The skeleton looks vaguely human, but is just six inches long. Found in 2003 in the Atacama Desert of northern Chile, it has hardened teeth, 10 ribs instead of 12, big eye sockets and an elongated, pointy skull. Since its discovery, the tiny form has sparked curiosity and speculation—and more than a few stories of aliens.

Now, as Carl Zimmer for The New York Times reports, a team of scientists finally know how this tiny mummy came to be. A new study published in Genome Research presents DNA analysis of bone marrow cells from the skeleton. The results suggest that the remains belonged to a child who likely had genetic mutations resulting in a bone disorder that caused the unexpected form.

The study began in 2012 when Garry P. Nolan, an immunologist at Stanford University and lead researcher on the project, heard of the U.F.O. documentary, “Sirius,” which featured the tiny form as possible evidence of aliens. At the time, the film was still in production, so Nolan reached out to producers and offered to examine the mummy's DNA, Zimmer writes.

"This was an unusual specimen with some fairly extraordinary claims put forward. ... it would be an example of how to use modern science to answer the question "what is it?" Nolan says in a press release.

The skeleton’s owner — it ended up in a private collection after it was found — sent Nolan X-ray images and bone marrow samples collected from the ribs and right humerus.

Nolan's initial analysis suggested that Ata, as the remains are known, was indeed a human with an estimated bone age of six to eight years at the time of death. This latest study adds to the find, revealing that Ata was a girl of Chilean descent. Her small stature and abnormal proportions were likely the result of genetic mutations largely associated with human growth, such as mutations in genes associated with dwarfism and scoliosis.

As Ian Sample reports for The Guardian, these genetic mutations can also explain the apparently advanced age of her bones. Based on this latest analysis, Nolan and his team believe Ata was born preterm, and was either a stillborn or died shortly after birth.

As Nolan explains in the statement, the "dramatic phenotype could in fact be explained with a relatively short list of mutations in genes known previously to be associated with bone development."

The specimen is not ancient, writes Gizmodo’s George Dvorsky, probably dating back around 40 years.

The researchers speculate in the paper that the mutations might have been caused by prenatal nitrate exposure since Ata was found in La Noria, an abandoned nitrate mining town in the Atacama region. But, as they write, "we can only speculate as to the cause."

This appears to be the first time some of the studied mutations were linked to abnormal bone growth and other developmental issues, writes Dvorsky. “It is quite surprising how many mutations this child has,” co-author of the study Atul Butte, a computational biologist at the University of California, San Francisco tells Dvorsky. “And that’s pretty relevant today. Children with rare and undiagnosed diseases are now more frequently getting genetic sequencing, and typically we in the medical field search for the ‘one gene’ with the problem.”

Nolan tells Sample the findings could help the research community better understand how mutations aged Ata’s bones. Developing drugs that mimic this accelerated bone development could be useful in mending breaks or fractures.