On July 13, astronauts aboard the International Space Station deployed a mini-satellite, a CubeSat that would study Milky Way’s halo in search of the universe’s missing matter.

For years, scientists have been puzzled by the mystery of "normal" matter making up the universe. Estimates taken from oldest light in the universe, when it was just 400,000 years since the Big Bang, indicate normal matter making up galaxies, stars, and planets is just five percent of the universe. The rest goes to the invisible dark matter (25 percent) and dark energy (70 percent) — an unknown form of energy thought to permeate all of space and accelerating the expansion of the universe.

This five percent might look little less for something encompassing everything we see around or observe from our telescopes, but the fact is it is so massive that we Earthlings haven’t fully accounted all of that, yet.

Hundreds of thousands of years after the birth of the universe, normal matter formed the gas, stars, planets, and entire galaxies. It evolved into what we see today, but according to current mass estimates, it is just half of what should be present.

“We should have all the matter today that we had back when the universe was 400,000 years old,” Philip Kaaret, HaloSat’s principal investigator, said in a statement. “Where did it go?”

Scientists have long believed that the missing matter could be present in the hot gas located in the space between galaxies or in the galactic halos — the extended region surrounding galaxies. The theory has not been proven, but the recently launched mini-satellite could provide some critical insight into it by studying the halo of our galaxy.

Essentially, the HaloSat will measure the intense X-rays emanating out of gas heated up to a whopping 2 million degrees Celsius (3.6 million degrees Fahrenheit) in the galactic halo. Unlike other X-ray telescopes, it will capture a wider view of the halo — approximately 100 square degrees at a time — and use the data collected to confirm if it’s spherical or shaped like a fried egg.

“If you think of the galactic halo in the fried egg model, it will have a different distribution of brightness when you look straight up out of it from Earth than when you look at wider angles,” Keith Jahoda, a HaloSat co-investigator, added. “If it’s in some quasi-spherical shape, compared to the dimensions of the galaxy, then you expect it to be more nearly the same brightness in all directions."

Once the shape is determined, scientists can use it to calculate the mass of the halo and confirm if the missing matter theory is true or not. The HaloSat will take a total of 90 minutes to complete a single orbit of Earth, but the observations will be taken only when it is on the nighttime side of the planet. This will help scientists filter out solar wind X-rays that carry the same spectral signature as they're trying to find and provide sufficient time for charging solar panels and transmitting the collected data.