A rocky planet about 40 light-years from Earth may have something that scientists have struggled to find on similar worlds—a lasting atmosphere.
The planet, called LHS 1140b, was first discovered in 2016, and new research published in Science suggests it may still be holding onto an atmosphere despite billions of years of exposure to its host star.
The finding is exciting because most rocky planets found around small, cool stars appear to have lost their atmospheres over time.
If LHS 1140b truly has one, it could become an important target in the search for potentially habitable worlds beyond our solar system.
LHS 1140b was discovered by University of Florida astronomer Jason Dittmann while searching for planets that pass in front of their stars, briefly causing the stars to dim.
Detecting these tiny changes from Earth is difficult because clouds, humidity and other weather conditions can interfere with observations.
To improve the search, Dittmann trained a machine learning program to tell the difference between signals caused by Earth’s atmosphere and those produced by an orbiting planet. This approach led to the discovery of LHS 1140b.
The planet is made of rock rather than gas and orbits within the habitable zone of its small, cool star, where temperatures may allow liquid water to exist under the right conditions. Another planet, LHS 1140c, also circles the same star but lies outside the habitable zone.
The new study focused on a surprising discovery. Using the Magellan Clay Telescope in Chile, researchers detected helium escaping from LHS 1140b. Helium can leak from a planet’s atmosphere, and this also happens on Earth. However, because LHS 1140b is an old planet, scientists expected that any helium would have escaped into space long ago. The fact that helium is still being detected suggests the planet is somehow replacing it, pointing to the possible existence of an atmosphere.
Earlier observations also helped solve the mystery. Soon after discovering the planet, Dittmann obtained X-ray observations of its star. These measurements showed how much high-energy radiation reaches the planet, allowing researchers to calculate how quickly helium should be escaping. Their calculations showed that without a continuing source of helium, none should remain today. This means the planet must be constantly replenishing its supply.
Even so, scientists cannot yet say for certain whether LHS 1140b has a stable atmosphere. One possibility is that the planet is mostly bare rock that occasionally releases gas from its interior. Another possibility is that it has a long-lasting atmosphere that slowly leaks helium into space, much like Earth does.
The next step is to search for other gases. LHS 1140b has been selected for the Rocky Worlds Director’s Discretionary Time Program, a joint effort using the James Webb Space Telescope and the Hubble Space Telescope to study rocky planets around dwarf stars. Over the next four to five years, Webb will search for gases such as water vapor and carbon dioxide. Finding these molecules would provide much stronger evidence that the planet has a stable atmosphere.
If future observations confirm that LHS 1140b has a long-lasting atmosphere, it would mark one of the first known Earth-sized rocky planets around a small star to retain one.
That would make it one of the most promising nearby worlds for scientists trying to understand which planets beyond our solar system might one day prove capable of supporting life.
Source: KSR.
Artist’s concept.
