Aside from the Moon, the brightest object in our night sky is planet Venus, whose thick cloud layer reflects around 75% of the Sun’s light. By comparison, Earth only reflects around 30% of incoming sunlight. A new analysis of data from ESA’s Cheops spacecraft shows that the ultra-short-period Neptune-sized exoplanet LTT 9779b reflects 80% of the light shone on it by its host star, LTT 9779, making it the shiniest exoplanet ever found. The reason for its high reflectivity is that it is covered by reflective clouds of metal and silicate.
LTT 9779 is a G8-type star located 260 light-years away in the constellation of Sculptor.
Also known as TOI-193, CD-38 15670 and HIC 117883, the star is around 2 billion years old and is metal-rich, having twice the amount of iron in its atmosphere than the Sun.
LTT 9779b was first discovered in 2020 by astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS).
The planet is 4.6 times larger than Earth and 29 times as massive. Its mean density is similar to that of Neptune and its atmosphere makes up around 9% of the total planetary mass.
The alien world has an orbital period of 19 hours and is located in the so-called ‘Neptunian desert,’ a region devoid of planets when we look at the population of planetary masses and sizes.
The stellar radiation heats the planet to 1,727 degrees Celsius (3,141 degrees Fahrenheit). At these temperatures, heavy elements like iron can be ionized in the atmosphere and molecules disassociated.
“Imagine a burning world, close to its star, with heavy clouds of metals floating aloft, raining down titanium droplets,” said Dr. James Jenkins, an astronomer at Diego Portales University and CATA.
LTT 9779b’s high albedo (the fraction of light that an object reflects) came as a surprise.
Any temperature above 100 degrees Celsius (212 degrees Fahrenheit) is too hot for clouds of water to form, but the temperature of this planet’s atmosphere should even be too hot for clouds…
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