Unusual Discovery of Water Vapor in a Giant Planet’s Atmosphere

An odd and surprising discovery was made when water vapor was detected in the atmosphere of a giant exoplanet. The Neptune-like planet, which has been named TOI-674 b, has a mass that is 23.6 times greater than Earth’s. It is located about 150 light-years away from us in the constellation Antlia.

During the recent virtual American Astronomical Society media briefings, Jonathan Brande, who is a doctoral student at the University of Kansas, stated, “We think we see water vapor on TOI-674 b, which is really exciting.” It’s also very odd because the planet completes a full orbit its host star (a red dwarf) every two days, so the radiation from the star should have stripped the planet of its atmosphere.

As a matter of fact, TOI-674 b orbits its star at a very close distance of just 0.025 AU (one AU is the distance of Earth to the sun), so it’s baffling as to why water vapor was detected. Furthermore, the planet would have temperatures of 680 degrees Fahrenheit (360 degrees Celsius).

Brande, as well as his advisor, astronomer Ian Crossfield from the University of Kansas, detected the water in TOI-674 b’s atmosphere by analyzing data from the Wide Field Camera 3 instrument on the Hubble Space Telescope. They studied the atmosphere when the planet traveled in front of its host star during three separate occasions.

TOI-674 b is one of only a few examples of water vapor being found on this type of planet. They have such short orbital periods that are so rare that astronomers call that area the “Neptune Desert”.

Another mystery is finding out where exactly TOI-674 b was formed, particularly in comparison to the water ice line (this is at a distance from the star where the temperature would be cold enough to sustain solid ice). In an interview with Astronomy, Brande explained this in further detail, “Planets forming closer to their host stars inside the water ice line should have less atmospheric water than those forming further away, outside the water ice line.”

It’s still unclear as to how much water is in the planet’s atmosphere, but if the amount can be calculated, experts would be able to determine where TOI-674 b formed. “...it almost certainly didn’t form this close to the star and needed to migrate into its current orbit somehow,” Brande added.

An artist’s impression of TOI-674 b can be seen here.