Orbiting a hot F-star in only 1.27 days, WASP-121b is a highly irradiated hot Jupiter found by Laëtitia Delrez et al using the WASP-South survey. A team led by Tom Evans at Exeter has now pointed the Hubble Space Telescope at WASP-121b and found that its atmosphere shows a “stratosphere”. That is, the higher layers of the atmosphere appear to be hotter than the lower layers.
This is possible if molecules high in the atmosphere absorb radiation very efficiently. The “stratosphere” interpretation comes from finding spectral features caused by water, but seeing them in emission (as expected if the atmospheric temperature increases with height) rather than in absorption (expected if the temperature declines with height).
The data show the Hubble spectrum observed during transit using the WFC3 instrument. The red line is a model including a stratosphere. The blue lines are, for comparison, colder “brown dwarfs” which don’t have a stratosphere. The WFC3 data (circles with error bars) clearly favour the stratosphere interpretation.
NASA have put out a press release about the discovery, while the press team at Exeter have produced an illustration of the highly irradiated planet:
The story has been picked up by CNN, The Telegraph, New Scientist, NDTV, phys.org, the Mail Online, the International Business Times, Gizmodo Australia and over 40 other news and science websites.
NASA have put out a press release about Hubble Space Telescope observations of WASP-33b.
WASP-33b is the hottest of the WASP planets, being the only one so far found orbiting a very hot A-type star. A team led by Korey Haynes from NASA’s Goddard Space Flight Center, have used Hubble to show that WASP-33b has a “stratosphere”. The spectrum in the infra-red is best explained by a temperature inversion caused by the presence of Titanium Oxide in the atmosphere.
Titanium Oxide is noted for its ability to absorb light, which is why it is often used in sunscreen lotion. NASA’s graphic shows how an absorbing layer in the atmosphere produces a “temperature inversion” with a hotter layer higher up:
WASP-33b’s stratosphere was detected by measuring the drop in light as the planet passed behind its star (top). Temperatures in the low stratosphere rise because of molecules absorbing radiation from the star (right). Without a stratosphere, temperatures would cool down at higher altitudes (left). [Image: NASA/GSFC]
By comparing models with and without a temperature inversion to the spectrum of WASP-33b, as observed with Hubble’s WFC3 instrument, Haynes et al “make a very convincing case that we have detected a stratosphere on an exoplanet”.
The figure shows the spectrum of WASP-33b (left) and the temperature profile of the atmosphere (right), both for models with a temperature inversion (red) and without an inversion (blue). (From Haynes et al 2015)
The work has been reported widely, in over 100 news and science websites, such as by SciTechDaily, Pioneer News, The Daily Mail, and NY City Today.