An artist’s concept of the planet HD 189733 b located 64 light-years from Earth.
| Photo Credit: Reuters

The planet known as HD 189733b, discovered in 2005, already had a reputation as a rather extreme place, a scorching hot gas giant a bit larger than Jupiter that is a striking cobalt blue colour and has molten glass rain that blows sideways in its fierce atmospheric winds. So how can you top that?

Add hydrogen sulfide, the chemical compound behind the stench of rotten eggs. Researchers said on Monday new data from the James Webb Space Telescope is giving a fuller picture of HD 189733b, already among the most thoroughly studied exoplanets, as planets beyond our solar system are called. A trace amount of hydrogen sulfide was detected in its atmosphere, a first for any exoplanet.

“Yes, the stinky smell would certainly add to its already infamous reputation. This is not a planet we humans want to visit, but a valuable target for furthering our understanding of planetary science,” said astrophysicist Guangwei Fu of Johns Hopkins University in Baltimore, lead author of the study published in the journal Nature.

It is a type called a “hot Jupiter” – gas giants similar to the largest planet in our solar system, only much hotter owing to their close proximity to their host stars. This planet orbits 170 times closer to its host star than Jupiter does to the sun. It completes one orbit every two days as opposed to the 12 years Jupiter takes for one orbit of the sun.

In fact, its orbit is 13 times nearer to its host star than our innermost planet Mercury is to the sun, leaving the temperature on the side of the planet facing the star at about 1,700 degrees Fahrenheit (930 degrees Celsius).

“They are quite rare,” Fu said of hot Jupiters. “About less than one in 100 star systems have them.”

This planet is located 64 light-years from Earth, considered in our neighbourhood within the Milky Way galaxy, in the constellation Vulpecula. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km).

“The close distance makes it bright and easy for detailed studies. For example, the hydrogen sulfide detection reported here would be much more challenging to make on other faraway planets,” Fu said.

The star it orbits is smaller and cooler than the sun, and only about a third as luminous. That star is part of a binary system, meaning it is gravitationally bound to another star.

Webb, which became operational in 2022, observes a wider wavelength range than earlier space telescopes, allowing for more thorough examinations of exoplanet atmospheres.

“Our research finds that HD 189733b is more similar to Jupiter than previously known,” Arizona State University astrophysicist and study co-author Luis Welbanks said. “This planet is very much like Jupiter, but just hotter.”

Jupiter, too, has trace amounts of hydrogen sulfide in its atmosphere. This planet is about 10% larger than Jupiter in diameter and mass.

In addition to detecting hydrogen sulfide, a sulfur-containing molecule, Webb observations showed that this planet has water and carbon dioxide in its atmosphere, as earlier data also indicated.

“With these three molecules, we are able to count the amount of oxygen, carbon and sulfur the planet has, giving us an opportunity to understand how the planet may have formed and whether it is different or not to the planets in our solar system,” Welbanks said.

The Webb observations also ruled out the presence of methane in the planet’s atmosphere.

“Understanding the composition of this and other exoplanets allows us to understand how unique our own solar system is and helps us place our existence in context,” Welbanks added.

“While we are not searching for life on HD 189733b – it is too hot, made up mostly of hydrogen and helium, it’s not like Earth, et cetera – understanding its atmosphere allows us to understand how physics and chemistry behave under different environments and to begin to put together the ‘recipe’ for forming planets.”

An artist’s concept shows the exoplanet 55 Cancri e, also called Janssen, a so-called super-Earth, a rocky planet significantly larger than Earth but smaller than Neptune, along with the star it orbits in this undated illustration released by NASA.
| Photo Credit: Reuters

Astronomers have searched for years for rocky planets beyond our solar system with an atmosphere – a trait considered essential for any possibility of harbouring life. Well, they finally seem to have located one. But this hellish planet – apparently with a surface of molten rock – offers no hope for habitability.

Researchers said on Wednesday the planet is a “super-Earth” – a rocky world significantly larger than our planet but smaller than Neptune – and it orbits perilously close to a star dimmer and slightly less massive than our sun, rapidly completing an orbit every 18 hours or so.

Infrared observations using two instruments aboard the James Webb Space Telescope indicated the presence of a substantial – if inhospitable – atmosphere, perhaps continuously replenished by gases released from a vast ocean of magma.

“The atmosphere is likely rich in carbon dioxide or carbon monoxide, but can also have other gases such as water vapor and sulfur dioxide. The current observations cannot pinpoint the exact atmospheric composition,” said planetary scientist Renyu Hu of NASA’s Jet Propulsion Laboratory and Caltech, lead author of the study published in the journal Nature.

The Webb data also did not make clear the thickness of the atmosphere. Hu said it could be as thick as Earth’s or even thicker than that of Venus, whose toxic atmosphere is the densest in our solar system.

The planet, called 55 Cancri e or Janssen, is about 8.8 times more massive than Earth, with a diameter about twice that of our planet. It orbits its star at one-25th the distance between our solar system’s innermost planet Mercury and the sun. As a result, its surface temperature is about 3,140 degrees Fahrenheit (1,725 degrees Celsius/2,000 degrees Kelvin).

“Indeed, this is one of the hottest-known rocky exoplanets,” said astrophysicist and study co-author Brice-Olivier Demory of the University of Bern’s Center for Space and Habitability in Switzerland, using the term for planets beyond our solar system. “There are likely better places for a vacation spot in our galaxy.”

The planet is probably tidally locked, meaning it perpetually has the same side facing its star, much like the moon does toward Earth. The planet is located in our Milky Way galaxy about 41 light-years from Earth, in the constellation Cancer. A light year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). Four other planets, all gas giants, are known to orbit its host star.

That star is gravitationally bound to another star in a binary system. The other one is a red dwarf, the smallest kind of ordinary star. The distance between these companions is 1,000 times the distance between Earth and the sun, and light takes six days to get from one to the other.

After all their searching, the rocky exoplanet for which scientists finally found evidence of an atmosphere turned out to be one that probably should not even have one. Being so close to its star, any atmosphere should be stripped away by stellar irradiation and winds. But gases dissolved in the vast lava ocean thought to cover the planet may keep bubbling up to replenish the atmosphere, Hu said.

“The planet cannot be habitable,” Hu said, because it is too hot to have liquid water, considered a prerequisite for life.

All of the previous exoplanets found to have atmospheres were gaseous planets, not rocky ones. As Webb pushes the frontiers of exoplanet exploration, the discovery of a rocky one with an atmosphere represents progress.

On Earth, the atmosphere warms the planet, contains the oxygen people breathe, protects against solar radiation and creates the pressure needed for liquid water to remain on the planet’s surface.

“On Earth, atmosphere is key for life,” Demory said. “This result on 55 Cnc e entertains the hope that Webb could conduct similar investigations on planets that are much cooler than 55 Cnc e, which could support liquid water at their surface. But we are not there yet.”