Artwork: NASA, ESA, and G. Bacon (STScI)
Science: NASA, ESA, and T. Beatty (Pennsylvania State University)
NASA's Hubble Space Telescope has found a blistering hot planet
outside our solar system where it "snows" sunscreen. The problem is the
sunscreen (titanium oxide) precipitation only happens on the planet's
permanent nighttime side. Any possible visitors to the exoplanet, called
Kepler-13Ab, would need to bottle up some of that sunscreen, because
they won't find it on the sizzling hot, daytime side, which always faces
its host star.
Hubble astronomers suggest that powerful winds carry the titanium
oxide gas around to the colder nighttime side, where it condenses into
crystalline flakes, forms clouds, and precipitates as snow.
Kepler-13Ab's strong surface gravity — six times greater than Jupiter's —
pulls the titanium oxide snow out of the upper atmosphere and traps it
in the lower atmosphere.
Astronomers using Hubble didn't look for titanium oxide specifically.
Instead, they observed that the giant planet's atmosphere is cooler at
higher altitudes, which is contrary to what was expected. This finding
led the researchers to conclude that a light-absorbing gaseous form of
titanium oxide, commonly found in this class of star-hugging, gas giant
planet known as a "hot Jupiter," has been removed from the dayside's
atmosphere.
The Hubble observations represent the first time astronomers have
detected this precipitation process, called a "cold trap," on an
exoplanet.
Without the titanium oxide gas to absorb incoming starlight on the
daytime side, the atmospheric temperature grows colder with increasing
altitude. Normally, titanium oxide in the atmospheres of hot Jupiters
absorbs light and reradiates it as heat, making the atmosphere grow
warmer at higher altitudes.
These kinds of observations provide insight into the complexity of
weather and atmospheric composition on exoplanets, and may someday be
applicable to analyzing Earth-size planets for habitability.
"In many ways, the atmospheric studies we're doing on hot Jupiters
now are testbeds for how we're going to do atmospheric studies on
terrestrial, Earth-like planets," said lead researcher Thomas Beatty of
Pennsylvania State University in University Park. "Hot Jupiters provide
us with the best views of what climates on other worlds are like.
Understanding the atmospheres on these planets and how they work, which
is not understood in detail, will help us when we study these smaller
planets that are harder to see and have more complicated features in
their atmospheres."
Beatty's team selected Kepler-13Ab because it is one of the hottest
of the known exoplanets, with a dayside temperature of nearly 5,000
degrees Fahrenheit. Past observations of other hot Jupiters have
revealed that the upper atmospheres increase in temperature. Even at
their much colder temperatures, most of our solar system's gas giants
also exhibit this phenomenon.
Kepler-13Ab is so close to its parent star that it is tidally locked.
One side of the planet always faces the star; the other side is in
permanent darkness. (Similarly, our moon is tidally locked to Earth;
only one hemisphere is permanently visible from Earth.)
The observations confirm a theory from several years ago that this
kind of precipitation could occur on massive, hot planets with powerful
gravity.
"Presumably, this precipitation process is happening on most of the
observed hot Jupiters, but those gas giants all have lower surface
gravities than Kepler-13Ab," Beatty explained. "The titanium oxide snow
doesn't fall far enough in those atmospheres, and then it gets swept
back to the hotter dayside, revaporizes, and returns to a gaseous
state."
The researchers used Hubble's Wide Field Camera 3 to conduct
spectroscopic observations of the exoplanet's atmosphere in
near-infrared light. Hubble made the observations as the distant world
traveled behind its star, an event called a secondary eclipse. This type
of eclipse yields information on the temperature of the constituents in
the atmosphere of the exoplanet's dayside.
"These observations of Kepler-13Ab are telling us how condensates and
clouds form in the atmospheres of very hot Jupiters, and how gravity
will affect the composition of an atmosphere," Beatty explained. "When
looking at these planets, you need to know not only how hot they are but
what their gravity is like."
The Kepler-13 system resides 1,730 light-years from Earth.
The team's results appeared in The Astronomical Journal
Related Links
This site is not responsible for content found on external links
Contact
Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Thomas Beatty
Pennsylvania State University, University Park
814-863-7346
tbeatty@psu.edu
Space Telescope Science Institute, Baltimore, Maryland
410-338-4493 / 410-338-4514
dweaver@stsci.edu / villard@stsci.edu
Thomas Beatty
Pennsylvania State University, University Park
814-863-7346
tbeatty@psu.edu
