In a former exoplanetary, astronomers have directly photographed two giant planets orbiting a star that is a virtual twin of the Sun, albeit much younger.
The star is called TYC 8998-760-1 (after its identification number in Tycho’s catalog), and it’s about 310 light years away in the constellation Musca. It is part of a group of stars all born together called the Scorpius-Centaurus Association, which is useful because we know that those stars are all very young; The age of this star is about 17 million years old. The Sun is 4.6 billion years old, more than 250 times the age of this star.
It also allows astronomers to calculate the mass of the star, which is, get, 1.00 ± 0.02 times that of the Sun, which means it is almost exactly the same mass as the sun. That means it is a virtual twin of the Sun, if it is much younger, and studying it gives us clues as to how things might have been for the Sun when it was a baby.
In early 2020, astronomers found a giant planet orbiting the star (named TYC 8998-760-1b, so let’s call it “planet b”). It is far away, more than 24 billion km, or 162 times the Earth-Sun distance, and has a mass of about 14 times that of Jupiter. Many of the same astronomers found a second planet around the star (“planet c”), even farther: almost 50 billion km, 320 times the distance from Earth to the Sun, and with a mass of about 6 times Jupiter’s.
They are so far away that the glare from the star is greatly reduced, and that means both appear in a real picture taken from the star:
Coooooool Only direct images have been created from two other multi-planet star systems: HR 8799 and PDS 70, but the former is considerably more massive than the Sun, and the latter substantially less, making this new one a relevant system to study, especially from the planets. and its configuration is very different from ours.
The star itself has most of its light blocked by a coronagraph, a metal disk in the center of the camera’s field of view, which substantially reduces its brightness, allowing much fainter planets to be seen.
At this age, planets continue to glow due to the heat of their formation, making them bright in the infrared, where these images were taken. Planet b is more massive, making it hotter and brighter.
So how do you know these are planets and not very distant background stars or galaxies? To verify, they compared observations of the star taken three years apart. The star actually moves through space fast enough that during this time its motion is easily detected relative to background objects. If the two objects were planets, they would move with the star, and if they were background stars, we would see that the star moves quite a bit relative to them.
In fact, the objects moved with the star! That means they are real planets in good faith.
In fact, it is very interesting that the planets are so far from their star. Neptune is about 6 billion km from the Sun, approximately 30 times the Earth-Sun distance, so these two planets are Really far. It is unclear how such massive planets could form so far from the star.
Astronomers looked at the orbit simulations and discovered that if the two have nearly circular orbits, then they are stable for at least a billion years, in which case they formed so far from the star. If instead they are more elliptical, the orbits are no stable at that time. In that case, it is still possible that they formed there, but it is also possible that they used to orbit closer and found a more massive planet, and this caused them to be thrown at great distances, where we see them today.
That’s very interesting. There is an idea that there used to be five gas giants in our solar system (Jupiter, Saturn, Uranus, Neptune, and a fifth). At first, the fifth got too close to Jupiter and the gravity of the huge planet drove it out. This idea explains some strange features in the configuration of our solar systems; It is not proven but there is indirect evidence to support it. We can’t prove it because the smoking gun, the fifth planet, is gone. But here we see another system with a star almost exactly like the Sun, and two very distant planets, possibly ejected. That makes the local idea of the fifth planet a little more compelling.
This exoplanet imaging technology is fairly new, and as these observations show, sometimes you have to wait a few years to make sure you’re seeing planets. But this shows that we can, and that means we will find more.
We see planets everywhere and with a surprising variety of characteristics, but soon I bet we will also see systems that closely resemble ours. Whether they do, or seem completely strange, we still learn important things about our own home. I’m fine with that either way.
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