Astronomers in Belgium have identified a record of seven Earth-sized planets, all potentially habitable.

According to the research study, which was published in Nature last week, and findings from NASA, all seven planets could potentially support liquid water, which astronomers believe is key to sustaining life. Michael Gillon was the lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege in Belgium. 

The seven planets all orbit TRAPPIST-1, an ultracool dwarf star in the Aquarius constellation. TRAPPIST-1 is slightly bigger than Jupiter in size but weighs 80 times as much.

Laurence Trafton, UT astronomy researcher at the McDonald Observatory, said discovering these seven planets is a breakthrough for finding life outside Earth.

“We have been searching for Earth-size planets for a long time, and we finally got them down from Jupiter-sized to Neptune-size down to super-Earths,” Trafton said. “All of a sudden from the TRAPPIST-1 group, we see seven (planets) going around the same star; all Earth-sized and in the habitable zone.”

Adam Kraus, assistant professor of astronomy at UT, said TRAPPIST-1 was discovered a couple years ago by a ground-based planet search program.

“A group of astronomers started observing nearby low-mass small stars, with the idea that if (these stars) have planets (orbiting them), the planets will be oriented so that they pass along (Earth’s) line of sight and block some of the light from the star,” Kraus said.

He added that astronomers chose to study small stars because Earth-sized planets would block more light emitted from these stars. Kraus said this strategy works because the more light the planets block, the easier they are to detect.

Trafton said scientists and astronomers noticed three planets from the Trappist system get very close to the habitable zone, which encompasses the distances from the sun to where liquid water is possible.

“The habitable zone is the distance from the primary star (to) where it is either so cold that water freezes out entirely … or it is so warm that (water) evaporates,” he said. 

Trafton said the temperature at which liquid water exists, 0 to 100 degrees Celsius, allows for the maximum amount of chemical reactions, since most organic materials can exist in liquid, gas or solid form in this temperature region. These chemical reactions are crucial for life to exist, he said, adding that all life we currently know of is dependent on water. 

The astronomers then used the Spitzer Space Telescope to gather more precise and continuous data about the Trappist system, Kraus said. He added that after 500 hours of observation, Gillon identified four additional planets in the habitable zone.

Michael Endl, UT research scientist at the McDonald Observatory, said that planets located in the habitable zone aren’t necessarily livable for humans.

“They could all basically be habitable if they have the right atmospheric conditions,” Endl said. “Venus is in the classical habitable zone but you don’t want to buy a house on Venus!”

Endl said NASA’s Kepler missions have discovered similar multi-planet rocky systems orbiting larger stars, but these systems have usually not been in the habitable zone.

Today, scientists can detect the location and size of planets, Kraus said, but the long-term goals are measuring oxygen, ozone, carbon dioxide and possibly water. The James Webb telescope, which will launch in October 2018, will be able to help researchers discover more about the atmosphere of far-away planets, which could help identify if a planet contains living organisms. 

“The holy grail and ultimate goal concerning habitability is to detect biosignatures, (or) chemical footprints of life in a planet’s atmosphere,” Endl said.

Endl said in his opinion if there are form of life in the universe, they would be single-cell organisms, because for nearly 3 billion years, life on Earth was single-celled. 

Kraus said that he believes within two to three years, data from the James Webb telescope will be able to tell us whether or not there is life, single-celled or not, in the TRAPPIST-1 system.  

He added he is optimistic about the search for Earth-sized planets and extraterrestrial life.

“We will find something that we think is interesting — maybe a sign of life — I would bet within 10 years,” Kraus said.