Scientists have studied the planet LHS 1140b. It is an Earth-like world located several dozen light-years away. The researchers learned a great deal about the gaseous envelope surrounding this world.
How the Planet LHS 1140b Was Discovered
Nearly ten years after the discovery of LHS 1140b—a rocky exoplanet in the habitable zone around a low-mass star—a new study suggests that the object may possess its own atmosphere. Jason Dittmann, an associate professor of astronomy at the University of Florida, first discovered the planet in 2016. He is now a co-author of a new study published in the journal Science, which explains the possible presence of an atmosphere based on helium escaping from the planet. This was reported by phys.org.
The Magellan Clay Telescope at Las Campanas Observatory in Chile detected signs of helium escaping from the planet. However, the planet’s age suggests that its helium reserves should already have been depleted unless they were being continuously replenished, which points to the possible presence of an atmosphere.
In 2016, Dittmann used ground-based telescopes to search for planets using the transit method—when a planet briefly dims its light as it passes in front of a star. But ground-based observations are hampered by Earth’s atmosphere. To distinguish true transits from brightness changes caused by thin clouds, humidity fluctuations, or other atmospheric phenomena, he trained a machine learning algorithm to recognize signals of atmospheric origin and separate them from signals caused by the planet’s passage.
This method helped Dittmann discover LHS 1140b. Because of the characteristics of the planet’s orbit, it could be observed only a few times each year, so he tried to make the most effective use of the limited opportunities available to study it.
A Rocky World with an Atmosphere
Given the type of star it orbits, Dittmann noted that the planet’s temperature should be similar to Earth’s. It is composed of rocky material rather than gas and is located approximately 40 light-years away. The system also contains a second planet, LHS 1140c, which lies outside the habitable zone.
Many rocky exoplanets discovered in recent years have likely already lost their atmospheres to radiation from their parent stars. Given the age of LHS 1140b and the absence of atmospheres around similar planets, Dittmann and his team did not expect to detect helium.
“In this field, we had reached the conclusion that perhaps all these planets have no atmospheres and that we should focus on planets around Sun-like stars rather than smaller stars,” Dittmann said. “And now, at last, there is a planet with an atmosphere, and it turns out to be the very one on which I spent so many hours.”
What Does the Loss of Helium Indicate?
Immediately after the planet’s initial discovery, Dittmann requested X-ray data on the planetary system. This allowed him to determine how much energy the planet receives from its star, which several years later became a key factor in interpreting the helium signal.
The Magellan Clay Telescope subsequently detected helium escaping from the planet—a process that also occurs on Earth. The X-ray observations explained the rate at which the planet was losing helium under the influence of X-ray radiation from its host star. Therefore, the X-ray data demonstrated that the rocky body must be replenishing its helium reserves; otherwise, no helium would remain.
Future Study of the Atmosphere with the James Webb Telescope
The team initially proposed observing helium because it is the easiest element to detect. Now that potential evidence of an atmosphere has emerged, the group can proceed to investigate carbon dioxide and water in order to study the planet’s conditions in greater detail.
LHS 1140b is one of the targets selected for the Rocky Worlds Director’s Discretionary Time program, or DDT. Rocky Worlds DDT is a joint program involving the James Webb Space Telescope and the Hubble Space Telescope, dedicated to searching for evidence of atmospheres around rocky exoplanets orbiting dwarf stars.
Dittmann noted that the Rocky Worlds DDT program may be able to confirm or rule out the presence of an atmosphere around LHS 1140b within the next four or five years.
Now astronomers are wondering whether LHS 1140 b is a nearly bare rocky planet that only occasionally releases a small amount of gas that quickly dissipates into space, or whether it has a stable atmosphere that periodically loses some of its upper layers, as happens on Earth. Observations by the James Webb Space Telescope over the next four to five years should help detect water vapor and other atmospheric components. If water vapor is found, it would provide strong evidence for a stable atmosphere that could persist for billions of years.
