alert the suspect and impede the law enforcement investigation. That was a risk we could not take."

The observatory is set to open up again on Monday. It now has a new security service to help manage the unusual number of visitors who've been checking out the peak and the observatory for themselves.

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