Image copyright NASA Image caption Tests are being carried out to determine whether the cookies are safe to eat

Chocolate chip cookies have become the first food to be baked in space in a first-of-its-kind experiment.

Astronauts baked the cookies in a special zero-gravity oven at the International Space Station (ISS) last month.

Sealed in individual baking pouches, three of the cookies returned to Earth on the SpaceX Dragon spacecraft on 7 January.

The aim of the experiment was to study cooking options for long-haul trips.

The results of the experiment, carried out by astronauts Luca Parmitano and Christina Koch, were revealed this week.

The question is: how do they taste? The answer: nobody knows, yet.

A spokesman for Double Tree, the company that supplied the dough, told the BBC the cookies would "soon undergo additional testing by food science professionals to determine the final results of the experiment".

These tests will establish whether the cookies are safe to eat.

For the experiment, five cookies were baked over several days to determine the ideal cooking temperature and time.

Image copyright PA Media Image caption Five cookies were baked as part of the experiment

On Earth, it takes about 20 minutes to bake cookies at a temperature of around 150C (300F). The astronauts found that, in space, it takes far longer.

The first cookie - baked for 25 minutes - was undercooked, but the second - baked for 75 minutes - released a fresh scent in the ISS.

The fourth and fifth cookies - one baked for 120 minutes and left to cool for 25 minutes, and the other baked for 130 minutes and left to cool for 10 minutes - were deemed to be the most successful.

Image copyright PA Media Image caption The aim of the experiment was to test cooking options for long-haul space trips

As the cookies were baking, Mr Parmitano, an Italian astronaut for the European Space Agency, kept mission control abreast of their progress.

Tweeting from space in December, Ms Koch, a Nasa astronaut, wrote about making the cookies in space:

They were baked in a prototype oven built by NanoRacks and Zero G Kitchen, which create appliances for microgravity use in long-duration space flights.

A cargo craft containing the oven and baking ingredients took off from the US state of Virginia in November last year.

Zero G Kitchen describes the oven as "a cylindrical-shaped insulated container designed to hold and bake food samples in the microgravity environment".

The oven heats food through electric heating elements, similar to those found in a toaster oven, the company says.

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"While we have initial visual and scent feedback from the crew aboard the ISS, we're excited to dive into fully understanding the baking results," said Mary Murphy, senior internal payloads manager at NanoRacks.

DoubleTree said it planned to preserve the cookies where visitors could view them and learn more about the experiment.

The results will help experts with future efforts to make long-duration space travel more hospitable, the company said.