Hubble Observes Exoplanet that Snows Sunscreen

[bystander]

Hubble Observes Exoplanet that Snows Sunscreen
NASA | STScI | HubbleSite | 2017 Oct 26

Nighttime Titanium Oxide Snow Leaves Dayside Cloud-Free and Cooler

[img3="Image Credit: NASA, ESA, and G. Bacon (STScI)"]https://cdn.spacetelescope.org/archives ... o1736a.jpg[/img3][hr][/hr]

Travelers to the nightside of exoplanet Kepler-13Ab should pack an umbrella because they will be pelted with precipitation. But it's not the kind of watery precipitation that falls on Earth. On this alien world, the precipitation is in the form of sunscreen.

Ironically, the sunscreen (titanium oxide) is not needed on this side of the planet because it never receives any sunlight. But bottling up some sunlight protection is a good idea if travelers plan on visiting the sizzling hot, permanent dayside, which always faces its star. Visitors won't find any desperately needed sunscreen on this part of the planet.

Astronomers didn't detect the titanium oxide directly. They used Hubble to find that the atmospheric temperature grows increasingly colder with altitude on Kepler-13Ab, which was contrary to what they had expected. If titanium oxide were in the daytime atmosphere, it would absorb light and heat the upper atmosphere. Instead, high winds carry the titanium oxide around to the permanently dark side of the planet where it condenses to form clouds and precipitation. The planet's crushing gravity pulls all the titanium oxide so far down it can't be recycled back into the upper atmosphere on the daytime side.

The Hubble observations represent the first time astronomers have detected this precipitation process, called a "cold trap," on an exoplanet.

Kepler-13Ab is one of the hottest known planets, with a dayside temperature of nearly 5,000 degrees Fahrenheit. The Kepler-13 system resides 1,730 light-years from Earth.

Astronomers Discover Sunscreen Snow Falling on Hot Exoplanet
Eberly College of Science | Penn State University | 2017 Oct 26

Evidence for Atmospheric Cold-trap Processes in the Noninverted
Emission Spectrum of Kepler-13Ab Using HST/WFC3 - Thomas G. Beatty et al

• Astronomical Journal 154(4):158 (2017 Oct) DOI: 10.3847/1538-3881/aa899b
  arXiv.org > astro-ph > arXiv:1612.06409 > 19 Dec 2016 (v1), 13 Sep 2017 (v2)

[Ann]

Hubble observes exoplanet that snows sunscreen

Astronomynow wrote:

Click to view full size image

This illustration shows the seething hot planet Kepler-13Ab that circles very close to its
host star, Kepler-13A. Seen in the background is the star’s binary companion, Kepler-
13B, and the third member of the multiple-star system is the orange dwarf star Kepler-
13C. Credit: NASA, ESA, and G. Bacon (STScI)

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.

I checked up the host star, Kepler-13 A. I found some information about it, including the fact that it is a type A4 almost certainly main sequence star twice as massive as the Sun. To my great surprise, however, the page where I found the info claimed that while the apparent magnitude of Kepler-13 A is +10.00, the absolute magnitude of this star is +25.00! I don't think so!

Altair is an A7 V-IV type star whose absolute magnitude is ~ 2.2. So perhaps the absolute magnitude of Kepler-13 A is ~2.5.

Ann