Astronomers have discovered four nearby exoplanets they hope will help scientists learn about Earth's poorly understood teenage years.

The exoplanets were found orbiting two known stars, TOI 2076 and TOI 1807, which were born from the same gas cloud some 200 million years ago.

Both of the stars are K-dwarfs, or orange dwarfs, which are medium-sized, hydrogen-burning main sequence stars.

Because of their stability and moderate temperatures, K-dwarf stars are targeted by astronomers hunting for potentially habitable exoplanets.

Scientists are keen to survey the newly discovered exoplanets -- announced this week in the Astronomical Journal -- because all four are still in their formative years.

"The planets in both systems are in a transitional, or teenage, phase of their life cycle," study first author Christina Hedges said in a press release.

"They're not newborns, but they're also not settled down. Learning more about planets in this teen stage will ultimately help us understand older planets in other systems," said Hedges, an astronomer at the Bay Area Environmental Research Institute in Moffett Field, Calif.

The spectral signatures of TOI 2076's exoplanets were first spotted by Alex Hughes in 2019.

Hughes, who has since graduated with bachelor's degree in physics, was an undergraduate student at Loughborough University, in Britain, at the time.

While surveying TESS data, Hughes spotted repeated dips in TOI 2076's luminosity, suggesting the presence of a passing exoplanet.

Followup surveys, involving an international team of astronomers, revealed the presences of three different exoplanets.

The star's innermost planet, TOI 2076b, is roughly three times Earth's size and completes an orbit every 10 days. The other two exoplanets are each four times the size of Earth and complete orbits every 17 days.

"Discovering a planetary system that exists in this transitional 'teenage' period gives us a chance to test our models of this early evolution period and probe some of the questions we still have," said Hughes, who is now pursuing a masters degree in physics at University College London.

"I believe that TOI 2076 and TOI 1807 will help us better understand early formation and evolution processes, such that we can understand how our own solar system came to be," Hughes said.

The second star, TOI 1807, hosts just only a single planet, TOI 1807 b, which was first spotted by NASA astronomers in 2020.

"This discovery is important for two reasons. One is the age of the two stars. Investigating both the stars and their planets at this stage of evolution will give insights into our own solar system's early evolution," said Shaun Atherton, university physics teacher at Loughborough's School of Science.

"Second is the common origin of the two stars. Born in the same gas cloud, but having since moved apart, we can learn about how these two star systems have developed separately," Atherton said.

Planetary models suggest these young planets have thick atmospheres composed of the remnants of the protoplanetary disk of gas and dust from which they formed.

Sometimes, young planets are stripped of their initial atmosphere by solar winds. Rocky planets can develop secondary atmosphere via volcanic activity and other geochemical processes.

Astronomers hope followup studies can help them establish more accurate mass measurements for the four exoplanets, but interference from the young, hyperactive stars could make detailed analysis difficult, they said.

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