Tag Archives: WASP-69b

WASP-69b’s comet-like tail

The Keck Observatory have put out a press release saying that WASP-69b’s comet-like tail is at least 350,000 miles long, 7 times bigger than the planet itself. The tail results from evaporation of the planet’s atmosphere, caused by irradiation by its hot star.

The observations, reported in a paper led by Dakotah Tyler, a PhD student at UCLA, used the Keck/NIRSPEC spectrograph to study helium atoms in material boiling off the planet. They observed a transit of the planet across the face of its star, and detected helium absorption long after the transit itself had ended, showing that a plume of escaping gas was still absorbing some of the starlight.

An artist’s impression of evaporating planet WASP-69b and its comet-like tail. (Credit: W. M. Keck Observatory/Adam Makarenko)

“The WASP-69b system is a gem because we are able to study its atmospheric mass-loss in real-time,” says co-author, Erik Petigura. “This makes for a rare opportunity to understand the critical physics that shapes thousands of other planets.”

Helium absorption (yellow/green) is still seen after the end of transit (contact time T4), revealing the cometary tail.

The press release has led to coverage on multiple webpages, including in The New York Times, Newsweek, Arab Times, Forbes, Salon and others.

Aerosol particles make WASP-69b’s atmosphere hazy

“Aerosols have a critical role in establishing energy budgets, thermal structure, and dynamics in planetary atmospheres”, declares a new paper by Raissa Estrela et al.

Aerosols make the planet’s atmosphere hazy, an effect which is more pronounced at the blue end of the spectrum. Here is the spectrum of hot-Jupiter exoplanet WASP-69b, combining Hubble Space Telescope data from several observations.

The steeply rising spectrum (the y-axis shows effective planet size, with a larger size indicating more atmospheric absorption) is modelled (blue line) by including haze from aerosol scattering. The aerosols are found to extend from millibar pressures to microbar pressures.

The authors don’t yet know the composition of the aerosols, but suggest possibilities including hydrocarbons or magnesium silicate condensates. Overall they conclude that: “These results are consistent with theoretical expectations based on microphysics of the aerosol particles that have suggested haze can exist at microbar pressures in exoplanet atmospheres”.

Detecting helium envelopes around WASP planets

A new paper by Shreyas Vissapragada and colleagues reports a new technique for detecting material boiling off hot-Jupiter exoplanets. The idea is that helium atoms in escaping material should be strong absorbers of light at the wavelength of 1083.3 nm, one of the transitions of neutral helium. Thus, if one records a transit in an ultra-narrow-band filter around that wavelength, the planet should look bigger and so the transit should be deeper.

Vissapragada et al pointed the 200-inch Hale Telescope at a transit of WASP-69b. Here’s the result:

The blue line is the usual transit depth expected in continuum light. The data and fitted red line are the transit observed in the 1083.3-nm helium line. The authors compute that the extra depth of the transit implies that 30 million kilos of material is evaporating off the planet each second, as a result of stellar irradiation. This sounds a lot, but adds up to only a few percent of the planet’s mass over the host star’s lifetime.

Helium in WASP-69b, HAT-P-11b and HD 189733b

Earlier this year helium was found in the outer atmosphere of WASP-107b, the first detection of helium in an exoplanet. Several teams have now used similar techniques to find helium in WASP-69b, HAT-P-11b and HD 189733b, leading to a slew of papers and accompanying press releases from the Instituto de Astrofísica de Andalucía, the University of Exeter and others (see [1], [2], [3] and [4]).

Artist’s impression of an escaping envelope of helium surrounding WASP-69b. (Credit: Gabriel Perez Diaz, IAC)

Lisa Nortmann, lead author of the WASP-69b paper, explains that the helium is escaping from the atmosphere, forming a comet-like tail: “We observed a stronger and longer-lasting dimming of the starlight in a region of the spectrum where helium gas absorbs light. The longer duration of this absorption allows us to infer the presence of a tail.”

The press releases have led to extensive coverage including by CNN, the Daily Mail and Tech Times.

The IAA press release includes a video illustration of WASP-69b, created by Gabriel Perez Diaz of the IAC: