It all happened so fast. The first planet discovered orbiting another star was confirmed in 1991. It was found indirectly by measuring changes in its parent star’s speed toward and away from Earth caused by the planet’s gravity tugging on the star. By the early 2000s, we’d taken the first direct photos of extrasolar planets, which despite their sometimes large size, all appear no larger than stars in images. Today, witness this brief but stunning animation of four super-Jupiter planets orbiting the star HR 8799 with periods ranging from decades to centuries.
It took over 7 years using one of the 10-meter (394-inch) Keck telescopes to Wang and team make this all-too-brief time lapse video. The exoplanet system is located 129 light years from Earth in the constellation Pegasus.
HR 8799 is only 30 million years old, very young by stellar standards, and about 1.5 times the sun’s mass and 4.9 times its brilliance. Because it’s so bright and would otherwise overwhelm the light of the much fainter planets, the star has been digitally subtracted from the photos, so we can see the planets clearly.
They’re being dubbed super-Jupiters because each is about 5-7 times more massive that our own solar system’s biggest planet. You’d think being that much more massive, they’d be much bigger than Jupiter, but that’s not how gravity works. Planets up to 80 times Jupiter’s mass remain near its size because gravity’s grip pulls all that mass into a tighter ball. As a result, all four are just 1.2 to 1.3 times the size of Jupiter.
Astronomers have used spectrographs, instruments that spread a planet’s light out into a rainbow of colors called a spectrum, to look for fingerprints of atoms and molecules in each of the four planets’ atmospheres.
This animation, also created by Jason Wang, shows the exoplanet Beta Pictoris b, another super Jupiter, orbiting its parent star.
Planet b shows water in its spectrum along with ammonia, carbon dioxide and smidge of methane. Planet c contains ammonia, possibly some acetylene (a hydrocarbon and used as a fuel) but neither carbon dioxide nor substantial methane; Planet d contains acetylene, methane, and carbon dioxide but no ammonia; Planet e contains methane and acetylene but no ammonia or carbon dioxide. Interestingly, planet e’s spectrum resembles that of our planet Saturn.
At this rate, we’ll soon be looking at the first direct images of the disks of exoplanets and eventually features on those disks. Am I jumping too far ahead? Too optimistic? I’d like to think not!
** Want to know which bright naked eye stars are circled by exoplanets? Pick up a copy of my recently published book, Night Sky with the Naked Eye, at Amazon or Barnes and Noble. It covers all the great things you can see at night with just your eyeballs. No equipment required!