Tag: University of Arizona

Three Star Ballet, With Exoplanet

This artist's impression shows a view of the triple-star system HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears at the lower-left of the picture. Located about 320 light-years from Earth in the constellation of Centaurus (The Centaur), HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one of very few directly imaged planets. With a temperature of around 580 degrees Celsius and an estimated mass of four Jupiter masses, it is also one of the coldest and least massive directly-imaged exoplanets.

An artist’s impression of the triple-star system HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears at the lower-left of the picture. Located about 320 light-years from Earth in the constellation of Centaurus (The Centaur), HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one of very few directly imaged planets. (ESO/Luis Calcada)

It hardly seems possible, but researchers have detected a planet in apparently stable orbit within a three star system — a configuration now known as a trinary.

The ubiquity of binary stars has been understood for some time, and the presence of exoplanets orbiting around and within them is no longer a surprise.  But this newest planet detected — four times the mass of Jupiter — is most unusual because trinary systems are not known to be particularly conducive to keeping planets in orbit, and especially not a planet in an extremely wide (i.e., 550 year) orbit.

Yet this planet has found the sweet spot between the stars where it balances the gravitational pulls of the three.  The system is a relative toddler at 16 million years old, and so the researchers involved in its detection say it may later be ejected from the system.  But for now, it is the only known planet of its kind.

The discovery, reported in the journal Science, was made using the European Southern Observatory’s Very Large Telescope (VLT) in Chile’s Atacama desert.  The team was from the University of Arizona in Tucson and was led by Daniel Apai, an assistant professor of Astronomy and Planetary Sciences who leads a planet finding and observing group.  That team includes research doctoral student Kevin Wagner, the first author on the paper.

“It is not clear how this planet ended up on its wide orbit in this extreme system — and we can’t say yet what this means for our broader understanding of the types of planetary systems — but it shows that there is more variety out there than many would have deemed possible,” Wagner said.

This new planet is a gas giant and definitely not habitable, but the possible universe of exoplanets that just might meet some of the basic criteria for habitability may well have grown.

“What we do know is that planets in multi-star systems have been studied far less often, but are potentially just as numerous as planets in single-star systems,” Wagner said.… Read more

Cloudy, With a Chance of Iron Rain

Analysis of data from the Kepler space telescope has shown that roughly half of the dayside of the exoplanet Kepler-7b is covered by a large cloud mass. Statistical comparison of more than 1,000 atmospheric models show that these clouds are most likely made of Enstatite, a common Earth mineral that is in vapor form at the extreme temperature on Kepler-7b. These models varied the altitude, condensation, particle size, and chemical composition of the clouds to find the right reflectivity and color properties to match the observed signal from the exoplanet. Courtesy of NASA (edited by Jose-Luis Olivares/MIT)

Many exoplanets being discovered are covered with thick clouds, offering an opportunity to analyze their compositions but hiding the lower atmosphere and surface from measurement and view.  This artist rendering of Kepler-7b is based Kepler Space Telescope data and shows that half of the day-side of the planet is covered by a large cloud.  Statistical comparison of more than 1,000 atmospheric models show that these clouds are most likely made of enstatite, a common Earth mineral that is in vapor form at the extreme temperature on Kepler-7b. (NASA/ edited by Jose-Luis Olivares/MIT)

 

From an Earth-centric point of view, rain of course means falling water.  We can have storms with falling dust — I experienced a few of those while a reporter in India — but rain is pretty much exclusively H2O falling from the clouds. But as the study of exoplanets moves aggressively into the realm of characterizing these distant planets after they are detected, the concepts of rain and clouds are changing rapidly.

We already know that it rains methane on the moon Titan, sulfuric acid on Venus and ammonia, helium and, yes, water, on Jupiter and Saturn.  Some have even posited that carbon — in the form of graphite and then diamonds — falls from the “clouds” of Saturn and Jupiter, but the eye-catching view is widely disputed.

Now the clouds of exoplanets large and small are being rigorously scrutinized not only because they can potentially tell researchers a great deal about the planets below,  but also because especially thick clouds have become a major impediment to learning what many exoplanet atmospheres and even surfaces are made of.  Current telescopes and spectrometers just can’t see much through many of the thick ones.

Here’s why:  The chemical compositions of many exo-planetary clouds are so profoundly different from what is found in our solar system.  Hot gas exoplanets, for instance, tend to have clouds of irons and silicates — compounds that are in a gas form on the surface (such as it is), then rise into the atmospheres and form into grain-like solids when they get higher and colder.  For some smaller exoplanets, the composition tends to be salts such as zinc sulfide and potassium chloride.

The process of identifying the make-up of different clouds is very much a work in progress, as is an understanding of how thick or how patchy the clouds may be.

The light curve for the planet studied, which is some four times larger than Jupiter, shows differences in brightness as the planet rotates.

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